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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 IPSEC Working Group Douglas Maughan, Mark Schertler 2 INTERNET-DRAFT National Security Agency 3 draft-ietf-ipsec-isakmp-04.txt, .ps February 21, 1996 5 Internet Security Association and Key Management Protocol (ISAKMP) 7 Abstract 9 This memo describes a protocol utilizing security concepts 10 necessary for establishing Security Associations (SA) and crypto- 11 graphic keys in an Internet environment. A Security Association 12 protocol that negotiates, establishes, modifies and deletes 13 Security Associations and their attributes is required for an 14 evolving Internet, where there will be numerous security mecha- 15 nisms and several options for each security mechanism. The key 16 management protocol must be robust in order to handle public key 17 generation for the Internet community at large and private key 18 requirements for those private networks with that requirement. 19 The Internet Security Association and Key Management Protocol 20 (ISAKMP) defines the procedures for authenticating a communicat- 21 ing peer, creation and management of Security Associations, key 22 generation techniques, and threat mitigation (e.g. denial of 23 service and replay attacks). All of these are necessary to es- 24 tablish and maintain secure communications (via IP Security Ser- 25 vice or any other security protocol) in an Internet environment. 27 Status of this memo 29 This document is being submitted to the IETF Internet Protocol Security 30 (IPSEC) Working Group for consideration as a method for the establish- 31 ment and management of security associations and their appropriate secu- 32 rity attributes. Additionally, this document proposes a method for key 33 management to support IPSP and IPv6. Publication of this document does 34 not imply acceptance of the concepts discussed by the IPSEC Working Group. 35 Comments are solicited and should be addressed to the authors and/or the 36 working group mailing list at ipsec@ans.net. 38 This document is an Internet Draft. Internet Drafts are working documents 39 of the Internet Engineering Task Force (IETF), its Areas, and its Working 40 Groups. Note that other groups may also distribute working documents as 41 Internet Drafts. 43 Internet Drafts are draft documents valid for a maximum of six months. 44 Internet Drafts may be updated, replaced, or obsoleted by other documents 45 at any time. It is not appropriate to use Internet Drafts as reference 46 material or to cite them other than as ``working draft'' or ``work in 47 progress.'' 49 To learn the current status of any Internet-Draft, please check the ``1id- 50 abstracts.txt'' listing contained in the Internet- Drafts Shadow Di- 51 rectories on ds.internic.net (US East Coast), nic.nordu.net (Europe), 52 ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). 54 Distribution of this document is unlimited. 56 Contents 58 1 Introduction 5 59 1.1 Authentication . . . . . . . . . . . . . . . . . . . . . . . . . 6 60 1.1.1Certificate Authorities . . . . . . . . . . . . . . . . . . . 6 61 1.1.2Entity Naming . . . . . . . . . . . . . . . . . . . . . . . . 7 62 1.1.3ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 7 63 1.2 Security Associations and Management . . . . . . . . . . . . . . 8 64 1.2.1Security Associations and Registration . . . . . . . . . . . . 8 65 1.2.2ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 9 66 1.3 Public Key Cryptography . . . . . . . . . . . . . . . . . . . . . 9 67 1.3.1Key Exchange Properties . . . . . . . . . . . . . . . . . . . 9 68 1.3.2ISAKMP Requirements . . . . . . . . . . . . . . . . . . . . . 11 69 1.4 ISAKMP Protection . . . . . . . . . . . . . . . . . . . . . . . . 11 70 1.4.1Anti-Clogging (Denial of Service) . . . . . . . . . . . . . . 11 71 1.4.2Connection Hijacking . . . . . . . . . . . . . . . . . . . . . 11 72 1.4.3Man-in-the-Middle Attacks . . . . . . . . . . . . . . . . . . 12 73 1.5 Multicast Communications . . . . . . . . . . . . . . . . . . . . 12 75 2 Description of the Protocol 13 76 2.1 ISAKMP Architecture . . . . . . . . . . . . . . . . . . . . . . . 13 77 2.2 ISAKMP Packet Exchanges . . . . . . . . . . . . . . . . . . . . . 14 78 2.2.1Base Exchange . . . . . . . . . . . . . . . . . . . . . . . . 14 79 2.2.2Identity Protection Exchange . . . . . . . . . . . . . . . . . 14 80 2.2.3Authentication Only Exchange . . . . . . . . . . . . . . . . . 15 81 2.3 ISAKMP Details . . . . . . . . . . . . . . . . . . . . . . . . . 16 82 2.3.1Basic ISAKMP Concepts . . . . . . . . . . . . . . . . . . . . 16 83 2.3.2ISAKMP Header Format . . . . . . . . . . . . . . . . . . . . . 17 84 2.3.3SPI Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 20 85 2.3.4General Message Processing . . . . . . . . . . . . . . . . . . 21 86 2.3.5Transport Protocol . . . . . . . . . . . . . . . . . . . . . . 23 87 2.3.6RESERVED Fields . . . . . . . . . . . . . . . . . . . . . . . 23 88 2.3.7Anti-Clogging Token (``Cookie'') Creation . . . . . . . . . . 23 89 3 Security Association Establishment 25 90 3.1 Security Association Initialization . . . . . . . . . . . . . . . 25 91 3.1.1SA Initialization Procedures . . . . . . . . . . . . . . . . . 26 92 3.2 Authentication and Key Exchange . . . . . . . . . . . . . . . . . 28 93 3.2.1Authentication Payload Format . . . . . . . . . . . . . . . . 28 94 3.2.2Key Exchange Payload Format . . . . . . . . . . . . . . . . . 29 95 3.2.3Authentication and Key Exchange Procedures . . . . . . . . . . 30 96 3.3 Security Association Negotiation . . . . . . . . . . . . . . . . 32 97 3.3.1SA Negotiation Procedures . . . . . . . . . . . . . . . . . . 32 99 4 Security Association Modification 38 100 4.1 Modification Procedures . . . . . . . . . . . . . . . . . . . . . 38 101 5 Security Association Deletion 38 102 5.1 Deletion Procedures . . . . . . . . . . . . . . . . . . . . . . . 39 104 6 Notification Message 41 105 6.1 Notify Message Types . . . . . . . . . . . . . . . . . . . . . . 42 106 6.2 Notification Procedures . . . . . . . . . . . . . . . . . . . . . 42 108 7 Conclusions 44 110 A IP Security DOI 45 111 A.1 IP Security Proposal Formats . . . . . . . . . . . . . . . . . . 45 112 A.2 ESP SA and AH SA Proposals . . . . . . . . . . . . . . . . . . . 48 113 A.3 Oakley Proposal . . . . . . . . . . . . . . . . . . . . . . . . . 51 114 A.4 Attribute Class Assigned Numbers . . . . . . . . . . . . . . . . 53 115 A.5 Attribute Value Assigned Numbers . . . . . . . . . . . . . . . . 54 116 A.5.1Sensitivity Level Assigned Numbers . . . . . . . . . . . . . . 54 117 A.5.2Key Exchange Identifiers (KEI) Assigned Numbers . . . . . . . 54 118 A.5.3Encryption Transform Assigned Numbers . . . . . . . . . . . . 54 119 B ISAKMP Scenarios 55 120 B.1 Oakley Scenario . . . . . . . . . . . . . . . . . . . . . . . . . 55 121 B.2 Virtual Private Network Scenario . . . . . . . . . . . . . . . . 57 123 C Security Association Attributes 60 124 1 Introduction 126 This document describes an Internet Security Association and Key Manage- 127 ment Protocol (ISAKMP). ISAKMP combines the security concepts of authen- 128 tication, key management, and security associations to establish the re- 129 quired security for government, commercial, and private communications on 130 the Internet. ISAKMP extends the assertion in [DOW92] that authentica- 131 tion and key exchanges must be combined for better security to include se- 132 curity association exchanges. The security required for communications 133 depends on the individual network configurations and environments. Orga- 134 nizations are setting up Virtual Private Networks (VPN) that will require 135 one set of security functions for communications within the VPN and possi- 136 bly many different security functions for communications outside the VPN 137 to support geographically separate organizational components, customers, 138 suppliers, sub-contractors (with their own VPNs), government, and others. 139 Departments within large organizations may require a number of security 140 associations to separate and protect data (e.g. personnel data, company 141 proprietary data, medical) on internal networks and other security associ- 142 ations to communicate inter-department. Nomadic users wanting to ``phone 143 home'' represent another set of security requirements. These requirements 144 must be tempered with bandwidth challenges. Smaller groups of people may 145 meet their security requirements by setting up ``Webs of Trust''. ISAKMP 146 exchanges provide these assorted networking communities the ability to 147 present peers with the security functionality it supports in an authen- 148 ticated and protected manner for agreement upon a common interoperable se- 149 curity association. 151 Security associations must support different encryption algorithms, au- 152 thentication mechanisms, and key establishment algorithms for other secu- 153 rity protocols, as well as IP Security. Security associations must also 154 support host-oriented certificates for lower layer protocols and user- 155 oriented certificates for higher level protocols. Algorithm and mecha- 156 nism independence is required in applications such as e-mail, remote lo- 157 gin, and file transfer, as well as in session oriented protocols, routing 158 protocols, and link layer protocols. ISAKMP provides a common security 159 association and key establishment protocol for this wide range of security 160 protocols, applications, security requirements, and network environments. 162 ISAKMP is not bound to any specific cryptographic algorithm, key gener- 163 ation technique, or security mechanism. This flexibility is beneficial 164 for a number of reasons. First, it supports the dynamic communications 165 environment described above. Second, the independence from specific secu- 166 rity mechanisms and algorithms provides a forward migration path to better 167 mechanisms and algorithms. When improved security mechanisms are devel- 168 oped or new attacks against current encryption algorithms, authentica- 169 tion mechanisms and key exchanges are discovered, ISAKMP will allow the 170 updating of the algorithms and mechanisms without having to develop a com- 171 pletely new KMP or patch the current one. 173 ISAKMP has basic requirements for its authentication and key exchanges 174 components. These requirements guard against denial of service, replay / 175 reflection, man-in-the-middle, and connection hijacking attacks. This is 176 important because these are the types of attacks that are targeted against 177 protocols. Complete Security Association (SA) support, which provides 178 mechanism and algorithm independence, and protection from protocol threats 179 are the strengths of ISAKMP. 181 1.1 Authentication 183 A very important step in establishing secure network communications is au- 184 thentication of the entity at the other end of the communication. Many 185 authentication mechanisms are available. Authentication mechanisms fall 186 into two catagories of strength - weak and strong. Passwords are an exam- 187 ple of a mechanism that provides weak authentication. Reasons for this 188 include the fact that most users pick easy to guess passwords and when 189 used over an unprotected network are easily read by network sniffers. 190 Digital signatures, such as the Digital Signature Standard (DSS) and the 191 Rivest-Shamir-Adleman (RSA) signature, are public key based strong authen- 192 tication mechanisms. When using digital signatures each entity requires a 193 public and a private key. Certificates are an essential part of a digital 194 signature authentication mechanism. Certificates bind a specific enti- 195 ties identity (be it host, network, user, or application) to its public 196 keys and possibly other security-related information such as privileges, 197 clearances, and compartments. Authentication based on digital signatures 198 requires a trusted third party or certificate authority to create, sign 199 and properly distribute certificates. For more detailed information on 200 digital signatures, such as DSS and RSA, and certificates see [Schneier]. 202 1.1.1 Certificate Authorities 204 Certificates require an infrastructure for generation, verification, man- 205 agement and distribution. The Internet Policy Registration Authority 206 (IPRA) [RFC-1422] has been established to direct this infrastructure for 207 the IETF. The IPRA certifies Policy Certification Authorities (PCA). PCAs 208 control Certificate Authorities (CA) which certify users and subordi- 209 nate entities. Current certificate related work includes the Domain Name 210 System (DNS) Security Extensions [DNSSEC] which will provide signed en- 211 tity keys in the DNS. The Public Key Infrastucture (PKIX) working group 212 is specifying an Internet profile for X.509 certificates. There is also 213 work going on in industry to develop X.500 Directory Services which would 214 provide X.509 certificates to users. The U.S. Post Office is developing 215 a (CA) hierarchy. The NIST Public Key Infrastructure Working Group has 216 also been doing work in this area. The DOD Multi Level Information System 217 Security Initiative (MISSI) program has begun deploying a certificate in- 218 frastructure for the U.S. Government. Alternatively, if no infrastructure 219 exists, the PGP Web of Trust certificates can be used to provide user au- 220 thentication and privacy in a community of users who know and trust each 221 other. 223 1.1.2 Entity Naming 225 An entity's name is its identity and is bound to its public keys in cer- 226 tificates. The CA MUST define the naming semantics for the certificates 227 it issues. See the UNINETT PCA Policy Statements [Berge] for an example 228 of how a CA defines its naming policy. When the certificate is verified, 229 the name is verified and that name will have meaning within the realm of 230 that CA. An example is the DNS security extensions which make DNS servers 231 CAs for the zones and nodes they serve. Resource records are provided for 232 public keys and signatures on those keys. The names associatied with the 233 keys are IP addresses and domain names which have meaning to entities ac- 234 cessing the DNS for this information. A Web of Trust is another example. 235 When webs of trust are set up, names are bound with the public keys. In 236 PGP the name is usaully the entities e-mail address which has meaning to 237 those, and only those, who understand e-mail. Another web of trust could 238 use an entirely different naming scheme. 240 1.1.3 ISAKMP Requirements 242 Strong authentication MUST be provided on ISAKMP exchanges. Without being 243 able to authenticate the entity at the other end, the Security Association 244 (SA) and session key established are suspect. Without authentication you 245 are unable to trust an entity's identification, this makes access control 246 questionable. Encryption (e.g. ESP) and integrity (e.g. AH) will pro- 247 tect subsequent communications from passive eavesdroppers, but the SA and 248 key may be established with an adversary who performed an active man-in- 249 the-middle attack and is now stealing all your personnal data. 251 A digital signature algorithm MUST be used within ISAKMP's authentication 252 component. However, ISAKMP does not mandate a specific signature algo- 253 rithm or certificate authority (CA). ISAKMP allows an entity initiating 254 communications to indicate which CAs it supports. After selection of a 255 CA, the protocol provides the messages required to support the actual au- 256 thentication exchange. The protocol provides a facility for identifica- 257 tion of different certificate authorities, certificate types (e.g. X.509, 258 PKCS #7, PGP, DNS SIG and KEY records), and the exchange of the certifi- 259 cates identified. 261 ISAKMP utilizes digital signatures, based on public cryptography, for au- 262 thentication. There are other strong authentication systems available, 263 which could be specified as additional optional authentication mechanisms 264 for ISAKMP. Some of these authentication systems rely on a trusted third 265 party called a key distribution center (KDC) to distribute secret session 266 keys. An example is Kerberos, where the trusted third party is the Ker- 267 beros server, which holds secret keys for all clients and servers within 268 it's network domain. A clients proof it holds it's secret key provides 269 its authenticaton to a server. 271 The ISAKMP specification does not specify the protocol for communicating 272 with the trusted third parties (TTP) or certificate directory services. 273 These protocols are defined by the TTP and directory service themselves 274 and are outside the scope of this specification. 276 1.2 Security Associations and Management 278 A Security Association (SA) is a relationship between two or more entities 279 that describes how the entities will utilize security services to communi- 280 cate securely. This relationship is represented by a set of information 281 that can be considered a contract between the entities. The information 282 must be agreed upon and shared between all the entities. Sometimes the 283 information alone is referred to as an SA, but this is just a physical in- 284 stantiation of the existing relationship. The existence of this relation- 285 ship, represented by the information, is what provides the agreed upon se- 286 curity information needed by entities to securely interoperate. All enti- 287 ties must adhere to the SA for secure communications to be possible. When 288 accessing SA attributes, entities use a pointer or identifier refered to 289 as the Security Parameter Index (SPI). See [RFC-1825] for details on IP 290 Security SAs and SPIs definitions. 292 1.2.1 Security Associations and Registration 294 The SA attributes required and recommended for the IP Security (AH, ESP) 295 are defined in [RFC-1825]. The attributes specified for an IP Security SA 296 include, but are not limited to, authentication mechanism, cryptographic 297 algorithm, algorithm mode, key length, and Initialization Vector (IV). 298 Other protocols that provide algorithm and mechanism independent security 299 MUST define their SA attributes requirements. The separation of ISAKMP 300 from a specific SA definition is important to ensure ISAKMP can establish 301 SAs for all possible security protocols and applications. 303 NOTE: See Appendix C for a discussion of SA attributes that should be con- 304 sidered when defining a security protocol or application. 306 In order to facilitate easy identification of specific attributes (e.g. 307 a specific encryption algorithm) among different network entites the at- 308 tributes must be assigned identifiers and these identifiers must be reg- 309 istered by a central authority. The Internet Assigned Numbers Authority 310 (IANA) provides this function for the Internet. 312 1.2.2 ISAKMP Requirements 314 Security Association (SA) establishment MUST be part of the key manage- 315 ment protocol defined for IP based networks. The SA concept is required 316 to support security protocols in a diverse and dynamic networking envi- 317 ronment. Just as authentication and key exchange must be linked to pro- 318 vide assurance that the key is established with the authenticated party 319 [DOW92], SA establishment must be linked with the authentication and the 320 key exchange protocol. 322 ISAKMP provides the protocol exchanges to establish a security association 323 between entities. First, an initial protocol exchange allows a basic set 324 of security attributes to be agreed upon. This basic set provides protec- 325 tion for subsequent ISAKMP exchanges. It also indicates the authentica- 326 tion method and key exchange that will be performed as part of the ISAKMP 327 protocol. If a basic set of security attributes is already in place on 328 the communicating entities the initial ISAKMP exchange may be skipped and 329 the key and authentication exchanges issued directly. After the basic set 330 of security attributes has been agreed upon, initial identity authenti- 331 cated, and required keys generated, another security attribute exchange 332 takes place to establish the complete SA which will be used for subsequent 333 communications by the entity that invoked ISAKMP. The basic set of SA at- 334 tributes that MUST be implemented to provide ISAKMP interoperability are 335 defined in Appendix A. *These atributes will be moved to a separate docu- 336 ment to maintain separation of protocol and attributes.* 338 1.3 Public Key Cryptography 340 Public key cryptography is the most flexible, scalable, and efficient way 341 for users to obtain the shared secrets and session keys needed to support 342 the large number of ways Internet users will interoperate. Many key gen- 343 eration algorithms, that have different properties, are available to users 344 (see [DOW92] and [ANSI]). Properties of key exchange protocols include 345 the key establishment method, authentication, symmetry, perfect forward 346 secrecy, and back traffic protection. 348 1.3.1 Key Exchange Properties 350 Key Establishment (Key Generation / Key Transport) The two common methods 351 of using public key cryptography for key establishment are key transport 352 and key generation. An example of key transport is the use of the RSA al- 353 gorithm to encrypt a randomly generated session key (for encrypting subse- 354 quent communications) with the recipient's public key. The encrypted ran- 355 dom key is then sent to the recipient, who decrypts it using his private 356 key. At this point both sides have the same session key, however it was 357 created based on input from only one side of the communications. The ben- 358 efit of the key transport method is that it has less computational over- 359 head then the following method. The Diffie-Hellman (D-H) algorithm il- 360 lustrates key generation using public key cryptography. The D-H algorithm 361 is begun by two users exchanging public information. Each user then math- 362 ematically combines the other's public information along with their own 363 secret information to compute a shared secret value. This secret value 364 can be used as a session key or as a key encryption key for encrypting 365 a randomly generated session key. This method generates a session key 366 based on public and secret information held by both users. The benefit 367 of the D-H algorithm is that the key used for encrypting messages is based 368 on information held by both users. Assuming checks for weak values nei- 369 ther party can force the session key to a predetermined value. Detailed 370 descriptions of these algorithms can be found in [Schneier]. There are a 371 number of variations on these two key generation schemes and these varia- 372 tions do not necessarily interoperate. 374 Key Exchange Authentication Key exchanges may be authenticated during the 375 protocol or after protocol completion. Authentication of the key exchange 376 during the protocol is provided when each party provides proof it has the 377 secret session key before the end of the protocol. Proof can be provided 378 by encrypting known data in the secret session key during the protocol ex- 379 change. Authentication after the protocol must occur in subsequent commu- 380 nications. Authentication during the protocol is preferred so subsequent 381 communications are not initiated if the secret session key is not estab- 382 lished with the desired party. 384 Key Exchange Symmetry A key exchange provides symmetry if either party can 385 initiate the exchange and exchanged messages can cross in transit with- 386 out effecting the key that is generated. This is desirable so that com- 387 putation of the keys does not require either party to know who initiated 388 the exchange. While key exchange symmetry is desirable, symmetry in the 389 entire KMP may provide a vulnerablity to reflection attacks. The entire 390 ISAKMP SA establishment is asymetrical. 392 Back Traffic Protection / Perfect Forward Secrecy Perfect forward secrecy 393 is provided by a key exchange protocol if disclosure of long-term cryp- 394 tographic keying material (e.g. public signature keys) does not compro- 395 mise previously generated keys. Back traffic protection is provided by 396 the independent generation of each key such that subsequent keys are not 397 dependent on any previous key. There is a subtle difference. Past ses- 398 sion keys will NOT be obtainable if the long-term key is compromised in 399 perfect forward secrecy; Past session keys will NOT be obtainable if the 400 current session key is compromised in back traffic protecion. 402 The difficulty of numerical factoring of large numbers has proven that 403 cryptographic keys can protect information for a considerable length of 404 time. However, this is based on the assumption that keys used for protec- 405 tion of communications are destroyed after use and not kept for any rea- 406 son. 408 1.3.2 ISAKMP Requirements 410 An authenticate key exchange MUST be supported by ISAKMP. Users SHOULD 411 choose additional key establishment algorithms based on their require- 412 ments. ISAKMP does not specify a specific key exchange. Requirements 413 that should be evaluated when choosing a key establishment algorithm in- 414 clude establishment method (generation vs. transport), perfect forward 415 secrecy, back traffic protection, computational overhead, key escrow, and 416 key strength. Based on user requirements, ISAKMP allows an entity initi- 417 ating communications to indicate which key exchanges it supports. After 418 selection of a key exchange, the protocol provides the messages required 419 to support the actual key establishment. 421 1.4 ISAKMP Protection 423 1.4.1 Anti-Clogging (Denial of Service) 425 Of the numerous security services available, protection against denial of 426 service always seems to be one of the most difficult to address. Phil 427 Karn in his Internet-Draft [Karn] has introduced a mechanism to provide 428 a measure of denial of service protection through the use of a ``cookie'' 429 exchange. This anti-clogging token (ACT) is aimed at protecting the com- 430 puting resources from attack without spending excessive CPU resources to 431 determine its authenticity. As described in [Karn], an exchange prior to 432 CPU-intensive public key operations can thwart some denial of service at- 433 tempts (e.g. simple flooding with bogus IP source addresses). As noted 434 by Karn, absolute protection against denial of service is impossible, but 435 this anti-clogging token provides a technique for making it easier to han- 436 dle. 438 1.4.2 Connection Hijacking 440 ISAKMP prevents connection hijacking by linking the authentication, key 441 exchange and security association exchanges. This linking prevents an 442 attacker from allowing the authentication to complete and then jumping 443 in and impersonating one entity to the other during the key and security 444 association exchanges. 446 1.4.3 Man-in-the-Middle Attacks 448 Man-in-the-Middle attacks include interception, insertion, deletion, and 449 modification of messages, reflecting messages back at the sender, re- 450 playing old messages and redirecting messages. ISAKMP features prevent 451 these types of attacks from being successful. The linking of the ISAKMP 452 exchanges prevents the insertion of messages in the protocol exchange. 453 The ISAKMP protocol state machine is defined so deleted messages will not 454 cause a partial SA to be created, the state machine will clear all state 455 and return to idle. The state machine also prevents reflection of a mes- 456 sage from causing harm. The requirement for a new cookie with time vari- 457 ant material for each new SA establishment prevents attacks that involve 458 replaying old messages. The ISAKMP strong authentication requirement pre- 459 vents an SA from being established with other then the intended party. 460 Messages may be redirected to a different destination or modified but this 461 will be detected and an SA will not be established. The ISAKMP specifica- 462 tion defines where abnormal processing has occurred and recommends notify- 463 ing the appropriate party of this abnormality. 465 1.5 Multicast Communications 467 While future Internet communications will increasingly be of a multicast 468 nature, this document is presenting a security association and key man- 469 agement protocol from the unicast point of view. It is expected that mul- 470 ticast communications will require the same security services as unicast 471 communications and may introduce the need for additional security ser- 472 vices. The issues of distributing SPIs for multicast traffic are pre- 473 sented in [RFC-1825]. Multicast security issues are also discussed in 474 [BC]. Upon agreement and implementation of a security association pro- 475 tocol for the Internet unicast environment, we fully intend to examine any 476 additional security requirements for multicast communications. For an in- 477 troduction to the issues related to multicast security consult the Inter- 478 net Drafts, [Spar94a] and [Spar94b], describing Sparta's research in this 479 area. 481 2 Description of the Protocol 483 The Internet Security Association and Key Management Protocol (ISAKMP) de- 484 fines procedures and packet formats to establish, negotiate, modify and 485 delete Security Associations (SA). SAs contain all the information re- 486 quired for execution of IP security services, such as the IP Authentica- 487 tion Header (AH), the IP Encapsulating Security Payload (ESP), and routing 488 protocol authentication mechanisms. ISAKMP includes packet formats for 489 exchanging key generation and authentication data. These formats provide 490 a consistent method of transferring key and authentication data that is 491 independent of the key generation technique, encryption algorithm or au- 492 thentication mechanism. 494 2.1 ISAKMP Architecture 496 The following figure is a high level view of the placement of ISAKMP in a 497 network architecture. 499 +-------------+ +--------------+ 500 ! Negotiation ! Situation ! Application ! 501 ! Server !<---- ! Process ! 502 +-------------+ ! +--------------+ 503 ! ISAKMP ! ! ! Appl Protocol! 504 +-------------+ ! SPI +--------------+ 505 ! v ! 506 +---------------------------------------------+ 507 ! Sockets ! 508 +---------------------------------------------+ 509 ! Transport Protocol (TCP / UDP) ! 510 +---------------------------------------------+ 511 ! IP ! 512 +---------------------------------------------+ 513 ! Link Layer Protocol ! 514 +---------------------------------------------+ 516 Figure 1: ISAKMP Relationships 518 The negotiation server is an application process which interfaces with the 519 different policy databases (security, network access, cryptographic, au- 520 thentication, etc.) that a system may require. It calls upon ISAKMP to 521 deliver the data required to establish an SA and key and authenticate the 522 exchange. The negotiation server can be invoked manually by a user or au- 523 tomatically by an up-call from a security protocol when it requires an SA. 525 The situation contains the identification and credential information re- 526 quired by the negotiation server to make policy decisions. The negotia- 527 tion server returns a SPI when an SA is established. 529 2.2 ISAKMP Packet Exchanges 531 The Exchange field in the ISAKMP header currently has three values de- 532 fined: the base exchange, the identity protection exchange, and the au- 533 thentication only exchange. These exchanges define the flow of the ISAKMP 534 packets during SA establishment. The diagrams in 2.2.1, 2.2.2, and 2.2.3 535 show the packet exchange ordering for each exchange type and provide ba- 536 sic notes describing what has happened after each packet exchange. These 537 exchanges are a high level summary of the packet flow, they do not show 538 processing or error handling. Detailed connection establishment process- 539 ing is defined in sections 3 through 6. 541 2.2.1 Base Exchange 543 Sections 3.1 through 3.3 describe the three basic phases: SA Initial- 544 ization, Key Exchange and Authentication, and SA Negotiation, that com- 545 prise the base exchange. The base exchange contains the minimum number of 546 packet exchanges in order to reduce latency associated with SA establish- 547 ment. 549 Base Exchange 550 ___Initiator_____Direction____Responder_____ Note 551 ISA_INIT_REQ => 552 <= ISA_INIT_RESP 553 Basic SA selected 554 ISA_AUTH&KE_REQ => 555 <= ISA_AUTH&KE_RESP 556 Identity Verified 557 Key Generated 558 Encryption Begun 559 ISA_NEG_REQ => 560 <= ISA_NEG_RESP SA Completed 562 2.2.2 Identity Protection Exchange 564 The identity protection exchange starts and ends the same as the base ex- 565 change, but separates the key exchange payload and the authentication pay- 566 loads into separate packets. In this exchange, the key exchange is trans- 567 mitted first followed by the strong authentication exchange. The benefit 568 of this exchange is the ability to communicate with a person without dis- 569 closing either party's identity to passive attackers on the network. 571 The ISA_KE_REQ and ISA_KE_RESP packets used for the key exchange portion of 572 this exchange contain an ISAKMP header followed by the key exchange pay- 573 load. The ISA_AUTH_REQ and ISA_AUTH_RESP packet used for the authentication 574 portion of this exchange contain an ISAKMP header followed by the authen- 575 tication payload. 577 Identity Protection Exchange 578 __Initiator___Direction___Responder___ Note 579 ISA_INIT_REQ => 580 <= ISA_INIT_RESP 581 Basic SA selected 582 ISA_KE_REQ => 583 <= ISA_KE_RESP 584 Key Generated 585 Encryption Begun 586 ISA_AUTH_REQ => 587 <= ISA_AUTH_RESP 588 Identity Verified 589 ISA_NEG_REQ => 590 <= ISA_NEG_RESP SA Completed 592 2.2.3 Authentication Only Exchange 594 The authentication only exchange starts and ends the same as the base ex- 595 change. In this exchange, the authentication information is the only in- 596 formation transmitted. The benefit of this exchange is the ability to 597 perform only an authentication exchange without the computational expense 598 of computing keys. Using this exchange, none of the transmitted informa- 599 tion will be encrypted. 601 The ISA_AUTH_REQ and ISA_AUTH_RESP packet used for the authentication only 602 exchange contain an ISAKMP header followed by the authentication payload. 604 Authentication Only Exchange 605 __Initiator___Direction___Responder___ Note 606 ISA_INIT_REQ => 607 <= ISA_INIT_RESP 608 Basic SA selected 609 ISA_AUTH_REQ => 610 <= ISA_AUTH_RESP 611 Identity Verified 612 ISA_NEG_REQ => 613 <= ISA_NEG_RESP SA Completed 615 2.3 ISAKMP Details 617 The following sections contain the details of ISAKMP. Sections 2.3.1 618 through 2.3.7 cover details that are pertinent to the entire protocol. 619 Sections 3 through 6 define the establishment, modification, and deletion 620 services, defined as exchanges, offered by the protocol. The appendices 621 provide examples of SAs and key exchanges. 623 2.3.1 Basic ISAKMP Concepts 625 Domain of Interpretation The Domain of Interpretation (DOI) identifier is 626 used to interpret the payloads of ISAKMP payloads. The concept of a DOI 627 is based on previous work by the IETF CIPSO Working Group, but extended 628 beyond security label interpretation to include naming and interpretation 629 of security services. The DOI defines: 631 o The set of information that will be used to determine the required 632 security services (this information is called a situation). 634 o The set of security policies that must be supported. 636 o Syntax rules for the specification of proposed security services. A 637 set of security services is called a protection suite. 639 o A common scheme for identifying cryptographic mechansisms, including 640 encryption algorithms, key exchange algorithms, and certificate 641 authorities. 643 o A naming scheme for the cryptographic algorithms supported within the 644 domain, and for common Key Exchange Identifiers. 646 Specifications of the rules for individual DOIs will be presented in sep- 647 arate documents. The rules for the Internet Security DOI is contained in 648 Appendix A. 650 A system may support multiple Domains of Interpretation. All systems MUST 651 support the Internet Security DOI. 653 Situation A situation contains all of the security-relevant information 654 that a system considers necessary to decide the security services required 655 to protect the session being negotiated. For example, in the Internet 656 Security DOI (see Appendix A), the situation consists of only the address 657 of the peer being contacted. In other DOIs, the situation may include 658 security classifications, modes of operation (normal vs. emergency), etc. 660 Protection Suite A protection suite is a list of the security services 661 that must be applied at various security protocols. For example, a pro- 662 tection suite may consist of DES encryption in IP ESP, and keyed MD5 in 663 IP AH. All of the protections in a suite must be treated as a single unit. 664 This is because security services in different security protocols can have 665 subtle interactions, and the effects of a suite must be analyzed and veri- 666 fied as a whole. 668 Proposal A proposal is a list, in decreasing order of preference, of the 669 protection suites that a system considers acceptable to protect traffic 670 under a given situation. 672 2.3.2 ISAKMP Header Format 674 ISAKMP has a fixed header format (shown in Figure 2) followed by a vari- 675 able length payload, optional digital signature, and optional padding. A 676 fixed header simplifies parsing, providing the benefit of protocol parsing 677 software that is less complex and easier to implement. The fixed header 678 contains the information required by the protocol to maintain state, pro- 679 cess payloads and prevent attacks (e.g. denial of service and replay). 680 Based on the message type, each header is followed by a payload specific 681 to the message type. The payload for each message is defined in sections 682 3 through 6. Following the payload portion of the ISAKMP packet is a dig- 683 ital signature. This field is dependent on the negotiation of Security 684 Association attributes and may not be present. 686 1 2 3 687 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 ! ! 690 ~ Initiator-Cookie ~ 691 ! ! 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 ! ! 694 ~ Responder-Cookie ~ 695 ! ! 696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 ! Message Type ! Exch ! Vers ! Length ! 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 ! Security Parameter Index (SPI) ! 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 ! Auxillary (SPI) ! 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 704 Figure 2: ISAKMP Header Format 706 o Message Type (1 octet) - Indicates the type of message. A suffix of 707 REQ denotes a Request message type and an RESP suffix denotes a 708 Response message type. The format and processing for each message is 709 defined in sections 3 through 6. 711 __ISAKMP_Message___Message_Type_ 712 RESERVED 0 713 ISA_INIT_REQ 1 714 ISA_INIT_RESP 2 715 ISA_KE_REQ 3 716 ISA_KE_RESP 4 717 ISA_AUTH_REQ 5 718 ISA_AUTH_RESP 6 719 ISA_AUTH&KE_REQ 7 720 ISA_AUTH&KE_RESP 8 721 ISA_NEG_REQ 9 722 ISA_NEG_RESP 10 723 ISA_MODIFY_REQ 11 724 ISA_MODIFY_RESP 12 725 ISA_NOTIFY 13 726 ISA_DELETE 14 727 ISA_NEW_GROUP_REQ 15 728 ISA_NEW_GROUP_RESP 16 729 IANA Use 17-127 730 Future Use 128-255 732 o Exchange (4 bits) - indicates the type of exchange, see section 2.2 733 for a description of the Message Types exchanged in each of these 734 Exchange Types. 736 ___ISAKMP_Exchange___Exchange_Type__ 737 RESERVED 0 738 Base 1 739 Identity Protection 2 740 Authentication Only 3 741 Future Use 4 - 15 743 o Version (4 bits) - indicates the version of the ISAKMP protocol in 744 use. 746 o Length (2 octets) - Length of total message (header + payload) in 747 octets. 749 o SPI (4 octets) - Security Parameter Index. The receiving entity's 750 SPI is always in this field, except for the ISA_INIT packets. The use 751 of the SPI field is described in Section 2.3.3 753 o Auxillary SPI (4 octets) - The use of the Auxiliary SPI field is 754 described in 2.3.3 756 o Initiator Cookie (8 octets) - Cookie of entity that initiated SA 757 establishment, SA modify or SA delete. 759 o Responder Cookie (8 octets) - Cookie of entity that is responding to 760 an SA establishment, SA modify or SA delete request. 762 2.3.3 SPI Usage 764 While bootstrapping secure channels between systems, ISAKMP cannot assume 765 the existence of security services, and must provide some protections for 766 itself. Therefore, ISAKMP distinguishes two different types of SPIs. The 767 first type of SPI, called a negotiation SPI, refers to a ``local'' secu- 768 rity association, implemented by the ISAKMP service itself. The second 769 type is called a protection SPI, and is used to refer to the SA being de- 770 veloped on behalf of other security protocols. Negotiation SPIs are mean- 771 ingless outside of the negotiation server, while protection SPIs will be 772 used by protocols such as AH and ESP. 774 Although SPIs are classified two different ways, all SPIs must be selected 775 from the same SPI-space, so that the ISAKMP service can uniquely identify 776 an SA based on a SPI. 778 In general, the SPI field in the ISAKMP header contains the receiving en- 779 tity's negotiation SPI. The only exception to this is the ISA_INIT_REQUEST 780 message, because the receiver has not yet established a reciving SPI for 781 the session. In the ISA_INIT_REQUEST message, the the SPI field contains 782 the SPI that the sender will be using for the session. 784 The Auxiliary SPI field is necessary because ISAKMP needs both a handle on 785 the internal ``negotiation SA'', in order to protect or unprotect messages 786 from ISAKMP peers, as well as a handle for the protection SA that is being 787 developed. 789 The following table describes the contents of the two SPI fields for each 790 of the message types: 792 __ISAKMP_Message_______SPI_____Auxiliary_SPI__ 793 ISA_INIT_REQ REQ NEG SPI 0 794 ISA_INIT_RESP REQ NEG SPI REC NEG SPI 795 ISA_KE_REQ REC NEG SPI REQ SPI 796 ISA_KE_RESP REQ NEG SPI REC SPI 797 ISA_AUTH_REQ REC NEG SPI REQ NEG SPI 798 ISA_AUTH_RESP REQ NEG SPI REC NEG SPI 799 ISA_AUTH&KE_REQ REC NEG SPI REQ NEG SPI 800 ISA_AUTH&KE_RESP REQ NEG SPI REC NEG SPI 801 ISA_NEG_REQ REC NEG SPI REQ PROT SPI 802 ISA_NEG_RESP REC NEG SPI REC PROT SPI 803 ISA_MODIFY_REQ REC NEG SPI REC SPI 804 ISA_MODIFY_RESP REQ NEG SPI REQ SPI 805 ISA_NOTIFY REC NEG SPI REC SPI 806 ISA_DELETE REQ NEG SPI REQ SPI 807 ISA_NEW_GROUP_REQ REC NEG SPI 0 808 ISA_NEW_GROUP_RESPREQ NEG SPI 0 810 Notes: 812 REQ NEG SPI = Requestor's negotiation SPI 813 REC NEG SPI = Receiver's negotiation SPI 814 REQ PROT SPI = Requestor's protection SPI 815 REC PROT SPI = Receiver's protection SPI 816 REQ SPI = Requestor's SPI (either negotiation or protection) 817 REC SPI = Receiver's SPI (either negotiation or protection) 819 For KE messages: if the messages are establishing keys for a negotiation 820 session, the SPI is a negotiation SPI. Otherwise, the Auxiliary SPI is a 821 protection SPI. 823 For MODIFY, NOTIFY, and DELETE messages: the Auxiliary SPI can refer to 824 either type of SPI. 826 2.3.4 General Message Processing 828 Every ISAKMP message has basic processing applied to insure protocol re- 829 liability, and to minimize threats, such as denial of service and replay 830 attacks. 832 When transmitting an ISAKMP packet, the transmitting entity (initiator or 833 responder) does the following: 835 1. Sets a timer and initializes a retry counter. 837 2. If the timer expires, the ISAKMP packet is resent and the retry 838 counter is decremented. 840 3. If the retry counter reaches zero (0), the event, RETRY LIMIT 841 REACHED, is logged in the appropriate system audit file. 843 4. The ISAKMP protocol machine clears all states and returns to IDLE. 845 When an ISAKMP packet is received, the receiving entity (initiator or re- 846 sponder) does the following: 848 1. Verifies the Initiator and Responder ``cookies''. If the cookie 849 validation fails, the message is discarded and the following actions 850 are taken: 852 (a) The event, INVALID COOKIE, is logged in the appropriate system 853 audit file. 855 (b) No response is sent to the initiating entity. This will cause 856 the transmission timer of the initiating entity to expire and 857 force retransmission of the message. 859 2. Check the Message Type field to confirm it is valid. If the Message 860 Type field validation fails, the message is discarded and the 861 following actions are taken: 863 (a) The event, INVALID MESSAGE TYPE, is logged in the appropriate 864 system audit file. 866 (b) No response is sent to the initiating entity. This will cause 867 the transmission timer of the initiating entity to expire and 868 force retransmission of the message. 870 3. Check the Exchange field to confirm it is valid for the Message Type 871 requested. If the Exchange field validation fails, the message is 872 discarded and the following actions are taken: 874 (a) The event, INVALID EXCHANGE TYPE, is logged in the appropriate 875 system audit file. 877 (b) No response is sent to the initiating entity. This will cause 878 the transmission timer of the initiating entity to expire and 879 force retransmission of the message. 881 4. Check SPI to ensure it is valid for the Message Type and Exchange 882 being performed. If the SPI validation fails, the message is 883 discarded and the following actions are taken: 885 (a) The event, INVALID SPI, is logged in the appropriate system audit 886 file. 888 (b) No response is sent to the initiating entity. This will cause 889 the transmission timer of the initiating entity to expire and 890 force retransmission of the message. 892 5. The message payload is processed. Individual message processing is 893 described in sections 3 through 6. Depending on the Message Type, a 894 valid message results in a response being sent to the transmitting 895 entity (message originator). The procedures for sending these 896 responses are also outline in sections 3 through 6. 898 2.3.5 Transport Protocol 900 ISAKMP can be implemented over any transport protocol or IP itself. The 901 User Datagram Protocol (UDP) is minimum requirement for interoperability. 902 The ISAKMP well-known port is TBD. 904 2.3.6 RESERVED Fields 906 The existence of RESERVED fields are strictly used to preserve byte align- 907 ment. All RESERVED fields in the ISAKMP protocol MUST be set to zero (0) 908 when a packet is issued. The receiver SHOULD check the RESERVED fields 909 for zero (0) and discard the packet if other values are found. 911 2.3.7 Anti-Clogging Token (``Cookie'') Creation 913 Phil Karn's Internet Draft [Karn] states that cookie generation is imple- 914 mentation dependent, but must satisfy some basic requirements: 916 1. The cookie must depend on the specific parties. This prevents 917 an attacker from obtaining a cookie using a real IP address and 918 UDP port, and then using it to swamp the victim with Diffie- 919 Hellman requests from randomly chosen IP addresses or ports. 921 2. It must not be possible for anyone other than the issuing 922 entity to generate cookies that will be accepted by that 923 entity. This implies that the issuing entity must use local 924 secret information in the generation and subsequent 925 verification of a cookie. It must not be possible to deduce 926 this secret information from any particular cookie. 928 3. The cookie generation function must be fast to thwart attacks 929 intended to sabotage CPU resources. 931 Karn's suggested method for creating the cookie is to perform a fast hash 932 (e.g. MD5) over the IP Source and Destination Address, the UDP Source and 933 Destination Ports and a locally generated secret random value. ISAKMP 934 requires that the cookie be unique for each SA establishment, SA modify 935 and SA delete to help prevent replay attacks, therefore the date and time 936 MUST be added to the information hashed. 938 3 Security Association Establishment 940 Security Association (SA) Establishment is the process of agreeing upon 941 and exchanging all the security information that is required in an SA. The 942 following sections, 3.1 to 3.3, describe the three basic phases that com- 943 prise SA Establishment: SA Initialization, Key and Authentication infor- 944 mation exchange, and SA Negotiation. 946 3.1 Security Association Initialization 948 The initialization exchange of SA establishment is composed of the 949 ISA_INIT_REQ and ISA_INIT_RESP packets shown in figure 3. The ISA_INIT pack- 950 ets exchange ``cookies'', and options for a key generation technique, an 951 encryption algorithm and an authentication mechanism. The ``cookies'' 952 are used to prevent replay and denial of service attacks. Authentication 953 and encryption for the ISAKMP exchanges are provided by the authentication 954 mechanism and encryption algorithm selected. The key generation technique 955 selected creates keys for use by the authentication mechanism and encryp- 956 tion algorithm. The keys may also be used as any of the following: ac- 957 tual session keys, to create the session keys, or to protect the exchange 958 of the actual session keys for the SA. If the key, encryption algorithm, 959 and authentication mechanism are only used to protect ISAKMP exchanges, 960 then new options can be picked during the negotiation phase (described in 961 Section 3.3) for use in protecting the actual data communications. If en- 962 cryption is not required for the SA, the encryption algorithm options are 963 not exchanged. 965 o ISAKMP Header - Described in Section 2.3.2 967 o Next Payload (1 octet) - Identifies the next payload in an ISAKMP 968 message if more then one is carried in a message. 970 o Payload Length (1 octet) - Specifies the payload length in 4-octet 971 units. 973 o Situation - Variable length field containing the situation for an SA 974 (described in section 2.3.1). 976 o Proposal - Variable length field containing a list of proposed 977 protection suites for an SA (described in section 2.3.1). 979 The format and content of both the situation and proposal is DOI-specific. 980 The format of the Internet Security situation and proposal is described in 981 Appendix A. 983 3.1.1 SA Initialization Procedures 985 When issuing an ISA_INIT_REQ message, the initiating entity does the fol- 986 lowing: 988 1. Create initiator cookie. See Section 2.3.7 for details. 990 2. Generate a unique pseudo-random negotiation SPI. See Section 2.3.2 991 for details. 993 3. Determine the relevant security characteristics of the session (the 994 situation). 996 4. Generate a proposal for protecting a session under that situation. 998 5. Construct an ISA_INIT_REQ packet. 1000 6. Transmit the packet to the destination host as described in Section 1001 2.3.4. 1003 When an ISA_INIT_REQ message is received, the receiving entity does the 1004 following: 1006 1. Check the ISAKMP header as described in Section 2.3.4. 1008 2. Unpack the ISA_INIT_REQ payload. 1010 3. Determine if the given situation can be protected. If not, the pro- 1011 tocol machine must send a rejection notification and return to IDLE. 1013 4. Determine if it can use any of the proposed protection suites to 1014 protect the session. If none of the proposed suites are acceptable, 1015 then the protocol machine must send a rejection notification, clear 1016 all state and return to IDLE. 1018 5. Create responder cookie. See Section 2.3.7 for details. 1020 6. Generate a unique pseudo-random SPI. See Section 2.3.2 for details. 1022 7. Construct an ISA_INIT_RESP packet containing the situation and the 1023 chosen protection suite. 1025 8. Transmit the packet to the initiating host as described in Section 1026 2.3.4. 1028 When an ISA_INIT_RESP message is received, the receiving entity (original 1029 initiator) does the following: 1031 1. Check the ISAKMP header as described in Section 2.3.4. 1033 2. Unpack the ISA_INIT_RESP payload. 1035 3. Determine that the situation returned is the same as the one sent. 1036 If not, the protocol machine must send a rejection notification and 1037 possibly resend the ISA_INIT_REQ message. 1039 4. Determine if the returned protection suite is among the set of valid 1040 choices. If the entire proposal was rejected, the event 1041 PROPOSAL_REJECTED is logged to the appropriate audit file. If an 1042 invalid protection suite was returned, the receiving entity does the 1043 following: 1045 (a) The event, INVALID ATTRIBUTES, is logged in the appropriate 1046 system audit file. 1048 (b) Clear all state and return to IDLE. Any further communication 1049 must start the SA initialization procedures from the beginning. 1051 If a valid protection suite was selected, the receiving entity does 1052 the following: 1054 (a) Configure protocol machine based on protection suite selected. 1056 (b) Transition to Authentication and Key Exchange (see Section 3.2). 1058 3.2 Authentication and Key Exchange 1060 During the authentication and key exchange phase, information required to 1061 confirm the identities of the parties wishing to establish the SA and es- 1062 tablish session keys for use during the SA establishment is exchanged. 1063 Depending on the key exchange algorithms, the original key may be used 1064 during data communications or a new one may be created and exchanged dur- 1065 ing the negotiation phase (described in section 3.3). This original or 1066 new key would be used in protecting the actual data communications. 1068 The packets that carry the authentication and key exchange payloads have 1069 the format shown in Figure 4. When the ISA_AUTH&KE_REQ and ISA_AUTH&KE_RESP 1070 packets are used, the Authentication Payload SHOULD be processed first to 1071 strongly authenticate the packet issuer, followed by the processing of the 1072 Key Exchange Payload. The authentication and key exchange payloads (shown 1073 in Figures 5 and 6) are general formats which support many types of au- 1074 thentication and key exchange mechanisms. The detailed specification of 1075 these fields will be specified in companion RFCs. These companion RFCs 1076 will define the standard authentication and key exchange mechanisms that 1077 need to be implemented to assure compliance with this specification. The 1078 format for the Internet Security DOI key exchange and authentication pay- 1079 loads is described in A 1081 3.2.1 Authentication Payload Format 1083 This section specifies the encoding of the authentication payload for the 1084 ISA_AUTH_REQ, ISA_AUTH_RESP, ISA_AUTH&KE_REQ, and ISA_AUTH&KE_RESP messages. 1085 As described in section 2.2.3, when the ISA_AUTH_REQ and ISA_AUTH_RESP pack- 1086 ets are transmitted alone, the key exchange payload is not present. The 1087 format of these messages is shown in Figure 5. 1089 o Authentication Authority (2 octets) - This field identifies the party 1090 that generated the certificates used for authentication. Authorities 1091 must be assigned an identifier by the Internet Assigned Numbers 1092 Authority (IANA). Before being assigned an identifier, an authority 1093 must publish an RFC defining the authority's domain. [RFC-1422] 1094 describes the Internet Policy Registration Authority (IPRA) and the 1095 procedures for achieving this registration. 1097 If PGP certificates, based on the ``web of trust'', are carried in 1098 the authentication payload the Authentication Authority value is one 1099 (1). 1101 Example certificate authorities that would have to register for an 1102 identifier are: 1104 -- RSA Commercial Certificate Authority 1105 (http://www_csc.rsa.com/netsite) 1107 -- Stable Large E-mail Database (SLED) (http://www.four11.com) 1109 -- U.S. Postal Service. 1111 o Authentication Type (2 octets) - This field indicates the 1112 authentication payload format. This field is used by authentication 1113 authorities that support more than one certificate type. The 1114 authentication types supported by an authentication authority must be 1115 defined in the RFC required for authentication authority 1116 registration. Examples are: 1118 -- PKCS #7 certificates 1120 -- PGP certificates 1122 -- DNS Signed Keys 1124 -- Kerberos Tokens 1126 -- X.509 certificates 1128 o Length (2 octets) - Length of the Authentication Data field in 1129 octets. 1131 o Authentication Data (variable) - Actual authentication data. The 1132 type of certificate is indicated by the Authentication Type field. 1134 3.2.2 Key Exchange Payload Format 1136 A variety of key exchanges can be supported in the key exchange phase. 1137 Some examples of key exchanges which may be used in this protocol are Oak- 1138 ley [Oakley], Diffie-Hellman, the enhanced Diffie-Hellman key exchange de- 1139 scribed in X9.42 [ANSI], the Key Exchange Algorithm (KEA) on the FORTEZZA 1140 card, and the RSA-based key exchange used by PGP. This protocol will also 1141 support key exchanges that include key escrow or data recovery techniques, 1142 but does not mandate their use. 1144 ISAKMP supports both public and private key generation techniques. Both 1145 types must register with IANA to obtain a Key Exchange Identifier (KEI). 1147 Before published public key exchanges can obtain a KEI, an RFC defining 1148 the key exchange payload format and key generation procedures MUST be sub- 1149 mitted. Private key exchanges SHOULD be documented in an RFC when regis- 1150 tering for a KEI. 1152 The encoding of the key exchange payload is dependent on the specific key 1153 exchange and, therefore, is not specified in this Internet draft. Each 1154 key exchange must define the following information: (a) System parame- 1155 ters, (b) Key establishment algorithm, and (c) Key derivation procedure 1156 (dependent on key exchange type). See [Oakley] for an example of a key 1157 exchange that can be executed during the ISAKMP key exchange phase. 1159 As described in section 2.2.2, when the ISA_KE_REQ and ISA_KE_RESP packets 1160 are transmitted alone, the authentication payload is not present. Once 1161 the key exchange is completed, then the authentication payload is sent 1162 separately using the format described in section 3.2.1 1164 3.2.3 Authentication and Key Exchange Procedures 1166 When issuing an ISA_AUTH&KE_REQ packet, the initiating entity will do the 1167 following: 1169 1. Create the ISAKMP Header. 1171 2. Create the authentication payload. 1173 3. Create the key exchange payload based on KEI. 1175 4. Construct an ISA_AUTH&KE_REQ packet. 1177 5. Generate an authentication signature using the authentication 1178 attributes and options selected in the initialization phase. 1180 6. Transmit the packet to the responding host as described in Section 1181 2.3.4. 1183 When an ISA_AUTH&KE_REQ packet is received, the receiving entity will do 1184 the following: 1186 1. Check the ISAKMP header as described in Section 2.3.4. 1188 2. Verify the initiator's signature. The ISA_AUTH&KE_REQ packet is 1189 processed and the calculated signature is compared to the signature 1190 contained in the ISA_AUTH&KE_REQ packet. If these signatures are not 1191 identical, the message is discarded and the following actions are 1192 taken: 1194 (a) The event, INVALID SIGNATURE, is logged in the appropriate system 1195 audit file. 1197 (b) No response is sent to the initiating entity. This will cause 1198 the transmission timer of the initiating entity to expire and 1199 force retransmission of the message. 1201 3. Unpack the ISA_AUTH&KE_REQ packet. 1203 4. Create the ISAKMP Header. 1205 5. Create the authentication payload. 1207 6. Create the key exchange payload based on KEI. 1209 7. Construct an ISA_AUTH&KE_RESP packet. 1211 8. Generate an authentication signature, to authenticate responder to 1212 initiator, using the authentication attributes and options selected. 1214 9. Transmit the packet to the initiating host as described in Section 1215 2.3.4. 1217 10. Begin key calculation in the background, if necessary. 1219 When an ISA_AUTH&KE_RESP message is received, the receiving entity (origi- 1220 nal initiator) will do the following: 1222 1. Check the ISAKMP header as described in Section 2.3.4. 1224 2. Verify the initiator's signature. The ISA_AUTH&KE_RESP packet is 1225 processed and the calculated signature is compared to the signature 1226 contained in the ISA_AUTH&KE_RESP packet. If these signatures are not 1227 identical, the message is discarded and the following actions are 1228 taken: 1230 (a) The event, INVALID SIGNATURE, is logged in the appropriate system 1231 audit file. 1233 (b) No response is sent to the initiating entity. This will cause 1234 the transmission timer of the initiating entity to expire and 1235 force retransmission of the message. 1237 3. Calculate key, if necessary. 1239 4. Transition to Security Association Negotiation. 1241 3.3 Security Association Negotiation 1243 The SA Negotiation phase allows the initiating entity to present SA at- 1244 tributes that it wishes to use for secure communications to a respond- 1245 ing entity. These SA attributes may include additional options for the 1246 attributes agreed upon during the initialization phase, as well as ad- 1247 ditional attributes required for an SA. As an example, the SA parame- 1248 ters for the IP AH and IP ESP security mechanisms are cited in the Secu- 1249 rity Architecture for the Internet Protocol [RFC-1825]. The format for 1250 the ISA_NEG_REQ and ISA_NEG_RESP packets is the same as the ISA_INIT_REQ and 1251 ISA_INIT_RESP shown in Figure 3. All fields shown in Figure 3 exist for 1252 the ISA_NEG_REQ and ISA_NEG_RESP packets. 1254 3.3.1 SA Negotiation Procedures 1256 When issuing an ISA_NEG_REQ packet, the initiating entity does the follow- 1257 ing: 1259 1. Determine SA attributes to be negotiated. This may include changing 1260 some attributes from the original SA initialization. 1262 2. Construct an ISA_NEG_REQ packet. 1264 3. Depending on the SA Attributes established in the SA initialization 1265 phase, apply the agreed upon security services. 1267 (a) If the SA requires authentication, the ISA_NEG_REQ packet is pro- 1268 cessed (or signed) and the signature placed as noted in Figure 2. 1270 (b) If the SA requires encryption and the encryption algorithm is a 1271 block encryption algorithm, then padding up to the block size 1272 MUST be placed as noted in Figure 2. 1274 (c) If the SA requires encryption, the ISA_NEG_REQ payload and 1275 Signature are encrypted. 1277 4. Transmit the packet to the responding host as described in Section 1278 2.3.4. 1280 When an ISA_NEG_REQ packet is received, the receiving entity does the fol- 1281 lowing: 1283 1. Check the ISAKMP header as described in Section 2.3.4. 1285 2. Depending on the SA Attributes, apply the agreed upon security 1286 services. 1288 (a) If the SA requires encryption, decrypt the ISA_NEG_REQ payload and 1289 Signature. If the decryption fails, the message is discarded and 1290 the following actions are taken: 1292 i. The event, DECRYPTION FAILED, is logged in the appropriate 1293 system audit file. 1295 ii. No response is sent to the initiating entity. This will 1296 cause the transmission timer of the initiating entity to 1297 expire and force retransmission of the message. 1299 (b) If the SA requires authentication, the ISA_NEG_REQ packet is 1300 processed and the calculated signature is compared to the 1301 signature contained in the ISA_NEG_REQ packet. If these signatures 1302 are not identical, the message is discarded and the following 1303 actions are taken: 1305 i. The event, INVALID SIGNATURE, is logged in the appropriate 1306 system audit file. 1308 ii. No response is sent to the initiating entity. This will 1309 cause the transmission timer of the initiating entity to 1310 expire and force retransmission of the message. 1312 3. Unpack the ISA_NEG_REQ packet payload and determine the highest 1313 priority SA attributes supported. If none of the SA attribute 1314 options are supported, the ISA_NEG_RESP packet will have the value zero 1315 (0) in the Number of Sets field and an SA will not be established. 1317 4. If the SA negotiation is requesting a key change or new 1318 authentication mechanism, then generate the appropriate information 1319 and include it as an attribute in the ISA_NEG_RESP payload. 1321 5. Construct an ISA_NEG_RESP packet. 1323 6. Depending on the SA Attributes, apply the agreed upon security 1324 services. 1326 (a) If the SA requires authentication, the ISA_NEG_RESP packet is 1327 processed and the signature placed as noted in Figure 2. 1329 (b) If the SA requires encryption and the encryption algorithm is a 1330 block encryption algorithm, then padding up to the block size 1331 MUST be placed as noted in Figure 2. 1333 (c) If the SA requires encryption, the ISA_NEG_RESP payload and 1334 Signature are encrypted. 1336 7. Transmit the packet to the initiating host as described in Section 1337 2.3.4. 1339 8. If required, begin calculation of the new session key in the 1340 background. 1342 9. Return appropriate data (i.e. SA, SPI) to negotiation server, clear 1343 all state, and return to IDLE. 1345 When an ISA_NEG_RESP message is received, the receiving entity (original 1346 initiator) does the following: 1348 1. Check the ISAKMP header as described in Section 2.3.4. 1350 2. Depending on the SA Attributes, apply the agreed upon security 1351 services. 1353 (a) If the SA requires encryption, decrypt the ISA_NEG_RESP payload and 1354 Signature. If the decryption fails, the message is discarded and 1355 the following actions are taken: 1357 i. The event, DECRYPTION FAILED, is logged in the appropriate 1358 system audit file. 1360 ii. No response is sent to the initiating entity. This will 1361 cause the transmission timer of the initiating entity to 1362 expire and force retransmission of the message. 1364 (b) If the SA requires authentication, the ISA_NEG_RESP packet is 1365 processed and the calculated signature is compared to the 1366 signature contained in the ISA_NEG_RESP packet. If these 1367 signatures are not identical, the message is discarded and the 1368 following actions are taken: 1370 i. The event, INVALID SIGNATURE, is logged in the appropriate 1371 system audit file. 1373 ii. No response is sent to the initiating entity. This will 1374 cause the transmission timer of the initiating entity to 1375 expire and force retransmission of the message. 1377 3. Unpack the ISA_NEG_RESP payload and verify the SA attributes selected 1378 by responder are valid. If the attribute sets (or lists) are invalid 1379 or the responder rejected all proposed attribute sets (or lists), the 1380 receiving entity does the following: 1382 (a) The event, INVALID ATTRIBUTES, is logged in the appropriate 1383 system audit file. 1385 (b) Clear all state and return to IDLE. 1387 If the attribute set (or list) is valid, the receiving entity does 1388 the following: 1390 (a) Configure the protocol machine based on the attribute set (or 1391 list) selected. 1393 4. If required, begin calculation of the new session key in the 1394 background. 1396 5. Return appropriate data (i.e. SA, SPI) to negotiation server, clear 1397 all state, and return to IDLE. 1399 1 2 3 1400 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1402 ~ ISAKMP Header ~ 1403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1404 ! Next Payload ! Payload Len ! RESERVED ! 1405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1406 ! Domain of Interpretation ! 1407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1408 ! ! 1409 ~ Situation ~ 1410 ! ! 1411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1412 ! ! 1413 ~ Proposal ~ 1414 ! ! 1415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1417 Figure 3: ISA_INIT_REQ and ISA_INIT_RESP Packet Format 1419 1 2 3 1420 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 ~ ISAKMP Header ~ 1423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1424 ! Next Payload ! Payload Len ! RESERVED ! 1425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1426 ~ ~ 1427 ! Authentication Payload ! 1428 ~ ~ 1429 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1430 ! Next Payload ! Payload Len ! RESERVED ! 1431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1432 ~ ~ 1433 ! Key Exchange Payload ! 1434 ~ ~ 1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1437 Figure 4: ISA_AUTH&KE_REQ and ISA_AUTH&KE_RESP Packet Format 1438 1 2 3 1439 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1441 ! Next Payload ! Payload Len ! RESERVED ! 1442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1443 ! Authentication Authority ! Reserved ! 1444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1445 ! Authentication Type ! Length ! 1446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1447 ~ ~ 1448 ! Authentication Data ! 1449 ~ ~ 1450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1452 Figure 5: Authentication Payload Format 1454 1 2 3 1455 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1457 ! Next Payload ! Payload Len ! RESERVED ! 1458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1459 ! KEI ! Length ! 1460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1461 ~ ~ 1462 ! Key Exchange Data ! 1463 ~ ~ 1464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1466 Figure 6: Key Exchange Payload Format 1468 o KEI (2 octets) - Key Exchange Identifier 1470 o Length (2 octets) - Length of payload in octets 1472 o Key Exchange Data (variable) - Data (i.e. public values) required to 1473 create session key. 1475 4 Security Association Modification 1477 Security Association modification provides the ability to update security 1478 association attributes and parameters within an existing SA without having 1479 to establish a new SA. The use of this exchange can provide performance 1480 benefits without sacrificing the security of the existing communication. 1481 The most common use of this exchange will be to re-key an existing SA. 1482 The format for the ISA_MODIFY packet is the same as the ISA_INIT_REQ and 1483 ISA_INIT_RESP shown in Figure 3. 1485 4.1 Modification Procedures 1487 The procedure for exchanging information to modify an SA are similiar to 1488 the SA negotiation exchange. The details of SA modification will be de- 1489 scribed in this section as they are solidified during prototype develop- 1490 ment. 1492 5 Security Association Deletion 1494 During communications it is possible that hosts may be compromised or that 1495 information may be intercepted during transmission. Determining whether 1496 this has occurred is not an easy task and is outside the scope of this 1497 Internet-Draft. However, if it is discovered that transmissions are being 1498 compromised, then it is necessary to delete the current SA and establish a 1499 new SA. 1501 The ISA_DELETE packet (shown in Figure 7) provides a controlled method of 1502 informing a peer entity that the initiating entity has deleted an SA(s). 1503 The ISA_DELETE packet allows for the deletion of any number of SAs with 1504 a single message. The receiving entity SHOULD clean up its local SA 1505 database. The receiving entity may be using the SA for secure communi- 1506 cations with more than one party and would not want to actually delete the 1507 SA from its database in this case. However, upon receipt of an ISA_DELETE 1508 packet the SAs listed in the SPIs field of the packet cannot be used with 1509 the initiating entity. The SA Establishment procedure must be invoked to 1510 re-establish secure communications. 1512 o SPI Count - Number of security associations to be deleted 1514 o Length - length of payload in octets 1516 o SPIs - Initiator's Security Parameter Index(s) to be deleted 1518 5.1 Deletion Procedures 1520 When issuing an ISA_DELETE packet, the issuing entity (initiator or re- 1521 sponder) does the following: 1523 1. Create initiator cookie. See Section 2.3.7 for details. 1525 2. Determine SPI of receiving entity. 1527 3. Construct the ISA_DELETE packet. 1529 4. Depending on the SA Attributes, apply the agreed upon security 1530 services. 1532 (a) If the SA requires authentication, the ISA_DELETE packet is 1533 processed and the signature placed as noted in Figure 2. 1535 (b) If the SA requires encryption, the ISA_DELETE payload and 1536 Signature are encrypted. 1538 5. Transmit the packet to the destination host as described in Section 1539 2.3.4. 1541 6. Update the local SA database to reflect the SPI deletions. 1543 Upon receipt of an ISA_DELETE packet, the receiving entity (initiator or 1544 responder) does the following: 1546 1 2 3 1547 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1549 ~ ISAKMP Header ~ 1550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1551 ! SPI Count ! Length ! 1552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1553 ~ ~ 1554 ! SPIs ! 1555 ~ ~ 1556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1558 Figure 7: SA Delete Payload Format 1560 1. Check the ISAKMP header as described in Section 2.3.4. 1562 2. Depending on the SA Attributes, apply the agreed upon security 1563 services in the following order. 1565 (a) If the SA requires encryption, decrypt the ISA_DELETE payload and 1566 Signature. If the decryption fails, the message is discarded and 1567 the following actions are taken: 1569 i. The event is logged in the appropriate system audit file. 1571 ii. Because the ISA_DELETE packet is a unidirectional message a 1572 retransmission will not be performed. The local security 1573 policy will dictate the procedures for continuing. However, 1574 we recommend that the SPIs in the ISA_DELETE packet be checked 1575 to see if the originator was the communicating party. If so, 1576 then these SAs can be deleted from the local SA database. We 1577 also recommend that an ISA_NOTIFY packet with an Error Message 1578 Type (see Section 6) be sent to the originator of the 1579 ISA_DELETE packet. If the SPIs do not match those of the 1580 originator, then no further action should be taken. 1582 (b) If the SA requires authentication, the ISA_DELETE packet is 1583 processed and the calculated signature is compared to the 1584 signature contained in the ISA_DELETE packet. If these signatures 1585 are not identical, the message is discarded and the following 1586 actions are taken: 1588 i. The event is logged in the appropriate system audit file. 1590 ii. Because the ISA_DELETE packet is a unidirectional message a 1591 retransmission will not be performed. The local security 1592 policy will dictate the procedures for continuing. However, 1593 we recommend that the SPIs in the ISA_DELETE packet be checked 1594 to see if the originator was the communicating party. If so, 1595 then these SAs can be deleted from the local SA database. We 1596 also recommend that an ISA_NOTIFY packet with an Error Message 1597 Type (see Section 6) be sent to the originator of the 1598 ISA_DELETE packet. If the SPIs do not match those of the 1599 originator, then no further action should be taken. 1601 3. Unpack the ISA_DELETE payload. 1603 4. Update the local SA database to reflect the SPI deletions. 1605 6 Notification Message 1607 The ISAKMP ISA_NOTIFY packet contains information one party wants to send 1608 to another. Notification information can be error messages specifying 1609 why a SA could not be established. It can also be status data that a 1610 process managing an SA database wishes to communicate with a peer pro- 1611 cess. For example, a secure front end or security gateway may use the 1612 ISA_NOTIFY message to synchronize SA communication (see Appendix B.2). 1613 The ISA_NOTIFY packet is unidirectional. 1615 1 2 3 1616 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1618 ~ ISAKMP Header ~ 1619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1620 ! Notify Message Type ! Length ! 1621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1622 ~ ~ 1623 ! Notify Payload ! 1624 ~ ~ 1625 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1627 Figure 8: ISA NOTIFY Payload Format 1629 o Notify Message Type (2 octets) 1631 ______Notification_______Notify_Message_Type__ 1632 RESERVED 0 1633 Error 1-16383 1634 Reserved for Future Use 16384-32767 1635 Status 32768-49151 1636 DOI Specific 49152-65536 1638 o Length (2 octets) - length of payload in octets 1640 o Notify Payload (variable) - Value dependent on the Notify Message 1641 Type 1643 6.1 Notify Message Types 1645 Notify Messages - Errors Types 1646 __________Errors___________Value_Payload__ 1647 DOI-NOT-SUPPORTED 1 1648 SITUATION-NOT-SUPPORTED 2 1649 INVALID-COOKIE 3 1650 INVALID-VERSION-NO 4 1651 INVALID-MESSAGE-TYPE 5 1652 INVALID-EXCHANGE-TYPE 6 1653 INVALID-SPI 7 1654 ATTRIBUTES-NOT-SUPPORTED 8 1655 NO-PROPOSAL-CHOOSEN 9 1656 BAD-PROPOSAL-SYNTAX 10 1657 ATTRIBUTES-NOT-SUPPORTED 11 1658 INVALID-SIGNATURE 12 1659 DECRYPTION-FAILED 13 1661 Notify Messages - Status Types 1662 __Status____Value____Payload____ 1663 CONNECTED 32769 1665 6.2 Notification Procedures 1667 When issuing an ISA_NOTIFY message, the issuing entity (initiator or re- 1668 sponder) does the following: 1670 1. Create initiator cookie. See Section 2.3.7 for details. 1672 2. Determine SPI of receiving entity. 1674 3. Construct ISA_NOTIFY packet. 1676 4. Depending on the SA Attributes, apply the agreed upon security 1677 services. 1679 (a) If the SA requires authentication, the ISA_NOTIFY packet is 1680 processed and the signature placed as noted in Figure 2. 1682 (b) If the SA requires encryption, the ISA_NOTIFY payload and 1683 Signature are encrypted. 1685 5. Transmit the packet to the destination host as described in Section 1686 2.3.4. 1688 Upon receipt of an ISA_NOTIFY message, the receiving entity (initiator or 1689 responder) does the following: 1691 1. Check the ISAKMP header as described in Section 2.3.4. 1693 2. Depending on the SA Attributes, apply the agreed upon security 1694 services in the following order. 1696 (a) If the SA requires encryption, decrypt the ISA_NOTIFY payload and 1697 Signature. If the decryption fails, the message is discarded and 1698 the following actions are taken: 1700 i. The event is logged in the appropriate system audit file. 1702 ii. Because the ISA_NOTIFY packet is a unidirectional message a 1703 retransmission will not be performed. The local security 1704 policy will dictate the procedures for continuing. 1706 (b) If the SA requires authentication, the ISA_NOTIFY packet is 1707 processed and the calculated signature is compared to the 1708 signature contained in the ISA_NOTIFY packet. If these signatures 1709 are not identical, the message is discarded and the following 1710 actions are taken: 1712 i. The event is logged in the appropriate system audit file. 1714 ii. Because the ISA_NOTIFY packet is a unidirectional message a 1715 retransmission will not be performed. The local security 1716 policy will dictate the procedures for continuing. 1718 3. Unpack the ISA_NOTIFY payload. 1720 4. Depending on the Notify Message Type, additional processing may be 1721 necessary. 1723 7 Conclusions 1725 The Internet Security Association and Key Management Protocol (ISAKMP) is 1726 a well designed protocol aimed at the Internet of the future. The mas- 1727 sive growth of the Internet will lead to great diversity in network uti- 1728 lization, communications, security requirements, and security mechanisms. 1729 ISAKMP contains all the features that will be needed for this dynamic and 1730 expanding communications environment. 1732 ISAKMP's Security Association (SA) feature coupled with authentication 1733 and key establishment provides the security and flexibility that will be 1734 needed for future growth and diversity. This security diversity of multi- 1735 ple key exchange techniques, encryption algorithms, authentication mecha- 1736 nisms, security services, and security attributes will allow users to se- 1737 lect the appropriate security for their network, communications, and secu- 1738 rity needs. The SA feature allows users to specify and negotiate security 1739 requirements with other users. An additional benefit of supporting multi- 1740 ple techniques in a single protocol is that as new techniques are devel- 1741 oped they can easily be added to the protocol. This provides a path for 1742 the growth of Internet security services. ISAKMP supports both publicly 1743 or privately defined SAs, making it ideal for government, commercial, and 1744 private communications. 1746 ISAKMP provides the ability to establish SAs for multiple security proto- 1747 cols and applications. These protocols and applications may be session- 1748 oriented or sessionless. Having one SA establishment protocol that sup- 1749 ports multiple security protocols eliminates the need for multiple, nearly 1750 identical authentication, key exchange and SA establishment protocols when 1751 more than one security protocol is in use or desired. Just as IP has pro- 1752 vided the common networking layer for the Internet, a common security es- 1753 tablishment protocol is needed if security is to become a reality on the 1754 Internet. ISAKMP provides the common base that allows all other security 1755 protocols to interoperate. 1757 ISAKMP follows good security design principles. It is not coupled to 1758 other insecure transport protocols, therefore it is not vulnerable or 1759 weakened by attacks on other protocols. Also, when more secure transport 1760 protocols are developed, ISAKMP can be easily migrated to them. ISAKMP 1761 also provides protection against protocol related attacks. This protec- 1762 tion provides the assurance that the SAs and keys established are with the 1763 desired party and not with an attacker. 1765 ISAKMP also follows good protocol design principles. Protocol specific 1766 information only is in the protocol header, following the design prin- 1767 ciples of IPv6. The data transported by the protocol is separated into 1768 functional payloads. As the Internet grows and evolves, new payloads to 1769 support new security functionality can be added without modifying the en- 1770 tire protocol. 1772 A IP Security DOI 1774 The IP Security DOI Assigned Number for IPv4 is one (1). The situation 1775 for DOI 1 is an IPv4 address. The IP Security DOI Assigned Number for 1776 IPv6 is two (2). The situation for DOI 2 is an IPv6 address. 1778 A.1 IP Security Proposal Formats 1780 This section defines the IP Security syntax for SA proposals and secu- 1781 rity attributes. The SA proposals for a security protocol (i.e. ESP) are 1782 carried in an SA payload. The SA payload is sent in the following mes- 1783 sages: ISA_INIT_REQ, ISA_INIT_RESP, ISA_NEG_REQ, ISA_NEG_RESP, ISA_MOD_REQ, 1784 and 1785 ISA_MOD_RESP. This syntax groups the security attributes needed to perform 1786 a security function together. The proposal and attribute formats are de- 1787 fined so additions or modifications to the proposals or attributes do not 1788 require a modification to the protocol. 1790 Figure 9 shows the SA proposal format which contains the SA attributes. 1791 There can be one or more SA attribute in each SA proposal. There can one 1792 or more SA proposals sent for each security protocol, but only one re- 1793 sponse per security protocol is allowed. A negative response, such as: 1794 IMPROPER SA PROPOSAL FORMAT, is returned in an ISA_NOTIFY message. 1796 1 2 3 1797 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1799 ! Protocol # ! Proposal # ! Proposal Len ! RESERVED ! 1800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1801 ! ! 1802 + + 1803 . . 1804 . SA Attributes . 1805 . . 1806 + + 1807 ! ! 1808 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1810 Figure 9: SA Proposal Format 1812 o Protocol Number (1 octet) - Identifies the security protocol 1813 requiring the SA attributes proposed. Uses the same values as the 1814 IPv4 Protocol field [RFC-1700]. 1816 o Proposal Number (1 octet) - Unique proposal identifier for the given 1817 security protocol. 1819 o Proposal Length (1 octet) - Specifies the proposal length in 4-octet 1820 units. Each IP Security proposal is an integer multiple of 4 octets 1821 long. 1823 o SA Attributes - Variable length field containing the attributes for 1824 an SA. 1826 Figure 10 shows the SA attribute format. The most significant bit of the 1827 Attribute Class defines a grouping of attributes within a proposal. The 1828 second most significant bit indicates whether the attribute is of type 1829 basic or variable percision integer (VPI). Negative responses, such as: 1830 UNKNOWN SA ATTRIBUTE, are returned in an ISA_NOTIFY message. 1832 o Attribute Class (2 octets) - Unique identifier for each general class 1833 of attribute type. ENCRYPTION ALGORITHM is an example of an 1834 attribute class. (See A.4 for the assigned attribute class values 1835 for ESP, AH, and Oakley.) 1837 The most significant bit (SET) of the Attribute Class is for indicating 1838 a grouping of attributes within a proposal. If the SET bit is one (1) 1839 the following attribute belongs with the current attribute. There can be 1840 two or more attributes in a group. If the SET bit is zero (0) either the 1841 1 2 3 1842 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1844 !S!T! ! TYP=0 VPI Length ! 1845 !E!Y! Attribute Class ! TYP=1 SA Attribute Value ! 1846 !T!P! ! ! 1847 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1848 . . 1849 . TYP=0 VPI Present . 1850 . . 1851 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1853 Figure 10: Attribute Format 1855 attribute is the last in a set or is an individual attribute. Attributes 1856 should be grouped together when a security policy decision must be made 1857 based on how attributes relate to each other, in addition to individual 1858 meaning. 1860 The second most significant bit (TYP) of the Attribute Class is for indi- 1861 cating whether the attribute is a basic type or a variable percision inte- 1862 ger (VPI). If the TYP bit is a zero (0) then the attribute is a VPI type. 1863 If the TYP bit is a one (1) then the attribute is a basic type. 1865 Figure 11 shows the basic SA attribute format and Figure 12 shows the VPI 1866 SA attribute format. 1868 1 2 3 1869 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1871 !S!1! Attribute Class ! SA Attribute Value ! 1872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1874 Figure 11: Basic Attribute Format 1876 o Value (2 octets) - The value of the SA attribute as defined by the 1877 Attribute class. (See A.5 for the assigned attribute values for IP 1878 Security.) 1879 1 2 3 1880 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1882 !S!0! Attribute Class ! VPI Length ! 1883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1884 . . 1885 . VPI . 1886 . . 1887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1889 Figure 12: VPI Attribute Format 1891 o VPI Length (2 octets) - Specifies the VPI's length in 4-octet units. 1892 Each VPI is an integer multiple of 4 octets long. 1894 o VPI - Variable Percision Integer. The field is aligned so the most 1895 significant bit is in the first 4-octet word following the VPI 1896 Length. 1898 A.2 ESP SA and AH SA Proposals 1900 The ESP and AH SAs are defined in [RFC-1825]. This section defines the 1901 format for the ESP and AH SA proposals. The attribute class fields are 1902 as they would appear in an ESP or AH SA Proposal. The attribute value and 1903 VPI fields contain examples of the information they would contain. 1905 Note: The Lifetime fields (Key and SA) can be either basic or VPI at- 1906 tributes. Therefore when parsing the Attribute Class, the TYP bit must 1907 always be checked. 1909 1 2 3 1910 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1911 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1912 ! AH ! Proposal # ! Proposal Len ! RESERVED ! 1913 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1914 !1!1! Authentication Alg ! MD5 ! 1915 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1916 !0!1! Authentication Mode ! KEYED ! 1917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1918 !0!1! Auth Key Exch Id ! Oakley New Group Mode ! 1919 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1920 !0!0! Key Lifetime ! 1! 1921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1922 ! Time (in seconds) ! 1923 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1924 !0!0! SA Lifetime ! 1! 1925 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1926 ! Time (in seconds) ! 1927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1928 !0!0! IP Source Address(es) ! 1! 1929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1930 ! IPv4 Address ! 1931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1932 !0!1! Sensitivity Level ! SECRET ! 1933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1935 Figure 13: AH Proposal Format 1936 1 2 3 1937 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1938 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1939 ! ESP ! Proposal # ! Proposal Len ! RESERVED ! 1940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1941 !1!1! Encryption Algorithm ! DES ! 1942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1943 !0!1! Encryption Mode ! CBC ! 1944 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1945 !0!1! Encryption Transform ! RFC-1828 ! 1946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1947 !0!1! Enc Key Exch Id ! Oakley EXTERNAL KEY MODE ! 1948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1949 !0!0! Crypotgraphic Synch ! Length ! 1950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1951 ! MPI ! 1952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1953 !0!1! Replay Protection ! Present / Absent ! 1954 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1955 !1!1! Authentication Alg ! MD5 ! 1956 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1957 !0!1! Authentication Mode ! KEYED ! 1958 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1959 !0!1! Auth Key Exch Id ! Oakley PRIVATE GROUP MODE ! 1960 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1961 !0!1! Key Lifetime ! Time (in seconds) ! 1962 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1963 !0!0! SA Lifetime ! 1! 1964 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1965 ! Time (in seconds) ! 1966 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1967 !0!0! IP Source Address(es) ! 4! 1968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1969 ! IPv6 Address ! 1970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1971 !0!1! Sensitivity Level ! SECRET ! 1972 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1974 Figure 14: ESP Proposal Format 1976 A.3 Oakley Proposal 1978 The Oakley proposal format contains the SA attributes that are exchanged 1979 in the ISA_INIT messages in order to establish the required security at- 1980 tributes for the key and authentication exchange. See [Oakley] for fur- 1981 ther details. 1983 Note: The three figures 15, 16, and 17 are all combine to make one pro- 1984 posal. They are shown seperately for reading and formatting ease. 1986 1 2 3 1987 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1989 ! Oakley ! Proposal # ! Proposal Len ! RESERVED ! 1990 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1991 ! EHA Format ! 1992 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1993 ! Group Format ! 1994 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1996 Figure 15: Oakley Proposal Format 1998 1 2 3 1999 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2000 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2001 !0!1! Auth / Priv Flag ! PRIV ! 2002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2003 !0!1! Encryption Algorithm ! DES ! 2004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2005 !0!1! Hash Algorithm ! MD5 ! 2006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2007 !1!1! Authentication Alg ! RSA ! 2008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2009 !0!1! Authentication Mode ! KEYED ! 2010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2012 Figure 16: Oakley Proposal - EHA Format 2013 1 2 3 2014 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2015 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2016 !1!1! Group Description ! MODP ! 2017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2018 !1!0! Field Size ! Length ! 2019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2020 ! MPI ! 2021 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2022 !1!0! Prime ! Length ! 2023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2024 ! MPI ! 2025 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2026 !1!0! Generator1 ! Length ! 2027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2028 ! MPI ! 2029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2030 !1!0! Generator2 ! Length ! 2031 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2032 ! MPI ! 2033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2034 !1!0! Curve-p1 ! Length ! 2035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2036 ! MPI ! 2037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2038 !1!0! Curve-p2 ! Length ! 2039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2040 ! MPI ! 2041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2042 !1!0! Largest Prime Factor ! Length ! 2043 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2044 ! MPI ! 2045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2046 !1!0! Order of Group ! Length ! 2047 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2048 ! MPI ! 2049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2050 !0!0! Strength of Group ! Length ! 2051 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2052 ! MPI ! 2053 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2055 Figure 17: Oakley Proposal - Group Format 2057 A.4 Attribute Class Assigned Numbers 2059 Values for attribute classes are specified in the most recent ``Assigned 2060 Numbers'' RFC [RFC-1700]. Presented in the following tables are the val- 2061 ues for ESP, AH, and Oakley SAs. In the Attribute Type Column, a ``B'' 2062 means basic encoding and ``V'' mean Variable Percision Integer. 2064 AH and ESP Attribute Classes 2065 ___________________Class_____________________Assigned_Value__Attribute_Type__ 2066 RESERVED 0 x 2067 RESERVED 1 x 2068 Authentication Algorithm 2 B 2069 Authentication Mode 3 B 2070 Authentication KEI(s) 4 B 2071 Encryption Algorithm 5 B 2072 Encryption Mode 6 B 2073 Encryption Transform 7 B 2074 Encyption KEI(s) 8 B 2075 Size of cryptographic synchronization or IV 9 B/V 2076 Replay Protection 10 B 2077 Key Lifetime 11 B/V 2078 Rekey Value 12 B/V 2079 SA Lifetime 13 B/V 2080 IP Source Address(es) 14 V 2081 Sensitivity Level 15 B 2083 Oakley Attributes Classes 2084 __________________Class____________________Assigned_Value__Attribute_Type__ 2085 Auth / Private Flag 16 B 2086 Hash Algorithm 17 B 2087 Group Description 18 B 2088 Group Type 19 B 2089 Field Element Size 20 V 2090 Print (P) or Irreducible Field Polynomial 21 V 2091 Generator (1 or 2 values) 22 V 2092 Curve Parameters (2 values) 23 V 2093 Largest Prime Factor of the Group Size 24 V 2094 Order of the Group 25 V 2095 Strength of Group 26 V 2097 Attribute class values 27-1024 are reserved for IANA Use. Attribute 2098 class values 1025-15360 are reserved for future use. Attribute class val- 2099 ues 15360-16384 are reserved for private use. 2101 A.5 Attribute Value Assigned Numbers 2103 A.5.1 Sensitivity Level Assigned Numbers 2105 Sensitivity Level 2106 _____Level_____Assigned_Value 2107 Not In Use 0 2108 Unclassified 1 2109 FOUO 2 2110 Undefined 3 2111 Confidential 4 2112 Secret 5 2113 Top Secret 6 2115 Sensitivity values 7-1024 are reserved for IANA Use. Values 1025-15360 2116 are reserved for future use. Values 15360-16384 are reserved for private 2117 use. 2119 A.5.2 Key Exchange Identifiers (KEI) Assigned Numbers 2121 Key Exchange Identifiers (KEI) 2122 _____Key_Exchange_____Assigned_Value_ 2123 Reserved 0 2124 Oakley Main Mode 1 2125 Oakley ISAKMP Mode 2 2126 Oakley Quick Mode 3 2127 Oakley External Mode 4 2129 KEI values 5-1024 are reserved for IANA Use. Values 1025-15360 are re- 2130 served for future use. Values 15360-16384 are reserved for private use. 2132 A.5.3 Encryption Transform Assigned Numbers 2134 Encryption Transforms 2135 _____Transform_____Assigned_Value 2136 Reserved 0 2137 RFC-1829 1 2138 DES-CBC w/Replay 2 2140 Encryption Transform values 3-1024 are reserved for IANA Use. Values 2141 1025-15360 are reserved for future use. Values 15360-16384 are reserved 2142 for private use. 2144 B ISAKMP Scenarios 2146 Examples scenerios are are presented to help illustrate the ISAKMP's abil- 2147 ity to support multiple authentication methods and key exchanges. 2149 B.1 Oakley Scenario 2151 ___________|_______________Oakley_Scenario_____________________________Entity 2152 N#1SI#1NTERNETNSE#2ntity #2 2153 _______|| _______|| 2155 | | Establish Initial SA Between NSs| | 2156 | | | | 2157 | | ISA_INIT_REQ | | 2158 | | ============> | | 2159 | | ISA_INIT_RESP | | 2160 | | <============ | | 2161 | | | | 2162 | | Oakley Key Exchange Between NSs | | 2163 | | | | 2164 | | ISA_KE_REQ | | 2165 | | ==============> | | 2166 | | ISA_KE_RESP | | 2167 | | <=============== | | 2168 | | | | 2169 | | Oakley Authentication Exchange | | 2170 | | | | 2171 | | ISA_AUTH_REQ | | 2172 | | ==============> | | 2173 | | ISA_AUTH_RESP | | 2174 | | <=============== | | 2175 | | ISA_AUTH_REQ | | 2176 | | ==============> | | 2177 | | ISA_AUTH_RESP | | 2178 | | <=============== | | 2179 | | | | 2180 | | Protected Traffic | | 2181 | | NS#1 to NS#2 | | 2182 |_____|_ |______| 2184 ___________|_________Oakley_Scenario_continued______________________EntityN# 2185 1SI#1NTERNETNSE#2ntity #2 2186 _______|| _______|| 2188 | | SA Established NS#1 to NS#2 | | 2189 | | | | 2190 | |Establish SA Between Entities | | 2191 | | | | 2192 | | ISA_NEG_REQ | | 2193 | | ============> | | 2194 | | ISA_NEG_RESP | | 2195 | | <============ | | 2196 | | | | 2197 | | Oakley External Key Exchange | | 2198 | | Between Entities | | 2199 | | | | 2200 | | ISA_KE_REQ | | 2201 | | ==============> | | 2202 | | ISA_KE_RESP | | 2203 | | <=============== | | 2204 | | ISA_KE_REQ | | 2205 | | ==============> | | 2206 | | | | 2207 | | | | 2208 | | Protected Traffic | | 2209 | | Entity#1 to Entity#2 | | 2210 |______| <==============> |______| 2212 The diagrams above only shows ISAKMP messages exchanges. Shown are the 2213 exchanges to initiate SAs between entities and negotiation servers and 2214 the exchanges for the Oakley key exchange and authentication. The formats 2215 and contents of the messages can be found in [Oakley] and Appendix A. See 2216 Section 2.1 for the relationship of ISAKMP to the protocol stack. 2218 When an entity, which can be a process, application, security protocol, 2219 etc., wishes to establish communications with a peer entity a call is made 2220 to the negotiation server (NS). NS#1 checks the local security policy to 2221 determine if an SA is required. If an SA is required, then NS#1 checks 2222 if it has the appropriate SAs established with the peer NS (NS#2). If a 2223 negotiation SA (NS-to-NS SA) is exists, NS#1 can proceed to the start of 2224 the second diagram. If a negotiation SA needs to be established, the NSs 2225 exchange ISA_INIT messages to determine the security attributes, key ex- 2226 change, and authentication to be used for the negotiation SA. In our exam- 2227 ple the Oakley key exchange and authentication is choosen. The ISA_KE and 2228 ISA_AUTH messages are exchanged according to the rules defined in the key 2229 exchange. Oakley requires two key exchange messages and four authentica- 2230 tion messages. Once these exchanges are complete a negotiation SA between 2231 NSs is established. In the second diagram the negotiation SA is used to 2232 protect the remaining exchanges shown. The NSs now exchange ISA_NEG mes- 2233 sages to create a SA for the entity itself. In our example an Oakley Ex- 2234 ternal Key Exchange is now performed to establish a new key for the entity 2235 to entity SA. Once this SA is established, protected communications takes 2236 place. 2238 B.2 Virtual Private Network Scenario 2240 This scenario shows how ISAKMP can be used in a Virtual Public Network 2241 (VPN). The ability to establish SAs for more than just ESP and AH and one 2242 of the uses of the ISA_NOTIFY message are also illustrated. 2244 __________________|_________Virtual_Public_Network_Scenario____________________ 2245 ____________EndSSystemF#1EI#1NTERNETSFEE#2nd System #2 2246 ________|| ________|| 2247 Establish ES#1 To | | | | 2248 SFE#1 Connection | | | | 2250 SYN | | | | 2251 ===> | | | | 2252 | |Establish Connection Between SFEs | | 2253 | | | | 2254 | | SYN | | 2255 | | ===> | | 2256 | | SYN, ACK | | 2257 | | <======= | | 2258 | | ACK | | 2259 | | ===> | | 2260 | | | | 2261 | | Establish SA Between SFEs | | 2262 | | | | 2263 | | ISA_INIT_REQ | | 2264 | | ============> | | 2265 | | ISA_INIT_RESP | | 2266 | | <============ | | 2267 | | ISA_KE&AUTH_REQ | | 2268 | | ==============> | | 2269 | | ISA_KE&AUTH_RESP | | 2270 | | <=============== | | 2271 | | Secure Connection | 2272 |Establish SFE#2 2273 | | Between SFEs | |to ES#2 2274 Connection 2275 | | | | 2276 | | | |SYN 2277 | | | |===> 2278 | | | |SYN, ACK 2279 | | | |<======= 2280 | | | |ACK 2281 | | | |===> 2282 | | ISA_NOTIFY(Status == Connected) | | 2283 SYN, ACK | | <==================== | | 2284 <======= | | | | 2285 ACK | | | | 2286 ===> | | | | 2287 | | | | 2288 | | Protected Traffic | | 2289 | | ES#1 to ES#2 | | 2290 |_______| <==============> |_______| 2292 The diagram shows an End System (ES) using a connection oriented proto- 2293 col (we use TCP as an example) establishing a connection with another ES. 2294 Both ES are behind Secure Front Ends (SFE) (e.g. firewalls). The connec- 2295 tion establishment from End System #1 (ES#1) is intercepted by its Secure 2296 Front End (SFE #1). SFE#1 establishes a connection and then a Security 2297 Association (SA), using normal ISAKMP SA establishment procedures, with 2298 SFE #2. Next SFE #2 establishes a connection with ES #2. Upon successful 2299 completion SFE #2 sends an ISA_NOTIFY with Status equal Connected. SFE #1 2300 completes it's connection with ES #1 and normal end to end communications 2301 takes place secured between SFE #1 and SFE #2. If SFE #2 had been unable 2302 to establish a connection with ES #2 it would have returned an ISA_NOTIFY 2303 with Status equal Not Connected with an optional reason code. 2305 C Security Association Attributes 2307 This appendix contains a list of security attributes that should be con- 2308 sidered when defining a Security Association (SA) for a security proto- 2309 col or application. As an example, the security attributes culled from 2310 this list and required for an IP Security (AH, ESP) SA are defined in 2311 [RFC-1825]. The separation of ISAKMP from a specific SA definition is im- 2312 portant to ensure ISAKMP can establish SAs for all possible security func- 2313 tionality. Each security function will be required to maintain a database 2314 of current SAs. This list is based upon an e-mail message [Kent94] to the 2315 IPSEC mail list from Steve Kent. 2317 The authors welcome input on what are meaningful security attributes for 2318 an SA. 2320 1. SAID.INBOUND 2322 2. SAID.OUTBOUND 2324 3. ENCAPSULATION 2326 4. INBOUND-CRITERIA 2328 (a) IP-DESTINATION-ADDRESS 2330 (b) IP-SOURCE-ADDRESS 2332 (c) NEXT-PROTOCOL 2334 (d) IP-SECURITY-LABEL 2336 (e) TRANSPORT-DESTINATION-PORT 2338 (f) TRANSPORT-SOURCE-PORT 2340 5. PEER-ADDRESS 2342 6. AUTHENTICATION 2344 (a) ENABLED 2346 (b) MECHANISM 2348 o DIGITAL SIGNATURE 2349 i. KEY.INBOUND (Peer's Public Key) 2351 ii. KEY.OUTBOUND (Initator's Private Key) 2353 7. ENCRYPTION 2355 (a) ENABLED 2357 (b) ALGORTIHM 2359 (c) KEY.INBOUND 2361 (d) KEY.OUTBOUND 2363 (e) IV.INBOUND 2365 (f) IV.OUTBOUND 2367 8. INTEGRITY 2369 (a) ENABLED 2371 (b) PLAINTEXT 2373 (c) DIRECTION.ENABLED 2375 (d) DIRECTION.VALUE 2377 (e) ALGORITHM 2379 (f) KEY.OUTBOUND 2381 (g) KEY.INBOUND 2383 9. COMPRESSION 2385 (a) ENABLED 2387 (b) ALGORITHM 2389 10. REPLAY 2391 (a) ENABLED 2392 (b) SIZE 2394 (c) NUMBER.OUTBOUND 2396 (d) NUMBER.INBOUND 2398 (e) WINDOW.SIZE 2400 (f) WINDOW 2402 11. FRAGMENTATION 2404 (a) INBOUND 2406 (b) OUTBOUND 2408 12. KEY-MANAGEMENT 2410 (a) NEGOTIATED 2412 (b) TECHNIQUE 2414 (c) PARAMETERS 2416 (d) REKEY 2418 o GRACE 2420 o NEXT-SA 2422 o TIME-BASED 2424 i. ENABLE 2426 ii. TRIGGER 2428 o TRAFFIC-BASED 2430 i. ENABLE 2432 ii. PACKET-COUNT.INBOUND 2434 iii. PACKET-COUNT.OUTBOUND 2435 iv. TRIGGER.INBOUND 2437 v. TRIGGER.OUTBOUND 2439 Security Considerations 2441 Cryptographic analysis techniques are improving at a steady pace. The 2442 continuing improvement in processing power makes once computational pro- 2443 hibitive cryptographic attacks more realistic. New cryptographic algo- 2444 rithms and public key generation techniques are also being developed at a 2445 steady pace. New security services and mechanisms are being developed at 2446 an accelerated pace. A consistent method of choosing from a variety of 2447 security services and mechanisms and to exchange attributes required by 2448 the mechanisms is important to security in the complex structure of the 2449 Internet. However a system that locks itself into a single cryptographic 2450 algorithm, key exchange technique, or security mechanism will become in- 2451 creasingly vulnerable as time passes. 2453 UDP is an unreliable datagram protocol and therefore its use in ISAKMP in- 2454 troduces a number of security considerations. Since UDP is unreliable, 2455 but a key management protocol must be reliable, the reliability is built 2456 into ISAKMP. While ISAKMP utilizes UDP as its transport mechanism, it 2457 doesn't soley rely on any UDP information (e.g. checksum, length) for its 2458 processing. 2460 Another issue that must be considered in the development of IKMP is the 2461 effect of firewalls on the protocol. Many firewalls filter out all UDP 2462 packets, making reliance on UDP questionable in certian environments. 2464 A number of very important security considerations are presented in 2465 [RFC-1825]. One bares repeating. Once a private session key is created 2466 it must be safely stored. Failure to properly protect the private key 2467 from access both internal and external to the system completely nullifies 2468 any protect provided by the IP Security services. 2470 Acknowledgements 2472 Marsha Gross, Bill Kutz, Mike Oehler, Mark Schneider, and Pete Sell pro- 2473 vided significant input and review to this document. 2475 Scott Carlson ported the TIS DNSSEC prototype to FreeBSD for use with the 2476 ISAKMP prototype. 2478 Jeff Turner and Steve Smalley have contributed to the prototype develop- 2479 ment and integration with ESP and AH. 2481 Thanks to Carl Muckenhirn of SPARTA, Inc. for his assistance with LaTeX. 2483 References 2485 [ANSI] ANSI, X9.42: Public Key Cryptography for the Financial Services 2486 Industry -- Establishment of Symmetric Algorithm Keys Using 2487 Diffie-Hellman, Working Draft, October 26, 1995. 2489 [RFC-1825] Randall Atkinson, Security Architecture for the Internet 2490 Protocol, RFC-1825, August, 1995. 2492 [BC] Ballarie, A. and J. Crowcroft, Multicast-specific Security Threats 2493 and Countermeasures, Proceedings of 1995 ISOC Symposium on Networks 2494 & Distributed Systems Security, pp. 17-30, Internet Society, San 2495 Diego, CA, February 1995. 2497 [Berge] Berge, N.H., UNINETT PCA Policy Statements, Internet-Draft, work 2498 in progress, November, 1995. 2500 [DOW92] W. Diffie, M.Wiener, P. Van Oorschot, Authentication and 2501 Authenticated Key Exchanges, Designs, Codes, and Cryptography, 2, 2502 107-125, Kluwer Academic Publishers, 1992. 2504 [DNSSEC] Eastlake III, D. and C. Kaufman, Domain Name System Protocol 2505 Security Extensions, Internet-Draft, work in progress, Feb, 1996. 2507 [Karn] Karn P. and B. Simpson, The Photuris Key Management Protocol, 2508 Internet-Draft, work in progress, February, 1996. 2510 [RFC-1422] Steve Kent, Privacy Enhancement for Internet Electronic Mail: 2511 Part II: Certificate-Based Key Management, RFC-1422, February 1993. 2513 [Kent94] Steve Kent, IPSEC SMIB, e-mail to ipsec@ans.net, August 10, 2514 1994. 2516 [RFC-1212] McCloghrie K. and M. Rose, Concise MIB Definitions, RFC-1212, 2517 March 26, 1991. 2519 [RFC-1213] McCloghrie K. and M. Rose, Management Information Base for 2520 Network Management of TCP/IP-based Internets: MIB-II, RFC-1213, 2521 March 26, 1991. 2523 [Oakley] H. K. Orman, The Oakley Key Determination Protocol, 2524 Internet-Draft, work in progress, February, 1996. 2526 [RFC-1700] Reynolds, J. and J. Postel, Assigned Numbers, STD 2, RFC-1700, 2527 October, 1994. 2529 [RFC-1155] Rose M. and K. McCloghrie, Structure and Identification of 2530 Management Information for TCP/IP-based Internets, RFC-1155, May, 2531 1990. 2533 [Secu] SECUREWARE INC., Peer Authentication and Key Management Protocol 2534 Specification, Version 2.2, October 27, 1995. 2536 [Schneier] Bruce Schneier, Applied Cryptography - Protocols, Algorithms, 2537 and Source Code in C, John Wiley & Sons, Inc., 1994. 2539 [Spar94a] Harney H., C. Muckenhirn, and T. Rivers, Group Key Management 2540 (GKMP) Architecture, SPARTA, Inc., Internet-Draft, September, 1994. 2542 [Spar94b] Harney H., C. Muckenhirn, and T. Rivers, Group Key Management 2543 (GKMP) Specification, SPARTA, Inc., Internet-Draft, September, 1994. 2545 Addresses of Authors 2547 The two authors are with: 2549 National Security Agency 2550 ATTN: R23 2551 9800 Savage Road 2552 Ft. Meade, MD. 20755-6000 2554 Douglas Maughan 2555 Phone: 301-688-0847 2556 E-mail:wdmaugh@tycho.ncsc.mil 2558 Mark Schertler 2559 Phone: 301-688-0849 2560 E-mail:mjs@tycho.ncsc.mil