draft-ietf-bfd-secure-sequence-numbers-07.txt   draft-ietf-bfd-secure-sequence-numbers-08.txt 
Network Working Group M. Jethanandani Network Working Group M. Jethanandani
Internet-Draft Kloud Services Internet-Draft Kloud Services
Updates: 5880 (if approved) S. Agarwal Updates: 5880 (if approved) S. Agarwal
Intended status: Standards Track Cisco Systems, Inc Intended status: Standards Track Cisco Systems, Inc
Expires: June 19, 2021 A. Mishra Expires: September 9, 2021 A. Mishra
O3b Networks O3b Networks
A. Saxena A. Saxena
Ciena Corporation Ciena Corporation
A. Dekok A. Dekok
Network RADIUS SARL Network RADIUS SARL
December 16, 2020 March 8, 2021
Secure BFD Sequence Numbers Secure BFD Sequence Numbers
draft-ietf-bfd-secure-sequence-numbers-07 draft-ietf-bfd-secure-sequence-numbers-08
Abstract Abstract
This document describes a security enhancement for the sequence This document describes a security enhancement for the sequence
number used in BFD control packets. This document updates RFC 5880. number used in BFD control packets. This document updates RFC 5880.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 19, 2021. This Internet-Draft will expire on September 9, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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the symmetric algorithm to produce the ciphertext, which is then the symmetric algorithm to produce the ciphertext, which is then
inserted in place of the sequence number. inserted in place of the sequence number.
Upon receiving the BFD Control packet, the receiver decrypts the Upon receiving the BFD Control packet, the receiver decrypts the
ciphertext using the same provisioned shared key to produce the ciphertext using the same provisioned shared key to produce the
received sequence number. It compares the received sequence number received sequence number. It compares the received sequence number
against the expected sequence number. The mechanism used for against the expected sequence number. The mechanism used for
comparing is an implementation detail (implementations may pre- comparing is an implementation detail (implementations may pre-
calculate the expected sequence number, or decrypt the received calculate the expected sequence number, or decrypt the received
sequence number before comparing against expected value). To sequence number before comparing against expected value). To
tolerate dropped frames, the receiver MUST compare the received tolerate dropped frames, the receiver must compare the received
sequence number against the current expected sequence number sequence number against the current expected sequence number. BFD
(previous received sequence number + 1) and N subsequent expected [RFC5880] mentions that received sequence number should be between
sequence numbers (where N is greater than or equal to the detect (bfd.RcvAuthSeq(+1) to bfd.RcvAuthSeq+(3*Detect Mult) inclusive.
multiplier). Note: The first sequence number can be obtained using Note: The first sequence number can be obtained using the same
the same logic as used in determining Local Discriminator value for principles stated in BFD [RFC5880] i.e. (using bfd.AuthSeqKnown and
the session or by using a random number. bfd.RcvAuthSeq)
K: symmetric key K: symmetric key
S: sequence number S: sequence number
S': encrypted sequence number OR ciphertext result S': encrypted sequence number OR ciphertext result
O: original RFC 5880 packet with monotonically increasing sequence O: original RFC 5880 packet with monotonically increasing sequence
number number
f(S, K) = S', where f is a symmetric encryption algorithm f(S, K) = S', where f is a symmetric encryption algorithm
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authentication. On successful authentication, it decrypts the authentication. On successful authentication, it decrypts the
ciphertext with the same key used to encrypt it, in order to obtain ciphertext with the same key used to encrypt it, in order to obtain
the original sequence number. If it is greater than the previously the original sequence number. If it is greater than the previously
received monotonically increasing sequence number, then the receiver received monotonically increasing sequence number, then the receiver
knows it's a valid sequence number. knows it's a valid sequence number.
4. Impact of using a hash 4. Impact of using a hash
Under this proposal, every packet's sequence number is encoded in Under this proposal, every packet's sequence number is encoded in
ciphertext. Therefore, there is some impact on the system and its ciphertext. Therefore, there is some impact on the system and its
performance while encryption/decryption. As security measures go, performance while doing encryption/decryption. As security measures
this enhancement greatly increases the security of the packet with or go, this enhancement greatly increases the security of the packet
without authentication of the entire packet. with or without authentication of the entire packet.
5. IANA Considerations 5. IANA Considerations
This document makes no request of IANA. This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an Note to RFC Editor: this section may be removed on publication as an
RFC. RFC.
6. Security Considerations 6. Security Considerations
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BFD session to be operationally down. BFD session to be operationally down.
The symmetric algorithm and key size will determine the difficulty The symmetric algorithm and key size will determine the difficulty
for an attacker to decipher the key from the transmitted BFD frames. for an attacker to decipher the key from the transmitted BFD frames.
The sequential nature of the payload (sequence numbers) simplifies The sequential nature of the payload (sequence numbers) simplifies
the decoding of the key. It is, therefore, recommended to use longer the decoding of the key. It is, therefore, recommended to use longer
keys or more secure symmetric algorithms. keys or more secure symmetric algorithms.
7. Acknowledgements 7. Acknowledgements
The authors would like to thank Jeff Hass and Reshad Rahman for their The authors would like to thank Jeff Haas and Reshad Rahman for their
reviews of and suggestions for the document. reviews of and suggestions for the document.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
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