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If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (September 2002) is 7894 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'HIP' is defined on line 276, but no explicit reference was found in the text Summary: 5 errors (**), 0 flaws (~~), 4 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Scott Bradner 3 Harvard University 4 Allison Mankin 5 USC/ISI 6 Jeffrey I. Schiller 7 Massachusetts Institute of Technology 8 September 2002 10 A Framework for Purpose Built Keys (PBK) 12 14 Status of this Memo 16 This document is an Internet-Draft and is subject to the provisions 17 of Section 10 of RFC2026. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet- Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 Copyright Notice 37 Copyright (C) The Internet Society (2002). All Rights Reserved. 39 Abstract 41 This memo considers the need to authenticate the source of a network 42 communication where the actual identity of the source is not 43 important but it is important to be sure that the source can not be 44 spoofed and that successive messages in the communication come from 45 the same source. This memo defines the use of specially generated 46 public/private key pairs, known as Purpose Built Keys (PBKs), to 47 provide this assurance. This memo is not a full specification of a 49 Purpose Built Keys Framework September 2002 51 PBK protocol, but rather a model or framework for development of PBK 52 in applications. 54 1.0 Introduction 56 There are many cases in Internet protocols where cryptographic 57 mechanisms can add significant security improvement. However most 58 such mechanisms rely on associating keys to entities, ultimately 59 requiring an enterprise-wide, multi-enterprise, or even more widely 60 deployed Public Key Infrastructure (PKI). 62 In the absence of security mechanisms, many protocols are 63 continuously vulnerable to attack. 65 However there are many circumstances where we can improve overall 66 security by narrowing the window of vulnerability, so that if we 67 assume that some operation is performed securely, we can secure all 68 future transactions. 70 There are also cases where the actual identity of the initiator of a 71 network communication is not an important piece of information, yet 72 it is important to know that successive packets are from that same 73 source. One example of this is in mobile IPv6. Mobile IPv6 contains 74 a rebinding option that enables a mobile node to tell the other end 75 of a communication that the IP address for the mobile node has 76 changed. It is clearly important to know that any such rebinding 77 request actually came from the correct mobile node even if the 78 identity of the user of that mobile node does not need to be known. 80 Note that it is not that the identity of the user here is unimportant 81 to the network (the node user may well authenticate to an AAA service 82 or other access manager at the start of network activity), but rather 83 that it is unimportant to accomplish that level of authentication for 84 the purpose of rebinding. 86 This memo describes the use of a temporary public/private key pair 87 that is generated by a host for each case where the consistency of 88 authentication needs to be assured. For example, a new key pair 89 would be generated before each mobile IP session and discarded when 90 the session was complete. 92 This use of these host-generated temporary keys is confined to the 93 parties in a communication and does not require that the keys be 94 registered with or known by any third party. Thus this mechanism 95 does not require that any support infrastructure exist outside of the 96 protocol support in the corresponding hosts and it can be deployed 97 incrementally as host support becomes available. It also scales well 99 Purpose Built Keys Framework September 2002 101 since the operations are confined to the end systems involved in the 102 communication. 104 By not using registered keys, this mechanism preserves user anonymity 105 as long as the identity of the users are not obtained by some other 106 process during the communication. 108 By using a challenge-response confirmation step, this mechanism can 109 work in environments where the IP addresses in the packet stream 110 could be modified in the path between the correspondents. The 111 challenge-response makes it much harder for a man-in-the-middle 112 attacker to issue requests in the name of a correspondent. 114 The PBK mechanism does not require the use of a reliable protocol. 115 It is intended to used with transport or application protocols. It 116 differs from IPSec in that it is applied on demand by an application 117 or by a transport protocol. 119 When this mechanism is used with applications the PBK's public key 120 can be used in an identity for a web-cookie like function, but the 121 use is under the control of the node that initiates the connection 122 rather than under the control of the server. 124 2.0 Conceptual Overview 126 Following is a conceptual step-by-step description of the PBK process 127 when operating below the transport layer. 129 First some definitions: 130 initiating node: the node initiating the conversation 131 receiving node: the node at the other end of the conversation 133 Before an initiating node initiates a connection during which it will 134 need to prove that it is the same node that started the connection, 135 it creates a public/private key pair for use during the connection. 136 This is known as a purpose-built key (PBK) pair. 138 The initiating node then creates a Purpose-Built ID (PBID) by 139 performing a cryptographic hash of the public part of the PBK. This 140 PBID will be used as an identity token for the node. 142 The initiating node then initiates the connection. The PBID is sent 143 along with the initial packets in the connection. In IPv6 this could 144 be done in an end-to-end option header, in IPv4 as a header option. 145 (These option ideas are for transport level use of the PBK - if the 146 PBK was used from within HTTP or another application, the PBID's 147 location would be in the application.). The PBID does not need to 148 appear in all of the packets; it just has to be reliably conveyed to 150 Purpose Built Keys Framework September 2002 152 the receiving node. Reliability may be obtained by carrying it on 153 enough packets so that a return packet indicates it was received 154 eventually. This is the simplest approach; depending on requirements 155 and the application, the PBID may well be transported reliably. 157 The receiving node stores the PBID and the source IP address that 158 were in the received packet in a table. 160 At some time in the connection before the proof of identity is 161 needed, the initiating node sends its public key to the receiving 162 node. This again could be done in IP-level options or in an 163 application-level exchange. The receiving node verifies that the 164 received public key hashes to the previously provided PBID. 166 When the initiating node wants to perform some operation, such as a 167 mobile IPv6 address rebinding, it sends the operation request along 168 with the PBID. The message is signed using the private part of the 169 PBK. If replay protection is necessary, a nonce value (a 170 monotonically increasing value) or timestamp may be included with the 171 operation request. 173 When the receiving node gets such an operation request it verifies 174 the digital signature and returns a challenge packet. The challenge 175 packet is sent to the IP address that was in the source IP address 176 field of the packet that contained the request. The challenge packet 177 contains a random number test value generated by the receiving node. 179 When the initiating node receives the challenge packet it encrypts 180 the test value in its private key and sends the result back to 181 receiving node. 183 When the receiving node gets the challenge response it decrypts the 184 test value using the stored public key associated with the PBID. If 185 the results match then the receiving node can be sure that the node 186 that sent the operation request was the correct initiating node. 188 The PBKs would normally be discarded at the end of the communication 189 but in those cases where a continuity of identity is needed over 190 multiple sessions the PBKs could be retained until the requirement 191 was over. 193 3.0 Notes on the design 195 The hash of the public key is used as the PBID so that the 196 relationship between an offered PBID and public key can be 197 established. If a receiving node is in possession of the private key 198 and the hash of the corresponding public key matches an offered PBID, 199 it can be sure that it has the correct PBID for that public key. 201 Purpose Built Keys Framework September 2002 203 Retransmission algorithms, where they are needed, must be conformant 204 with RFC 2914 [RFC2914]. 206 The challenge / response exchange has to take place synchronized 207 within the data stream if the processing of packets after the 208 operation request would be different that before the operation 209 request, as it would be for mobile IPv6. This would mean suspending 210 normal transmission until the challenge / response exchange was 211 completed. 213 The challenge is sent to the source address in the packet and this 214 address is not included in the digital signature on the operation 215 request packet so that this mechanism can work through any address 216 modifying devices that may be in the path. 218 In the cases where commands could be issued by both ends of a 219 communication, as would be the case in mobile IPv6 if both ends were 220 mobile, separate PBKs would be created by each end and the mechanism 221 would be run independently by each end. 223 4.0 Security Considerations 225 This whole document is about security. Specifically the memo 226 discusses how to perform authenticated operations in an environment 227 where there is no existing security infrastructure or an environment 228 where network addresses might change during the course of the 229 communication. 231 In the absence of a security infrastructure such as a PKI, it is not 232 always possible to authenticate one party to another. In the absence 233 of any cryptographic security mechanism, internet transactions are 234 continuously at risk of compromise. With PBKs it is possible to 235 leverage an initial "leap of faith" so that presuming an initial 236 transaction has not been tampered with (say the exchange of PBID's at 237 the beginning of an association between two parties), future 238 transactions can be secured. 240 5.0 Acknowledgements 242 Some of these same concepts are explored in [HIP.] 244 6.0 Author's Addresses 246 Scott Bradner 247 Harvard University 248 Cambridge MA 02138 250 Phone +1 617 495 3864 252 Purpose Built Keys Framework September 2002 254 email sob@harvard.edu 256 Allison Mankin 257 University of Southern California, Information Sciences Institute 258 4350 N. Fairfax Drive, Suite 620 259 Arlington, VA 22203 260 Phone: +1 703 812 3706 261 email: mankin@isi.edu 263 Jeffrey I. Schiller 264 Massachusetts Institute of Technology 265 MIT Room W92-190 266 77 Massachusetts Avenue 267 Cambridge, MA 02139-4307 268 Phone: +1 617 253 0161 269 email: jis@mit.edu 271 Informative References 273 [RFC2914] Floyd, S., "Congestion Control Principles", RFC 2914, 274 September 2000. 276 [HIP] Moskowitz, R., "Host Identity Payload Architecture", "Host 277 Identity Payload Protocol", http://homebase.htt-consult.com/~hip, 278 2001. 280 Full Copyright statement 282 Copyright (C) The Internet Society (2002). All Rights Reserved. 283 This document and translations of it may be copied and furnished to 284 others, and derivative works that comment on or otherwise explain it 285 or assist in its implementation may be prepared, copied, published 286 and distributed, in whole or in part, without restriction of any 287 kind, provided that the above copyright notice and this paragraph are 288 included on all such copies and derivative works. However, this 289 document itself may not be modified in any way, such as by removing 290 the copyright notice or references to the Internet Society or other 291 Internet organizations, except as needed for the purpose of 292 developing Internet standards in which case the procedures for 293 copyrights defined in the Internet Standards process must be 294 followed, or as required to translate it into languages other than 295 English. 297 The limited permissions granted above are perpetual and will not be 298 revoked by the Internet Society or its successors or assigns. 300 Purpose Built Keys Framework September 2002 302 This document and the information contained herein is provided on An 303 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 304 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 305 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF INFORMATION HEREIN 306 WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 307 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.