| Mobile Ad hoc Networking (MANET) | U. Herberg |
| Internet-Draft | Fujitsu Laboratories of America |
| Intended status: Standards Track | T. Clausen |
| Expires: May 18, 2012 | LIX, Ecole Polytechnique |
| November 15, 2011 |
MANET Cryptographical Signature TLV Definition
draft-ietf-manet-packetbb-sec-07
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 Internet-Draft will expire on May 18, 2012.
Copyright (c) 2011 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.
This document specifies: Section 12:
This document requests from IANA:
Finally, this document defines, in
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:
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 MANET routing protocol, or by an extension of a MANET routing protocol, according to its specification.
This document specifies how to include a cryptographic signature for a packet, a message, and addresses in address blocks within a message, by way of such TLVs. This document also specifies how to treat "mutable" fields, specifically the <msg-hop-count> and <msg-hop-limit> fields, 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 describes a generic framework for creating signatures, and how to include these signatures in TLVs. In Section 12, an example method for calculating such signatures is given, using a cryptographic function over the hash value of the content to be signed.
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. MANET routing 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 Section 12, 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 document specifies a syntactical representation of security related information for use with [RFC5444] addresses, messages, and packets, as well as establishes IANA registrations and registries.
Moreover, this document provides guidelines how MANET routing protocols and MANET routing protocol extensions, using this specification, should treat Signature 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 requests assignment of 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 utilizes these "Type Extension" registries so created, in order to specify internal structure (and accompanying processing) of the <value> field of a TLV.
For example, and as defined in this document, a SIGNATURE TLV with Type Extension = 0 specifies that the <value> field has no pre-defined internal structure, but is simply a sequence of octets. A SIGNATURE TLV with Type Extension = 1 specifies that the <value> field has a pre-defined internal structure, and defines its interpretation (specifically, the <value> field consists of a cryptographic operation over a hash value, with fields indicating which hash function and cryptographic operation has been used, specified in Section 12).
Other documents may request assignments for other Type Extensions, and must if so specify their internal structure (if any) and interpretation.
The value of the Signature TLV is:
<value> := <signature-value>
where:
Note that this does not stipulate how to calculate the <signature-value>, nor the internal structure hereof, if any; such MUST be specified by way of the Type Extension for the SIGNATURE TLV type, see Section 13. This document specifies two such type-extensions, for signatures without pre-defined structures, and for signatures constructed by way of a cryptographic operation over a hash-value.
The value of the Timestamp TLV is:
<value> := <time-value>
where:
A timestamp is essentially "freshness information". As such, its setting and interpretation is to be determined by the MANET routing protocol, or MANET routing protocol extension, that uses the timestamp, 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 6.
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 7. 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 6. 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 7. 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 6. 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 MANET routing protocol or MANET 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 7. 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.
The basic signature proposed, represented by way of a SIGNATURE TLV with Type Extension = 0, is a simple bit-field containing the cryptographic signature. This assumes that the mechanism stipulating how signatures 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 <signature-value> for when using Type Extension = 0 is:
<signature-value> := <signature-data>
where:
One 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 = 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-value> := <hash-function>
<cryptographic-function>
<key-index>
<signature-data>
where: Section 13.
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 implicitly available 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 MUST 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, in accordance with Section 8.1.
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. The considerations in Section 9.1 MUST be applied.
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 MANET routing protocol or MANET 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 considerations in Section 10.2 MUST be applied.
The sample message depicted in Figure 5 is derived from appendix D of [RFC5444]. The message contains a SIGNATURE Message TLV, with the value representing a 16 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 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 = 40 | Msg. Orig Addr|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Originator Address (cont) | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hop Count | Message Sequence Number | Msg. TLV Block|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length = 30 | SIGNATURE | MTLVF = 144 | MTLVExt = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Value Len = 19 | Hash Func | Crypto Func | Key Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Signature Value (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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.
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 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.
IANA is requested to make allocations from the "Packet TLV Types" namespace of [RFC5444] for the Packet TLVs specified in Table 1.
| 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 Section 12 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 |
IANA is requested to make allocations from the "Message TLV Types" namespace of [RFC5444] for the Message TLVs specified in Table 2.
| 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 Section 12 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 |
IANA is requested to make allocations from the "Address Block TLV Types" namespace of [RFC5444] for the Packet TLVs specified in Table 3.
| 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 Section 12 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 |
IANA is requested to create a new registry for hash functions that can be used when creating a signature, as specified in Section 12 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 Section 12 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. 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 MANET routing protocol or MANET routing protocol extension. As such, it has the same security considerations as [RFC5444].
In addition, a MANET routing protocol or MANET routing protocol extension that uses this specification 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 MANET 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 Bo Berry (Cisco), Alan Cullen (BAE), Justin Dean (NRL), Christopher Dearlove (BAE), Paul Lambert (Marvell), Jerome Milan (Ecole Polytechnique) 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-olsrv2-13.txt, October 2011. |