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'1' -- Possible downref: Non-RFC (?) normative reference: ref. '2' -- Possible downref: Non-RFC (?) normative reference: ref. '3' -- Possible downref: Non-RFC (?) normative reference: ref. '4' ** Obsolete normative reference: RFC 1750 (ref. '8') (Obsoleted by RFC 4086) ** Downref: Normative reference to an Informational RFC: RFC 1983 (ref. '9') ** Downref: Normative reference to an Informational RFC: RFC 2104 (ref. '12') ** Obsolete normative reference: RFC 2279 (ref. '14') (Obsoleted by RFC 3629) ** Obsolete normative reference: RFC 2234 (ref. '15') (Obsoleted by RFC 4234) ** Obsolete normative reference: RFC 2373 (ref. '16') (Obsoleted by RFC 3513) ** Obsolete normative reference: RFC 2434 (ref. '17') (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 2440 (ref. '18') (Obsoleted by RFC 4880) ** Obsolete normative reference: RFC 2574 (ref. '19') (Obsoleted by RFC 3414) ** Obsolete normative reference: RFC 3164 (ref. '20') (Obsoleted by RFC 5424) -- Duplicate reference: RFC3339, mentioned in '23', was also mentioned in '22'. -- Possible downref: Non-RFC (?) normative reference: ref. '24' Summary: 15 errors (**), 0 flaws (~~), 16 warnings (==), 13 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 syslog Working Group J. Kelsey 3 Internet-Draft 4 Expires: May 26, 2006 J. Callas 5 PGP Corporation 6 A. Clemm 7 Cisco Systems 8 November 22, 2005 10 Signed syslog Messages 11 draft-ietf-syslog-sign-17.txt 13 Status of this Memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt. 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 36 This Internet-Draft will expire on May 26, 2006. 38 Copyright Notice 40 Copyright (C) The Internet Society (2005). 42 Abstract 44 This document describes a mechanism to add origin authentication, 45 message integrity, replay-resistance, message sequencing, and 46 detection of missing messages to the transmitted syslog messages. 47 This specification draws upon the work defined in RFC xxx, "The 48 syslog Protocol", however it may be used atop any message delivery 49 mechanism, even that defined in RFC 3164, "The BSD syslog Protocol", 50 or in the RAW mode of "RFC 3195, "The Reliable Delivery of syslog". 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 2. Conventions Used in this Document . . . . . . . . . . . . . . 6 56 3. syslog Message Format . . . . . . . . . . . . . . . . . . . . 7 57 4. Signature Block Format and Fields . . . . . . . . . . . . . . 8 58 4.1. syslog Packets Containing a Signature Block . . . . . . . 8 59 4.2. Version . . . . . . . . . . . . . . . . . . . . . . . . . 9 60 4.3. Reboot Session ID . . . . . . . . . . . . . . . . . . . . 9 61 4.4. Signature Group and Signature Priority . . . . . . . . . . 9 62 4.5. Global Block Counter . . . . . . . . . . . . . . . . . . . 11 63 4.6. First Message Number . . . . . . . . . . . . . . . . . . . 11 64 4.7. Count . . . . . . . . . . . . . . . . . . . . . . . . . . 12 65 4.8. Hash Block . . . . . . . . . . . . . . . . . . . . . . . . 12 66 4.9. Signature . . . . . . . . . . . . . . . . . . . . . . . . 12 67 5. Payload and Certificate Blocks . . . . . . . . . . . . . . . . 13 68 5.1. Preliminaries: Key Management and Distribution Issues . . 13 69 5.2. Building the Payload Block . . . . . . . . . . . . . . . . 14 70 5.3. Building the Certificate Block . . . . . . . . . . . . . . 14 71 5.3.1. Version . . . . . . . . . . . . . . . . . . . . . . . 15 72 5.3.2. Reboot Session ID . . . . . . . . . . . . . . . . . . 15 73 5.3.3. Signature Group and Signature Priority . . . . . . . . 16 74 5.3.4. Total Payload Block Length . . . . . . . . . . . . . . 16 75 5.3.5. Index into Payload Block . . . . . . . . . . . . . . . 16 76 5.3.6. Fragment Length . . . . . . . . . . . . . . . . . . . 16 77 5.3.7. Signature . . . . . . . . . . . . . . . . . . . . . . 16 78 6. Redundancy and Flexibility . . . . . . . . . . . . . . . . . . 17 79 6.1. Redundancy . . . . . . . . . . . . . . . . . . . . . . . . 17 80 6.1.1. Certificate Blocks . . . . . . . . . . . . . . . . . . 17 81 6.1.2. Signature Blocks . . . . . . . . . . . . . . . . . . . 17 82 6.2. Flexibility . . . . . . . . . . . . . . . . . . . . . . . 18 83 7. Efficient Verification of Logs . . . . . . . . . . . . . . . . 19 84 7.1. Offline Review of Logs . . . . . . . . . . . . . . . . . . 19 85 7.2. Online Review of Logs . . . . . . . . . . . . . . . . . . 20 86 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 87 8.1. Cryptography Constraints . . . . . . . . . . . . . . . . . 22 88 8.2. Packet Parameters . . . . . . . . . . . . . . . . . . . . 22 89 8.3. Message Authenticity . . . . . . . . . . . . . . . . . . . 23 90 8.4. Sequenced Delivery . . . . . . . . . . . . . . . . . . . . 23 91 8.5. Replaying . . . . . . . . . . . . . . . . . . . . . . . . 23 92 8.6. Reliable Delivery . . . . . . . . . . . . . . . . . . . . 23 93 8.7. Sequenced Delivery . . . . . . . . . . . . . . . . . . . . 23 94 8.8. Message Integrity . . . . . . . . . . . . . . . . . . . . 24 95 8.9. Message Observation . . . . . . . . . . . . . . . . . . . 24 96 8.10. Man In The Middle . . . . . . . . . . . . . . . . . . . . 24 97 8.11. Denial of Service . . . . . . . . . . . . . . . . . . . . 24 98 8.12. Covert Channels . . . . . . . . . . . . . . . . . . . . . 24 99 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 100 9.1. Version Field . . . . . . . . . . . . . . . . . . . . . . 26 101 9.2. SIG Field . . . . . . . . . . . . . . . . . . . . . . . . 28 102 9.3. Key Blob Type . . . . . . . . . . . . . . . . . . . . . . 28 103 10. Authors and Working Group Chair . . . . . . . . . . . . . . . 29 104 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 30 105 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30 106 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32 107 Intellectual Property and Copyright Statements . . . . . . . . . . 33 109 1. Introduction 111 This document describes a mechanism that adds origin authentication, 112 message integrity, replay resistance, message sequencing, and 113 detection of missing messages to syslog. Essentially, this is 114 accomplished by sending a special syslog message. The contents of 115 this syslog message is called a Signature Block. Each Signature 116 Block contains, in effect, a detached signature on some number of 117 previously sent messages. It is cryptographically signed and 118 contains the hashes of previously sent syslog messages. 120 While most implementations of syslog involve only a single device as 121 the generator of each message and a single receiver as the collector 122 of each message, provisions need to be made to cover situations in 123 which messages are sent to multiple receivers. This concerns in 124 particular situations in which different messages are sent to 125 different receivers, meaning that some messages are sent to some 126 receivers but not to others. The required differentiation of 127 messages is generally performed based on the Priority value of the 128 individual messages. For example, messages from any Facility with a 129 Severity value of 3, 2, 1 or 0 may be sent to one collector while all 130 messages of Facilities 4, 10, 13, and 14 may be sent to another 131 collector. Appropriate syslog-sign messages must be kept with their 132 proper syslog messages. To address this, syslog-sign uses a 133 signature-group. A signature group identifies a group of messages 134 that are all kept together for signing purposes by the device. A 135 Signature Block always belongs to exactly one signature group and it 136 always signs messages belonging only to that signature group. 138 Additionally, a device will send a Certificate Block to provide key 139 management information between the sender and the receiver. This 140 Certificate Block has a field to denote the type of key material 141 which may be such things as a PKIX certificate, an OpenPGP 142 certificate, or even an indication that a key had been 143 predistributed. In the cases of certificates being sent, the 144 certificates may have to be split across multiple packets. 146 The receiver of the previous messages may verify that the digital 147 signature of each received message matches the signature contained in 148 the Signature Block. A collector may process these Signature Blocks 149 as they arrive, building an authenticated log file. Alternatively, 150 it may store all the log messages in the order they were received. 151 This allows a network operator to authenticate the log file at the 152 time the logs are reviewed. 154 This specification is independent of the actual transport protocol 155 selected. The best application of this mechanism will be to use it 156 with the syslog protocol as defined in RFC xxxx [23] as it utilizes 157 the STRUCTURED-DATA elements defined in that document. It may be 158 used with syslog packets over traditional UDP [5] as described in RFC 159 3164 [20]. It may also be used with the Reliable Delivery of syslog 160 as described in RFC 3195 [21], and it may be used with other message 161 delivery mechanisms. Other efforts to define event notification 162 messages should consider this specification in their design. 164 2. Conventions Used in this Document 166 The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 167 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" that 168 appear in this document are to be interpreted as described in RFC 169 2119 [13]. 171 3. syslog Message Format 173 This specification does not rely upon any specific syslog message 174 format. It is RECOMMENDED to be used within the syslog protocol as 175 defined in RFC xxxx [23]. It MAY be transported over a traditional 176 syslog message format such as that defined in the informational RFC 177 3164 [20], or it MAY be used over the Reliable Delivery of syslog 178 Messages as defined in RFC 3195 [21]. Care must be taken when 179 choosing a transport for this mechanism, however. Since the device 180 generating the Signature Block message signs each message in its 181 entirety, it is imperative that the messages MUST NOT be changed in 182 transit. It is equally imperative that the syslog-sign messages MUST 183 NOT be changed in transit. Specifically, a relay as described in RFC 184 3164 MAY make changes to a syslog packet if specific fields are not 185 found. If this occurs, the entire mechanism described in this 186 document is rendered useless. 188 For convenience, this document will use the syslog message format in 189 the terms described in RFC xxxx [23]. Along with the other fields, 190 that document describes the concept of STRUCTURED DATA. STRUCTURED 191 DATA is defined in the form of SD ELEMENTS(SDEs). An SDE consists of 192 a name and parameter name - value pairs. The name is referred to as 193 SD-ID. The name-value pairs are referred to as SD-PARAM, or SD 194 Parameters, with the name constituting the SD-PARAM-NAME, the value 195 constituting the SD-PARAM-VALUE. This document defines the way to 196 use SDEs to convey the signing of syslog messages. The MSG part of 197 the syslog message as defined in RFC xxxx [23] will simply be empty - 198 it is not intended for interpretation by humans but by applications 199 that use those messages to build an authenticated log. Having said 200 that, as stated above, this mechanism should be considered to be 201 independent of the SD-ID definitions and the fields defined here 202 should be considered to be applicable to other message transports. 203 When used in conjunction with a syslog message format other than the 204 one defined in RFC xxxx [23], the format of the message payload will 205 simply happen to follow SDE format. 207 4. Signature Block Format and Fields 209 This section describes the Signature Block format and the fields used 210 within the Signature Block. 212 4.1. syslog Packets Containing a Signature Block 214 Signature Block messages MUST be encompassed within completely formed 215 syslog messages. It SHOULD also contain valid APP-NAME, PROCID, and 216 MSGID fields when used with RFC xxxx [23]. Similarly, it SHOULD 217 contain a valid TAG field when used with traditional syslog [20]. In 218 the latter case, it is RECOMMENDED that the TAG field have the value 219 of "syslog " (without the double quotes) to signify that this message 220 was generated by the syslog process. The CONTENT field of the syslog 221 Signature Block messages MUST be encoded as an SD ELEMENT, as defined 222 in RFC xxxx [23]. 224 The SD-ID must have the value of "ssign". 226 The SDE contains the fields of the Signature Block encoded as SD 227 Parameters, as specified in the following. The Signature Block is 228 composed of the following fields. The value of each field must be 229 printable ASCII, and any binary values are base-64 encoded. 231 Field SD-PARAM-NAME Size in bytes 232 ----- ------------- ---- -- ----- 234 Version VER 4 236 Reboot Session ID RSID 1-10 238 Signature Group SG 1 240 Signature Priority SPRI 1-3 242 Global Block Counter GBC 1-10 244 First Message Number FMN 1-10 246 Count CNT 1-2 248 Hash Block HB variable, size of hash 249 (base-64 encoded binary) 251 Signature SIGN variable 252 (base-64 encoded binary) 254 A Signature Block is accordingly encoded as follows (xxx denoting a 255 placeholder for the particular value: 257 "[ssign VER=xxx RSID=xxx SG=xxx SPRI=xxx GBC=xxx FMN=xxx CNT=xxx 258 HB=xxx SIGN=xxx]". 260 The fields are described below. 262 4.2. Version 264 The signature group version field is 4 characters in length and is 265 terminated with a space character. The value in this field specifies 266 the version of the syslog-sign protocol. This is extensible to allow 267 for different hash algorithms and signature schemes to be used in the 268 future. The value of this field is the grouping of the protocol 269 version (2 bytes), the hash algorithm (1 byte) and the signature 270 scheme (1 byte). 272 Protocol Version - 2 bytes with the first version as described in 273 this document being value of 01 to denote Version 1. 275 Hash Algorithm - 1 byte with the definition that 1 denotes SHA1 as 276 defined in FIPS-180-1.1995 [2]. 278 Signature Scheme - 1 byte with the definition that 1 denotes 279 OpenPGP DSA - RFC 2440 [18], FIPS.186-1.1998 [1]. 281 As such, the version, hash algorithm and signature scheme defined in 282 this document may be represented as "0111" (without the quote marks). 284 4.3. Reboot Session ID 286 The reboot session ID is a value between 1 and 10 bytes. The 287 acceptable values for this are between 0 and 9999999999. A reboot 288 session ID is expected to increase whenever a device reboots in order 289 to allow receivers to uniquely distinguish messages and message 290 signatures across reboots. A device needs to hence support 291 persisting previous reboot session ID across reboots. In cases where 292 a device does not support this capability, the reboot session ID MUST 293 always be set to a value of 0. Otherwise, it MUST increase whenever 294 a device reboots, starting with a value of 1. If the value latches 295 at 9999999999, then manual intervention may be required to reset it 296 to 0. Implementors MAY wish to consider using the snmpEngineBoots 297 value as a source for this counter as defined in RFC 2574 [19]. 299 4.4. Signature Group and Signature Priority 301 The SG identifier as described above may take on any value from 0-3 302 inclusive. The SPRI may take any value from 0-191. These fields 303 taken together allows network administrators to associate groupings 304 of syslog messages with appropriate Signature Blocks and Certificate 305 Blocks. For example, in some cases, network administrators may send 306 syslog messages of Facilities 0 through 15 to one destination while 307 sending messages with Facilities 16 through 23 to another. 308 Associated Signature Blocks should be sent to these different syslog 309 servers as well. 311 In some cases, an administrator may wish the Signature Blocks to go 312 to the same destination as the syslog messages themselves. This may 313 be to different syslog servers if the destinations of syslog messages 314 is being controlled by the Facilities or the Severities of the 315 messages. In other cases, administrators may wish to send the 316 Signature Blocks to an altogether different destination. 318 Syslog-sign provides four options for handling signature groups, 319 linking them with PRI values so they may be routed to the destination 320 commensurate with the appropriate syslog messages. In all cases, no 321 more than 192 signature groups (0-191) are permitted. The signature 322 group field indicates how to interpret the signature priority field. 323 The signature priority field contains information about the signature 324 group that the Signature Block pertains to. (Note the distinction 325 between signature group and signature group field: The signature 326 group that the Signature Block pertains to is indicated by the 327 signature priority (SPRI) field. The signature group field (SG) does 328 not indicate a signature group, but how to correctly interpret the 329 SPRI field.) 331 a. '0' -- There is only one signature group. All Signature Block 332 messages use a single PRI value which is the same SPRI value. In 333 this case, the administrators want all Signature Blocks to be 334 sent to a single destination; the Signature Block signs all 335 messages regardless of their PRI value. In all likelihood, all 336 of the syslog messages will also be going to that same 337 destination. 339 b. '1' -- Each PRI value has its own signature group. Signature 340 Blocks for a given signature group have SPRI = PRI for that 341 signature group. In this case, the administrator of a device may 342 not know where any of the syslog messages will ultimately go. 343 This use ensures that a Signature Block follows each of the 344 syslog messages to each destination. The SPRI correspondsss to 345 the identifier of the signature group, coinciding with the PRI 346 value of each of the signed syslog messages. 348 c. '2' -- Each signature group contains a range of PRI values. 349 Signature groups are assigned sequentially. A Signature Block 350 for a given signature group has its own SPRI value denoting the 351 highest PRI value in that signature group. For flexibility, the 352 PRI does not have to be that upper-boundary SPRI value. 354 d. '3' -- Signature groups are not assigned with any simple 355 relationship to PRI values. This has to be some predefined 356 arrangement between the sender and the intended receivers, 357 requiring configuration by a system administrator. 359 One reasonable way to configure some installations is to have only 360 one signature group with SIG=0. The devices send messages to many 361 collectors and also send a copy of each Signature Block to each 362 collector. This won't allow any collector to detect gaps in the 363 messages, but it allows all messages that arrive at each collector to 364 be put into the right order, and to be verified. It also allows each 365 collector to detect duplicates and any messages that are not 366 associated with a Signature Block. 368 4.5. Global Block Counter 370 The global block counter is a value representing the number of 371 Signature Blocks sent out by syslog-sign before this one, in this 372 reboot session. This takes at least 1 byte and at most 10 bytes 373 displayed as a decimal counter and the acceptable values for this are 374 between 0 and 9999999999. If the value latches at 9999999999, then 375 the reboot session counter must be incremented by 1 and the global 376 block counter resumes at 0. Note that this counter crosses signature 377 groups; it allows us to roughly synchronize when two messages were 378 sent, even though they went to different collectors. 380 In case a device does not support an incrementing reboot session ID 381 (that is, the value of the reboot session ID is 0), a device MAY 382 reset the global block counter to 0 after a reboot occurs. Note that 383 in this case, applications need to apply extra consideration when 384 authenticating a log, and situations in which reboots occur 385 frequently may result in losing the ability to verify the proper 386 sequence in which messages were sent and hence jeopardizing integrity 387 of the log. 389 4.6. First Message Number 391 This is a value between 1 and 10 bytes. It contains the unique 392 message number within this signature group of the first message whose 393 hash appears in this block. The very first message of the reboot 394 session will be numbered "1". 396 For example, if this signature group has processed 1000 messages so 397 far and message number 1001 is the first message whose hash appears 398 in this Signature Block, then this field contains 1001. 400 4.7. Count 402 The count is a 1 or 2 byte field displaying the number of message 403 hashes to follow. The valid values for this field are between 1 and 404 99. Note that the number of hashes that are included in the 405 Signature Block MUST be chosen such that the length of the resulting 406 syslog message does not exceed the maximum permissable syslog message 407 length. 409 4.8. Hash Block 411 The hash block is a block of hashes, each separately encoded in 412 base-64. Each hash in the hash block is the hash of the entire 413 syslog message represented by the hash. The hashing algorithm used 414 effectively specified by the Version field determines the size of 415 each hash, but the size MUST NOT be shorter than 160 bits. It is 416 base-64 encoded as per RFC 2045. 418 4.9. Signature 420 This is a digital signature, encoded in base-64, as per RFC 2045. 421 The signature is calculated over all fields but excludes the space 422 characters between them. The Version field effectively specifies the 423 original encoding of the signature. The signature is a signature 424 over the entire data, including all of the PRI, HEADER, and hashes in 425 the hash block. To reiterate, the signature is calculated over the 426 completely formatted syslog-message, excluding spaces between fields, 427 and also excluding this signature field (the value of the signature 428 SD Parameter). 430 5. Payload and Certificate Blocks 432 Certificate Blocks and Payload Blocks provide key management in 433 syslog-sign. Their purpose is to support key management using public 434 key cryptosystems. 436 5.1. Preliminaries: Key Management and Distribution Issues 438 A Payload Block contains public key certificate information that is 439 to be conveyed to the receiver. A Payload Block is not sent 440 directly, but in (one or more) fragments. Those fragments are termed 441 Certificate Blocks. All devices send at least one Certificate Block 442 at the beginning of a new reboot session, carrying public key 443 information that is to be in effect for the reboot session. 445 There are three key points to understand about Certificate Blocks: 447 a. They handle a variable-sized payload, fragmenting it if necessary 448 and transmitting the fragments as legal syslog messages. This 449 payload is built (as described below) at the beginning of a 450 reboot session and is transmitted in pieces with each Certificate 451 Block carrying a piece. Note that there is exactly one Payload 452 Block per reboot session. 454 b. The Certificate Blocks are digitally signed. The device does not 455 sign the Payload Block, but the signatures on the Certificate 456 Blocks ensure its authenticity. Note that it may not even be 457 possible to verify the signature on the Certificate Blocks 458 without the information in the Payload Block; in this case the 459 Payload Block is reconstructed, the key is extracted, and then 460 the Certificate Blocks are verified. (This is necessary even 461 when the Payload Block carries a certificate, since some other 462 fields of the Payload Block aren't otherwise verified.) In 463 practice, most installations keep the same public key over long 464 periods of time, so that most of the time, it's easy to verify 465 the signatures on the Certificate Blocks, and use the Payload 466 Block to provide other useful per-session information. 468 c. The kind of Payload Block that is expected is determined by what 469 kind of key material is on the collector that receives it. The 470 device and collector (or offline log viewer) has both some key 471 material (such as a root public key, or predistributed public 472 key), and an acceptable value for the Key Blob Type in the 473 Payload Block, below. The collector or offline log viewer MUST 474 NOT accept a Payload Block of the wrong type. 476 5.2. Building the Payload Block 478 The Payload Block is built when a new reboot session is started. 479 There is a one-to-one correspondence of reboot sessions to Payload 480 Blocks. That is, each reboot session has only one Payload Block, 481 regardless of how many signature groups it may support. A Payload 482 Block MUST have the following fields. Each of these fields are 483 separated by a single space character. (Note that because a Payload 484 Block is not carried in a syslog message directly, only the 485 corresponding Certificate Blocks, it does not need to be encoded as 486 an SD ELEMENT.) 488 a. Unique identifier of sender; by default, the sender's IP address 489 in dotted-decimal (IPv4) or colon-separated (IPv6) notation. 491 b. Full local time stamp for the device at the time the reboot 492 session started. This must be in TIMESTAMP-3339 format. 494 c. Key Blob Type, a one-byte field which holds one of five values: 496 1. 'C' -- a PKIX certificate. 498 2. 'P' -- an OpenPGP certificate. 500 3. 'K' -- the public key whose corresponding private key is 501 being used to sign these messages. 503 4. 'N' -- no key information sent; key is predistributed. 505 5. 'U' -- installation-specific key exchange information 507 d. The key blob, consisting of the raw key data, if any, base-64 508 encoded. 510 5.3. Building the Certificate Block 512 The Certificate Block must get the Payload Block to the collector. 513 Since certificates can legitimately be much longer than 1024 bytes, 514 each Certificate Block carries a piece of the Payload Block. Note 515 that the device MAY make the Certificate Blocks of any legal length 516 (that is, any length less than 1024 bytes) which holds all the 517 required fields. Software that processes Certificate Blocks MUST 518 deal correctly with blocks of any legal length. 520 Like a Signature Block, the Certificate Block is encoded as an SD 521 Element per RFC xxxx [23] and carried in its own syslog message. The 522 SD-ID of the Certificate Block is "ssign-cert". The Certificate 523 Block is composed of the following fields, each of which is encoded 524 as an SD Parameter with parameter name as indicated. Each field must 525 be printable ASCII, and any binary values are base-64 encoded. 527 Field SD-PARAM-NAME Size in bytes 528 ----- ------------- ---- -- ----- 530 Version VER 4 532 Reboot Session ID RSID 1-10 534 Signature Group SG 1 536 Signature Priority SPRI 1-3 538 Total Payload Block Length TPBL 1-8 540 Index into Payload Block INDEX 1-8 542 Fragment Length FLEN 1-3 544 Payload Block Fragment FRAG variable 545 (base-64 encoded binary) 547 Signature SIGN variable 548 (base-64 encoded binary) 550 A Certificate Block is accordingly encoded as follows (xxx denoting a 551 placeholder for the particular value: 553 "[ssign-cert VER=xxx RSID=xxx SG=xxx SPRI=xxx TBPL=xxx INDEX=xxx 554 FLEN=xxx FRAG=xxx SIGN=xxx]". 556 The fields will be explained below. 558 5.3.1. Version 560 The signature group version field is 4 characters in length and is 561 terminated with a space character. This field is identical in nature 562 to the Version field described in Section 4.2. As such, the version, 563 hash algorithm and signature scheme defined in this document may be 564 represented as "0111" (without the quote marks). 566 5.3.2. Reboot Session ID 568 The Reboot Session ID is identical in characteristics to the RSID 569 field described in Section 4.3. 571 5.3.3. Signature Group and Signature Priority 573 The SIG field is identical in characteristics to the SIG field 574 described in Section 4.9. Also, the SPRI field is identical to the 575 SPRI field described there. 577 5.3.4. Total Payload Block Length 579 The Total Payload Block Length is a value representing the total 580 length of the Payload Block in bytes in decimal. This will be one to 581 eight bytes. 583 5.3.5. Index into Payload Block 585 This is a value between 1 and 8 bytes. It contains the number of 586 bytes into the Payload Block where this fragment starts. The first 587 byte of the first fragment is numbered "1". 589 5.3.6. Fragment Length 591 The total length of this fragment expressed as a decimal integer. 592 This will be one to three bytes. 594 5.3.7. Signature 596 This is a digital signature, encoded in base-64, as per RFC 2045. 597 The signature is calculated over all fields but excludes the space 598 characters between them. The Version field effectively specifies the 599 original encoding of the signature. The signature is a signature 600 over the entire data, including all of the PRI, HEADER, and hashes in 601 the hash block. This is consistent with the method of calculating 602 the signature as specified in Section 4.9. To reiterate, the 603 signature is calculated over the completely formatted syslog-message, 604 excluding spaces between fields, and also excluding this signature 605 field. 607 6. Redundancy and Flexibility 609 There is a general rule that determines how redundancy works and what 610 level of flexibility the device and collector have in message 611 formats: in general, the device is allowed to send Signature and 612 Certificate Blocks multiple times, to send Signature and Certificate 613 Blocks of any legal length, to include fewer hashes in hash blocks, 614 etc. 616 6.1. Redundancy 618 Syslog messages are sent over unreliable transport, which means that 619 they can be lost in transit. However, the collector must receive 620 Signature and Certificate Blocks or many messages may not be able to 621 be verified. Sending Signature and Certificate Blocks multiple times 622 provides redundancy; since the collector MUST ignore Signature/ 623 Certificate Blocks it has already received and authenticated, the 624 device can in principle change its redundancy level for any reason, 625 without communicating this fact to the collector. 627 Although the device isn't constrained in how it decides to send 628 redundant Signature and Certificate Blocks, or even in whether it 629 decides to send along multiple copies of normal syslog messages, here 630 we define some redundancy parameters below which may be useful in 631 controlling redundant transmission from the device to the collector. 633 6.1.1. Certificate Blocks 635 certInitialRepeat = number of times each Certificate Block should be 636 sent before the first message is sent. 638 certResendDelay = maximum time delay in seconds to delay before next 639 redundant sending. 641 certResendCount = maximum number of sent messages to delay before 642 next redundant sending. 644 6.1.2. Signature Blocks 646 sigNumberResends = number of times a Signature Block is resent. 648 sigResendDelay = maximum time delay in seconds from original sending 649 to next redundant sending. 651 sigResendCount = maximum number of sent messages to delay before next 652 redundant sending. 654 6.2. Flexibility 656 The device may change many things about the makeup of Signature and 657 Certificate Blocks in a given reboot session. The things it cannot 658 change are: 660 * The version 662 * The number or arrangements of signature groups 664 It is legitimate for a device to send out short Signature Blocks, in 665 order to keep the collector able to verify messages quickly. In 666 general, unless something verified by the Payload Block or 667 Certificate Blocks is changed within the reboot session ID, any 668 change is allowed to the Signature or Certificate Blocks during the 669 session. 671 7. Efficient Verification of Logs 673 The logs secured with syslog-sign may either be reviewed online or 674 offline. Online review is somewhat more complicated and 675 computationally expensive, but not prohibitively so. 677 7.1. Offline Review of Logs 679 When the collector stores logs and reviewed later, they can be 680 authenticated offline just before they are reviewed. Reviewing these 681 logs offline is simple and relatively cheap in terms of resources 682 used, so long as there is enough space available on the reviewing 683 machine. Here, we consider that the stored log files have already 684 been separated by sender, reboot session ID, and signature group. 685 This can be done very easily with a script file. We then do the 686 following: 688 a. First, we go through the raw log file, and split its contents 689 into three files. Each message in the raw log file is classified 690 as a normal message, a Signature Block, or a Certificate Block. 691 Certificate Blocks and Signature Blocks are stored in their own 692 files. Normal messages are stored in a keyed file, indexed on 693 their hash values. 695 b. We sort the Certificate Block file by index value, and check to 696 see if we have a set of Certificate Blocks that can reconstruct 697 the Payload Block. If so, we reconstruct the Payload Block, 698 verify any key-identifying information, and then use this to 699 verify the signatures on the Certificate Blocks we've received. 700 When this is done, we have verified the reboot session and key 701 used for the rest of the process. 703 c. We sort the Signature Block file by firstMessageNumber. We now 704 create an authenticated log file, which consists of some header 705 information, and then a sequence of message number, message text 706 pairs. We next go through the Signature Block file. For each 707 Signature Block in the file, we do the following: 709 1. Verify the signature on the Block. 711 2. For each hashed message in the Block: 713 a. Look up the hash value in the keyed message file. 715 b. If the message is found, write (message number, message 716 text) to the authenticated log file. 718 3. Skip all other Signature Blocks with the same 719 firstMessageNumber. 721 d. The resulting authenticated log file contains all messages that 722 have been authenticated, and implicitly indicates (by missing 723 message numbers) all gaps in the authenticated messages. 725 It's pretty easy to see that, assuming sufficient space for building 726 the keyed file, this whole process is linear in the number of 727 messages (generally two seeks, one to write and the other to read, 728 per normal message received), and O(N lg N) in the number of 729 Signature Blocks. This estimate comes with two caveats: first, the 730 Signature Blocks arrive very nearly in sorted order, and so can 731 probably be sorted more cheaply on average than O(N lg N) steps. 732 Second, the signature verification on each Signature Block almost 733 certainly is more expensive than the sorting step in practice. We 734 haven't discussed error-recovery, which may be necessary for the 735 Certificate Blocks. In practice, a very simple error-recovery 736 strategy is probably good enough -- if the Payload Block doesn't come 737 out as valid, then we can just try an alternate instance of each 738 Certificate Block, if such are available, until we get the Payload 739 Block right. 741 It's easy for an attacker to flood us with plausible-looking 742 messages, Signature Blocks, and Certificate Blocks. 744 7.2. Online Review of Logs 746 Some processes on the collector machine may need to monitor log 747 messages in something very close to real-time. This can be done with 748 syslog-sign, though it is somewhat more complex than the offline 749 analysis. This is done as follows: 751 a. We have an output queue, into which we write (message number, 752 message text) pairs which have been authenticated. Again, we'll 753 assume we're handling only one signature group, and only one 754 reboot session ID, at any given time. 756 b. We have three data structures: A queue into which (message 757 number, hash of message) pairs is kept in sorted order, a queue 758 into which (arrival sequence, hash of message) is kept in sorted 759 order, and a hash table which stores (message text, count) 760 indexed by hash value. In this file, count may be any number 761 greater than zero; when count is zero, the entry in the hash 762 table is cleared. 764 c. We must receive all the Certificate Blocks before any other 765 processing can really be done. (This is why they're sent first.) 766 Once that's done, any Certificate Block that arrives is 767 discarded. 769 d. Whenever a normal message arrives, we add (arrival sequence, hash 770 of message) to our message queue. If our hash table has an entry 771 for the message's hash value, we increment its count by one; 772 otherwise, we create a new entry with count = 1. When the 773 message queue is full, we roll the oldest messages off the queue 774 by taking the last entry in the queue, and using it to index the 775 hash table. If that entry has count is 1, we delete the entry in 776 the hash table; otherwise, we decrement its count. We then 777 delete the last entry in the queue. 779 e. Whenever a Signature Block arrives, we first check to see if the 780 firstMessageNumber value is too old, or if another Signature 781 Block with that firstMessageNumber has already been received. If 782 so, we discard the Signature Block unread. Otherwise, we check 783 its signature, and discard it if the signature isn't valid. A 784 Signature Block contains a sequence of (message number, message 785 hash) pairs. For each pair, we first check to see if the message 786 hash is in the hash table. If so, we write out the (message 787 number, message text) in the authenticated message queue. 788 Otherwise, we write the (message number, message hash) to the 789 message number queue. This generally involves rolling the oldest 790 entry out of this queue: before this is done, that entry's hash 791 value is again searched for in the hash table. If a matching 792 entry is found, the (message number, message text) pair is 793 written out to the authenticated message queue. In either case, 794 the oldest entry is then discarded. 796 f. The result of this is a sequence of messages in the authenticated 797 message queue, each of which has been authenticated, and which 798 are combined with numbers showing their order of original 799 transmission. 801 It's not too hard to see that this whole process is roughly linear in 802 the number of messages, and also in the number of Signature Blocks 803 received. The process is susceptible to flooding attacks; an 804 attacker can send enough normal messages that the messages roll off 805 their queue before their Signature Blocks can be processed. 807 8. Security Considerations 809 Normal syslog event messages are unsigned and have most of the 810 security attributes described in Section 6 of RFC 3164. This 811 document also describes Certificate Blocks and Signature Blocks which 812 are signed syslog messages. The Signature Blocks contains signature 813 information of previously sent syslog event messages. All of this 814 information may be used to authenticate syslog messages and to 815 minimize or obviate many of the security concerns described in RFC 816 3164. 818 8.1. Cryptography Constraints 820 As with any technology involving cryptography, you should check the 821 current literature to determine if any algorithms used here have been 822 found to be vulnerable to attack. 824 This specification uses Public Key Cryptography technologies. The 825 proper party or parties must control the private key portion of a 826 public-private key pair. Any party that controls a private key may 827 sign anything they please. 829 Certain operations in this specification involve the use of random 830 numbers. An appropriate entropy source should be used to generate 831 these numbers. See RFC 1750 [8]. 833 8.2. Packet Parameters 835 The message length must not exceed 1024 bytes. Various problems may 836 result if a device sends out messages with a length greater than 1024 837 bytes. As seen in RFC 3164, relays MAY truncate messages with 838 lengths greater than 1024 bytes which would result in a problem for 839 receivers trying to validate a hash of the packet. In this case, as 840 with all others, it is best to be conservative with what you send but 841 liberal in what you receive, and accept more than 1024 bytes. 843 Similarly, senders must rigidly enforce the correctness of the 844 message body. This document specifies an enhancement to the syslog 845 protocol but does not stipulate any specific syslog message format. 846 Nonetheless, problems may arise if the receiver does not fully accept 847 the syslog packets sent from a device, or if it has problems with the 848 format of the Certificate Block or Signature Block messages. 850 Finally, receivers must not malfunction if they receive syslog 851 messages containing characters other than those specified in this 852 document. 854 8.3. Message Authenticity 856 Event messages being sent through syslog do not strongly associate 857 the message with the message sender. That fact is established by the 858 receiver upon verification of the Signature Block as described above. 859 Before a Signature Block is used to ascertain the authenticity of an 860 event message, it may be received, stored and reviewed by a person or 861 automated parser. Both of these should maintain doubt about the 862 authenticity of the message until after it has been validated by 863 checking the contents of the Signature Block. 865 With the Signature Block checking, an attacker may only forge 866 messages if they can compromise the private key of the true sender. 868 8.4. Sequenced Delivery 870 Event messages may be recorded and replayed by an attacker. However 871 the information contained in the Signature Blocks allows a reviewer 872 to determine if the received messages are the ones originally sent by 873 a device. This process also alerts the reviewer to replayed 874 messages. 876 8.5. Replaying 878 Event messages may be recorded and replayed by an attacker. However 879 the information contained in the Signature Blocks will allow a 880 reviewer to determine if the received messages are the ones 881 originally sent by a device. This process will also alert the 882 reviewer to replayed messages. 884 8.6. Reliable Delivery 886 RFC 3195 may be used for the reliable delivery of all syslog 887 messages. This document acknowledges that event messages sent over 888 UDP may be lost in transit. A proper review of the Signature Block 889 information may pinpoint any messages sent by the sender but not 890 received by the receiver. The overlap of information in subsequent 891 Signature Block information allows a reviewer to determine if any 892 Signature Block messages were also lost in transit. 894 8.7. Sequenced Delivery 896 Related to the above, syslog messages delivered over UDP not only may 897 be lost, but they may arrive out of sequence. The information 898 contained in the Signature Block allows a receiver to correctly order 899 the event messages. Beyond that, the timestamp information contained 900 in the packet may help the reviewer to visually order received 901 messages even if they are received out of order. 903 8.8. Message Integrity 905 syslog messages may be damaged in transit. A review of the 906 information in the Signature Block determines if the received message 907 was the intended message sent by the sender. A damaged Signature 908 Block or Certificate Block will be evident since the receiver will 909 not be able to validate that it was signed by the sender. 911 8.9. Message Observation 913 Event messages, Certificate Blocks and Signature Blocks are all sent 914 in plaintext. Generally this has had the benefit of allowing network 915 administrators to read the message when sniffing the wire. However, 916 this also allows an attacker to see the contents of event messages 917 and perhaps to use that information for malicious purposes. 919 8.10. Man In The Middle 921 It is conceivable that an attacker may intercept Certificate Blocks 922 and insert their own Certificate information. In that case, the 923 attacker would be able to receive event messages from the actual 924 sender and then relay modified messages, insert new messages, or 925 deleted messages. They would then be able to construct a Signature 926 Block and sign it with their own private key. The network 927 administrators should verify that the key contained in the 928 Certificate Block is indeed the key being used on the actual device. 929 If that is indeed the case, then this MITM attack will not succeed. 931 8.11. Denial of Service 933 An attacker may be able to overwhelm a receiver by sending it invalid 934 Signature Block messages. If the receiver is attempting to process 935 these messages online, it may consume all available resources. For 936 this reason, it may be appropriate to just receive the Signature 937 Block messages and process them as time permits. 939 As with any system, an attacker may also just overwhelm a receiver by 940 sending more messages to it than can be handled by the infrastructure 941 or the device itself. Implementors should attempt to provide 942 features that minimize this threat. Such as only receiving syslog 943 messages from known IP addresses. 945 8.12. Covert Channels 947 Nothing in this protocol attempts to eliminate covert channels. 948 Indeed, the unformatted message syntax in the packets could be very 949 amenable to sending embedded secret messages. In fact, just about 950 every aspect of syslog messages lends itself to the conveyance of 951 covert signals. For example, a collusionist could send odd and even 952 PRI values to indicate Morse Code dashes and dots. 954 9. IANA Considerations 956 Two syslog packet types are specified in this document; the Signature 957 Block and the Certificate Block. Each of these has several fields 958 specified that should be controlled by the IANA. Essentially these 959 packet types may be differentiated based upon the value in the Cookie 960 field. The Signature Block packet may be identified by a value of 961 "@#sigSIG" in the Cookie field. The Certificate Block packet may be 962 identified by a value of "@#sigCER" in the Cookie field. Each of 963 these packet types share fields that should be consistent; 964 specifically, the Certificate Block packet types may be considered to 965 be an announcement of capabilities and the Signature Block packets 966 SHOULD have the same values in the fields described in this section. 967 This document allows that there may be some really fine reason for 968 the values to be different between the two packet types but the 969 authors and contributors can't see any valid reason for that at this 970 time. 972 This document also upholds the Facilities and Severities listed in 973 RFC 3164 [20]. Those values range from 0 to 191. This document also 974 instructs the IANA to reserve all other possible values of the 975 Severities and Facilities above the value of 191 and to distribute 976 them via the consensus process as defined in RFC 2434 [17]. 978 The following fields are to be controlled by the IANA in both the 979 Signature Block packets and the Certificate Block packets. 981 9.1. Version Field 983 The Version field (Ver) is a 4 byte field. The first two bytes of 984 this field define the version of the Signature Block packets and the 985 Certificate Block Packets. This allows for future efforts to 986 redefine the subsequent fields in the Signature Block packets and 987 Certificate Block packets. A value of "00" is reserved and not used. 988 This document describes the fields for the version value of "01". It 989 is expected that this value be incremented monotonically with decimal 990 values up through "50" for IANA assigned values. Values "02" through 991 "50" will be assigned by the IANA using the "IETF Consensus" policy 992 defined in RFC 2434 [17]. It is not anticipated that these values 993 will be reused. Values of "51" through "99" will be vendor-specific, 994 and values in this range are not to be assigned by the IANA. 996 In the case of vendor-specific assigned Version numbers, all 997 subsequent values defined in the packet will then have vendor- 998 specific meaning. They may, or may not, align with the values 999 assigned by the IANA for these fields. For example, a vendor may 1000 choose to define their own Version of "51" still containing values of 1001 "1" for the Hash Algorithm and Signature Scheme which aligns with the 1002 IANA assigned values as defined in this document. However, they may 1003 then choose to define a value of "5" for the Signature Group for 1004 their own reasons. 1006 The third byte of the Ver field defines the Hash Algorithm. It is 1007 envisioned that this will also be a monotonically increasing value 1008 with a maximum value of "9". The value of "1" is defined in this 1009 document as the first assigned value and is SHA1 FIPS-180-1.1995 [2]. 1010 Subsequent values will be assigned by the IANA using the "IETF 1011 Consensus" policy defined in RFC 2434 [17]. 1013 The forth and final byte of the Ver field defines the Signature 1014 Scheme. It is envisioned that this too will be a monotonically 1015 increasing value with a maximum value of "9". The value of "1" is 1016 defined in this document as OpenPGP DSA - RFC 2440 [18], FIPS.186- 1017 1.1998 [1]. Subsequent values will be assigned by the IANA using the 1018 "IETF Consensus" policy defined in RFC 2434 [17]. The fields, values 1019 assigned in this document and ranges are illustrated in the following 1020 table. 1022 Field Value Defined IANA Assigned Vendor Specific 1023 in this Document Range Range 1024 ----- ---------------- ------------- --------------- 1025 Ver 1026 ver 01 01-50 50-99 1027 hash 1 0-9 -none- 1028 sig 1 0-9 -none- 1030 If either the Hash Algorithm field or the Signature Scheme field is 1031 needed to go beyond "9" within the current version (first two bytes), 1032 the IANA should increment the first two bytes of this 4 byte field to 1033 be the next value with the definition that all of the subsequent 1034 values of fields described in this section are reset to "0" while 1035 retaining the latest definitions given by the IANA. For example, 1036 consider the case that the first two characters are "23" and the 1037 latest Signature Algorithm is 4. Let's say that the latest Hash 1038 Algorithm value is "9" but a better Hash Algorithm is defined. In 1039 that case, the IANA will increment the first two bytes to become 1040 "24", retain the current Hash Algorithm to be "0", define the new 1041 Hash Algorithm to be "1" in this scheme, and define the current 1042 Signature Scheme to also be "0". This example is illustrated in the 1043 following table. 1045 Current New - Equivalent New with Later 1046 to "Current" Algorithms 1047 ------- -------------- --------------- 1048 ver = 23 ver = 24 ver = 24 1049 hash = 9 hash = 0 hash = 1 1050 sig = 4 sig = 0 sig = 0 1052 9.2. SIG Field 1054 The SIG field values are numbers as defined in Section 4.4. Values 1055 "0" through "3" are assigned in this document. The IANA shall assign 1056 values "4" through "7" using the "IETF Consensus" policy defined in 1057 RFC 2434 [17]. Values "8" and "9" shall be left as vendor specific 1058 and shall not be assigned by the IANA. 1060 9.3. Key Blob Type 1062 Section Section 5.2 defines five, one character identifiers for the 1063 key blob type. These are the uppercase letters, "C", "P", "K", "N", 1064 and "U". All other uppercase letters shall be assigned by the IANA 1065 using the "IETF Consensus" policy defined in RFC 2434 [17]. 1066 Lowercase letters are left as vendor specific and shall not be 1067 assigned by the IANA. 1069 10. Authors and Working Group Chair 1071 The working group can be contacted via the mailing list: 1073 syslog-sec@employees.org 1075 The current Chair of the Working Group may be contacted at: 1077 Chris Lonvick 1078 Cisco Systems 1079 Email: clonvick@cisco.com 1081 The authors of this draft are: 1083 John Kelsey 1084 Email: kelsey.j@ix.netcom.com 1086 Jon Callas 1087 Email: jon@callas.org 1089 Alexander Clemm 1090 Email: alex@cisco.com 1092 11. Acknowledgements 1094 The authors wish to thank Alex Brown, Chris Calabrese, Carson Gaspar, 1095 Drew Gross, Chris Lonvick, Darrin New, Marshall Rose, Holt Sorenson, 1096 Rodney Thayer, Andrew Ross, Rainer Gerhards, Albert Mietus, and the 1097 many Counterpane Internet Security engineering and operations people 1098 who commented on various versions of this proposal. 1100 12. References 1102 [1] National Institute of Standards and Technology, "Digital 1103 Signature Standard", FIPS PUB 186-1, December 1998, 1104 . 1106 [2] National Institute of Standards and Technology, "Secure Hash 1107 Standard", FIPS PUB 180-1, April 1995, 1108 . 1110 [3] American National Standards Institute, "USA Code for 1111 Information Interchange", ANSI X3.4, 1968. 1113 [4] Menezes, A., van Oorschot, P., and S. Vanstone, ""Handbook of 1114 Applied Cryptography", CRC Press", 1996. 1116 [5] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1117 August 1980. 1119 [6] Mockapetris, P., "Domain names - concepts and facilities", 1120 STD 13, RFC 1034, November 1987. 1122 [7] Mockapetris, P., "Domain names - implementation and 1123 specification", STD 13, RFC 1035, November 1987. 1125 [8] Eastlake, D., Crocker, S., and J. Schiller, "Randomness 1126 Recommendations for Security", RFC 1750, December 1994. 1128 [9] Malkin, G., "Internet Users' Glossary", RFC 1983, August 1996. 1130 [10] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 1131 Extensions (MIME) Part One: Format of Internet Message Bodies", 1132 RFC 2045, November 1996. 1134 [11] Oehler, M. and R. Glenn, "HMAC-MD5 IP Authentication with 1135 Replay Prevention", RFC 2085, February 1997. 1137 [12] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing 1138 for Message Authentication", RFC 2104, February 1997. 1140 [13] Bradner, S., "Key words for use in RFCs to Indicate Requirement 1141 Levels", BCP 14, RFC 2119, March 1997. 1143 [14] Yergeau, F., "UTF-8, a transformation format of ISO 10646", 1144 RFC 2279, January 1998. 1146 [15] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1147 Specifications: ABNF", RFC 2234, November 1997. 1149 [16] Hinden, R. and S. Deering, "IP Version 6 Addressing 1150 Architecture", RFC 2373, July 1998. 1152 [17] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 1153 Considerations Section in RFCs", BCP 26, RFC 2434, 1154 October 1998. 1156 [18] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, 1157 "OpenPGP Message Format", RFC 2440, November 1998. 1159 [19] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) 1160 for version 3 of the Simple Network Management Protocol 1161 (SNMPv3)", RFC 2574, April 1999. 1163 [20] Lonvick, C., "The BSD Syslog Protocol", RFC 3164, August 2001. 1165 [21] New, D. and M. Rose, "Reliable Delivery for syslog", RFC 3195, 1166 November 2001. 1168 [22] Klyne, G. and C. Newman, "Date and Time on the Internet: 1169 Timestamps", RFC 3339, July 2002. 1171 [23] Klyne, G. and C. Newman, "Date and Time on the Internet: 1172 Timestamps", RFC 3339, July 2002. 1174 [24] Schneier, B., "Applied Cryptography Second Edition: protocols, 1175 algorithms, and source code in C", 1996. 1177 Authors' Addresses 1179 John Kelsey 1181 Email: kelsey.j@ix.netcom.com 1183 Jon Callas 1184 PGP Corporation 1186 Email: jon@callas.org 1188 Alexander Clemm 1189 Cisco Systems 1191 Email: alex@cisco.com 1193 Intellectual Property Statement 1195 The IETF takes no position regarding the validity or scope of any 1196 Intellectual Property Rights or other rights that might be claimed to 1197 pertain to the implementation or use of the technology described in 1198 this document or the extent to which any license under such rights 1199 might or might not be available; nor does it represent that it has 1200 made any independent effort to identify any such rights. 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