Integrity Check Value and Timestamp TLV Definitions for Mobile Ad Hoc Networks (MANETs)
draft-herberg-manet-rfc6622-bis-00

Abstract

This document extends and replaces RFC 6622. It describes general and flexible TLVs for representing cryptographic Integrity Check Values (ICVs) (i.e., digital signatures or Message Authentication Codes (MACs)) as well as timestamps, using the generalized Mobile Ad Hoc Network (MANET) packet/message format defined in RFC 5444. It defines two Packet TLVs, two Message TLVs, and two Address Block TLVs for affixing ICVs and timestamps to a packet, a message, and an address, respectively.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

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."

This Internet-Draft will expire on August 5, 2013.

Copyright Notice

Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Applicability Statement
• 4. Security Architecture
• 5. Overview and Functioning
• 6. General ICV TLV Structure
• 7. General Timestamp TLV Structure
• 8. Packet TLVs
• 8.1. Packet ICV TLV
• 8.2. Packet TIMESTAMP TLV
• 9. Message TLVs
• 9.1. Message ICV TLV
• 9.2. Message TIMESTAMP TLV
• 10. Address Block TLVs
• 10.1. Address Block ICV TLV
• 10.2. Address Block TIMESTAMP TLV
• 11. ICV: Basic
• 12. ICV: Cryptographic Function over a Hash Value
• 12.1. General ICV TLV Structure
• 12.1.1. Rationale
• 12.2. Considerations for Calculating the ICV
• 12.2.1. Packet ICV TLV
• 12.2.2. Message ICV TLV
• 12.2.3. Address Block ICV TLV
• 12.3. Example of a Message Including an ICV
• 13. IANA Considerations
• 13.1. Expert Review: Evaluation Guidelines
• 13.2. Packet TLV Type Registrations
• 13.3. Message TLV Type Registrations
• 13.4. Address Block TLV Type Registrations
• 13.5. Hash Functions
• 13.6. Cryptographic Functions
• 14. Security Considerations
• 15. Acknowledgements
• 16. References
• 16.1. Normative References
• 16.2. Informative References
• Authors' Addresses

1. Introduction

This document, which extends and replaces [RFC6622], specifies

• Two TLVs for carrying Integrity Check Values (ICVs) and timestamps in packets, messages, and address blocks as defined by [RFC5444].
• A generic framework for ICVs, accounting (for Message TLVs) for mutable message header fields (<msg-hop-limit> and <msg‑hop‑count>), where these fields are present in messages.

This document describes, and updates where required, IANA registries for recording code points for hash-functions, cryptographic functions, and ICV calculations.

Moreover, in Section 12, this document defines the following:

• One common method for generating ICVs as a cryptographic function, calculated over the hash value of the content.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

This document uses the terminology and notation defined in [RFC5444]. In particular, the following TLV fields from [RFC5444] are used in this specification:

<msg-hop-limit>

is the hop limit of a message, as specified in Section 5.2 of [RFC5444].

<msg-hop-count>

is the hop count of a message, as specified in Section 5.2 of [RFC5444].

<length>

is the length of a TLV in octets, as specified in Section 5.4.1 of [RFC5444].

3. Applicability Statement

MANET routing protocols using the format defined in [RFC5444] are accorded the ability to carry additional information in control messages and packets, through the inclusion of TLVs. Information so included MAY be used by a MANET routing protocol, or by an extension of a MANET routing protocol, according to its specification.

This document specifies how to include an ICV for a packet, a message, and addresses in address blocks within a message, by way of such TLVs. This document also specifies a) how to treat "mutable" fields, specifically the <msg-hop-count> and <msg-hop-limit> fields, if present in the message header when calculating ICVs, such that the resulting ICV can be correctly verified by any recipient, and b) how to include this ICV.

This document describes a generic framework for creating ICVs, and how to include these ICVs in TLVs. In Section 12, an example method for calculating such ICVs is given, using a cryptographic function over the hash value of the content.

4. Security Architecture

Basic MANET routing protocol specifications are often "oblivious to security"; however, they have a clause allowing a control message to be rejected as "badly formed" or "insecure" prior to the message being processed or forwarded. MANET routing protocols such as the Neighborhood Discovery Protocol (NHDP) [RFC6130] and the Optimized Link State Routing Protocol version 2 [OLSRv2] recognize external reasons (such as failure to verify an ICV) for rejecting a message that would be considered "invalid for processing". This architecture is a result of the observation that with respect to security in MANETs, "one size rarely fits all" and that MANET routing protocol deployment domains have varying security requirements ranging from "unbreakable" to "virtually none". The virtue of this approach is that MANET routing protocol specifications (and implementations) can remain "generic", with extensions providing proper security mechanisms specific to a deployment domain.

The MANET routing protocol "security architecture", in which this specification situates itself, can therefore be summarized as follows:

• Security-oblivious MANET routing protocol specifications, with a clause allowing an extension to reject a message (prior to processing/forwarding) as "badly formed" or "insecure".
• MANET routing protocol security extensions, rejecting messages as "badly formed" or "insecure", as appropriate for a given security requirement specific to a deployment domain.
• Code points and an exchange format for information, necessary for specification of such MANET routing protocol security extensions.

This document addresses the last of the issues listed above by specifying a common exchange format for cryptographic ICVs, making reservations from within the Packet TLV, Message TLV, and Address Block TLV registries of [RFC5444], to be used (and shared) among MANET routing protocol security extensions.

For the specific decomposition of an ICV into a cryptographic function over a hash value (specified in Section 12), this document reports two IANA registries for code points for hash functions and cryptographic functions adhering to [RFC5444].

With respect to [RFC5444], this document is

• Intended to be used in the non-normative, but intended, mode of use described in Appendix B of [RFC5444].
• A specific example of the Security Considerations section of [RFC5444] (the authentication part).

5. Overview and Functioning

This document specifies a syntactical representation of security-related information for use with [RFC5444] addresses, messages, and packets, and also reports and updates IANA registrations of TLV types and type extension registries for these TLV types.

Moreover, this document provides guidelines for how MANET routing protocols and MANET routing protocol extensions using this specification should treat ICV and Timestamp TLVs, and mutable fields in messages. This specification does not represent a stand-alone protocol; MANET routing protocols and MANET routing protocol extensions, using this specification, MUST provide instructions as to how to handle packets, messages, and addresses with security information, associated as specified in this document.

This document reports previously assigned TLV types from the registries defined for Packet, Message, and Address Block TLVs in [RFC5444]. When a TLV type is assigned from one of these registries, a registry for type extensions for that TLV type is created by IANA. This document reports and updates these type extension registries, in order to specify internal structure (and accompanying processing) of the <value> field of a TLV.

For example, and as defined in this document, an ICV TLV with type extension = 0 specifies that the <value> field has no pre-defined internal structure but is simply a sequence of octets. An ICV TLV with type extension = 1 specifies that the <value> field has a pre-defined internal structure and defines its interpretation. An ICV TLV with type extension = 2 specifies a modified version of this definition. (Specifically, with type extension = 1 or type extension = 2, the <value> field consists of a cryptographic operation over a hash value, with fields indicating which hash function and cryptographic operation have been used; this is specified in Section 12. The difference between the two type extensions is that the ICV TLV with type extension = 2 also protects the source address of the IP datagram carrying the packet, message, or address block.)

Other documents can request assignments for other type extensions; if they do so, they MUST specify their internal structure (if any) and interpretation.

6. General ICV TLV Structure

The value of the ICV TLV is

   <value> := <ICV-value>
                        

where

<ICV-value>

is a field, of <length> octets, which contains the information to be interpreted by the ICV verification process, as specified by the type extension.

Note that this does not stipulate how to calculate the <ICV-value> nor the internal structure thereof, if any; such information MUST be specified by way of the type extension for the ICV TLV type. See Section 13. This document specifies three such type extensions -- one for ICVs without pre-defined structures, and two for ICVs constructed by way of a cryptographic operation over a hash value.

7. General Timestamp TLV Structure

The value of the Timestamp TLV is

   <value> := <time-value>
        

where

<time-value>

is an unsigned integer field, of length <length>, which contains the timestamp.

Note that this does not stipulate how to calculate the <time‑value> nor the internal structure thereof, if any; such information MUST be specified by way of the type extension for the TIMESTAMP TLV type. See Section 13.

A timestamp is essentially "freshness information". As such, its setting and interpretation are to be determined by the MANET routing protocol, or MANET routing protocol extension, that uses the timestamp and can, for example, correspond to a UNIX timestamp, GPS timestamp, or a simple sequence number.

8. Packet TLVs

Two Packet TLVs are defined: one for including the cryptographic ICV of a packet and one for including the timestamp indicating the time at which the cryptographic ICV was calculated.

8.1. Packet ICV TLV

A Packet ICV TLV is an example of an ICV TLV as described in Section 6.

The following considerations apply:

• Because packets as defined in [RFC5444] are never forwarded by routers, no special considerations are required regarding mutable fields (e.g., <msg-hop-count> and <msg-hop-limit>), if present, when calculating the ICV.
• Any Packet ICV TLVs already present in the Packet TLV block MUST be removed before calculating the ICV, and the Packet TLV block size MUST be recalculated accordingly. Removed ICV TLVs MUST be restored after having calculated the ICV value.

The rationale for removing any Packet ICV TLV already present prior to calculating the ICV is that several ICVs may be added to the same packet, e.g., using different ICV functions.

8.2. Packet TIMESTAMP TLV

A Packet TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 7. If a packet contains a TIMESTAMP TLV and an ICV TLV, the TIMESTAMP TLV SHOULD be added to the packet before any ICV TLV, in order that it be included in the calculation of the ICV.

9. Message TLVs

Two Message TLVs are defined: one for including the cryptographic ICV of a message and one for including the timestamp indicating the time at which the cryptographic ICV was calculated.

9.1. Message ICV TLV

A Message ICV TLV is an example of an ICV TLV as described in Section 6. When determining the <ICV-value> for a message, the following considerations MUST be applied:

• The fields <msg-hop-limit> and <msg-hop-count>, if present, MUST both be assumed to have the value 0 (zero) when calculating the ICV.
• Any Message ICV TLVs already present in the Message TLV block MUST be removed before calculating the ICV, and the message size as well as the Message TLV block size MUST be recalculated accordingly. Removed ICV TLVs MUST be restored after having calculated the ICV value.

The rationale for removing any Message ICV TLV already present prior to calculating the ICV is that several ICVs may be added to the same message, e.g., using different ICV functions.

9.2. Message TIMESTAMP TLV

A Message TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 7. If a message contains a TIMESTAMP TLV and an ICV TLV, the TIMESTAMP TLV SHOULD be added to the message before the ICV TLV, in order that it be included in the calculation of the ICV.

10. Address Block TLVs

Two Address Block TLVs are defined: one for associating a cryptographic ICV to an address and one for including the timestamp indicating the time at which the cryptographic ICV was calculated.

10.1. Address Block ICV TLV

An Address Block ICV TLV is an example of an ICV TLV as described in Section 6. The ICV is calculated over the address, concatenated with any other values -- for example, any other Address Block TLV <value> fields -- associated with that address. A MANET routing protocol or MANET routing protocol extension using Address Block ICV TLVs MUST specify how to include any such concatenated attribute of the address in the verification process of the ICV. When determining the <ICV‑value> for an address, the following consideration MUST be applied:

• If other TLV values are concatenated with the address for calculating the ICV, these TLVs MUST NOT be Address Block ICV TLVs already associated with the address.

The rationale for not concatenating the address with any ICV TLV values already associated with the address when calculating the ICV is that several ICVs may be added to the same address, e.g., using different ICV functions.

10.2. Address Block TIMESTAMP TLV

An Address Block TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 7. If both a TIMESTAMP TLV and an ICV TLV are associated with an address, the TIMESTAMP TLV <value> MUST be covered when calculating the value of the ICV to be contained in the ICV TLV value (i.e., concatenated with the associated address and any other values as described in Section 10.1).

11. ICV: Basic

The basic ICV, represented by way of an ICV TLV with type extension = 0, is a simple bit-field containing the cryptographic ICV. This assumes that the mechanism stipulating how ICVs are calculated and verified is established outside of this specification, e.g., by way of administrative configuration or external out-of-band signaling. Thus, the <ICV-value>, when using type extension = 0, is

   <ICV-value> := <ICV-data>
                        

where

<ICV-data>

is an unsigned integer field, of length <length>, which contains the cryptographic ICV.

12. ICV: Cryptographic Function over a Hash Value

One common way of calculating an ICV is applying a cryptographic function over a hash value of the content. This decomposition is specified in this section, using either type extension = 1 or type extension = 2, in the ICV TLVs.

12.1. General ICV TLV Structure

The following data structure allows representation of a cryptographic ICV, including specification of the appropriate hash function and cryptographic function used for calculating the ICV:

                <ICV-value> := <hash-function>
                               <cryptographic-function>
                               <key-id-length>
                               <key-id>
                               <ICV-data>
                        

where Section 13.

<hash-function>

is an 8-bit unsigned integer field specifying the hash function.

<cryptographic-function>

is an 8-bit unsigned integer field specifying the cryptographic function.

<key-id-length>

is an 8-bit unsigned integer field specifying the length of the <key-id> field in number of octets. The value 0x00 is reserved for using a pre-installed, shared key.

<key-id>

is a field specifying the key identifier of the key that was used to calculate the ICV of the message, which allows unique identification of different keys with the same originator. It is the responsibility of each key originator to make sure that actively used keys that it issues have distinct key identifiers. If <key-id-length> equals 0x00, the <key-id> field is not contained in the TLV, and a pre-installed, shared key is used.

<ICV-data>

is an unsigned integer field, whose length is <length> - 3 - <key-id-length>, and which contains the cryptographic ICV.

The version of this TLV, specified in this section, assumes that calculating the ICV can be decomposed into

ICV-value = cryptographic-function(hash-function(content))

The hash function and the cryptographic function correspond to the entries in two IANA registries, which are reported by this specification and are described in

12.1.1. Rationale

The rationale for separating the hash function and the cryptographic function into two octets instead of having all combinations in a single octet -- possibly as a TLV type extension -- is that adding further hash functions or cryptographic functions in the future may lead to a non-contiguous number space.

The rationale for not including a field that lists parameters of the cryptographic ICV in the TLV is that, before being able to validate a cryptographic ICV, routers have to exchange or acquire keys (e.g., public keys). Any additional parameters can be provided together with the keys in that bootstrap process. It is therefore not necessary, and would even entail an extra overhead, to transmit the parameters within every message. One implicitly available parameter is the length of the ICV, which is <length> - 3 - <key-id-length>, and which depends on the choice of the cryptographic function.

12.2. Considerations for Calculating the ICV

The considerations listed in the following subsections MUST be applied when calculating the ICV for Packet, Message, and Address ICV TLVs, respectively.

12.2.1. Packet ICV TLV

When determining the <ICV-value> for a packet, with type extension = 1, the ICV is calculated over the fields <hash-function>, <cryptographic-function>, <key‑id‑length>, and -- if present -- <key-id> (in that order), concatenated with the entire packet, including the packet header, all Packet TLVs (other than Packet ICV TLVs), and all included Messages and their message headers, in accordance with Section 8.1. When determining the <ICV-value> for a packet, with type extension = 2, the same procedure is used, except that the source address of the IP datagram carrying the packet is also concatenated, in the first position, with the data used.

12.2.2. Message ICV TLV

When determining the <ICV-value> for a message, with type extension = 1, the ICV is calculated over the fields <hash-function>, <cryptographic-function>, <key‑id‑length>, and -- if present -- <key-id> (in that order), concatenated with the entire message. The considerations in Section 9.1 MUST be applied. When determining the <ICV-value> for a message, with type extension = 2, the same procedure is used, except that the source address of the IP datagram carrying the message is also concatenated, in the first position, with the data used.

12.2.3. Address Block ICV TLV

When determining the <ICV-value> for an address, block, with type extension = 2, the ICV is calculated over the fields <hash-function>, <cryptographic-function>, <key-id-length>, and -- if present -- <key-id> (in that order), concatenated with the address, and concatenated with any other values -- for example, any other address block TLV <value> that is associated with that address. A MANET routing protocol or MANET routing protocol extension using Address Block ICV TLVs MUST specify how to include any such concatenated attribute of the address in the verification process of the ICV. The considerations in Section 10.1 MUST be applied. When determining the <ICV-value> for an address block, with type extension = 2, the same procedure is used, except that the source address of the IP datagram carrying the address block is also concatenated, in the first position, with the data used.

12.3. Example of a Message Including an ICV

The sample message depicted in Figure 1 is derived from Appendix D of [RFC5444]. The message contains an ICV Message TLV, with the value representing an ICV that is 16 octets long of the whole message, and a key identifier that is 4 octets long. The type extension of the Message TLV is 1, for the specific decomposition of an ICV into a cryptographic function over a hash value, as specified in Section 12.

   0                   1                   2                   3  
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | PV=0 |  PF=8  |    Packet Sequence Number     | Message Type  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | MF=15 | MAL=3 |      Message Length = 44      | Msg. Orig Addr|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |       Message Originator Address (cont)       |   Hop Limit   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |   Hop Count   |    Message Sequence Number    | Msg. TLV Block|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | Length = 27   |     ICV       |  MTLVF = 144  |  MTLVExt = 1  |  
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |Value Len = 23 |   Hash Func   |  Crypto Func  |Key ID length=4|
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          Key Identifier                       |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          ICV Value                            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          ICV Value (cont)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          ICV Value (cont)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                          ICV Value (cont)                     |        
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+