syslog Working Group J. Kelsey Internet-Draft NIST Intended status: Standards Track J. Callas Expires: June 11, 2007 PGP Corporation A. Clemm Cisco Systems December 8, 2006 Signed syslog Messages draft-ietf-syslog-sign-20.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 11, 2007. Copyright Notice Copyright (C) The IETF Trust (2006). Kelsey, et al. Expires June 11, 2007 [Page 1] Internet-Draft Signed syslog Messages December 2006 Abstract This document describes a mechanism to add origin authentication, message integrity, replay resistance, message sequencing, and detection of missing messages to the transmitted syslog messages. This specification draws upon the work defined in RFC xxxx, "The syslog Protocol", however it may be used atop any message delivery mechanism, even that defined in RFC 3164, "The BSD syslog Protocol", or in the RAW mode of RFC 3195, "The Reliable Delivery of syslog". Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions Used in this Document . . . . . . . . . . . . . . 6 3. syslog Message Format . . . . . . . . . . . . . . . . . . . . 7 4. Signature Blocks . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. syslog Messages Containing a Signature Block . . . . . . . 9 4.2. Signature Block Format and Fields . . . . . . . . . . . . 9 4.2.1. Version . . . . . . . . . . . . . . . . . . . . . . . 10 4.2.2. Reboot Session ID . . . . . . . . . . . . . . . . . . 11 4.2.3. Signature Group and Signature Priority . . . . . . . . 11 4.2.4. Global Block Counter . . . . . . . . . . . . . . . . . 13 4.2.5. First Message Number . . . . . . . . . . . . . . . . . 14 4.2.6. Count . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.7. Hash Block . . . . . . . . . . . . . . . . . . . . . . 14 4.2.8. Signature . . . . . . . . . . . . . . . . . . . . . . 15 5. Payload and Certificate Blocks . . . . . . . . . . . . . . . . 16 5.1. Preliminaries: Key Management and Distribution Issues . . 16 5.2. Payload Block . . . . . . . . . . . . . . . . . . . . . . 17 5.3. Certificate Block . . . . . . . . . . . . . . . . . . . . 17 5.3.1. syslog Messages Containing a Certificate Block . . . . 18 5.3.2. Certificate Block Format and Fields . . . . . . . . . 18 6. Redundancy and Flexibility . . . . . . . . . . . . . . . . . . 21 6.1. Redundancy . . . . . . . . . . . . . . . . . . . . . . . . 21 6.1.1. Configuration Parameters for Certificate Blocks . . . 21 6.1.2. Configuration Parameters for Signature Blocks . . . . 21 6.2. Flexibility . . . . . . . . . . . . . . . . . . . . . . . 22 7. Efficient Verification of Logs . . . . . . . . . . . . . . . . 23 7.1. Offline Review of Logs . . . . . . . . . . . . . . . . . . 23 7.2. Online Review of Logs . . . . . . . . . . . . . . . . . . 24 8. Security Considerations . . . . . . . . . . . . . . . . . . . 26 8.1. Cryptography Constraints . . . . . . . . . . . . . . . . . 26 8.2. Packet Parameters . . . . . . . . . . . . . . . . . . . . 26 8.3. Message Authenticity . . . . . . . . . . . . . . . . . . . 27 8.4. Sequenced Delivery . . . . . . . . . . . . . . . . . . . . 27 8.5. Replaying . . . . . . . . . . . . . . . . . . . . . . . . 27 8.6. Reliable Delivery . . . . . . . . . . . . . . . . . . . . 27 Kelsey, et al. Expires June 11, 2007 [Page 2] Internet-Draft Signed syslog Messages December 2006 8.7. Sequenced Delivery . . . . . . . . . . . . . . . . . . . . 27 8.8. Message Integrity . . . . . . . . . . . . . . . . . . . . 28 8.9. Message Observation . . . . . . . . . . . . . . . . . . . 28 8.10. Man In The Middle Attacks . . . . . . . . . . . . . . . . 28 8.11. Denial of Service . . . . . . . . . . . . . . . . . . . . 28 8.12. Covert Channels . . . . . . . . . . . . . . . . . . . . . 28 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 9.1. Structured data and syslog messages . . . . . . . . . . . 30 9.2. Version Field . . . . . . . . . . . . . . . . . . . . . . 30 9.3. SG Field . . . . . . . . . . . . . . . . . . . . . . . . . 32 9.4. Key Blob Type . . . . . . . . . . . . . . . . . . . . . . 32 10. Authors and Working Group Chairs . . . . . . . . . . . . . . . 33 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 12.1. Normative References . . . . . . . . . . . . . . . . . . . 35 12.2. Informative References . . . . . . . . . . . . . . . . . . 35 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Intellectual Property and Copyright Statements . . . . . . . . . . 38 Kelsey, et al. Expires June 11, 2007 [Page 3] Internet-Draft Signed syslog Messages December 2006 1. Introduction This document describes a mechanism that adds origin authentication, message integrity, replay resistance, message sequencing, and detection of missing messages to syslog. Essentially, this is accomplished by sending a special syslog message. The contents of this syslog message is called a Signature Block. Each Signature Block contains, in effect, a detached signature on some number of previously sent messages. It is cryptographically signed and contains the hashes of previously sent syslog messages. While most implementations of syslog involve only a single sender as the generator of each message and a single receiver as the collector of each message, provisions need to be made to cover situations in which messages are sent to multiple receivers. This concerns in particular situations in which different messages are sent to different receivers, which means that some messages are sent to some receivers but not to others. The required differentiation of messages is generally performed based on the Priority value of the individual messages. For example, messages from any Facility with a Severity value of 3, 2, 1 or 0 may be sent to one collector while all messages of Facilities 4, 10, 13, and 14 may be sent to another collector. Appropriate syslog-sign messages must be kept with their proper syslog messages. To address this, syslog-sign uses a signature group. A signature group identifies a group of messages that are all kept together for signing purposes by the sender. A Signature Block always belongs to exactly one signature group and it always signs messages belonging only to that signature group. Additionally, a sender will send a Certificate Block to provide key management information between the sender and the receiver. This Certificate Block has a field to denote the type of key material which may be such things as a PKIX certificate, an OpenPGP certificate, or even an indication that a key had been predistributed. In the cases of certificates being sent, the certificates may have to be split across multiple packets. The receiver of the previous messages may verify that the hash of each received message matches the signed hash contained in the Signature Block. A collector may process these Signature Blocks as they arrive, building an authenticated log file. Alternatively, it may store all the log messages in the order they were received. This allows a network operator to authenticate the log file at the time the logs are reviewed. This specification is independent of the actual transport protocol selected. The mechanism is especially suitable for use with the syslog protocol as defined in RFC xxxx [14] because it utilizes the Kelsey, et al. Expires June 11, 2007 [Page 4] Internet-Draft Signed syslog Messages December 2006 STRUCTURED-DATA elements defined in that document. It may also be used with syslog packets over traditional UDP [4] as described in RFC 3164 [10]. It may also be used with the Reliable Delivery of syslog as described in RFC 3195 [11], and it may be used with other message delivery mechanisms. Designers of other efforts to define event notification mechanisms are encouraged to consider this specification in their design. NOTE to RFC editor: replace xxxx with actual RFC number for this document and remove this note Kelsey, et al. Expires June 11, 2007 [Page 5] Internet-Draft Signed syslog Messages December 2006 2. Conventions Used in this Document The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [9]. Kelsey, et al. Expires June 11, 2007 [Page 6] Internet-Draft Signed syslog Messages December 2006 3. syslog Message Format This specification does not rely upon any specific syslog message format. It is RECOMMENDED to be implemented in conjunction with the syslog protocol as defined in RFC xxxx [14]. It MAY be transported over a traditional syslog message format such as that defined in the informational RFC 3164 [10], or it MAY be used over the Reliable Delivery of syslog Messages as defined in RFC 3195 [11]. Care must be taken when choosing a transport for this mechanism, however. Because the device generating the Signature Block message signs each message in its entirety, it is imperative that the messages MUST NOT be changed in transit. It is equally imperative that the syslog-sign messages MUST NOT be changed in transit. Specifically, a relay as described in RFC 3164 MAY make changes to a syslog packet if specific fields are not found. If this occurs, the entire mechanism described in this document is rendered useless. Likewise, any truncation of messages that occurs between sending and receiving renders the mechanism useless. For this reason, syslog sender and receiver implementations implementing this specification MUST support messages of up to and including 2048 octets in length, in order to minimize the chances of truncation from happening. Likewise, while syslog sender and receiver implementations MAY support messages with a length larger than 2048 octets, implementors need to be aware that any message truncations that occur render the mechanism useless. For convenience, this document uses the syslog message format in the terms described in RFC xxxx [14]. Along with the other fields, that document describes the concept of STRUCTURED DATA (SD). STRUCTURED DATA is defined in the form of SD ELEMENTS (SDEs). An SDE consists of a name and a set of parameter name - value pairs. The SDE name is referred to as SD-ID. The name-value pairs are referred to as SD- PARAM, or SD Parameters, with the name constituting the SD-PARAM- NAME, the value constituting the SD-PARAM-VALUE. The special syslog messages that are defined in this document include definitions of SDEs to convey parameters that relate to the signing of syslog messages. When used in conjunction with RFC xxxx [14], the syslog messages defined in this document carry the signature and certificate data as STRUCTURED DATA, as defined, while the MSG part of the syslog messages is simply empty - the contents of the messages is not intended for interpretation by humans but by applications that use those messages to build an authenticated log. Having said that, as stated above, the mechanism defined in this document is applicable to other message transports as well. When used in conjunction with a syslog message format other than the one defined in RFC xxxx [14], Kelsey, et al. Expires June 11, 2007 [Page 7] Internet-Draft Signed syslog Messages December 2006 specifically, a syslog message format that does not include STRUCTURED DATA, the format of the message payload will simply happen to follow STRUCTURED DATA format. Kelsey, et al. Expires June 11, 2007 [Page 8] Internet-Draft Signed syslog Messages December 2006 4. Signature Blocks This section describes the format of the Signature Block and the fields used within the Signature Block, as well as the syslog messages used to carry the Signature Block. 4.1. syslog Messages Containing a Signature Block There is a need to distinguish the Signature Block itself from the syslog message that is used to carry a Signature Block Signature Blocks MUST be encompassed within completely formed syslog messages. Syslog messages that contain a Signature Block are also referred to as Signature Block messages. A Signature Block message that is compliant with RFC xxxx [14] MUST contain valid APP-NAME, PROCID, and MSGID fields. Specifically, as value for APP-NAME, "syslog" (without the double quotes) MUST be used. As value for MSG-ID, "sig" (without the double quotes) MUST be used. As value for the PRI field, 110 MUST be used, corresponding to facility 13 and severity 6 (informational). The Signature Block is carried as Structured Data within the Signature Block message, per the definitions that follow in the next section. Similarly, when used with traditional syslog [10], the Signature Block message MUST contain a valid TAG field. The TAG field MUST have the value of "syslog" (without the double quotes) to signify that this message was generated by the syslog process. The Signature Block is carried as part of the MSG part, whose syntax happens to follow structured data format per RFC xxxx [14], as specified in the next section. Again, note that all of those fields pertain to the syslog message used to carry the Signature Block. They are not part of the Signature Block itself. In addition, the syslog messages defined as part of syslog-sign themselves (Signature Block messages and Certificate Block messages) are generally not signed by a Signature Block. Receivers that implement syslog-sign know to distinguish messages that are associated with syslog-sign from the syslog messages that are subjected to signing and process them differently. 4.2. Signature Block Format and Fields The content of a Signature Block message is the Signature Block. The Signature Block MUST be encoded as an SD ELEMENT, as defined in RFC xxxx [14]. The SD-ID MUST have the value of "ssign". Kelsey, et al. Expires June 11, 2007 [Page 9] Internet-Draft Signed syslog Messages December 2006 The SDE contains the fields of the Signature Block encoded as SD Parameters, as specified in the following. The Signature Block is composed of the following fields. The value of each field MUST be printable ASCII, and any binary values MUST be base 64 encoded, as defined in RFC 4648 [13]. Field SD-PARAM-NAME Size in bytes ----- ------------- ---- -- ----- Version VER 4 Reboot Session ID RSID 1-10 Signature Group SG 1 Signature Priority SPRI 1-3 Global Block Counter GBC 1-10 First Message Number FMN 1-10 Count CNT 1-2 Hash Block HB variable, size of hash (base 64 encoded binary) Signature SIGN variable (base 64 encoded binary) A Signature Block is accordingly encoded as follows, where xxx denotes a placeholder for the particular value: "[ssign VER=xxx RSID=xxx SG=xxx SPRI=xxx GBC=xxx FMN=xxx CNT=xxx HB=xxx SIGN=xxx]". The fields are separated by single spaces and are described below. 4.2.1. Version The Signature Block version field is 4 characters in length. The value in this field specifies the version of the syslog-sign protocol. This is extensible to allow for different hash algorithms and signature schemes to be used in the future. The value of this field is the grouping of the protocol version (2 bytes), the hash algorithm (1 byte) and the signature scheme (1 byte). Protocol Version - 2 bytes with the first version as described in this document being value of 01 to denote Version 1. Kelsey, et al. Expires June 11, 2007 [Page 10] Internet-Draft Signed syslog Messages December 2006 Hash Algorithm - 1 byte with the definition that 1 denotes SHA1 as defined in FIPS-180-2.2002 [2]. Signature Scheme - 1 byte with the definition that 1 denotes OpenPGP DSA - RFC 2440 [6], FIPS.186-2.2000 [1]. As such, the version, hash algorithm and signature scheme defined in this document may be represented as "0111" (without the quote marks). 4.2.2. Reboot Session ID The reboot session ID is a decimal value that has a length between 1 and 10 bytes. The acceptable values for this are between 0 and 9999999999. A reboot session ID is expected to increase whenever a sender reboots in order to allow receivers to uniquely distinguish messages and message signatures across reboots. A device needs to hence support persisting previous reboot session ID across reboots. In cases where a sender does not support this capability, the reboot session ID MUST always be set to a value of 0, which indicates that this capability is not supported. Otherwise, it MUST increase whenever a sender reboots, starting with a value of 1. If the value latches at 9999999999, then manual intervention may be required to reset it to 1. Implementors MAY wish to consider using the snmpEngineBoots value as a source for this counter as defined in RFC 3414 [7]. 4.2.3. Signature Group and Signature Priority The SG identifier may take on any value from 0-3 inclusive. The SPRI may take on any value from 0-191 inclusive. These fields taken together allow network administrators to associate groupings of syslog messages with appropriate Signature Blocks and Certificate Blocks. Groupings of syslog messages that are signed together are also referred to as signature groups. A Signature Block contains only hashes of those syslog messages that are part of the same signature group. For example, in some cases, network administrators might send syslog messages of Facilities 0 through 15 to one destination while those with Facilities 16 through 23 to another. In such cases, associated Signature Blocks should likely be sent to the corresponding syslog servers as well, signing the syslog messages that are intended for each destination separately. This way, each syslog destination receives Signature Blocks for all syslog messages that it receives, and only for those. The ability to to associate different categories of syslog messages with different signature groups, signed in separate Signature Blocks, provides administrators with flexibility to that regard. Kelsey, et al. Expires June 11, 2007 [Page 11] Internet-Draft Signed syslog Messages December 2006 Syslog-sign provides four options for handling signature groups, linking them with PRI values so they may be routed to the destination commensurate with the appropriate syslog messages. In all cases, no more than 192 distinct signature groups (0-191) are permitted. The signature group to which a Signature Block pertains is indicated by the signature priority (SPRI) field. The signature group (SG) field indicates how to interpret the signature priority field. (Note that the SG field does not indicate the signature group itself, as its name might suggest.) The SG field can have one of the following values: a. '0' -- There is only one signature group. In this case, the administrators want all Signature Blocks to be sent to a single destination; in all likelihood, all of the syslog messages will also be going to that same destination. Signature Blocks sign all messages regardless of their PRI value. This means that in effect, the Signature Block's SPRI value can be ignored. However, it is RECOMMENDED that a single SPRI value is used for all Signature Blocks. Furthermore, it is RECOMMENDED to use 110 as that value, the same value that is used for the PRI field of the Signature Block message. This way, the PRI of the Signature Block message matches the SPRI of the Signature Block that it contains. b. '1' -- Each PRI value is associated with its own signature group. Signature Blocks for a given signature group have SPRI = PRI for that signature group. In other words, the SPRI of the Signature Block matches the PRI value of the syslog messages that are part of the signature group and hence signed by the Signature Block. An SG value of 1 can for example be used when the administrator of a device does not know where any of the syslog messages will ultimately go but anticipates that messages with different PRI values will be collected and processed separately. Having a signature group per PRI value provides administrators with a large degree of flexibility with regards to how to divide up the processing syslog messages and their signatures after they are received, at the same time allowing Signature Blocks to follow the corresponding syslog messages to their eventual destination. c. '2' -- Each signature group contains a range of PRI values. Signature groups are assigned sequentially. A Signature Block for a given signature group has its own SPRI value denoting the highest PRI value of syslog messages in that signature group. The lowest PRI value of syslog messages in that signature group will be one larger than the SPRI value of the next signature group or "0" in case there is no other signature group with a lower SPRI value. The specific signature groups and ranges they Kelsey, et al. Expires June 11, 2007 [Page 12] Internet-Draft Signed syslog Messages December 2006 are associated with are subject to configuration by a system administrator. d. '3' -- Signature groups are not assigned with any of the above relationships to PRI values of the syslog messages they sign. Instead, another scheme is used, which is outside the scope of this specification. There has to be some predefined arrangement between the sender and the intended receivers as to which syslog messages are to be included in which signature group, requiring configuration by a system administrator. This provides administrators also with the flexibility to group syslog messages into signature groups along criteria that are not tied to the PRI value. One reasonable way to configure some installations is to have only one signature group, indicated with SG=0, and have the device send a copy of each Signature Block to each collector. In that case, collectors that are not configured to receive every syslog message will still receive signatures for every message, even ones they are not supposed to receive. While the collector will not be able to detect gaps in the messages (because the presence of a signature does not tell the collector whether or not the corresponding message would be of the collector's concern), it does allow all messages that do arrive at each collector to be put into the right order and to be verified. It also allows each collector to detect duplicates. 4.2.4. Global Block Counter The global block counter is a decimal value representing the number of Signature Blocks sent by syslog-sign before the current one, in this reboot session. This takes at least 1 byte and at most 10 bytes displayed as a decimal counter. The acceptable values for this are between 0 and 9999999999, starting with 0. If the value of the global block counter latches at 9999999999 and the reboot session ID has a value other than 0 (indicating the fact that persisting of the reboot session ID is supported), then the reboot session ID MUST be incremented by 1 and the global block counter resumes at 0. In the case in which the reboot session ID is in fact 0 and persisting of reboot session IDs is not supported, when the global block counter latches, it resumes at 0 also in this case but the reboot session ID MUST NOT be incremented and remains at 0. Note that the global block counter crosses signature groups; it allows us to roughly synchronize when two messages were sent, even though they went to different collectors. Because a reboot results in the start of a new reboot session, the sender MUST reset the global block counter to 0 after a reboot Kelsey, et al. Expires June 11, 2007 [Page 13] Internet-Draft Signed syslog Messages December 2006 occurs. Applications need to apply extra consideration to the possibility that a reboot occurred when authenticating a log, and situations in which reboots occur frequently may result in losing the ability to verify the proper sequence in which messages were sent and hence jeopardizing integrity of the log. 4.2.5. First Message Number This is a decimal value between 1 and 10 bytes. It contains the unique message number within this signature group of the first message whose hash appears in this block. The very first message of the reboot session is numbered "1". For example, if this signature group has processed 1000 messages so far and message number 1001 is the first message whose hash appears in this Signature Block, then this field contains 1001. 4.2.6. Count The count is a 1 or 2 byte field that indicates the number of message hashes to follow. The valid values for this field are between 1 and 99. Note that the number of hashes included in the Signature Block MUST be chosen such that the length of the resulting syslog message does not exceed the maximum permissable syslog message length. 4.2.7. Hash Block The hash block is a block of hashes, each separately encoded in base 64. Each hash in the hash block is the hash of the entire syslog message represented by the hash, independent of the underlying transport. Hashes are ordered from left to right in the order of occurrence of the syslog messages that they represent. With RFC xxxx [14], the "entire syslog message" refers to what is described as the syslog message excluding transport parts that are described in RFC xxxx [15] and RFC xxxx [16], and excluding other parts that may be defined in future transports. The hash value will be the result of the hashing algorithm run across the syslog message, starting with the < of the PRI portion of the header part of the message and ending with the Unicode byte order mask, BOM. The hash algorithm used and indicated by the Version field determines the size of each hash, but the size MUST NOT be shorter than 160 bits. It is base 64 encoded as per RFC 4648 [13]. Analogously, with syslog messages per RFC 3164 [10], the "entire syslog message" refers to the message starting with the < of the PRI portion of the header part of the message and ending with the character preceding the < of the subsequent message, and the hashing Kelsey, et al. Expires June 11, 2007 [Page 14] Internet-Draft Signed syslog Messages December 2006 algoritm is applied accordingly. The number of hashes in a hash block SHOULD be chosen such that the resulting Signature Block message does not exceed a length of 2048 octets in order to avoid the possibility that truncation occurs. When more hashes need to sent than fit inside a Signature Block message, it is advisable to start a new Signature Block. 4.2.8. Signature This is a digital signature, encoded in base 64 per RFC 4648 [13]. The signature is calculated over the completely formatted syslog- message, including all of the PRI, HEADER, and hashes in the hash block, excluding spaces between fields, and also excluding the signature field (SD Parameter Name "SIGN" and corresponding value). Kelsey, et al. Expires June 11, 2007 [Page 15] Internet-Draft Signed syslog Messages December 2006 5. Payload and Certificate Blocks Certificate Blocks and Payload Blocks provide key management in syslog-sign. Their purpose is to support key management that uses public key cryptosystems. 5.1. Preliminaries: Key Management and Distribution Issues A Payload Block contains public key certificate information that is to be conveyed to the receiver. A Payload Block is not sent directly, but in (one or more) fragments. Those fragments are termed Certificate Blocks. All devices send at least one Certificate Block at the beginning of a new reboot session, carrying public key information in effect for the reboot session. There are three key points to understand about Certificate Blocks: a. They handle a variable-sized payload, fragmenting it if necessary and transmitting the fragments as legal syslog messages. This payload is built (as described below) at the beginning of a reboot session and is transmitted in pieces with each Certificate Block carrying a piece. Note that there is exactly one Payload Block per reboot session. b. The Certificate Blocks are digitally signed. The device does not sign the Payload Block, but the signatures on the Certificate Blocks ensure its authenticity. Note that it may not even be possible to verify the signature on the Certificate Blocks without the information in the Payload Block; in this case the Payload Block is reconstructed, the key is extracted, and then the Certificate Blocks are verified. (This is necessary even when the Payload Block carries a certificate, because some other fields of the Payload Block are not otherwise verified.) In practice, most installations keep the same public key over long periods of time, so that most of the time, it is easy to verify the signatures on the Certificate Blocks, and use the Payload Block to provide other useful per-session information. c. The kind of Payload Block that is expected is determined by what kind of key material is on the collector that receives it. The device and collector (or offline log viewer) has both some key material (such as a root public key or predistributed public key) and an acceptable value for the Key Blob Type in the Payload Block, below. The collector or offline log viewer MUST NOT accept a Payload Block of the wrong type. Kelsey, et al. Expires June 11, 2007 [Page 16] Internet-Draft Signed syslog Messages December 2006 5.2. Payload Block The Payload Block is built when a new reboot session is started. There is a one-to-one correspondence between reboot sessions and Payload Blocks. That is, each reboot session has only one Payload Block, regardless of how many signature groups it supports. A Payload Block MUST have the following fields. Each of these fields are separated by a single space character. (Note that because a Payload Block is not carried in a syslog message directly, only the corresponding Certificate Blocks, it does not need to be encoded as an SD ELEMENT.) a. Unique identifier of sender; by default, the sender's IP address in dotted-decimal (IPv4) or colon-separated (IPv6) notation. b. Full local time stamp for the device at the time the reboot session started. This must be in TIMESTAMP-3339 format, that is, in time stamp format per RFC 3339 [12]. c. Key Blob Type, a one-byte field which holds one of five values: 1. 'C' -- a PKIX certificate. 2. 'P' -- an OpenPGP certificate. 3. 'K' -- the public key whose corresponding private key is being used to sign these messages. 4. 'N' -- no key information sent; key is predistributed. 5. 'U' -- installation-specific key exchange information d. The key blob, if any, base 64 encoded per RFC 4648 [13] and consisting of the raw key data. 5.3. Certificate Block The Certificate Block must get the Payload Block to the collector. The Certificate Block itself needs to be distinguished from the syslog message that carries it, refererred to as a Certificate Block message. Because certificates can legitimately be much longer than 2048 bytes, each Certificate Block carries a piece of the Payload Block. Note that the device MAY make the Certificate Blocks of any legal length (that is, any length less than 2048 bytes) that holds all the required fields. Software that processes Certificate Blocks MUST deal correctly with blocks of any legal length. The length of the Kelsey, et al. Expires June 11, 2007 [Page 17] Internet-Draft Signed syslog Messages December 2006 piece of the Payload Block that a Certificate Block is to carry SHOULD be chosen such that the length of the Certificate Block message does not exceed 2048 octets. 5.3.1. syslog Messages Containing a Certificate Block As with a Signature Block, each Certificate Block is carried in its own syslog message, referred to as a Certificate Block message. When used with RFC xxxx [14], the Certificate Block message MUST contain valid APP-NAME, PROCID, and MSGID fields. Specifically, as value for APP-NAME, "syslog" (without the double quotes) MUST be used. As value for MSG-ID, "cert" (without the double quotes) MUST be used. As value for the the PRI field, the value 110 MUST be used, corresponding to facility 13 and severity 6 (informational). The Certificate Block is carried as Structured Data within the Certificate Block message, per the definitions that follow in the next section. Similarly, when used with traditional syslog [10], the Certificate Block message SHOULD contain a valid TAG field. It is RECOMMENDED that the TAG field have the value of "syslog" (without the double quotes) to signify that this message was generated by the syslog process. The Certificate Block is carried as part of the MSG part, whose syntax happens to follow structured data format per RFC xxxx [14], as specified in the next section. Again, note that all of those fields pertain to the syslog message used to carry the Certificate Block. They are not part of the Certificate Block itself. 5.3.2. Certificate Block Format and Fields The contents of a Certificate Block message is the Certificate Block itself. Like a Signature Block, the Certificate Block is encoded as an SD Element per RFC xxxx [14]. The SD-ID of the Certificate Block is "ssign-cert". The Certificate Block is composed of the following fields, each of which is encoded as an SD Parameter with parameter name as indicated. Each field must be printable ASCII, and any binary values are base 64 encoded per RFC 4648 [13]. Kelsey, et al. Expires June 11, 2007 [Page 18] Internet-Draft Signed syslog Messages December 2006 Field SD-PARAM-NAME Size in bytes ----- ------------- ---- -- ----- Version VER 4 Reboot Session ID RSID 1-10 Signature Group SG 1 Signature Priority SPRI 1-3 Total Payload Block Length TPBL 1-8 Index into Payload Block INDEX 1-8 Fragment Length FLEN 1-3 Payload Block Fragment FRAG variable (base 64 encoded binary) Signature SIGN variable (base 64 encoded binary) A Certificate Block is accordingly encoded as follows, where xxx denotes a placeholder for the particular value: "[ssign-cert VER=xxx RSID=xxx SG=xxx SPRI=xxx TBPL=xxx INDEX=xxx FLEN=xxx FRAG=xxx SIGN=xxx]". The fields are separated by single spaces and are described below. 5.3.2.1. Version The signature group version field is 4 characters in length. This field is identical in format and meaning to the Version field described in Section 4.2.1. As such, the version, hash algorithm and signature scheme defined in this document may be represented as "0111" (without the quote marks). 5.3.2.2. Reboot Session ID The Reboot Session ID is identical in format and meaning to the RSID field described in Section 4.2.2. 5.3.2.3. Signature Group and Signature Priority The SIG field is identical in format and meaning to the SIG field described in Section 4.2.8. Also, the SPRI field is identical in Kelsey, et al. Expires June 11, 2007 [Page 19] Internet-Draft Signed syslog Messages December 2006 format and meaning to the SPRI field described there. 5.3.2.4. Total Payload Block Length The Total Payload Block Length is a value representing the total length of the Payload Block in bytes, expressed as a decimal with one to eight bytes. 5.3.2.5. Index into Payload Block This is a value between 1 and 8 bytes. It contains the number of bytes into the Payload Block at which this fragment starts. The first byte of the first fragment is numbered "1". 5.3.2.6. Fragment Length The total length of this fragment expressed as a decimal integer with one to three bytes. 5.3.2.7. Signature This is a digital signature, encoded in base 64, as per RFC 4648 [13]. The Version field effectively specifies the original encoding of the signature. The signature is calculated over the completely formatted syslog message, including all of the PRI, HEADER, and certificate block, excluding spaces between fields, and also excluding the signature field itself (SD Parameter Name "SIGN" and corresponding value). Kelsey, et al. Expires June 11, 2007 [Page 20] Internet-Draft Signed syslog Messages December 2006 6. Redundancy and Flexibility There is a general rule that determines how redundancy works and what level of flexibility the sender and receiver have in message formats: in general, the sender is allowed to send Signature and Certificate Blocks multiple times, to send Signature and Certificate Blocks of any legal length, to include fewer hashes in hash blocks, etc. 6.1. Redundancy Syslog messages are in general sent over unreliable transport, which means that they can be lost in transit. However, if a collector does not receive Signature and Certificate Blocks, many messages may not be able to be verified. Sending Signature and Certificate Blocks multiple times provides redundancy; since the collector MUST ignore Signature/Certificate Blocks it has already received and authenticated, the sender can in principle change its redundancy level for any reason, without communicating this fact to the collector. Although the sender is not constrained in how it decides to send redundant Signature and Certificate Blocks, or even in whether it decides to send along multiple copies of normal syslog messages, we define some redundancy parameters below which may be useful in controlling redundant transmission from the sender to the collector, and which may be useful for administrators to configure. 6.1.1. Configuration Parameters for Certificate Blocks certInitialRepeat = number of times each Certificate Block should be sent before the first message is sent. certResendDelay = maximum time delay in seconds to delay before next redundant sending. certResendCount = maximum number of sent messages to delay before next redundant sending. 6.1.2. Configuration Parameters for Signature Blocks sigNumberResends = number of times a Signature Block is resent. sigResendDelay = maximum time delay in seconds from original sending to next redundant sending. sigResendCount = maximum number of sent messages to delay before next redundant sending. Kelsey, et al. Expires June 11, 2007 [Page 21] Internet-Draft Signed syslog Messages December 2006 6.2. Flexibility The device may change many things about the makeup of Signature and Certificate Blocks in a given reboot session. The things it cannot change are: * The version * The number or arrangements of signature groups It is legitimate for a device to send short Signature Blocks, in order to allow the collector to verify messages quickly. In general, unless something verified by the Payload Block or Certificate Blocks is changed within the reboot session ID, any change is allowed to the Signature or Certificate Blocks during the session. Kelsey, et al. Expires June 11, 2007 [Page 22] Internet-Draft Signed syslog Messages December 2006 7. Efficient Verification of Logs The logs secured with syslog-sign may be reviewed either online or offline. Online review is somewhat more complicated and computationally expensive, but not prohibitively so. 7.1. Offline Review of Logs When the collector stores logs to be reviewed later, they can be authenticated offline just before they are reviewed. Reviewing these logs offline is simple and relatively inexpensive in terms of resources used, so long as there is enough space available on the reviewing machine. Here, we consider that the stored log files have already been separated by sender, reboot session ID, and signature group. This can be done easily with a script file. We then do the following: a. First, we go through the raw log file and split its contents into three files. Each message in the raw log file is classified as a normal message, a Signature Block, or a Certificate Block. Certificate Blocks and Signature Blocks are stored in their own files. Normal messages are stored in a keyed file, indexed on their hash values. b. We sort the Certificate Block file by INDEX value, and check to see whether we have a set of Certificate Blocks that can reconstruct the Payload Block. If so, we reconstruct the Payload Block, verify any key-identifying information, and then use this to verify the signatures on the Certificate Blocks we have received. When this is done, we have verified the reboot session and key used for the rest of the process. c. We sort the Signature Block file by First Message Number. We now create an authenticated log file, which consists of some header information, and then a sequence of message number, message text pairs. We next go through the Signature Block file. For each Signature Block in the file, we do the following: 1. Verify the signature on the Block. 2. For each hashed message in the Block: a. Look up the hash value in the keyed message file. b. If the message is found, write (message number, message text) to the authenticated log file. Kelsey, et al. Expires June 11, 2007 [Page 23] Internet-Draft Signed syslog Messages December 2006 3. Skip all other Signature Blocks with the same First Message Number. d. The resulting authenticated log file contains all messages that have been authenticated and implicitly indicates (by missing message numbers) all gaps in the authenticated messages. One can see that, assuming sufficient space for building the keyed file, this whole process is linear in the number of messages (generally two seeks, one to write and the other to read, per normal message received), and O(N lg N) in the number of Signature Blocks. This estimate comes with two caveats: first, the Signature Blocks arrive very nearly in sorted order, and so can probably be sorted more cheaply on average than O(N lg N) steps. Second, the signature verification on each Signature Block almost certainly is more expensive than the sorting step in practice. We have not discussed error-recovery, which may be necessary for the Certificate Blocks. In practice, a simple error-recovery strategy is probably enough -- if the Payload Block is not valid, then we can just try alternate instances of each Certificate Block, if such are available, until we get the Payload Block right. It is easy for an attacker to flood us with plausible-looking messages, Signature Blocks, and Certificate Blocks. 7.2. Online Review of Logs Some processes on the collector machine may need to monitor log messages in close to real-time. This can be done with syslog-sign, though it is somewhat more complex than offline verification. This is done as follows: a. We have an authenticated message file, into which we write (message number, message text) pairs which have been authenticated. Again, we will assume that we are handling only one signature group, and only one reboot session ID at any given time. b. We have three data structures: A queue into which (message number, hash of message) pairs is kept in sorted order, a queue into which (arrival sequence, hash of message) is kept in sorted order, and a hash table which stores (message text, count) indexed by hash value. In the hash table, count may be any number greater than zero; when count is zero, the entry in the hash table is cleared. c. We must receive all the Certificate Blocks before any other processing can really be done. (This is why they are sent Kelsey, et al. Expires June 11, 2007 [Page 24] Internet-Draft Signed syslog Messages December 2006 first.) Once that is done, any Certificate Block that arrives is discarded. d. Whenever a normal message arrives, we add (arrival sequence, hash of message) to our message queue. If our hash table has an entry for the message's hash value, we increment its count by one; otherwise, we create a new entry with count = 1. If the message queue is full, we roll the oldest messages off the queue by taking the last entry in the queue, and using it to index the hash table. If that entry has count 1, we delete the entry from the hash table; otherwise, we decrement its count. We then delete the last entry in the queue. e. Whenever a Signature Block arrives, we first check to see whether the First Message Number value is too old to still be of interest, or if another Signature Block with that First Message Number has already been received. If so, we discard the Signature Block unread. Otherwise, we check its signature, and discard it if the signature is not valid. A Signature Block contains a sequence of (message number, message hash) pairs. For each pair, we first check to see if the message hash is in the hash table. If so, we write the (message number, message text) into the authenticated message queue. Otherwise, we write the (message number, message hash) to the message number queue. This generally involves rolling the oldest entry out of this queue: before this is done, that entry's hash value is again searched for in the hash table. If a matching entry is found, the (message number, message text) pair is written out to the authenticated message file. In either case, the oldest entry is then discarded. f. The result of this is a sequence of messages in the authenticated message file, each of which has been authenticated, and which are labeled with numbers showing their order of original transmission. One can see that this whole process is roughly linear in the number of messages, and also in the number of Signature Blocks received. The process is susceptible to flooding attacks; an attacker can send enough normal messages that the messages roll off their queue before their Signature Blocks can be processed. Kelsey, et al. Expires June 11, 2007 [Page 25] Internet-Draft Signed syslog Messages December 2006 8. Security Considerations Normal syslog event messages are unsigned and have most of the security attributes described in Section 6 of RFC 3164 [10], and in Section 8 of RFC xxxx [14]. This document also describes Certificate Blocks and Signature Blocks which are signed syslog messages. The Signature Blocks contains signature information of previously sent syslog event messages. All of this information may be used to authenticate syslog messages and to minimize or obviate many of the security concerns described in RFC 3164 and RFC xxxx [14]. 8.1. Cryptography Constraints As with any technology involving cryptography, one should check the current literature to determine whether any algorithms used here have been found to be vulnerable to attack. This specification uses Public Key Cryptography technologies. The proper party or parties must control the private key portion of a public-private key pair. Any party that controls a private key may sign anything they please. Certain operations in this specification involve the use of random numbers. An appropriate entropy source should be used to generate these numbers. See RFC 4086 [8] and NIST 800-90 [3]. 8.2. Packet Parameters The message length must not exceed 2048 bytes. Various problems may result if a sender sends out messages with a length greater than 2048 bytes, as (per RFC xxxx [14])relays MAY truncate messages with lengths greater than 2048 bytes which would make it impossible for receivers to to validate a hash of the packet. In this case, as with all others, to increase the chance of interoperability it tends to be best to be conservative with what you send but liberal in what you are able to receive. Similarly, senders must rigidly enforce the correctness of the message body. Problems may arise if the receiver does not fully accept the syslog packets sent from a device, or if it has problems with the format of the Certificate Block or Signature Block messages. Finally, receivers must not malfunction if they receive syslog messages containing characters other than those specified in this document. Kelsey, et al. Expires June 11, 2007 [Page 26] Internet-Draft Signed syslog Messages December 2006 8.3. Message Authenticity Syslog does not strongly associate the message with the message sender. That fact is established by the receiver upon verification of the Signature Block as described above. Before a Signature Block is used to ascertain the authenticity of an event message, it may be received, stored and reviewed by a person or automated parser. Both of these should maintain doubt about the authenticity of the message until after it has been validated by checking the contents of the Signature Block. With the Signature Block checking, an attacker may only forge messages if they can compromise the private key of the true sender. 8.4. Sequenced Delivery Event messages may be recorded and replayed by an attacker. However the information contained in the Signature Blocks allows a reviewer to determine if the received messages are the ones originally sent by a sender. This process also alerts the reviewer to replayed messages. 8.5. Replaying Event messages may be recorded and replayed by an attacker. However the information contained in the Signature Blocks will allow a reviewer to determine if the received messages are the ones originally sent by a device. This process will also alert the reviewer to replayed messages. 8.6. Reliable Delivery RFC 3195 or RFC xxxx [16] may be used for the reliable delivery of syslog messages. This document acknowledges that event messages sent over UDP may be lost in transit. A proper review of the Signature Block information may pinpoint any messages sent by the sender but not received by the receiver. The overlap of information in subsequent Signature Block information allows a reviewer to determine if any Signature Block messages were also lost in transit. 8.7. Sequenced Delivery Related to the above, syslog messages delivered over UDP not only may be lost, but they may also arrive out of sequence. The information contained in the Signature Block allows a receiver to order the syslog messages. Beyond that, the timestamp information contained in the message may help the reviewer to order received messages even if they are received out of order. Kelsey, et al. Expires June 11, 2007 [Page 27] Internet-Draft Signed syslog Messages December 2006 8.8. Message Integrity Syslog messages may be damaged in transit. A review of the information in the Signature Block determines whether the received message was the intended message sent by the sender. A damaged Signature Block or Certificate Block is evident because the receiver will not be able to validate that it was signed by the sender. 8.9. Message Observation Event messages, Certificate Blocks, and Signature Blocks are all sent in plaintext. Generally this has had the benefit of allowing network administrators to read the message when sniffing the wire. However, this also allows an attacker to see the contents of event messages and perhaps to use that information for malicious purposes. 8.10. Man In The Middle Attacks It is conceivable that an attacker may intercept Certificate Block messages and insert its own Certificate information. In that case, the attacker would be able to receive event messages from the actual sender and then relay modified messages, insert new messages, or delete messages. It would then be able to construct a Signature Block and sign it with its own private key. Network administrators should verify that the key contained in the Payload Block is indeed the key being used on the actual device. If that is indeed the case, then this MITM attack will not succeed. 8.11. Denial of Service An attacker may be able to overwhelm a receiver by sending it invalid Signature Block messages. If the receiver is attempting to process these messages online, this attack may consume all available resources. For this reason, it may be appropriate to simply receive the Signature Block messages and process them as time permits. As with any system, an attacker may also just overwhelm a receiver by sending more messages to it than it can handle. Implementors should attempt to provide features that minimize this threat, such as only accepting syslog messages from known IP addresses. 8.12. Covert Channels Nothing in this protocol attempts to eliminate covert channels. Indeed, the unformatted message syntax in the packets could be very amenable to sending embedded secret messages. In fact, just about every aspect of syslog messages lends itself to the conveyance of covert signals. For example, a collusionist could send odd and even Kelsey, et al. Expires June 11, 2007 [Page 28] Internet-Draft Signed syslog Messages December 2006 PRI values to indicate Morse Code dashes and dots. Kelsey, et al. Expires June 11, 2007 [Page 29] Internet-Draft Signed syslog Messages December 2006 9. IANA Considerations 9.1. Structured data and syslog messages This document specifies two syslog message types to carry Signature Blocks and Certificate Blocks, respectively: the Signature Block message and the Certificate Block message. Each of these has values for several syslog message fields specified that need to be controlled by the IANA. Specifically, with regards to RFC xxxx [14], IANA is instructed to add the following Structured Data Elements to the appropriate registry, consisting of SD-ID and and PARAM-NAME values as follows: SD-ID "ssign" (without the double quotes), with the associated PARAM- NAME values: VER, RSID, SG, SPRI, GBC, FMN, CNT, HB, SIGN SD-ID "ssign-cert" (without the double quotes), with the associated PARAM-NAME values: VER, RSID, SG, SPRI, TBPL, INDEX, FLEN, FRAG, SIGN In addition, IANA is instructed to add values for the APP-NAME and MSGID of syslog messages per RFC xxxx [14] to an appropriate registry, as follows: APP-NAME field: value "syslog" (without the double quotes), with the following values for MSGID fields: "sig", "cert" (without the double quotes) This document also upholds the Facilities and Severities listed in RFC xxxx [14]. Those values range from 0 to 191. This document also instructs the IANA to reserve all other possible values of the Severities and Facilities above the value of 191 and to distribute them via the consensus process as defined in RFC 2434 [5]. In addition, several fields need to be controlled by the IANA in both the Signature Block and the Certificate Block, as outlined in the following sections. 9.2. Version Field The Version field (Ver) is a 4 byte field. The first two bytes of this field define the version of the Signature Block packets and the Certificate Block Packets. This allows for future efforts to redefine the subsequent fields in the Signature Block packets and Certificate Block packets. A value of "00" is reserved and not used. This document describes the fields for the version value of "01". It is expected that this value be incremented monotonically with decimal values up through "50" for IANA assigned values. Values "02" through Kelsey, et al. Expires June 11, 2007 [Page 30] Internet-Draft Signed syslog Messages December 2006 "50" will be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [5]. It is not anticipated that these values will be reused. Values of "51" through "99" are vendor-specific, and values in this range are not to be assigned by the IANA. In the case of vendor-specific assigned Version numbers, all subsequent values defined in the packet have vendor-specific meaning. They may, or may not, align with the values assigned by the IANA for these fields. For example, a vendor may choose to define its own Version of "51" still containing values of "1" for the Hash Algorithm and Signature Scheme which aligns with the IANA assigned values as defined in this document. However, it may then choose to define a value of "5" for the Signature Group for its own reasons. The third byte of the Ver field defines the Hash Algorithm. It is envisioned that this will also be a monotonically increasing value with a maximum value of "9". The value of "1" is defined in this document as the first assigned value and is SHA1 FIPS-180-2.2002 [2]. Subsequent values will be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [5]. The fourth and final byte of the Ver field defines the Signature Scheme. It is envisioned that this too will be a monotonically increasing value with a maximum value of "9". The value of "1" is defined in this document as OpenPGP DSA - RFC 2440 [6], FIPS.186- 2.2000 [1]. Subsequent values will be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [5]. The fields, values assigned in this document and ranges are illustrated in the following table. Field Value Defined IANA Assigned Vendor Specific in this Document Range Range ----- ---------------- ------------- --------------- Ver ver 01 01-50 50-99 hash 1 0-9 -none- sig 1 0-9 -none- If the value of the Hash Algorithm field or the Signature Scheme field is needed to go beyond "9" within the current version (first two bytes), the IANA should increment the first two bytes of this 4 byte field to be the next value with the definition that all of the subsequent values of fields described in this section are reset to "0" while retaining the latest definitions given by the IANA. For example, consider the case that the first two characters are "23" and the latest Signature Algorithm is 4. Let's say that the latest Hash Algorithm value is "9" but a better Hash Algorithm is defined. In that case, the IANA will increment the first two bytes to become Kelsey, et al. Expires June 11, 2007 [Page 31] Internet-Draft Signed syslog Messages December 2006 "24", retain the current Hash Algorithm to be "0", define the new Hash Algorithm to be "1" in this scheme, and define the current Signature Scheme to also be "0". This example is illustrated in the following table. Current New - Equivalent New with Later to "Current" Algorithms ------- -------------- --------------- ver = 23 ver = 24 ver = 24 hash = 9 hash = 0 hash = 1 sig = 4 sig = 0 sig = 0 9.3. SG Field The SG field values are numbers as defined in Section 4.2.3. Values "0" through "3" are assigned in this document. The IANA shall assign values "4" through "7" using the "IETF Consensus" policy defined in RFC 2434 [5]. Values "8" and "9" shall be left as vendor specific and shall not be assigned by the IANA. 9.4. Key Blob Type Section Section 5.2 defines five, one character identifiers for the key blob type. These are the uppercase letters, "C", "P", "K", "N", and "U". All other uppercase letters shall be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [5]. Lowercase letters are left as vendor specific and shall not be assigned by the IANA. Kelsey, et al. Expires June 11, 2007 [Page 32] Internet-Draft Signed syslog Messages December 2006 10. Authors and Working Group Chairs Comments are solicited and should be addressed to the working group's mailing list and/or the authors. The working group can be contacted via the mailing list: syslog-sec@employees.org The current Chairs of the Working Group may be contacted at: Chris Lonvick Cisco Systems Email: clonvick@cisco.com David Harrington Huawei Technologies (USA) Email: ietfdbh@comcast.net dharrington@huawei.com Tel: +1-603-436-8634 The authors of this draft are: John Kelsey Email: John.Kelsey@nist.gov Jon Callas Email: jon@callas.org Alexander Clemm Email: alex@cisco.com Kelsey, et al. Expires June 11, 2007 [Page 33] Internet-Draft Signed syslog Messages December 2006 11. Acknowledgements The authors wish to thank Alex Brown, Chris Calabrese, Steve Chang, Carson Gaspar, Drew Gross, David Harrington, Chris Lonvick, Darrin New, Marshall Rose, Holt Sorenson, Rodney Thayer, Andrew Ross, Rainer Gerhards, Albert Mietus, and the many Counterpane Internet Security engineering and operations people who commented on various versions of this proposal. Kelsey, et al. Expires June 11, 2007 [Page 34] Internet-Draft Signed syslog Messages December 2006 12. References 12.1. Normative References [1] National Institute of Standards and Technology, "Digital Signature Standard", FIPS PUB 186-2, January 2000, . [2] National Institute of Standards and Technology, "Secure Hash Standard", FIPS PUB 180-2, August 2002, . [3] National Institute of Standards and Technology, "NIST Special Publication 800-90: Recommendation for Random Number Generation using Deterministic Random Bit Generators", June 2006, . [4] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [6] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, "OpenPGP Message Format", RFC 2440, November 1998. [7] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", December 2002. 12.2. Informative References [8] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Recommendations for Security", RFC 4086, June 2005. [9] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [10] Lonvick, C., "The BSD Syslog Protocol", RFC 3164, August 2001. [11] New, D. and M. Rose, "Reliable Delivery for syslog", RFC 3195, November 2001. [12] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. Kelsey, et al. Expires June 11, 2007 [Page 35] Internet-Draft Signed syslog Messages December 2006 [13] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [14] Gerhards, R., "The syslog Protocol, draft-ietf-syslog-protocol-17.txt (work in progress)", June 2006. [15] Okmianski, A., "Transmission of syslog Messages over UDP, draft-ietf-syslog-transport-udp-08.txt (work in progress)", November 2006. [16] Miao, F. and M. Yuzhi, "TLS Transport Mapping for syslog, draft-ietf-syslog-transport-tls-06.txt (work in progress)", December 2006. Kelsey, et al. Expires June 11, 2007 [Page 36] Internet-Draft Signed syslog Messages December 2006 Authors' Addresses John Kelsey NIST Email: john.kelsey@nist.gov Jon Callas PGP Corporation Email: jon@callas.org Alexander Clemm Cisco Systems Email: alex@cisco.com Kelsey, et al. Expires June 11, 2007 [Page 37] Internet-Draft Signed syslog Messages December 2006 Full Copyright Statement Copyright (C) The IETF Trust (2006). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Kelsey, et al. Expires June 11, 2007 [Page 38]