Mobile Ad hoc Networking (MANET) U. Herberg
Internet-Draft T. Clausen
Intended status: Experimental LIX, Ecole Polytechnique
Expires: September 30, 2011 March 29, 2011
Cryptographical Signatures in NHDP
draft-herberg-manet-nhdp-sec-01
Abstract
This document specifies an extension to the Neighbor Discovery
Protocol (NHDP) which uses cryptographic signatures in HELLO messages
to encounter a selection of security threats to NHDP.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability Statement . . . . . . . . . . . . . . . . . . . 3
4. Protocol Overview and Functioning . . . . . . . . . . . . . . 4
5. Transmitting a Message in NHDP . . . . . . . . . . . . . . . . 4
6. Signing a Message . . . . . . . . . . . . . . . . . . . . . . 5
7. Processing a Message . . . . . . . . . . . . . . . . . . . . . 5
8. Validating a Timestamp . . . . . . . . . . . . . . . . . . . . 6
9. Validating a Signature . . . . . . . . . . . . . . . . . . . . 6
10. Parameters and Constants . . . . . . . . . . . . . . . . . . . 7
11. Preconditions . . . . . . . . . . . . . . . . . . . . . . . . 7
12. Summary of NHDP Interaction . . . . . . . . . . . . . . . . . 7
13. Security Threats Alleviation Analysis . . . . . . . . . . . . 8
13.1. Jamming . . . . . . . . . . . . . . . . . . . . . . . . . 8
13.2. Identity Spoofing . . . . . . . . . . . . . . . . . . . . 8
13.3. Link Spoofing . . . . . . . . . . . . . . . . . . . . . . 8
13.4. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 8
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
15. Security Considerations . . . . . . . . . . . . . . . . . . . 9
16. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
This document describes how to use cryptographic signatures for
countering a selection of the security threats analyzed in
[NHDP-sec-threats]. It specifies the use of such signatures for
validating the identity of the originator of a HELLO message, the
validity of the content (i.e. links being advertised) of a HELLO
message, and the message integrity. The protection so offered
against the threats in [NHDP-sec-threats] is evaluated.
This document specifies TLVs for carrying cryptographic signatures in
HELLO messages using [RFC5444], and specifies extensions (as enabled
by [NHDP]) to the HELLO message processing in [NHDP].
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 RFC
2119 [RFC2119].
Additionally, this document uses the terminology of [RFC5444],
[packetbb-sec], [NHDP] and [NHDP-sec-threats].
3. Applicability Statement
o [NHDP] enables extensions to recognize additional reasons for
rejecting a message as malformed, and mentions security as an
explicit example.
o This document, therefore, elaborates on how this in details can be
done, providing a framework for signing and validating messages in
NHDP.
o Note that there is no "no one-size-fits-all", therefore this
document uses the containers for carrying signatures and
registries for cryptographic code-points as specified in
[packetbb-sec]. The specification should therefore be generally
be applicable where cryptographic signatures are thought an
appropriate security solution. Note that the the choice of the
cryptographic algorithm are to be made for each given deployment,
and that the choice of such is out of scope for this document.
o This document does not specify how to distribute cryptographic
keys, shared secrets, parameters for signature algorithms, etc.
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o Note also that this document assumes that a router which is able
to sign messages correctly (e.g. having valid cryptographic keys),
is considered trusted. This document does not handle compromised
routers with valid keys (e.g. a router that is compromised by a
computer virus).
Therefore:
o This document is generally applicable when [NHDP] is used, and
uses the [RFC5444] extension specified in [packetbb-sec].
4. Protocol Overview and Functioning
The framework presented in this document provides two
functionalities:
o Signing a HELLO message, and
o Checking whether a signed incoming HELLO message is valid.
When a router running NHDP is about to transmit a HELLO message on an
interface, this extension:
o Specifies to calculate a digital signature of the message, and
o Specifies how to add that signature to a message for transmission,
by way of a SIGNATURE TLV.
The framework allows to add several signatures with different hash
and cryptographic functions.
[NHDP] allows to reject incoming HELLO messages prior to processing
by NHDP for reasons such as invalid signatures. This extension
specifies that for each SIGNATURE TLV in the Message TLV Block of
that incoming message, the value of that TLV (i.e. the contained
signature) is verified.
5. Transmitting a Message in NHDP
HELLO messages are generated as specified in [NHDP]. In addition,
each HELLO message MUST set the <msg-orig-addr> as well as the <msg-
seq-num> field as specified in [RFC5444]. Before transmission of a
message, it is signed as described in Section 6.
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6. Signing a Message
This section specifies how to sign a message. Note that a message
may be signed several times using different signature algorithms.
The following constraints MUST be respected when signing a message:
o The originator address of the message MUST be included.
o The sequence number of the message MUST be included.
Optionally:
o A TIMESTAMP TLV (as defined in [packetbb-sec]) MAY be added to the
message if no such TLV is already included in the message TLV
block of that message. The value of the TIMESTAMP TLV is the
current POSIX timestamp (32-bit) of the router, and the type
extension is 1 (one).
For each signature algorithm that is used to sign the message:
1. All TLVs of type SIGNATURE are temporarily removed from the
message and stored in temporary variables. The message size is
recalculated accordingly, i.e. to the size of the message without
the SIGNATURE TLVs.
2. The signature value is calculated over the whole message (as
resulting after step 1) according to the chosen signature
algorithm.
3. A TLV of type SIGNATURE is added in the message TLV block. The
TLV value is set to the signature calculated in step 2 as well as
the chosen hash and cryptographic algorithms.
4. All other SIGNATURE TLVs that have been temporary removed, are
restored.
5. The message size is recalculated.
7. Processing a Message
NHDP specifies that
"On receiving a HELLO message, a router MUST first check if the
message is invalid for processing by this router"
and gives a number of conditions that will lead to a rejection of the
HELLO message if any of these conditions is true. The extension to
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NHDP, specified in this document, adds the following conditions for
rejecting a message:
o The message does not include the <msg-orig-addr> or the <msg-seq-
num> field.
o The message contains more than one TIMESTAMP TLV.
o Any signature of the message is invalid as specified in Section 9.
o The timestamp of the message is invalid as specified in Section 8.
8. Validating a Timestamp
This section specifies how to validate a message timestamp.
1. If the message includes a TIMESTAMP Message TLV, and the value of
the TIMESTAMP TLV differs from the current POSIX time of more
than MAX_TIMESTAMP_DIFF, the message MUST be discarded.
9. Validating a Signature
This section specifies how to validate a message signature.
1. For all SIGNATURE Message TLVs:
A. If the hash function and the cryptographic function defined
in that TLV are known to the router: goto step 2.
B. Otherwise goto step 1
2. If no signature algorithm has been recognized in step 1, the
message MUST be discarded.
3. All SIGNATURE TLVs are removed from the message, and the message
size is recalculated.
4. The signature is recalculated using the same hash function and
cryptographic function as indicated in the TLV, and compared with
the signature from the SIGNATURE TLV that has been removed in
step 3.
5. If the verification fails, the message MUST be discarded.
6. Otherwise:
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A. All SIGNATURE TLVs are restored.
B. The message size is restored.
7. The message can now be processed according to [NHDP].
10. Parameters and Constants
This document specifies the following parameters and constants:
o MAX_TIMESTAMP_DIFF - The maximum age a message that is to be
validated may have. If the current POSIX time of the router
validating the message minus the timestamp indicated in the
TIMESTAMP TLV of the message is greater than MAX_TIMESTAMP_DIFF,
the message will be discarded.
The following constraints apply to these parameters:
o MAX_TIMESTAMP_DIFF > 0
11. Preconditions
Before a router is able to sign or validate messages, it must
initially parameterize some security settings. In particular, it
MUST acquire the cryptographic key(s) and any parameters of the
cryptographic algorithm from all other routers that are to
participate in the network. This document does not specify how a
router acquires the cryptographic keys and parameters used in the
MANET.
12. Summary of NHDP Interaction
When the security mechanism as specified in this document is used,
the following MUST be observed:
o NHDP must generate HELLO messages as usual.
o NHDP MUST allow this security mechanism access to the HELLO
message after its generation and prior to transmission, in order
that a SIGNATURE TLV can be generated and inserted, as allowed by
Section 16 in [NHDP].
o Any other NHDP extension which adds information to a HELLO message
and which wishes this added information to be included when
calculating the cryptographic signature MUST do so prior to the
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HELLO message being handed off for signature generation.
o An incoming HELLO message MUST be processed according to this
specification prior to processing by [NHDP] as allowed in Section
16 in [NHDP].
o Any other NHDP extension, which has added information to a HELLO
message and which wishes that the HELLO message is rejected if a
cryptographic signature is not valid, MUST likewise process the
HELLO message only after its processing according to this
specification.
13. Security Threats Alleviation Analysis
This section analyzes which of the security threats that are detailed
in [NHDP-sec-threats] are alleviated by the framework presented in
this document.
13.1. Jamming
Since jamming is a physical layer issue, it cannot be alleviated by
protocols on the routing layer. This framework does not counteract
jamming attacks, therefore.
13.2. Identity Spoofing
As only routers possessing valid cryptographic keys are able to
correctly sig HELLO messages, identity spoofing is counteracted. If
a router does not have access to valid keys or does not sign messages
at all, it is not able to create HELLOs that are processed by
neighbor routers. Such wrongly signed or unsigned messages are
rejected by receiving routers as described in Section 9.
13.3. Link Spoofing
Link spoofing is counteracted by the framework specified in this
document, with the same argument as in Section 13.2. A router
without access to valid cryptographic keys cannot sign the message
correctly, and therefore the message will be rejected by any
receiving routers. Hence, all links postulated by an attacker are
ignored.
13.4. Replay Attack
Replay attacks are only counteracted if TIMESTAMP TLVs are included
in HELLO messages. This is optional, and depends on synchronized
clocks of all routers in the MANET. An attacker which records
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messages to replay them later can only do so in the time interval
between the timestamp that is contained in the TIMESTAMP TLV and
MAX_TIMESTAMP_DIFF seconds later. As an attacker cannot modify the
content of the TIMESTAMP TLV (since it does not possess the valid
cryptographic keys), it cannot replay messages after this time
interval. Within this time interval, however, it is still possible
to replay attacks.
14. IANA Considerations
This document has no actions for IANA.
15. Security Considerations
This document specifies a protocol extension to NHDP which allows to
alleviate some of the security threats of NHDP analyzed in
[NHDP-sec-threats].
If no synchronized clocks are available in the MANET, replay attacks
cannot be counteracted by this framework.
This framework does not avoid or detect security attacks by routers
possessing the cryptographic keys that is used to sign messages.
This specification depends on the quality of the used signature
algorithm and provides as such the same security considerations as
the hash function and the cipher algorithm.
This specification relies on an out-of-band protocol to distribute
keys and parameters. The security considerations of that protocol
apply.
This specification does not provide a key revocation mechanism.
16. Normative References
[NHDP] Clausen, T., Dearlove, C., and J. Dean, "Mobile Ad Hoc
Network (MANET) Neighborhood Discovery Protocol (NHDP)",
RFC 6130, March 2011.
[NHDP-sec-threats]
Herberg, U. and T. Clausen, "Security Threats for NHDP",
work in
progress draft-herberg-manet-nhdp-sec-threats-00.txt,
November 2009.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5444] Clausen, T., Dearlove, C., Dean, J., and C. Adjih,
"Generalized MANET Packet/Message Format", RFC 5444,
February 2009.
[packetbb-sec]
Herberg, U. and T. Clausen, "MANET Cryptographical
Signature TLV Definition", work in
progress draft-ietf-manet-packetbb-sec-03.txt, March 2011.
Authors' Addresses
Ulrich Herberg
LIX, Ecole Polytechnique
91128 Palaiseau Cedex,
France
Email: ulrich@herberg.name
URI: http://www.herberg.name/
Thomas Heide Clausen
LIX, Ecole Polytechnique
91128 Palaiseau Cedex,
France
Phone: +33 6 6058 9349
Email: T.Clausen@computer.org
URI: http://www.thomasclausen.org/
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