| Mobile Ad hoc Networking (MANET) | U. Herberg |
| Internet-Draft | T. Clausen |
| Intended status: Standards Track | LIX, Ecole Polytechnique |
| Expires: January 12, 2012 | July 11, 2011 |
MANET Cryptographical Signature TLV Definition
draft-ietf-manet-packetbb-sec-04
This document describes general and flexible TLVs (type-length-value structure) for representing cryptographic signatures as well as timestamps, using the generalized MANET packet/message format [RFC5444]. It defines two Packet TLVs, two Message TLVs, and two Address Block TLVs, for affixing cryptographic signatures and timestamps to a packet, message and address, respectively.
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This document specifies:
This document requests from IANA:
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].
MANET routing protocols using the format defined in [RFC5444] are accorded the ability to carry additional information in control messages and packets, through inclusion of TLVs. Information so included MAY be used by a routing protocol, or by an extension of a routing protocol, according to its specification.
This document specifies how to include a cryptographic signature for a packet, message or address by way of such TLVs. This document also specifies how to treat "mutable" fields (<msg-hop-count> and <msg-hop-limit>), if present, in the message header when calculating signatures, such that the resulting signature can be correctly verified by any recipient, and how to include this signature.
This document is split into two parts: (i) a generic framework of creating signatures in the presence of mutable fields, and how to include these signatures in TLVs, (ii) a specific description of how to calculate a signature, using a cryptographic function over the hash value of the content to be signed, in the Appendix Appendix A of this document. Note that (ii) is a possible and widely-used way of calculating a signature, but other means may exist. Such other means of calculating a signature have to be specified in another document. That new document MUST use the TLV structures specified in this document, as well as the described considerations when calculating the signatures.
Basic MANET routing protocol specifications are often "oblivious to security", however have a clause allowing a control message to be rejected as "badly formed" prior to it being processed or forwarded. Protocols such as [RFC6130] and [OLSRv2] recognize external reasons (such as failure to verify a signature) for rejecting a message as "badly formed", and therefore "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 deployment-domain specific security mechanisms.
The MANET routing protocol "security architecture", in which this specification situates itself, can therefore be summarized as follows:
This document addresses the last of these issues, by specifying a common exchange format for cryptographic signatures, 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 a signature into a cryptographic function over a hash value, specified in Appendix Appendix A, this document establishes two IANA registries for code-points for hash functions and cryptographic functions adhering to [RFC5444].
With respect to [RFC5444], this document:
This specification does not describe a protocol, nor does it mandate specific router or protocol behavior. It represents a purely syntactical representation of security related information for use with [RFC5444] addresses, messages and packets, as well as establishes IANA registrations and registries.
In this specification, the following TLV fields from [RFC5444] are used:
The following data structure allows a generic representation of a cryptographic signature. This <signature> data structure is specified, using the regular expression syntax of [RFC5444], as:
<signature> := <signature-value>
This generic specification allows for adding a signature in a TLV, using TLV type extension 0, and does not stipulate how to calculate the signature-value. Appendix Appendix A specifies a concrete calculation of the signature-value, using a cryptographic function over a hash function of the content to be signed. Other methods of how to calculate the signature-value may be specified in future documents.
The following data structure allows the representation of a timestamp. This <timestamp> data structure is specified as:
<timestamp> := <time-value>
where:
A timestamp is essentially "freshness information". As such, its setting and interpretation is to be determined by the routing protocol (or the extension to a routing protocol) that uses it, and may e.g. correspond to a UNIX-timestamp, GPS timestamp or a simple sequence number.
Two Packet TLVs are defined, for including the cryptographic signature of a packet, and for including the timestamp indicating the time at which the cryptographic signature was calculated.
A Packet SIGNATURE TLV is an example of a Signature TLV as described in Section 7.
The following considerations apply:
The rationale for removing any Packet SIGNATURE TLV already present prior to calculating the signature, is that several signatures may be added to the same packet, e.g., using different signature functions.
A Packet TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 8. If a packet contains a TIMESTAMP TLV and a SIGNATURE TLV, the TIMESTAMP TLV SHOULD be added to the packet before any SIGNATURE TLV, in order that it be included in the calculation of the signature.
Two Message TLVs are defined, for including the cryptographic signature of a message, and for including the timestamp indicating the time at which the cryptographic signature was calculated.
A Message SIGNATURE TLV is an example of a Signature TLV as described in Section 7. When determining the <signature-value> for a message, the following considerations must be applied:
The rationale for removing any Message SIGNATURE TLV already present prior to calculating the signature, is that several signatures may be added to the same message, e.g., using different signature functions.
A Message TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 8. If a message contains a TIMESTAMP TLV and a SIGNATURE TLV, the TIMESTAMP TLV SHOULD be added to the message before the SIGNATURE TLV, in order that it be included in the calculation of the signature.
Two Address Block TLVs are defined, for associating a cryptographic signature to an address, and for including the timestamp indicating the time at which the cryptographic signature was calculated.
An Address Block SIGNATURE TLV is an example of a Signature TLV as described in Section 7. The signature is calculated over the address, concatenated with any other values, for example, any other TLV value that is associated with that address. A routing protocol or routing protocol extension using Address Block SIGNATURE TLVs MUST specify how to include any such concatenated attribute of the address in the verification process of the signature.
An Address Block TIMESTAMP TLV is an example of a Timestamp TLV as described in Section 8. If both a TIMESTAMP TLV and a SIGNATURE TLV are associated with an address, the timestamp value should be considered when calculating the value of the signature.
This section specifies requests to IANA.
This specification defines:
This specification requests:
IANA is requested to assign the same numerical value to the Packet TLV, Message TLV and Address Block TLV types with the same name.
For the registries for TLV type extensions where an Expert Review is required, the designated expert SHOULD take the same general recommendations into consideration as are specified by [RFC5444].
For the Timestamp TLV, the same type extensions for all Packet, Message and Address TLVs should be numbered identically.
The Packet TLVs as specified in Table 1 must be allocated from the "Packet TLV Types" namespace of [RFC5444].
| Name | Type | Type Extension | Description |
|---|---|---|---|
| SIGNATURE | TBD1 | 0 | Signature of a packet |
| 1 | Signature, decomposed into cryptographic function over a hash value, as specified in Appendix Appendix A in this document. | ||
| 2-223 | Expert Review | ||
| 224-255 | Experimental Use | ||
| TIMESTAMP | TBD2 | 0 | Unsigned timestamp of arbitrary length, given by the TLV length field. The MANET routing protocol has to define how to interpret this timestamp |
| 1-223 | Expert Review | ||
| 224-255 | Experimental Use |
The Message TLVs as specified in Table 2 must be allocated from the "Message TLV Types" namespace of [RFC5444].
| Name | Type | Type Extension | Description |
|---|---|---|---|
| SIGNATURE | TBD3 | 0 | Signature of a message |
| 1 | Signature, decomposed into cryptographic function over a hash value, as specified in Appendix Appendix A in this document. | ||
| 2-223 | Expert Review | ||
| 224-255 | Experimental Use | ||
| TIMESTAMP | TBD4 | 0 | Unsigned timestamp of arbitrary length, given by the TLV length field. |
| 1-223 | Expert Review | ||
| 224-255 | Experimental Use |
The Address Block TLVs as specified in Table 3 must be allocated from the "Address Block TLV Types" namespace of [RFC5444].
| Name | Type | Type Extension | Description |
|---|---|---|---|
| SIGNATURE | TBD5 | 0 | Signature of an object (e.g. an address) |
| 1 | Signature, decomposed into cryptographic function over a hash value, as specified in Appendix Appendix A in this document. | ||
| 2-223 | Expert Review | ||
| 224-255 | Experimental Use | ||
| TIMESTAMP | TBD6 | 0 | Unsigned timestamp of arbitrary length, given by the TLV length field. |
| 1-223 | Expert Review | ||
| 224-255 | Experimental Use |
This document introduces three namespaces that have been registered: Packet TLV Types, Message TLV Types, and Address Block TLV Types. This section specifies IANA registries for these namespaces and provides guidance to the Internet Assigned Numbers Authority regarding registrations in these namespaces.
The following terms are used with the meanings defined in [BCP26]: "Namespace", "Assigned Value", "Registration", "Unassigned", "Reserved", "Hierarchical Allocation", and "Designated Expert".
The following policies are used with the meanings defined in [BCP26]: "Private Use", "Expert Review", and "Standards Action".
For the registries for the following tables where an Expert Review is required, the designated expert SHOULD take the same general recommendations into consideration as are specified by [RFC5444].
IANA is requested to create a new registry for the hash functions that can be used when creating a signature, as specified in the Appendix Appendix A of this document. The initial assignments and allocation policies are specified in Table 4.
| Hash function value | Algorithm | Description |
|---|---|---|
| 0 | none | The "identity function": the hash value of an object is the object itself |
| 1-223 | Expert Review | |
| 224-255 | Experimental Use |
IANA is requested to create a new registry for the cryptographic function, as specified in the Appendix Appendix A of this document. Initial assignments and allocation policies are specified in Table 5.
| Cryptographic function value | Algorithm | Description |
|---|---|---|
| 0 | none | The "identity function": the value of an encrypted hash is the hash itself |
| 1-223 | Expert Review | |
| 224-255 | Experimental Use |
This document does not specify a protocol itself. However, it provides a syntactical component for cryptographic signatures of messages and packets as defined in [RFC5444]. It can be used to address security issues of a protocol or extension that uses the component specified in this document. As such, it has the same security considerations as [RFC5444].
In addition, a protocol that includes this component MUST specify the usage as well as the security that is attained by the cryptographic signatures of a message or a packet.
As an example, a routing protocol that uses this component to reject "badly formed" messages if a control message does not contain a valid signature, should indicate the security assumption that if the signature is valid, the message is considered valid. It also should indicate the security issues that are counteracted by this measure (e.g. link or identity spoofing) as well as the issues that are not counteracted (e.g. compromised keys).
The authors would like to thank Jerome Milan (Ecole Polytechnique) for his advice as cryptographer. In addition, many thanks to Bo Berry (Cisco), Alan Cullen (BAE), Justin Dean (NRL), Christopher Dearlove (BAE), Paul Lambert (Marvell), and Henning Rogge (FGAN) for their constructive comments on the document.
| [BCP26] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, BCP 26, May 2008. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, BCP 14, March 1997. |
| [RFC5444] | Clausen, T.H., Dearlove, C.M., Dean, J.W. and C. Adjih, "Generalized MANET Packet/Message Format", RFC 5444, February 2009. |
| [RFC6130] | Clausen, T.H., Dean, J.W. and C.M. Dearlove, "MANET Neighborhood Discovery Protocol (NHDP)", RFC 6130, March 2011. |
| [OLSRv2] | Clausen, T.H., Dearlove, C.M. and P. Jacquet, "The Optimized Link State Routing Protocol version 2", work in progress draft-ietf-manet-olsrv2-11.txt, April 2010. |
This section specifies how to calculate the signature-value in a Signature TLV, as described in Section 7. A common way of calculating a signature is applying a cryptographic function on a hash value of the content. This decomposition is specified in the following, using a type extension of 1 in the Signature TLVs.
The following data structure allows representation of a cryptographic signature, including specification of the appropriate hash function and cryptographic function used for calculating the signature:
<signature> := <hash-function>
<cryptographic-function>
<key-index>
<signature-value>
where: Section 12.
The version of this TLV, specified in this section, assumes that calculating the signature can be decomposed into:
The hash function and the cryptographic function correspond to the entries in two IANA registries, set up by this specification in
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 TLV type extension - is twofold: First, if further hash functions or cryptographic functions are added in the future, the number space might not remain continuous. More importantly, the number space of possible combinations would be rapidly exhausted. As new or improved cryptographic mechanism are continuously being developed and introduced, this format should be able to accommodate such for the foreseeable future.
The rationale for not including a field that lists parameters of the cryptographic signature in the TLV is, that before being able to validate a cryptographic signature, 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 inherently included parameter is the length of the signature, which is <length> - 3 and which depends on the choice of the cryptographic function.
In the following, considerations are listed, which have to be applied when calculating the signature for Packet, Message and Address SIGNATURE TLVs, respectively.
When determining the <signature-value> for a Packet, the signature is calculated over the three fields <hash-function>, <cryptographic-function> and <key-index> (in that order), concatenated with the entire Packet, including the packet header, all Packet TLVs (other than Packet SIGNATURE TLVs) and all included Messages and their message headers.
When determining the <signature-value> for a message, the signature is calculated over the three fields <hash-function>, <cryptographic-function>, and <key-index> (in that order), concatenated with the entire message.
When determining the <signature-value> for an address, the signature is calculated over the three fields <hash-function>, <cryptographic-function>, and <key-index> (in that order), concatenated with the address, concatenated with any other values, for example, any other TLV value that is associated with that address. A routing protocol or routing protocol extension using Address Block SIGNATURE TLVs MUST specify how to include any such concatenated attribute of the address in the verification process of the signature.
The sample message depicted in Figure 4 is derived from the appendix of [RFC5444]. A SIGNATURE Message TLV has been added, with the value representing a 14 octet long signature of the whole message. The type extension of the Message TLV is 1, for the specific decomposition of a signature into a cryptographic function over a hash value, as specified in Appendix Appendix A.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 0 0 0| Packet Sequence Number | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 1 0 0 1 1|0 0 0 0 0 0 0 0 0 1 0 0 1 1 0 0| Orig Addr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator Address (cont) | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count | Message Sequence Number |0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 1 1 1 0| SIGNATURE |1 0 0 1 0 0 0 0|0 0 0 0 0 0 0 1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 1 0| Hash Func | Crypto Func | Key Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value (cont) | TLV Type |0 0 0 1 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 1 0| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value (cont) |0 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 1 0 0 0 0|0 0 0 0 0 0 1 0| Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid | Prefix Length |0 0 0 0 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0|0 0 0 0 0 0 1 1|1 0 0 0 0 0 0 0|0 0 0 0 0 0 1 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Head | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mid | Mid |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1| TLV Type |0 0 0 1 0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 1 0| Value | TLV Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 1 0 0 0 0 0| Index Start | Index Stop |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+