syslog Working Group J. Kelsey Internet-Draft NIST Intended status: Standards Track J. Callas Expires: March 31, 2008 PGP Corporation A. Clemm Cisco Systems September 28, 2007 Signed syslog Messages draft-ietf-syslog-sign-23.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 March 31, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Kelsey, et al. Expires March 31, 2008 [Page 1] Internet-Draft Signed syslog Messages September 2007 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 is intended to be used in conjunction with the work defined in RFC xxxx, "The syslog Protocol". Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Conventions Used in this Document . . . . . . . . . . . . . . 6 3. syslog Message Format . . . . . . . . . . . . . . . . . . . . 7 4. Signature Blocks . . . . . . . . . . . . . . . . . . . . . . . 8 4.1. syslog Messages Containing a Signature Block . . . . . . . 8 4.2. Signature Block Format and Fields . . . . . . . . . . . . 8 4.2.1. Version . . . . . . . . . . . . . . . . . . . . . . . 9 4.2.2. Reboot Session ID . . . . . . . . . . . . . . . . . . 10 4.2.3. Signature Group and Signature Priority . . . . . . . . 10 4.2.4. Global Block Counter . . . . . . . . . . . . . . . . . 12 4.2.5. First Message Number . . . . . . . . . . . . . . . . . 13 4.2.6. Count . . . . . . . . . . . . . . . . . . . . . . . . 14 4.2.7. Hash Block . . . . . . . . . . . . . . . . . . . . . . 14 4.2.8. Signature . . . . . . . . . . . . . . . . . . . . . . 14 5. Payload and Certificate Blocks . . . . . . . . . . . . . . . . 15 5.1. Preliminaries: Key Management and Distribution Issues . . 15 5.2. Payload Block . . . . . . . . . . . . . . . . . . . . . . 16 5.3. Certificate Block . . . . . . . . . . . . . . . . . . . . 16 5.3.1. syslog Messages Containing a Certificate Block . . . . 16 5.3.2. Certificate Block Format and Fields . . . . . . . . . 17 6. Redundancy and Flexibility . . . . . . . . . . . . . . . . . . 20 6.1. Redundancy . . . . . . . . . . . . . . . . . . . . . . . . 20 6.1.1. Configuration Parameters for Certificate Blocks . . . 20 6.1.2. Configuration Parameters for Signature Blocks . . . . 20 6.2. Flexibility . . . . . . . . . . . . . . . . . . . . . . . 21 7. Efficient Verification of Logs . . . . . . . . . . . . . . . . 22 7.1. Offline Review of Logs . . . . . . . . . . . . . . . . . . 22 7.2. Online Review of Logs . . . . . . . . . . . . . . . . . . 23 8. Security Considerations . . . . . . . . . . . . . . . . . . . 25 8.1. Cryptographic Constraints . . . . . . . . . . . . . . . . 25 8.2. Packet Parameters . . . . . . . . . . . . . . . . . . . . 25 8.3. Message Authenticity . . . . . . . . . . . . . . . . . . . 26 8.4. Replaying . . . . . . . . . . . . . . . . . . . . . . . . 26 8.5. Reliable Delivery . . . . . . . . . . . . . . . . . . . . 26 8.6. Sequenced Delivery . . . . . . . . . . . . . . . . . . . . 26 8.7. Message Integrity . . . . . . . . . . . . . . . . . . . . 26 8.8. Message Observation . . . . . . . . . . . . . . . . . . . 27 Kelsey, et al. Expires March 31, 2008 [Page 2] Internet-Draft Signed syslog Messages September 2007 8.9. Man In The Middle Attacks . . . . . . . . . . . . . . . . 27 8.10. Denial of Service . . . . . . . . . . . . . . . . . . . . 27 8.11. Covert Channels . . . . . . . . . . . . . . . . . . . . . 27 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 9.1. Structured Data and syslog messages . . . . . . . . . . . 28 9.2. Version Field . . . . . . . . . . . . . . . . . . . . . . 28 9.3. SG Field . . . . . . . . . . . . . . . . . . . . . . . . . 30 9.4. Key Blob Type . . . . . . . . . . . . . . . . . . . . . . 30 10. Working Group . . . . . . . . . . . . . . . . . . . . . . . . 31 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 12.1. Normative References . . . . . . . . . . . . . . . . . . . 33 12.2. Informative References . . . . . . . . . . . . . . . . . . 34 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 Intellectual Property and Copyright Statements . . . . . . . . . . 36 Kelsey, et al. Expires March 31, 2008 [Page 3] Internet-Draft Signed syslog Messages September 2007 1. Introduction This document describes a mechanism, called syslog-sign in this document, 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 originator and a single collector of each message, provisions need to be made to cover situations in which messages are sent to multiple collectors. This concerns, in particular, situations in which different messages are sent to different collectors, which means that some messages are sent to some collectors 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 originator. A Signature Block always belongs to exactly one signature group and always signs messages belonging only to that signature group. Additionally, a originator sends a Certificate Block to provide key management information between the originator and the collector. 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 collector 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. The mechanism described in this specification is intended to be used in conjunction with the syslog protocol as defined in RFC xxxx [8] as Kelsey, et al. Expires March 31, 2008 [Page 4] Internet-Draft Signed syslog Messages September 2007 its message delivery mechanism and uses the concept of STRUCTURED- DATA elements defined in that document. In fact, this specification mandates implementation of syslog protocol. Nevertheless, it is conceivable that the concepts underlying this mechanism could also be used in conjunction with other message delivery mechanisms. Designers of other efforts to define event notification mechanisms are therefore encouraged to consider this specification in their designs. NOTE to RFC editor: replace xxxx with the actual RFC number assigned to [8], replace zzzz with the actual RFC number assigned to [9], replace wwww with the actual RFC number assigned to [10], replace yyyy with the actual RFC number assigned to this document, and remove this note. Kelsey, et al. Expires March 31, 2008 [Page 5] Internet-Draft Signed syslog Messages September 2007 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 [11]. Kelsey, et al. Expires March 31, 2008 [Page 6] Internet-Draft Signed syslog Messages September 2007 3. syslog Message Format This specification is intended to be used in conjunction with the syslog protocol as defined in RFC xxxx [8]. The syslog protocol therefore MUST be supported by implementations of this specification. Because the originator generating the Signature Block message signs each message in its entirety, the messages MUST NOT be changed in transit. By the same token, the syslog-sign messages MUST NOT be changed in transit. Specifically, a relay as described in RFC xxxx [8] MAY make changes to a syslog packet. If this occurs, the 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 originator and collector implementations implementing this specification MUST support messages of up to and including 2048 octets in length, in order to minimize the chance of truncation. While syslog originator and collector 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. This specification uses the syslog message format described in RFC xxxx [8]. Along with other fields, that document describes the concept of Structured Data (SD). Structured Data is defined in terms 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, and the value constituting the SD-PARAM-VALUE. The syslog messages defined in this document carry the signature and certificate data as Structured Data. The special syslog messages defined in this document include for this purpose definitions of SDEs to convey parameters that relate to the signing of syslog messages. The MSG part of the syslog messages defined in this document SHOULD simply be empty -- the content of the messages is not intended for interpretation by humans but by applications that use those messages to build an authenticated log. Because the syslog messages defined in this document adhere to the format described in RFC xxxx [8], they identify the machine that originates the syslog message in the HOSTNAME field. Therefore, the signature and certificate data do not need to include an additional parameter to identify the machine that orginates the message. Kelsey, et al. Expires March 31, 2008 [Page 7] Internet-Draft Signed syslog Messages September 2007 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 is identified by the presence of an SD ELEMENT with an SD-ID with the value "ssign". In addition, a Signature Block message MUST contain valid APP-NAME, PROCID, and MSGID fields to be compliant with RFC xxxx [8]. This specification does not mandate particular values for these fields; however, for consistency, originators SHOULD use the same values for APP-NAME, PROCID, and MSGID fields for every Signature Block message that is sent, whichever values are chosen. It is RECOMMENDED (but not required) to use 110 as value for the PRI field, 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. A Signature Block message SHOULD NOT carry other Structured Data besides the Structured Data of the Signature Block itself. The syslog messages defined as part of syslog-sign themselves (Signature Block messages and Certificate Block messages) do not need to be signed by a Signature Block. Collectors that implement syslog- sign know to distinguish syslog messages that are associated with syslog-sign from those 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 [8]. The SD-ID MUST have the value of "ssign". 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 Kelsey, et al. Expires March 31, 2008 [Page 8] Internet-Draft Signed syslog Messages September 2007 defined in RFC 4648 [7]. Field SD-PARAM-NAME Size in octets ----- ------------- ---- -- ------ 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 times the number of hashes (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 values: [ssign VER="xxx" RSID="xxx" SG="xxx" SPRI="xxx" GBC="xxx" FMN="xxx" CNT="xxx" HB="xxx" SIGN="xxx"] Values of the fields constitute SD parameter values and are hence enclosed in quotes, per RFC xxxx [8]. The fields are separated by single spaces and are described below. 4.2.1. Version The Signature Block Version field is a decimal value that has a length of 4 octets, which may include leading zeroes. Each octet contains a decimal character in the range of "0" to "9". 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 octets), the hash algorithm (1 octet) and the signature scheme (1 octet). Kelsey, et al. Expires March 31, 2008 [Page 9] Internet-Draft Signed syslog Messages September 2007 Protocol Version - 2 octets, with "01" as the value for the protocol version that is described in this document. Hash Algorithm - 1 octet, where, in conjunction with Protocol Version 01, a value of "1" denotes SHA1 and a value of "2" denotes SHA256, as defined in FIPS-180-2.2002 [2]. Signature Scheme - 1 octet, where, in conjunction with Protocol Version 01, a value of "1" denotes OpenPGP DSA, defined in RFC 2440 [5] and FIPS.186-2.2000 [1]. The version, hash algorithm and signature scheme defined in this document would accordingly be represented as "0111" (if SHA1 is used as Hash Algorithm) and "0121" (if SHA256 is used as Hash Algorithm), respectively (without the quotation marks). The values of the Hash Algorithm and Signature Scheme are defined relative to the Protocol Version. If the single-octet representation of the values for Hash Algorithm and Signature Scheme were to ever represent a limitation, this limitation could be overcome by defining a new Protocol Version with additional Hash Algorithms and/or Signature Schemes, and having implementations support both Protocol Versions concurrently. 4.2.2. Reboot Session ID The Reboot Session ID is a decimal value that has a length between 1 and 10 octets. The acceptable values for this are between 0 and 9999999999. Leading zeroes MUST be omitted. A Reboot Session ID is expected to increase whenever an originator reboots in order to allow collectors to distinguish messages and message signatures across reboots. Hence, an originator needs to retain the previous Reboot Session ID across reboots. In cases where an originator 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 an originator reboots, starting with a value of 1. If the value reaches 9999999999, then manual intervention may be required to subsequently reset it to 1. Implementors MAY wish to consider using the snmpEngineBoots value as a source for this counter as defined in RFC 3414 [6]. 4.2.3. Signature Group and Signature Priority The SG parameter may take any value from 0-3 inclusive. The SPRI parameter may take 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 Kelsey, et al. Expires March 31, 2008 [Page 10] Internet-Draft Signed syslog Messages September 2007 also called 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 have originators send syslog messages of Facilities 0 through 15 to one collector and those with Facilities 16 through 23 to another. In such cases, associated Signature Blocks should likely be sent to the corresponding collectors as well, signing the syslog messages that are intended for each collector separately. This way, each collector receives Signature Blocks for all syslog messages that it receives, and only for those. The ability to associate different categories of syslog messages with different Signature Groups, signed in separate Signature Blocks, provides administrators with flexibility in this regard. 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 corresponding 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 be used for all Signature Blocks. Furthermore, it is RECOMMENDED to set that value to the same value as 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 an originator 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 Kelsey, et al. Expires March 31, 2008 [Page 11] Internet-Draft Signed syslog Messages September 2007 Signature Group per PRI value provides administrators with a large degree of flexibility with regard to how to divide up the processing of 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 previous Signature Group or "0" in case there is no other Signature Group with a lower SPRI value. The specific Signature Groups and ranges they 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 originator and the intended collectors 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 according to 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 originator 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 of a message that is missing 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. Likewise, configuring only one Signature Group can be a reasonable way to configure installations that involve relay chains, where one or more interim relays may or may not relay all messages to the same destination. 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 Kelsey, et al. Expires March 31, 2008 [Page 12] Internet-Draft Signed syslog Messages September 2007 this reboot session. This takes at least 1 octet and at most 10 octets displayed as a decimal counter. The acceptable values for this are between 0 and 9999999999, starting with 0. Leading zeroes MUST be omitted. If the value of the Global Block Counter has reached 9999999999 and the Reboot Session ID has a value other than 0 (indicating the fact that persistence 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. When the Reboot Session ID is 0 (i.e., persistent Reboot Session IDs are not supported) and the Global Block Counter reaches its maximum value, then the Global Block Counter is reset to 0 and the Reboot Session ID MUST remain at 0. Note that the Global Block Counter crosses Signature Groups; it allows one to roughly synchronize when two messages were sent, even though they went to different collectors and are part of different Signature Groups. Because a reboot results in the start of a new reboot session, the originator MUST reset the Global Block Counter to 0 after a reboot occurs. Applications need to take into account 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, hence jeopardizing the integrity of the log. 4.2.5. First Message Number This is a decimal value between 1 and 10 octets, with leading zeroes omitted. 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". This implies that when the Reboot Session ID increases, the message number is reset to 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. The message number is relative to the Signature Group to which it belongs; hence, a message number does not identify a message beyond its Signature Group. Should the message number reach 9999999999 within the same reboot session and Signature Group, the message number subsequently restarts at 1. In such event, the Global Block Counter will be vastly different between two occurrences of the same message number. Kelsey, et al. Expires March 31, 2008 [Page 13] Internet-Draft Signed syslog Messages September 2007 4.2.6. Count The count is a 1 or 2 octet field that indicates the number of message hashes to follow. The valid values for this field are 1 through 99. 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 permissible 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. The "entire syslog message" refers to what is described as the syslog message excluding transport parts that are described in RFC zzzz [9] and RFC wwww [10], 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. 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 without the use of padding. It is base 64 encoded as per RFC 4648 [7]. 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 be 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 [7]. 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 March 31, 2008 [Page 14] Internet-Draft Signed syslog Messages September 2007 5. Payload and Certificate Blocks Certificate Blocks and Payload Blocks provide key management for 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 collector. A Payload Block is sent at the beginning of a new reboot session, carrying public key information in effect for the reboot session. However, a Payload Block is not sent directly, but in (one or more) fragments. Those fragments are termed Certificate Blocks. Therefore, originators send at least one Certificate Block at the beginning of a new 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. There is exactly one Payload Block per reboot session. b. The Certificate Blocks are digitally signed. The originator 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 originator and collector (or offline log viewer) both have 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 March 31, 2008 [Page 15] Internet-Draft Signed syslog Messages September 2007 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. An originator creates a new Payload Block after each reboot. The Payload Block is used until the next reboot. A Payload Block MUST have the following fields: a. Full local time stamp for the originator at the time the reboot session started. This must be in the time stamp format specified in RFC xxxx [8] (essentially, time stamp format per RFC 3339 [12] with some further restrictions). b. Key Blob Type, a one-octet field containing 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 c. The key blob, if any, base 64 encoded per RFC 4648 [7] and consisting of the raw key data. The fields are separated by single space characters. 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. The Payload Block does not contain a field that identifies the reboot session; instead, the reboot session can be inferred from the Reboot Session ID parameter of the Certificate Blocks that are used to carry the Payload Block. 5.3. Certificate Block This section describes the format of the Certificate Block and the fields used within the Certificate Block, as well as the syslog messages used to carry Certificate Blocks. 5.3.1. syslog Messages Containing a Certificate Block Certificate Blocks are used to get the Payload Block to the collector. As with a Signature Block, each Certificate Block is carried in its own syslog message, called Certificate Block message. Kelsey, et al. Expires March 31, 2008 [Page 16] Internet-Draft Signed syslog Messages September 2007 Because certificates can legitimately be much longer than 2048 octets, the Payload Block can be split up into several pieces, with each Certificate Block carrying a piece of the Payload Block. Note that the originator MAY make the Certificate Blocks of any legal length (that is, any length that keeps the entire Certificate Block message within 2048 octets) that holds all the required fields. Software that processes Certificate Blocks MUST deal correctly with blocks of any legal length. The length of the fragment of the Payload Block that a Certificate Block carries MUST be at least 1 octet. The length SHOULD be chosen such that the length of the Certificate Block message does not exceed 2048 octets. A Certificate Block message is identified by the presence of an SD ELEMENT with an SD-ID with the value "ssign-cert". In addition, a Certificate Block message MUST contain valid APP-NAME, PROCID, and MSGID fields to be compliant with syslog protocol. Syslog-sign does not mandate particular values for these fields; however, for consistency, implementations SHOULD use the same value for APP-NAME, PROCID, and MSGID fields for every Certificate Block message, whichever values are chosen. It is RECOMMENDED to use 110 as value for the PRI field, corresponding to facility 13 and severity 6 (informational). The Certificate Block is carried as Structured Data within the Certificate Block message. A Certificate Block message SHOULD NOT carry other Structured Data besides the Structured Data of the Certificate Block itself. The MSG part of a Certificate Block message SHOULD be empty. 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. 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 [7]. Kelsey, et al. Expires March 31, 2008 [Page 17] Internet-Draft Signed syslog Messages September 2007 Field SD-PARAM-NAME Size in octets ----- ------------- ---- -- ------ 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 1-4 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 values: [ssign-cert VER="xxx" RSID="xxx" SG="xxx" SPRI="xxx" TBPL="xxx" INDEX="xxx" FLEN="xxx" FRAG="xxx" SIGN="xxx"] Values of the fields constitute SD parameter values and are hence enclosed in quotes, per RFC xxxx [8]. The fields are separated by single spaces and are described below. 5.3.2.1. Version The Signature Group version field is 4 octets in length. This field is identical in format and meaning to the Version field described in Section 4.2.1. 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 4.2.3. The SPRI field is identical in format Kelsey, et al. Expires March 31, 2008 [Page 18] Internet-Draft Signed syslog Messages September 2007 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 octets, expressed as a decimal with one to eight octets. 5.3.2.5. Index into Payload Block This is a decimal value between 1 and 8 octets, with leading zeroes omitted. It contains the number of octets into the Payload Block at which this fragment starts. The first octet 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 four octets. The fragment length must be at least 1. 5.3.2.7. Payload Block Fragment The Payload Block Fragment contains a fragment of the payload block, encoded in base 64, as per RFC 4648 [7]. Its length must match the indicated fragment length. 5.3.2.8. Signature This is a digital signature, encoded in base 64, as per RFC 4648 [7]. 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 March 31, 2008 [Page 19] Internet-Draft Signed syslog Messages September 2007 6. Redundancy and Flexibility There is a general rule that determines how redundancy works and what level of flexibility the originator and collector have in message formats: in general, the originator 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; because the collector MUST ignore Signature/Certificate Blocks it has already received and authenticated, the originator can in principle change its redundancy level for any reason, without communicating this fact to the collector. Although the transport 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 transport sender to the transport receiver, 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 Kelsey, et al. Expires March 31, 2008 [Page 20] Internet-Draft Signed syslog Messages September 2007 redundant sending. 6.2. Flexibility An originator 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 an originator to send short Signature Blocks to allow the collector to verify messages quickly. Kelsey, et al. Expires March 31, 2008 [Page 21] Internet-Draft Signed syslog Messages September 2007 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 presume that the stored log files have already been separated by originator, 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 message, or a Certificate Block message. Signature Blocks and Certificate Blocks are then 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. Skip all other Signature Blocks with the same First Message Kelsey, et al. Expires March 31, 2008 [Page 22] Internet-Draft Signed syslog Messages September 2007 Number. The resulting authenticated log file contains all messages that have been authenticated. In addition, it implicitly indicates all gaps in the authenticated messages (specifically in the case when all messages of the same Signature Group are sent to the same collector), because their message numbers are missing. 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 collector implementations 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 in which (message number, hash of message) pairs are kept in sorted order, a queue in which (arrival sequence, hash of message) pairs are kept in sorted order, and a hash table that stores (message text, count) pairs 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. Kelsey, et al. Expires March 31, 2008 [Page 23] Internet-Draft Signed syslog Messages September 2007 c. We must receive all the Certificate Blocks before any other processing can really be done. (This is why they are sent first.) Once that is done, any Certificate Block message 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 oldest 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 oldest entry in the queue. e. Whenever a Signature Block message 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. 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 whether 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 looked up in the hash table. If a matching entry is found, the (message number, message text) pair is written 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 March 31, 2008 [Page 24] Internet-Draft Signed syslog Messages September 2007 8. Security Considerations Normal syslog event messages are unsigned and have most of the security attributes described in Section 8 of RFC xxxx [8]. This document also describes Certificate Blocks and Signature Blocks, which are signed syslog messages. The Signature Blocks contain signature information for previously sent syslog event messages. All of this information can be used to authenticate syslog messages and to minimize or obviate many of the security concerns described in RFC xxxx [8]. 8.1. Cryptographic Constraints As with any technology involving cryptography, it is advisable to 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 have to control the private key portion of a public-private key pair. Any party that controls a private key can sign anything it pleases. 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 [13] and NIST SP 800-90 [3]. 8.2. Packet Parameters As an originator, it is advisable to avoid message lengths exceeding 2048 octets. Various problems might result if an originator were to send messages with a length greater than 2048 octets, because relays MAY truncate messages with lengths greater than 2048 octets which would make it impossible for collectors to validate a hash of the packet. 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. Originators need to rigidly enforce the correctness of message bodies. Problems may arise if the collector does not fully accept the syslog packets sent from an originator, or if it has problems with the format of the Certificate Block or Signature Block messages. Collectors are not to malfunction in case they receive malformed syslog messages or messages containing characters other than those specified in this document. In other words, they are to ignore such messages and continue working. Kelsey, et al. Expires March 31, 2008 [Page 25] Internet-Draft Signed syslog Messages September 2007 8.3. Message Authenticity Syslog does not strongly associate the message with the message originator. That association is established by the collector upon verification of the Signature Block. Before a Signature Block is used to ascertain the authenticity of an event message, it might be received, stored, and reviewed by a person or automated parser. It is advisable not to assume a message is authentic until after a message has been validated by checking the contents of the Signature Block. With the Signature Block checking, an attacker may only forge messages if it can compromise the private key of the true originator. 8.4. Replaying Event messages might be recorded and replayed by an attacker. Using the information contained in the Signature Blocks, a reviewer can determine whether the received messages are the ones originally sent by an originator. The reviewer can also identify messages that have been replayed. 8.5. Reliable Delivery RFC wwww [10] can be used for the reliable delivery of syslog messages. Event messages sent over UDP might be lost in transit. A reviewer can pinpoint any messages sent by the originator but not received by the collector by reviewing the Signature Block information. In addition, the information in subsequent Signature Blocks allows a reviewer to determine whether any Signature Block messages were lost in transit. 8.6. Sequenced Delivery Syslog messages delivered over UDP might not only be lost, but also arrive out of sequence. A reviewer can determine the original order of syslog messages and identify which messages were delivered out of order by examining the information in the Signature Block along with any timestamp information in the message. 8.7. Message Integrity Syslog messages might 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 originator. A damaged Signature Block or Certificate Block is evident because the collector will not be able to validate that it was signed by the originator. Kelsey, et al. Expires March 31, 2008 [Page 26] Internet-Draft Signed syslog Messages September 2007 8.8. Message Observation Event messages, Certificate Blocks, and Signature Blocks are all sent in plaintext. This allows 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. 8.9. Man In The Middle Attacks It is conceivable that an attacker might 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 originator 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 need to verify that the key contained in the Payload Block is indeed the key being used on the actual originator. If that is the case, then this MITM attack will not succeed. 8.10. Denial of Service An attacker might send invalid Signature Block messages to overwhelm the collector's processing capability and consume all available resources. For this reason, it can be appropriate to simply receive the Signature Block messages and process them only as time permits. An attacker might also just overwhelm a collector by sending more messages to it than it can handle. Implementors are advised to consider features that minimize this threat, such as only accepting syslog messages from known IP addresses. 8.11. Covert Channels Nothing in this protocol attempts to eliminate covert channels. 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 PRI values to indicate Morse Code dashes and dots. Kelsey, et al. Expires March 31, 2008 [Page 27] Internet-Draft Signed syslog Messages September 2007 9. IANA Considerations 9.1. Structured Data and syslog messages With regard to RFC xxxx [8], IANA is requested to add the following values to the registry entitled "syslog Structured Data id values": SD-ID PARAM_NAME ----- ---------- ssign VER RSID SG SPRI GBC FMN CNT HB SIGN ssign-cert VER RSID SG SPRI TBPL INDEX FLEN FRAG SIGN 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 IANA is requested to create three registries, each associated with a different subfield of the Version field of Signature Blocks and Certificate Blocks, described in Section 4.2.1 and Section 5.3.2.1, respectively. The first registry that IANA is requested to create is entitled "syslog-sign protocol version values". It is for the values of the Protocol Version subfield. The Protocol Version subfield constitutes the first 2 octets in the Version field. New values shall be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [4]. Assigned numbers are to be increased by 1, up to a maximum Kelsey, et al. Expires March 31, 2008 [Page 28] Internet-Draft Signed syslog Messages September 2007 value of "50". Protocol Version numbers of "51" through "99" are vendor-specific; values in this range are not to be assigned by the IANA. IANA is requested to register the Protocol Version values shown below. VALUE PROTOCOL VERSION ----- ---------------- 00 Reserved 01 Defined in RFC yyyy The second registry that IANA is requested to create is entitled "syslog-sign hash algorithm values". It is for the values of the Hash Algorithm subfield. The Hash Algorithm subfield constitutes the third octet in the Version field Signature Blocks and Certificate Blocks. New values shall be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [4]. Assigned values are to be increased by 1, up to a maximum value of "9". The values are registered relative to the Protocol Version. This means that the same Hash Algorithm value can be reserved for different Protocol Versions, possibly referring to a different hash algorithm each time. This makes it possible to deal with future scenarios in which the single octet representation becomes a limitation, as more Hash Algorithms can be supported by defining additional Protocol Versions that implementations might support concurrently. IANA is requested to register the Hash Algorithm values shown below. VALUE PROTOCOL VERSION HASH ALGORITHM ----- ---------------- -------------- 0 01 Reserved 1 01 SHA1 2 01 SHA256 The third registry that IANA is requested to create is entitled "syslog-sign signature scheme values". It is for the values of the Signature Scheme subfield. The Signature Scheme subfield constitutes the fourth octet in the Version field of Signature Blocks and Certificate Blocks. New values shall be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [4]. Assigned values are to be increased by 1, up to a maximum value of "9". This means that the same Signature Scheme value can be reserved for different Protocol Versions, possibly in each case referring to a different Signature Scheme each time. This makes it possible to deal with future scenarios in which the single octet representation becomes a limitation, as more Signature Schemes can be supported by defining additional Protocol Versions that implementations might support Kelsey, et al. Expires March 31, 2008 [Page 29] Internet-Draft Signed syslog Messages September 2007 concurrently. IANA is requested to register the Signature Scheme values shown below. VALUE PROTOCOL VERSION SIGNATURE SCHEME ----- ---------------- ---------------- 0 01 Reserved 1 01 OpenPGP DSA 9.3. SG Field IANA is requested to create a registry entitled "syslog-sign sg field values". It is for values of the SG Field as defined in Section 4.2.3. New values shall be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [4]. Assigned values are to be incremented by 1, up to a maximum value of "7". Values "8" and "9" shall be left as vendor specific and shall not be assigned by the IANA. IANA is requested to register the SG Field values shown below. VALUE MEANING ----- ------- 0 per RFC yyyy 1 per RFC yyyy 2 per RFC yyyy 3 per RFC yyyy 9.4. Key Blob Type IANA is requested to create a registry entitled "syslog-sign key blob type values". It is to register one-character identifiers for the key blob type, per Section 5.2. New values shall be assigned by the IANA using the "IETF Consensus" policy defined in RFC 2434 [4]. Uppercase letters may be assigned as values. Lowercase letters are left as vendor specific and shall not be assigned by the IANA. IANA is requested to register the key blob type values shown below. VALUE KEY BLOB TYPE ----- ------------ 'C' a PKIX certificate 'P' an OpenPGP certificate 'K' the public key whose corresponding private key is used to sign the messages 'N' no key information sent, key is predistributed 'U' installation-specific key exchange information Kelsey, et al. Expires March 31, 2008 [Page 30] Internet-Draft Signed syslog Messages September 2007 10. Working Group The working group can be contacted via the mailing list: syslog@ietf.org The current Chairs of the Working Group can 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 Kelsey, et al. Expires March 31, 2008 [Page 31] Internet-Draft Signed syslog Messages September 2007 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 March 31, 2008 [Page 32] Internet-Draft Signed syslog Messages September 2007 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] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [5] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer, "OpenPGP Message Format", RFC 2440, November 1998. [6] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", RFC 3414, December 2002. [7] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, October 2006. [8] Gerhards, R., "The syslog Protocol, draft-ietf-syslog-protocol-23.txt (work in progress)", September 2007. [9] Okmianski, A., "Transmission of syslog Messages over UDP, draft-ietf-syslog-transport-udp-12.txt (work in progress)", September 2007. [10] Miao, F. and M. Yuzhi, "TLS Transport Mapping for syslog, draft-ietf-syslog-transport-tls-10.txt (work in progress)", May 2007. Kelsey, et al. Expires March 31, 2008 [Page 33] Internet-Draft Signed syslog Messages September 2007 12.2. Informative References [11] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [12] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [13] Eastlake, D., Schiller, J., and S. Crocker, "Randomness Recommendations for Security", RFC 4086, June 2005. Kelsey, et al. Expires March 31, 2008 [Page 34] Internet-Draft Signed syslog Messages September 2007 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 March 31, 2008 [Page 35] Internet-Draft Signed syslog Messages September 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. 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 March 31, 2008 [Page 36]