Secure BFD Sequence Numbers
draft-ietf-bfd-secure-sequence-numbers-06
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (bfd WG) | |
|---|---|---|---|
| Authors | Mahesh Jethanandani , Sonal Agarwal , Ashesh Mishra , Ankur Saxena , Alan DeKok | ||
| Last updated | 2020-08-05 (Latest revision 2020-02-27) | ||
| Replaces | draft-sonal-bfd-secure-sequence-numbers | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Stream | WG state | Held by WG | |
| Document shepherd | Reshad Rahman | ||
| Shepherd write-up | Show Last changed 2020-06-14 | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | Reshad Rahman <rrahman@cisco.com> |
draft-ietf-bfd-secure-sequence-numbers-06
Network Working Group M. Jethanandani
Internet-Draft Kloud Services
Updates: 5880 (if approved) S. Agarwal
Intended status: Standards Track Cisco Systems, Inc
Expires: February 6, 2021 A. Mishra
O3b Networks
A. Saxena
Ciena Corporation
A. Dekok
Network RADIUS SARL
August 5, 2020
Secure BFD Sequence Numbers
draft-ietf-bfd-secure-sequence-numbers-06
Abstract
This document describes a security enhancement for the sequence
number used in BFD control packets. This document updates RFC 5880.
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
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Drafts is at https://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 February 6, 2021.
Copyright Notice
Copyright (c) 2020 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
(https://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
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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
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Theory of operation . . . . . . . . . . . . . . . . . . . . . 2
4. Impact of using a hash . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
BFD [RFC5880] section 6.7 describes the use of monotonically
incrementing 32-bit sequence numbers for use in authentication of BFD
packets. While this method protects against simple replay attacks,
the monotonically incrementing sequence numbers are predictable and
vulnerable to more complex attack vectors. This document proposes
the use of non-monotonically-incrementing sequence numbers in the BFD
authentication section to enhance the security of BFD sessions.
Specifically, the document presents a method to generate pseudo-
random sequence numbers on the frame by algorithmically hashing
monotonically increasing sequence numbers. Since the monotonically
increasing sequence number does not appear on the wire, it is
difficult for a third party to launch a replay attack.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Theory of operation
Instead of inserting a monotonically, sometimes occasionally,
increasing sequence number in BFD control packets, a hash is
inserted. The hash is computed, using a shared key, on the sequence
number. That computed hash is then inserted into the sequence number
field of the packet. In case of BFD Authentication
[I-D.ietf-bfd-optimizing-authentication], the sequence number used in
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computing an authenticated packet would be this new computed hash.
Even though the BFD Authentication
[I-D.ietf-bfd-optimizing-authentication] sequence number is
independent of this enhancement, it would benefit by using the
computed hash.
As currently defined in BFD [RFC5880], a BFD packet with
authentication will undergo the following steps, where:
[O]: original RFC 5880 packet with monotonically increasing sequence
number
[S]: pseudo random sequence number
[A]: Authentication
Sender Receiver
[O] [S] [A] ------------- [A] [S] [O]
This document proposes that for enhanced security in sequence number
encoding, the sender would identify a hash algorithm (symmetric) that
would create a 32 bit hash. The hashing key is provisioned securely
on the sender and receiver of the BFD session. The mechanism of
provisioning such a key is outside the scope of this document.
Instead of using the sequence number, the sender encodes the sequence
number with the hashing key to produce a hash.
Upon receiving the BFD Control packet, the receiver compares the
received sequence number against the expected sequence number. The
mechanism used for comparing is an implementation detail
(implementations may pre-calculate the expected hashed sequence
number, or decrypt the received sequence number before comparing
against expected value). To tolerate dropped frames, the receiver
MUST compare the received sequence number against the current
expected sequence number (previous received sequence number + 1) and
N subsequent expected sequence numbers (where N is greater than or
equal to the detect multiplier). Note: The first sequence number can
be obtained using the same logic as used in determining Local
Discriminator value for the session or by using a random number.
k: hashing key
s: sequence number
O: original RFC 5880 packet with monotonically increasing sequence
number
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R: remainder of packet
H1: hash of s
H2: hash of entire packet
A: H2 + insertion in packet
hash(s, k) = H1
hash((H1 + R), k) = H2
hash'((Packet - H2), k) == H2 ? Good packet : bad packet
hash'(H1, k) > previously received s ? Good sequence number : bad
sequence number
Sender Receiver
[O] [H1] [A] -------- [A] [H1] [O]
The above diagram describes how the sender encodes and receiver
decodes the sequence number. The sender starts by taking the
monotonically increasing sequence number and hashing it. It replaces
the sequence number with the hash. It then calculates the hash for
the entire packet and appends the hash value to the end of the
packet, before transmitting it.
The receiver hashes the entire packet without H2, and compares the
hash value with the received hash (H2). If the hash values are
equal, it is a good packet, else it is a bad packet. It then
calculates the hash on the received sequence number to retreive s.
If it is greater than the previously received monotically increasing
sequence number, then the receiver knows it's a valid sequence
number.
4. Impact of using a hash
Under this proposal, every packet's sequence number is encoded within
a hash. Therefore there is some impact on the system and its
performance while encoding/decoding the hash. As security measures
go, this enhancement greatly increases the security of the packet
with or without authentication of the entire packet.
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5. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
6. Security Considerations
While the proposed mechanism improves overall security of BFD
mechanism, the security consderations are listed below:
Because of the fast rate of BFD sesions and it is difficult to change
the keys (used for hashing the sequence number) during the operation
of a BFD session without affecting the stability of the BFD session.
It is, therefore, recommended to administratively disable the BFD
session before changing the keys. If the keys are not changed, an
attacker can use a replay attack.
Using this method allows the BFD end-points to detect a malicious
packet (the decrypted sequence number will not be in sequence) the
behavior of the session when such a packet is detected is based on
the implementation. A flood of such malicious packets may cause a
session to report BFD session to be operationally down.
The hashing algorithm and key size will determine the difficulty for
an attacker to decipher the key from the transmitted BFD frames. The
sequential nature of the payload (sequence numbers) simplifies the
decoding of the key. It is, therefore, recommended to use longer
keys or more secure hashing algorithms.
7. Acknowledgements
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
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8.2. Informative References
[I-D.ietf-bfd-optimizing-authentication]
Jethanandani, M., Mishra, A., Saxena, A., and M. Bhatia,
"Optimizing BFD Authentication", draft-ietf-bfd-
optimizing-authentication-11 (work in progress), July
2020.
Authors' Addresses
Mahesh Jethanandani
Kloud Services
Email: mjethanandani@gmail.com
Sonal Agarwal
Cisco Systems, Inc
170 W. Tasman Drive
San Jose, CA 95070
USA
Email: agarwaso@cisco.com
URI: www.cisco.com
Ashesh Mishra
O3b Networks
Email: mishra.ashesh@gmail.com
Ankur Saxena
Ciena Corporation
3939 North First Street
San Jose, CA 95134
USA
Email: ankurpsaxena@gmail.com
Alan DeKok
Network RADIUS SARL
100 Centrepointe Drive #200
Ottowa, ON K2G 6B1
Canada
Email: aland@freeradius.org
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