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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFCXXXX' is mentioned on line 682, but not defined ** Obsolete normative reference: RFC 4307 (Obsoleted by RFC 8247) Summary: 1 error (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Y. Nir 3 Internet-Draft Check Point 4 Obsoletes: 4307 (if approved) T. Kivinen 5 Updates: 7296 (if approved) INSIDE Secure 6 Intended status: Standards Track P. Wouters 7 Expires: August 20, 2017 Red Hat 8 D. Migault 9 Ericsson 10 February 16, 2017 12 Algorithm Implementation Requirements and Usage Guidance for IKEv2 13 draft-ietf-ipsecme-rfc4307bis-17 15 Abstract 17 The IPsec series of protocols makes use of various cryptographic 18 algorithms in order to provide security services. The Internet Key 19 Exchange (IKE) protocol is used to negotiate the IPsec Security 20 Association (IPsec SA) parameters, such as which algorithms should be 21 used. To ensure interoperability between different implementations, 22 it is necessary to specify a set of algorithm implementation 23 requirements and usage guidance to ensure that there is at least one 24 algorithm that all implementations support. This document updates 25 RFC 7296 and obsoletes RFC 4307 in defining the current algorithm 26 implementation requirements and usage guidance for IKEv2, and does 27 minor cleaning up of the IKEv2 IANA registry. This document does not 28 update the algorithms used for packet encryption using IPsec 29 Encapsulated Security Payload (ESP). 31 Status of This Memo 33 This Internet-Draft is submitted in full conformance with the 34 provisions of BCP 78 and BCP 79. 36 Internet-Drafts are working documents of the Internet Engineering 37 Task Force (IETF). Note that other groups may also distribute 38 working documents as Internet-Drafts. The list of current Internet- 39 Drafts is at http://datatracker.ietf.org/drafts/current/. 41 Internet-Drafts are draft documents valid for a maximum of six months 42 and may be updated, replaced, or obsoleted by other documents at any 43 time. It is inappropriate to use Internet-Drafts as reference 44 material or to cite them other than as "work in progress." 46 This Internet-Draft will expire on August 20, 2017. 48 Copyright Notice 50 Copyright (c) 2017 IETF Trust and the persons identified as the 51 document authors. All rights reserved. 53 This document is subject to BCP 78 and the IETF Trust's Legal 54 Provisions Relating to IETF Documents 55 (http://trustee.ietf.org/license-info) in effect on the date of 56 publication of this document. Please review these documents 57 carefully, as they describe your rights and restrictions with respect 58 to this document. Code Components extracted from this document must 59 include Simplified BSD License text as described in Section 4.e of 60 the Trust Legal Provisions and are provided without warranty as 61 described in the Simplified BSD License. 63 Table of Contents 65 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 66 1.1. Conventions Used in This Document . . . . . . . . . . . . 3 67 1.2. Updating Algorithm Implementation Requirements and Usage 68 Guidance . . . . . . . . . . . . . . . . . . . . . . . . 3 69 1.3. Updating Algorithm Requirement Levels . . . . . . . . . . 4 70 1.4. Document Audience . . . . . . . . . . . . . . . . . . . . 5 71 2. Algorithm Selection . . . . . . . . . . . . . . . . . . . . . 5 72 2.1. Type 1 - IKEv2 Encryption Algorithm Transforms . . . . . 5 73 2.2. Type 2 - IKEv2 Pseudo-random Function Transforms . . . . 7 74 2.3. Type 3 - IKEv2 Integrity Algorithm Transforms . . . . . . 8 75 2.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms . . . . . 9 76 2.5. Summary of Changes from RFC 4307 . . . . . . . . . . . . 10 77 3. IKEv2 Authentication . . . . . . . . . . . . . . . . . . . . 11 78 3.1. IKEv2 Authentication Method . . . . . . . . . . . . . . . 11 79 3.1.1. Recommendations for RSA key length . . . . . . . . . 12 80 3.2. Digital Signature Recommendations . . . . . . . . . . . . 12 81 4. Algorithms for Internet of Things . . . . . . . . . . . . . . 13 82 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 83 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 84 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 85 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 86 8.1. Normative References . . . . . . . . . . . . . . . . . . 16 87 8.2. Informative References . . . . . . . . . . . . . . . . . 16 88 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 90 1. Introduction 92 The Internet Key Exchange (IKE) protocol [RFC7296] is used to 93 negotiate the parameters of the IPsec SA, such as the encryption and 94 authentication algorithms and the keys for the protected 95 communications between the two endpoints. The IKE protocol itself is 96 also protected by cryptographic algorithms which are negotiated 97 between the two endpoints using IKE. Different implementations of 98 IKE may negotiate different algorithms based on their individual 99 local policy. To ensure interoperability, a set of "mandatory-to- 100 implement" IKE cryptographic algorithms is defined. 102 This document describes the parameters of the IKE protocol and 103 updates the IKEv2 specification. It changes the mandatory to 104 implement authentication algorithms of Section 4 of [RFC7296] by 105 saying RSA key lengths of less than 2048 SHOULD NOT be used. It does 106 not describe the cryptographic parameters of the AH or ESP protocols. 108 1.1. Conventions Used in This Document 110 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 111 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 112 document are to be interpreted as described in [RFC2119]. 114 When used in the tables in this document, these terms indicate that 115 the listed algorithm MUST, MUST NOT, SHOULD, SHOULD NOT or MAY be 116 implemented as part of an IKEv2 implementation. Additional terms 117 used in this document are: 119 SHOULD+ This term means the same as SHOULD. However, it is likely 120 that an algorithm marked as SHOULD+ will be promoted at 121 some future time to be a MUST. 122 SHOULD- This term means the same as SHOULD. However, an algorithm 123 marked as SHOULD- may be deprecated to a MAY in a future 124 version of this document. 125 MUST- This term means the same as MUST. However, it is expected 126 at some point that this algorithm will no longer be a MUST 127 in a future document. Although its status will be 128 determined at a later time, it is reasonable to expect that 129 if a future revision of a document alters the status of a 130 MUST- algorithm, it will remain at least a SHOULD or a 131 SHOULD- level. 132 IoT stands for Internet of Things. 134 1.2. Updating Algorithm Implementation Requirements and Usage Guidance 136 The field of cryptography evolves continuously. New stronger 137 algorithms appear and existing algorithms are found to be less secure 138 then originally thought. Therefore, algorithm implementation 139 requirements and usage guidance need to be updated from time to time 140 to reflect the new realityI The choices for algorithms must be 141 conservative to minimize the risk of algorithm compromise. 142 Algorithms need to be suitable for a wide variety of CPU 143 architectures and device deployments ranging from high end bulk 144 encryption devices to small low-power IoT devices. 146 The algorithm implementation requirements and usage guidance may need 147 to change over time to adapt to the changing world. For this reason, 148 the selection of mandatory-to-implement algorithms was removed from 149 the main IKEv2 specification and placed in this separate document. 151 1.3. Updating Algorithm Requirement Levels 153 The mandatory-to-implement algorithm of tomorrow should already be 154 available in most implementations of IKE by the time it is made 155 mandatory. This document attempts to identify and introduce those 156 algorithms for future mandatory-to-implement status. There is no 157 guarantee that the algorithms in use today may become mandatory in 158 the future. Published algorithms are continuously subjected to 159 cryptographic attack and may become too weak or could become 160 completely broken before this document is updated. 162 This document only provides recommendations for the mandatory-to- 163 implement algorithms or algorithms too weak that are recommended not 164 to be implemented. As a result, any algorithm listed at the IKEv2 165 IANA registry not mentioned in this document MAY be implemented. For 166 clarification and consistency with [RFC4307] an algorithm will be 167 denoted here as MAY only when it has been downgraded. 169 Although this document updates the algorithms to keep the IKEv2 170 communication secure over time, it also aims at providing 171 recommendations so that IKEv2 implementations remain interoperable. 172 IKEv2 interoperability is addressed by an incremental introduction or 173 deprecation of algorithms. In addition, this document also considers 174 the new use cases for IKEv2 deployment, such as Internet of Things 175 (IoT). 177 It is expected that deprecation of an algorithm is performed 178 gradually. This provides time for various implementations to update 179 their implemented algorithms while remaining interoperable. Unless 180 there are strong security reasons, an algorithm is expected to be 181 downgraded from MUST to MUST- or SHOULD, instead of MUST NOT. 182 Similarly, an algorithm that has not been mentioned as mandatory-to- 183 implement is expected to be introduced with a SHOULD instead of a 184 MUST. 186 The current trend toward Internet of Things and its adoption of IKEv2 187 requires this specific use case to be taken into account as well. 188 IoT devices are resource constrained devices and their choice of 189 algorithms are motivated by minimizing the footprint of the code, the 190 computation effort and the size of the messages to send. This 191 document indicates "(IoT)" when a specified algorithm is specifically 192 listed for IoT devices. Requirement levels that are marked as "IoT" 193 apply to IoT devices and to server-side implementations that might 194 presumably need to interoperate with them, including any general- 195 purpose VPN gateways. 197 1.4. Document Audience 199 The recommendations of this document mostly target IKEv2 implementers 200 as implementations need to meet both high security expectations as 201 well as high interoperability between various vendors and with 202 different versions. Interoperability requires a smooth move to more 203 secure cipher suites. This may differ from a user point of view that 204 may deploy and configure IKEv2 with only the safest cipher suite. 206 This document does not give any recommendations for the use of 207 algorithms, it only gives implementation recommendations for 208 implementations. The use of algorithms by users is dictated by the 209 security policy requirements for that specific user, and are outside 210 the scope of this document. 212 IKEv1 is out of scope of this document. IKEv1 is deprecated and the 213 recommendations of this document must not be considered for IKEv1, as 214 most IKEv1 implementations have been "frozen" and will not be able to 215 update the list of mandatory-to-implement algorithms. 217 2. Algorithm Selection 219 2.1. Type 1 - IKEv2 Encryption Algorithm Transforms 221 The algorithms in the below table are negotiated in the SA payload 222 and used for the Encrypted Payload. References to the specification 223 defining these algorithms and the ones in the following subsections 224 are in the IANA registry [IKEV2-IANA]. Some of these algorithms are 225 Authenticated Encryption with Associated Data (AEAD - [RFC5282]). 226 Algorithms that are not AEAD MUST be used in conjunction with one of 227 the integrity algorithms in Section 2.3. 229 +------------------------+----------+-------+---------+ 230 | Name | Status | AEAD? | Comment | 231 +------------------------+----------+-------+---------+ 232 | ENCR_AES_CBC | MUST | No | (1) | 233 | ENCR_CHACHA20_POLY1305 | SHOULD | Yes | | 234 | ENCR_AES_GCM_16 | SHOULD | Yes | (1) | 235 | ENCR_AES_CCM_8 | SHOULD | Yes | (IoT) | 236 | ENCR_3DES | MAY | No | | 237 | ENCR_DES | MUST NOT | No | | 238 +------------------------+----------+-------+---------+ 240 (1) - This requirement level is for 128-bit and 256-bit keys. 241 192-bit keys remain at MAY level. (IoT) - This requirement is for 242 interoperability with IoT. Only 128-bit keys are at SHOULD level. 243 192-bit and 256-bit remain at the MAY level. 245 ENCR_AES_CBC is raised from SHOULD+ for 128-bit keys and MAY for 246 256-bit keys in [RFC4307] to MUST. 192-bit keys remain at the MAY 247 level. ENCR_AES_CBC is the only shared mandatory-to-implement 248 algorithm with RFC4307 and as a result it is necessary for 249 interoperability with IKEv2 implementation compatible with RFC4307. 251 ENCR_CHACHA20_POLY1305 was not ready to be considered at the time of 252 RFC4307. It has been recommended by the Crypto Forum Research Group 253 (CFRG) of the IRTF as an alternative to AES-CBC and AES-GCM. It is 254 also being standardized for IPsec for the same reasons. At the time 255 of writing, there were not enough IKEv2 implementations supporting 256 ENCR_CHACHA20_POLY1305 to be able to introduce it at the SHOULD+ 257 level. 259 ENCR_AES_GCM_16 was not considered in RFC4307. At the time RFC4307 260 was written, AES-GCM was not defined in an IETF document. AES-GCM 261 was defined for ESP in [RFC4106] and later for IKEv2 in [RFC5282]. 262 The main motivation for adopting AES-GCM for ESP is encryption 263 performance compared to AES-CBC. This resulted in AES-GCM being 264 widely implemented for ESP. As the computation load of IKEv2 is 265 relatively small compared to ESP, many IKEv2 implementations have not 266 implemented AES-GCM. For this reason, AES-GCM is not promoted to a 267 greater status than SHOULD. The reason for promotion from MAY to 268 SHOULD is to promote the slightly more secure AEAD method over the 269 traditional encrypt+auth method. Its status is expected to be raised 270 once widely implemented. As the advantage of the shorter (and 271 weaker) ICVs is minimal, the 8 and 12 octet ICV's remain at the MAY 272 level. 274 ENCR_AES_CCM_8 was not considered in RFC4307. This document 275 considers it as SHOULD be implemented in order to be able to interact 276 with Internet of Things devices. As this case is not a general use 277 case for non-IoT VPNs, its status is expected to remain as SHOULD. 278 The 8 octet size of the ICV is expected to be sufficient for most use 279 cases of IKEv2, as far less packets are exchanged in those cases, and 280 IoT devices want to make packets as small as possible. The SHOULD 281 level is for 128-bit keys, 256-bit keys remains at MAY level. 283 ENCR_3DES has been downgraded from RFC4307 MUST- to SHOULD NOT. All 284 IKEv2 implementations already implement ENCR_AES_CBC, so there is no 285 need to keep support for the much slower ENCR_3DES. In addition, 286 ENCR_CHACHA20_POLY1305 provides a more modern alternative to AES. 288 ENCR_DES can be brute-forced using off-the-shelf hardware. It 289 provides no meaningful security whatsoever and therefore MUST NOT be 290 implemented. 292 2.2. Type 2 - IKEv2 Pseudo-random Function Transforms 294 Transform Type 2 algorithms are pseudo-random functions used to 295 generate pseudo-random values when needed. 297 +-------------------+----------+---------+ 298 | Name | Status | Comment | 299 +-------------------+----------+---------+ 300 | PRF_HMAC_SHA2_256 | MUST | | 301 | PRF_HMAC_SHA2_512 | SHOULD+ | | 302 | PRF_HMAC_SHA1 | MUST- | | 303 | PRF_AES128_XCBC | SHOULD | (IoT) | 304 | PRF_HMAC_MD5 | MUST NOT | | 305 +-------------------+----------+---------+ 307 (IoT) - This requirement is for interoperability with IoT 309 As no SHA2 based transforms were referenced in RFC4307, 310 PRF_HMAC_SHA2_256 was not mentioned in RFC4307. PRF_HMAC_SHA2_256 311 MUST be implemented in order to replace SHA1 and PRF_HMAC_SHA1. 313 PRF_HMAC_SHA2_512 SHOULD be implemented as a future replacement for 314 PRF_HMAC_SHA2_256 or when stronger security is required. 315 PRF_HMAC_SHA2_512 is preferred over PRF_HMAC_SHA2_384, as the 316 additional overhead of PRF_HMAC_SHA2_512 is negligible. 318 PRF_HMAC_SHA1 has been downgraded from MUST in RFC4307 to MUST- as 319 cryptographic attacks against SHA1 are increasing, resulting in an 320 industry-wide trend to deprecate its usage 322 PRF_AES128_XCBC is only recommended in the scope of IoT, as Internet 323 of Things deployments tend to prefer AES based pseudo-random 324 functions in order to avoid implementing SHA2. For the non-IoT VPN 325 deployment it has been downgraded from SHOULD in RFC4307 to MAY as it 326 has not seen wide adoption. 328 PRF_HMAC_MD5 has been downgraded from MAY in RFC4307 to MUST NOT. 329 Cryptographic attacks against MD5, such as collision attacks 330 mentioned in [TRANSCRIPTION], are resulting in an industry-wide trend 331 to deprecate and remove MD5 (and thus HMAC-MD5) from cryptographic 332 libraries. 334 2.3. Type 3 - IKEv2 Integrity Algorithm Transforms 336 The algorithms in the below table are negotiated in the SA payload 337 and used for the Encrypted Payload. References to the specification 338 defining these algorithms are in the IANA registry. When an AEAD 339 algorithm (see Section 2.1) is proposed, this algorithm transform 340 type is not in use. 342 +------------------------+----------+---------+ 343 | Name | Status | Comment | 344 +------------------------+----------+---------+ 345 | AUTH_HMAC_SHA2_256_128 | MUST | | 346 | AUTH_HMAC_SHA2_512_256 | SHOULD | | 347 | AUTH_HMAC_SHA1_96 | MUST- | | 348 | AUTH_AES_XCBC_96 | SHOULD | (IoT) | 349 | AUTH_HMAC_MD5_96 | MUST NOT | | 350 | AUTH_DES_MAC | MUST NOT | | 351 | AUTH_KPDK_MD5 | MUST NOT | | 352 +------------------------+----------+---------+ 354 (IoT) - This requirement is for interoperability with IoT 356 AUTH_HMAC_SHA2_256_128 was not mentioned in RFC4307, as no SHA2 based 357 transforms were mentioned. AUTH_HMAC_SHA2_256_128 MUST be 358 implemented in order to replace AUTH_HMAC_SHA1_96. 360 AUTH_HMAC_SHA2_512_256 SHOULD be implemented as a future replacement 361 of AUTH_HMAC_SHA2_256_128 or when stronger security is required. 362 This value has been preferred over AUTH_HMAC_SHA2_384, as the 363 additional overhead of AUTH_HMAC_SHA2_512 is negligible. 365 AUTH_HMAC_SHA1_96 has been downgraded from MUST in RFC4307 to MUST- 366 as cryptographic attacks against SHA1 are increasing, resulting in an 367 industry-wide trend to deprecate its usage 369 AUTH_AES_XCBC_96 is only recommended in the scope of IoT, as Internet 370 of Things deployments tend to prefer AES based pseudo-random 371 functions in order to avoid implementing SHA2. For the non-IoT VPN 372 deployment, it has been downgraded from SHOULD in RFC4307 to MAY as 373 it has not been widely adopted. 375 AUTH_DES_MAC, AUTH_HMAC_MD5_96, and AUTH_KPDK_MD5 were not mentioned 376 in RFC4307 so their default statuses were MAY. They have been 377 downgraded to MUST NOT. There is an industry-wide trend to deprecate 378 DES and MD5. MD5 support is being removed from cryptographic 379 libraries in general because its non-HMAC use is known to be subject 380 to collision attacks, for example as mentioned in [TRANSCRIPTION]. 382 2.4. Type 4 - IKEv2 Diffie-Hellman Group Transforms 384 There are several Modular Exponential (MODP) groups and several 385 Elliptic Curve groups (ECC) that are defined for use in IKEv2. These 386 groups are defined in both the [RFC7296] base document and in 387 extensions documents and are identified by group number. Note that 388 it is critical to enforce a secure Diffie-Hellman exchange as this 389 exchange provides keys for the session. If an attacker can retrieve 390 one of the private numbers (a or b) and the complementary public 391 value (g**b or g**a), then the attacker can compute the secret and 392 the keys used and decrypt the exchange and IPsec SA created inside 393 the IKEv2 SA. Such an attack can be performed off-line on a 394 previously recorded communication, years after the communication 395 happened. This differs from attacks that need to be executed during 396 the authentication which must be performed online and in near real- 397 time. 399 +--------+---------------------------------------------+------------+ 400 | Number | Description | Status | 401 +--------+---------------------------------------------+------------+ 402 | 14 | 2048-bit MODP Group | MUST | 403 | 19 | 256-bit random ECP group | SHOULD | 404 | 5 | 1536-bit MODP Group | SHOULD NOT | 405 | 2 | 1024-bit MODP Group | SHOULD NOT | 406 | 1 | 768-bit MODP Group | MUST NOT | 407 | 22 | 1024-bit MODP Group with 160-bit Prime | MUST NOT | 408 | | Order Subgroup | | 409 | 23 | 2048-bit MODP Group with 224-bit Prime | SHOULD NOT | 410 | | Order Subgroup | | 411 | 24 | 2048-bit MODP Group with 256-bit Prime | SHOULD NOT | 412 | | Order Subgroup | | 413 +--------+---------------------------------------------+------------+ 415 Group 14 or 2048-bit MODP Group is raised from SHOULD+ in RFC4307 as 416 a replacement for 1024-bit MODP Group. Group 14 is widely 417 implemented and considered secure. 419 Group 19 or 256-bit random ECP group was not specified in RFC4307, as 420 this group was not defined at that time. Group 19 is widely 421 implemented and considered secure. 423 Group 5 or 1536-bit MODP Group has been downgraded from MAY in 424 RFC4307 to SHOULD NOT. It was specified earlier, but is now 425 considered to be vulnerable to being broken within the next few years 426 by a nation state level attack, so its security margin is considered 427 too narrow. 429 Group 2 or 1024-bit MODP Group has been downgraded from MUST- in 430 RFC4307 to SHOULD NOT. It is known to be weak against sufficiently 431 funded attackers using commercially available mass-computing 432 resources, so its security margin is considered too narrow. It is 433 expected in the near future to be downgraded to MUST NOT. 435 Group 1 or 768-bit MODP Group was not mentioned in RFC4307 and so its 436 status was MAY. It can be broken within hours using cheap of-the- 437 shelves hardware. It provides no security whatsoever. 439 Group 22, 23 and 24 are MODP Groups with Prime Order Subgroups that 440 are not safe-primes. The seeds for these groups have not been 441 publicly released, resulting in reduced trust in these groups. These 442 groups were proposed as alternatives for group 2 and 14 but never saw 443 wide deployment. It has been shown that Group 22 with 1024-bit MODP 444 is too weak and academia have the resources to generate malicious 445 values at this size. This has resulted in Group 22 to be demoted to 446 MUST NOT. Group 23 and 24 have been demoted to SHOULD NOT and are 447 expected to be further downgraded in the near future to MUST NOT. 448 Since Group 23 and 24 have small subgroups, the checks specified in 449 "Additional Diffie-Hellman Test for the IKEv2" [RFC6989] section 2.2 450 first bullet point MUST be done when these groups are used. 452 2.5. Summary of Changes from RFC 4307 454 The following table summarizes the changes from RFC 4307. 456 RFC EDITOR: PLEASE REMOVE THIS PARAGRAPH AND REPLACE XXXX IN THE 457 TABLE BELOW WITH THE NUMBER OF THIS RFC 458 +---------------------+------------------+------------+ 459 | Algorithm | RFC 4307 | RFC XXXX | 460 +---------------------+------------------+------------+ 461 | ENCR_3DES | MUST- | MAY | 462 | ENCR_NULL | MUST NOT[errata] | MUST NOT | 463 | ENCR_AES_CBC | SHOULD+ | MUST | 464 | ENCR_AES_CTR | SHOULD | (*) | 465 | PRF_HMAC_MD5 | MAY | MUST NOT | 466 | PRF_HMAC_SHA1 | MUST | MUST- | 467 | PRF_AES128_XCBC | SHOULD+ | SHOULD | 468 | AUTH_HMAC_MD5_96 | MAY | MUST NOT | 469 | AUTH_HMAC_SHA1_96 | MUST | MUST- | 470 | AUTH_AES_XCBC_96 | SHOULD+ | SHOULD | 471 | Group 2 (1024-bit) | MUST- | SHOULD NOT | 472 | Group 14 (2048-bit) | SHOULD+ | MUST | 473 +---------------------+------------------+------------+ 475 (*) This algorithm is not mentioned in the above sections, so it 476 defaults to MAY. 478 3. IKEv2 Authentication 480 IKEv2 authentication may involve a signatures verification. 481 Signatures may be used to validate a certificate or to check the 482 signature of the AUTH value. Cryptographic recommendations regarding 483 certificate validation are out of scope of this document. What is 484 mandatory to implement is provided by the PKIX Community. This 485 document is mostly concerned with signature verification and 486 generation for the authentication. 488 3.1. IKEv2 Authentication Method 490 +--------+---------------------------------------+------------+ 491 | Number | Description | Status | 492 +--------+---------------------------------------+------------+ 493 | 1 | RSA Digital Signature | MUST | 494 | 2 | Shared Key Message Integrity Code | MUST | 495 | 3 | DSS Digital Signature | SHOULD NOT | 496 | 9 | ECDSA with SHA-256 on the P-256 curve | SHOULD | 497 | 10 | ECDSA with SHA-384 on the P-384 curve | SHOULD | 498 | 11 | ECDSA with SHA-512 on the P-521 curve | SHOULD | 499 | 14 | Digital Signature | SHOULD | 500 +--------+---------------------------------------+------------+ 502 RSA Digital Signature is widely deployed and therefore kept for 503 interoperability. It is expected to be downgraded in the future as 504 its signatures are based on the older RSASSA-PKCS1-v1.5 which is no 505 longer recommended. RSA authentication, as well as other specific 506 Authentication Methods, are expected to be replaced with the generic 507 Digital Signature method of [RFC7427]. 509 Shared Key Message Integrity Code is widely deployed and mandatory to 510 implement in the IKEv2 in the RFC7296. 512 ECDSA based Authentication Methods are also expected to be downgraded 513 as these do not provide hash function agility. Instead, ECDSA (like 514 RSA) is expected to be performed using the generic Digital Signature 515 method. 517 DSS Digital Signature is bound to SHA-1 and has the same level of 518 security as 1024-bit RSA. It is expected to be downgraded to MUST 519 NOT in the future. 521 Digital Signature [RFC7427] is expected to be promoted as it provides 522 hash function, signature format and algorithm agility. 524 3.1.1. Recommendations for RSA key length 526 +-------------------------------------------+------------+ 527 | Description | Status | 528 +-------------------------------------------+------------+ 529 | RSA with key length 2048 | MUST | 530 | RSA with key length 3072 and 4096 | SHOULD | 531 | RSA with key length between 2049 and 4095 | MAY | 532 | RSA with key length smaller than 2048 | SHOULD NOT | 533 +-------------------------------------------+------------+ 535 The IKEv2 RFC7296 mandates support for the RSA keys of size 1024 or 536 2048 bits, but key sizes less than 2048 are updated to SHOULD NOT as 537 there is industry-wide trend to deprecate key lengths less than 2048 538 bits. Since these signatures only have value in real-time, and need 539 no future protection, smaller keys were kept at SHOULD NOT instead of 540 MUST NOT. 542 3.2. Digital Signature Recommendations 544 When a Digital Signature authentication method is implemented, the 545 following recommendations are applied for hash functions: 547 +--------+-------------+----------+---------+ 548 | Number | Description | Status | Comment | 549 +--------+-------------+----------+---------+ 550 | 1 | SHA1 | MUST NOT | | 551 | 2 | SHA2-256 | MUST | | 552 | 3 | SHA2-384 | MAY | | 553 | 4 | SHA2-512 | SHOULD | | 554 +--------+-------------+----------+---------+ 556 When Digital Signature authentication method is used with RSA 557 signature algorithm, RSASSA-PSS MUST be supported and RSASSA- 558 PKCS1-v1.5 MAY be supported. 560 The following table lists recommendations for authentication methods 561 in RFC7427 [RFC7427] notation. These recommendations are applied 562 only if Digital Signature authentication method is implemented. 564 +------------------------------------+----------+---------+ 565 | Description | Status | Comment | 566 +------------------------------------+----------+---------+ 567 | RSASSA-PSS with SHA-256 | MUST | | 568 | ecdsa-with-sha256 | SHOULD | | 569 | sha1WithRSAEncryption | MUST NOT | | 570 | dsa-with-sha1 | MUST NOT | | 571 | ecdsa-with-sha1 | MUST NOT | | 572 | RSASSA-PSS with Empty Parameters | MUST NOT | (*) | 573 | RSASSA-PSS with Default Parameters | MUST NOT | (*) | 574 +------------------------------------+----------+---------+ 576 (*) Empty or Default parameters means it is using SHA1, which is at 577 level MUST NOT. 579 4. Algorithms for Internet of Things 581 Some algorithms in this document are marked for use with the Internet 582 of Things (IoT). There are several reasons why IoT devices prefer a 583 different set of algorithms from regular IKEv2 clients. IoT devices 584 are usually very constrained, meaning the memory size and CPU power 585 is so limited, that these clients only have resources to implement 586 and run one set of algorithms. For example, instead of implementing 587 AES and SHA, these devices typically use AES_XCBC as integrity 588 algorithm so SHA does not need to be implemented. 590 For example, IEEE Std 802.15.4 [IEEE-802-15-4] devices have a 591 mandatory to implement link level security using AES-CCM with 128 bit 592 keys. The IEEE Recommended Practice for Transport of Key Management 593 Protocol (KMP) Datagrams [IEEE-802-15-9] already provide a way to use 594 Minimal IKEv2 [RFC7815] over 802.15.4 to provide link keys for the 595 802.15.4 layer. 597 These devices might want to use AES-CCM as their IKEv2 algorithm, so 598 they can reuse the hardware implementing it. They cannot use the 599 AES-CBC algorithm, as the hardware quite often do not include support 600 for AES decryption needed to support the CBC mode. So despite the 601 AES-CCM algorithm requiring AEAD [RFC5282] support, the benefit of 602 reusing the crypto hardware makes AES-CCM the preferred algorithm. 604 Another important aspect of IoT devices is that their transfer rates 605 are usually quite low (in order of tens of kbits/s), and each bit 606 they transmit has an energy consumption cost associated with it and 607 shortens their battery life. Therefore, shorter packets are 608 preferred. This is the reason for recommending the 8 octet ICV over 609 the 16 octet ICV. 611 Because different IoT devices will have different constraints, this 612 document cannot specify the one mandatory profile for IoT. Instead, 613 this document points out commonly used algorithms with IoT devices. 615 5. Security Considerations 617 The security of cryptographic-based systems depends on both the 618 strength of the cryptographic algorithms chosen and the strength of 619 the keys used with those algorithms. The security also depends on 620 the engineering of the protocol used by the system to ensure that 621 there are no non-cryptographic ways to bypass the security of the 622 overall system. 624 The Diffie-Hellman Group parameter is the most important one to 625 choose conservatively. Any party capturing all IKE and ESP traffic 626 that (even years later) can break the selected DH group in IKE, can 627 gain access to the symmetric keys used to encrypt all the ESP 628 traffic. Therefore, these groups must be chosen very conservatively. 629 However, specifying an extremely large DH group also puts a 630 considerable load on the device, especially when this is a large VPN 631 gateway or an IoT constrained device. 633 This document concerns itself with the selection of cryptographic 634 algorithms for the use of IKEv2, specifically with the selection of 635 "mandatory-to-implement" algorithms. The algorithms identified in 636 this document as "MUST implement" or "SHOULD implement" are not known 637 to be broken at the current time, and cryptographic research so far 638 leads us to believe that they will likely remain secure into the 639 foreseeable future. However, this isn't necessarily forever and it 640 is expected that new revisions of this document will be issued from 641 time to time to reflect the current best practice in this area. 643 6. IANA Considerations 645 This document renames some of the names in the "Transform Type 1 - 646 Encryption Algorithm Transform IDs" registry of the "Internet Key 647 Exchange Version 2 (IKEv2) Parameters". All the other names have 648 ENCR_ prefix except 3, and all other entries use names in format of 649 uppercase words separated with underscores except 6. This document 650 changes those names to match others. 652 This document requests IANA to rename following entries for the AES- 653 GCM cipher [RFC4106] and the Camellia cipher [RFC5529]: 655 +---------------------------------------+----------------------+ 656 | Old name | New name | 657 +---------------------------------------+----------------------+ 658 | AES-GCM with a 8 octet ICV | ENCR_AES_GCM_8 | 659 | AES-GCM with a 12 octet ICV | ENCR_AES_GCM_12 | 660 | AES-GCM with a 16 octet ICV | ENCR_AES_GCM_16 | 661 | ENCR_CAMELLIA_CCM with an 8-octet ICV | ENCR_CAMELLIA_CCM_8 | 662 | ENCR_CAMELLIA_CCM with a 12-octet ICV | ENCR_CAMELLIA_CCM_12 | 663 | ENCR_CAMELLIA_CCM with a 16-octet ICV | ENCR_CAMELLIA_CCM_16 | 664 +---------------------------------------+----------------------+ 666 In addition to add this RFC as reference to both ESP Reference and 667 IKEv2 Reference columns for ENCR_AES_GCM entries, keeping the current 668 references there also, and also add this RFC as reference to the ESP 669 Reference column for ENCR_CAMELLIA_CCM entries, keeping the current 670 reference there also. 672 The final registry entries should be: 674 Number Name ESP Reference IKEv2 Reference 675 ... 676 18 ENCR_AES_GCM_8 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX] 677 19 ENCR_AES_GCM_12 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX] 678 20 ENCR_AES_GCM_16 [RFC4106][RFCXXXX] [RFC5282][RFCXXXX] 679 ... 680 25 ENCR_CAMELLIA_CCM_8 [RFC5529][RFCXXXX] - 681 26 ENCR_CAMELLIA_CCM_12 [RFC5529][RFCXXXX] - 682 27 ENCR_CAMELLIA_CCM_16 [RFC5529][RFCXXXX] - 684 7. Acknowledgements 686 The first version of this document was RFC 4307 by Jeffrey I. 687 Schiller of the Massachusetts Institute of Technology (MIT). Much of 688 the original text has been copied verbatim. 690 We would like to thank Paul Hoffman, Yaron Sheffer, John Mattsson, 691 Tommy Pauly, Eric Rescorla and Pete Resnick for their valuable 692 feedback and reviews. 694 8. References 696 8.1. Normative References 698 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 699 Requirement Levels", BCP 14, RFC 2119, 700 DOI 10.17487/RFC2119, March 1997, 701 . 703 [RFC4106] Viega, J. and D. McGrew, "The Use of Galois/Counter Mode 704 (GCM) in IPsec Encapsulating Security Payload (ESP)", 705 RFC 4106, DOI 10.17487/RFC4106, June 2005, 706 . 708 [RFC4307] Schiller, J., "Cryptographic Algorithms for Use in the 709 Internet Key Exchange Version 2 (IKEv2)", RFC 4307, 710 DOI 10.17487/RFC4307, December 2005, 711 . 713 [RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T. 714 Kivinen, "Internet Key Exchange Protocol Version 2 715 (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October 716 2014, . 718 [RFC5282] Black, D. and D. McGrew, "Using Authenticated Encryption 719 Algorithms with the Encrypted Payload of the Internet Key 720 Exchange version 2 (IKEv2) Protocol", RFC 5282, 721 DOI 10.17487/RFC5282, August 2008, 722 . 724 8.2. Informative References 726 [RFC7427] Kivinen, T. and J. Snyder, "Signature Authentication in 727 the Internet Key Exchange Version 2 (IKEv2)", RFC 7427, 728 DOI 10.17487/RFC7427, January 2015, 729 . 731 [RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman 732 Tests for the Internet Key Exchange Protocol Version 2 733 (IKEv2)", RFC 6989, DOI 10.17487/RFC6989, July 2013, 734 . 736 [RFC7815] Kivinen, T., "Minimal Internet Key Exchange Version 2 737 (IKEv2) Initiator Implementation", RFC 7815, 738 DOI 10.17487/RFC7815, March 2016, 739 . 741 [RFC5529] Kato, A., Kanda, M., and S. Kanno, "Modes of Operation for 742 Camellia for Use with IPsec", RFC 5529, 743 DOI 10.17487/RFC5529, April 2009, 744 . 746 [IKEV2-IANA] 747 "Internet Key Exchange Version 2 (IKEv2) Parameters", 748 . 750 [TRANSCRIPTION] 751 Bhargavan, K. and G. Leurent, "Transcript Collision 752 Attacks: Breaking Authentication in TLS, IKE, and SSH", 753 NDSS , feb 2016. 755 [IEEE-802-15-4] 756 "IEEE Standard for Low-Rate Wireless Personal Area 757 Networks (WPANs)", IEEE Standard 802.15.4, 2015. 759 [IEEE-802-15-9] 760 "IEEE Recommended Practice for Transport of Key Management 761 Protocol (KMP) Datagrams", IEEE Standard 802.15.9, 2016. 763 Authors' Addresses 765 Yoav Nir 766 Check Point Software Technologies Ltd. 767 5 Hasolelim st. 768 Tel Aviv 6789735 769 Israel 771 EMail: ynir.ietf@gmail.com 773 Tero Kivinen 774 INSIDE Secure 775 Eerikinkatu 28 776 HELSINKI FI-00180 777 FI 779 EMail: kivinen@iki.fi 780 Paul Wouters 781 Red Hat 783 EMail: pwouters@redhat.com 785 Daniel Migault 786 Ericsson 787 8400 boulevard Decarie 788 Montreal, QC H4P 2N2 789 Canada 791 Phone: +1 514-452-2160 792 EMail: daniel.migault@ericsson.com