draft-ietf-bfd-secure-sequence-numbers-05.txt   draft-ietf-bfd-secure-sequence-numbers-06.txt 
Network Working Group M. Jethanandani Network Working Group M. Jethanandani
Internet-Draft S. Agarwal Internet-Draft Kloud Services
Updates: 5880 (if approved) S. Agarwal
Intended status: Standards Track Cisco Systems, Inc Intended status: Standards Track Cisco Systems, Inc
Expires: August 30, 2020 A. Mishra Expires: February 6, 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
February 27, 2020 August 5, 2020
Secure BFD Sequence Numbers Secure BFD Sequence Numbers
draft-ietf-bfd-secure-sequence-numbers-05 draft-ietf-bfd-secure-sequence-numbers-06
Abstract Abstract
This document describes a security enhancements for the BFD packet's This document describes a security enhancement for the sequence
sequence number. number used in BFD control packets. This document updates RFC 5880.
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].
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.
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 August 30, 2020. This Internet-Draft will expire on February 6, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Theory of operations . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. Impact of using a hash . . . . . . . . . . . . . . . . . . . 4 3. Theory of operation . . . . . . . . . . . . . . . . . . . . . 2
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. Impact of using a hash . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
BFD [RFC5880] section 6.7 describes the use of monotonically BFD [RFC5880] section 6.7 describes the use of monotonically
incrementing 32-bit sequence numbers for use in authentication of BFD incrementing 32-bit sequence numbers for use in authentication of BFD
packets. While this method protects against simple replay attacks, packets. While this method protects against simple replay attacks,
the monotonically incrementing sequence numbers are predictable and the monotonically incrementing sequence numbers are predictable and
vulnerable to more complex attack vectors. This document proposes vulnerable to more complex attack vectors. This document proposes
the use of non-monotonically-incrementing sequence numbers in BFD the use of non-monotonically-incrementing sequence numbers in the BFD
authentication TLVs to enhance the security of BFD sessions. authentication section to enhance the security of BFD sessions.
Specifically, the document presents a method to generate pseudo- Specifically, the document presents a method to generate pseudo-
random sequence numbers on the frame by algorithmically hashing random sequence numbers on the frame by algorithmically hashing
monotonically increasing sequence numbers. Further security may be monotonically increasing sequence numbers. Since the monotonically
introduced by resetting un-encrypted sequence to a random value when increasing sequence number does not appear on the wire, it is
the 32-bit sequence number rolls-over. difficult for a third party to launch a replay attack.
2. Theory of operations 2. Requirements Language
Instead of monotonically increasing the sequence number or even The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
occasionally monotonically increasing the sequence number, the next "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
sequence number is generated by computing a hash on what would have document are to be interpreted as described in RFC 2119 [RFC2119].
been the next sequence number using a shared key. That computed hash
is then inserted into the sequence number field of the packet. In 3. Theory of operation
case of BFD Authentication [I-D.ietf-bfd-optimizing-authentication],
the sequence number used in computing an authenticated packet would
be this new computed hash. Even though the BFD Authentication
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
computing an authenticated packet would be this new computed hash.
Even though the BFD Authentication
[I-D.ietf-bfd-optimizing-authentication] sequence number is [I-D.ietf-bfd-optimizing-authentication] sequence number is
independent of this enhancement, it would benefit by using the independent of this enhancement, it would benefit by using the
computed hash. computed hash.
A normal BFD packet with authentication will undergo the following As currently defined in BFD [RFC5880], a BFD packet with
steps, where: authentication will undergo the following steps, where:
[O]: original RFC 5880 packet with monotonically increasing sequence [O]: original RFC 5880 packet with monotonically increasing sequence
number number
[S]: psuedo random sequence number [S]: pseudo random sequence number
[A]: Authentication [A]: Authentication
Sender Receiver Sender Receiver
[O] [S] [A] ------------- [A] [S] [O] [O] [S] [A] ------------- [A] [S] [O]
In order to encode a sequence number, the sender would identify a This document proposes that for enhanced security in sequence number
hash algorithm (symmetric) that would create a 32 bit hash. The encoding, the sender would identify a hash algorithm (symmetric) that
hashing key is provisioned securely on the sender and receiver of the would create a 32 bit hash. The hashing key is provisioned securely
BFD session. The mechanism of provisioning such a key is outside the on the sender and receiver of the BFD session. The mechanism of
scope of this draft. Instead of using the sequence number, the provisioning such a key is outside the scope of this document.
sender encodes the sequence number with the hashing key to produce a Instead of using the sequence number, the sender encodes the sequence
hash. number with the hashing key to produce a hash.
Upon receiving the BFD Control packet, the receiver compares the Upon receiving the BFD Control packet, the receiver compares the
received sequence number against the expected sequence number. The received sequence number against the expected sequence number. The
mechanism used for comparing is an implementation detail mechanism used for comparing is an implementation detail
(implementations may pre-calculate the expected hashed sequence (implementations may pre-calculate the expected hashed sequence
number, or decrypt the received sequence number before comparing number, or decrypt the received sequence number before comparing
against expected value). To tolerate dropped frames, the receiver against expected value). To tolerate dropped frames, the receiver
MUST compare the received sequence number against the current MUST compare the received sequence number against the current
expected seuqence number (previous received sequence number + 1) and expected sequence number (previous received sequence number + 1) and
N subsequent expected sequence numbers (where N is greater than or N subsequent expected sequence numbers (where N is greater than or
equal to the detect multiplier). Note: The first sequence number can equal to the detect multiplier). Note: The first sequence number can
be obtained using the same logic as the My Discriminator value. 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 k: hashing key
s: sequence number s: sequence number
O: original RFC 5880 packet with monotonically increasing sequence O: original RFC 5880 packet with monotonically increasing sequence
number number
R: remainder of packet R: remainder of packet
H1: hash of s H1: hash of s
H2: hash of entire packet H2: hash of entire packet
A: H2 + insertion in packet A: H2 + insertion in packet
hash(s, k) = H1 hash(s, k) = H1
hash((H1 + R), k) = H2 hash((H1 + R), k) = H2
hash'((Packet - H2), k) == H2 ? Good packet : bad packet hash'((Packet - H2), k) == H2 ? Good packet : bad packet
skipping to change at page 4, line 14 skipping to change at page 4, line 18
H2: hash of entire packet H2: hash of entire packet
A: H2 + insertion in packet A: H2 + insertion in packet
hash(s, k) = H1 hash(s, k) = H1
hash((H1 + R), k) = H2 hash((H1 + R), k) = H2
hash'((Packet - H2), k) == H2 ? Good packet : bad packet hash'((Packet - H2), k) == H2 ? Good packet : bad packet
hash'(H1, k) == s ? Good sequence number : bad sequence number hash'(H1, k) > previously received s ? Good sequence number : bad
sequence number
Sender Receiver Sender Receiver
[O] [H1] [A] -------- [A] [H1] [O] [O] [H1] [A] -------- [A] [H1] [O]
3. Impact of using a hash 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 Under this proposal, every packet's sequence number is encoded within
a hash. Therefore there is some impact on the system and its a hash. Therefore there is some impact on the system and its
performance while encoding/decoding the hash. As security measures performance while encoding/decoding the hash. As security measures
go, this enhancement greatly increases the security of the packet go, this enhancement greatly increases the security of the packet
with or without authentication of the entire packet. with or without authentication of the entire packet.
4. 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.
5. Security Considerations 6. Security Considerations
While the proposed mechanism improves overall security of BFD While the proposed mechanism improves overall security of BFD
mechanism, the security consderations are listed below: mechanism, the security consderations are listed below:
Because of the fast rate of BFD sesions and it is difficult to change 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 the keys (used for hashing the sequence number) during the operation
of a BFD session without affecting the stabiluty of the BFD session. of a BFD session without affecting the stability of the BFD session.
It is, therefore, recommended to admistratively disable the BFD It is, therefore, recommended to administratively disable the BFD
session before changing the keys. If the keys are not changed, an session before changing the keys. If the keys are not changed, an
attacker can use a replay attack. attacker can use a replay attack.
Using this method allows the BFD end-points to detect a malicious Using this method allows the BFD end-points to detect a malicious
packet (the decrypted sequence number will not be in sequence) the packet (the decrypted sequence number will not be in sequence) the
behavior of the session when such a packet is detected is based on behavior of the session when such a packet is detected is based on
the implementation. A flood of such malicious packets may cause a the implementation. A flood of such malicious packets may cause a
session to report BFD session to be operationally down. session to report BFD session to be operationally down.
The hashing algorithm and key size will determine the difficulty for The hashing algorithm and key size will determine the difficulty for
an attacker to decipher the key from the transmitted BFD frames. 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 decoding of the key. It is, therefore, recommended to use longer
keys or more secure hashing algorithms. keys or more secure hashing algorithms.
6. Acknowledgements 7. Acknowledgements
7. References 8. References
7.1. 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>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>. <https://www.rfc-editor.org/info/rfc5880>.
7.2. Informative References 8.2. Informative References
[I-D.ietf-bfd-optimizing-authentication] [I-D.ietf-bfd-optimizing-authentication]
Jethanandani, M., Mishra, A., Saxena, A., and M. Bhatia, Jethanandani, M., Mishra, A., Saxena, A., and M. Bhatia,
"Optimizing BFD Authentication", draft-ietf-bfd- "Optimizing BFD Authentication", draft-ietf-bfd-
optimizing-authentication-09 (work in progress), December optimizing-authentication-11 (work in progress), July
2019. 2020.
Authors' Addresses Authors' Addresses
Mahesh Jethanandani Mahesh Jethanandani
Cisco Systems, Inc Kloud Services
170 West Tasman Drive
San Jose, CA 95070
USA
Email: mjethanandani@gmail.com Email: mjethanandani@gmail.com
Sonal Agarwal Sonal Agarwal
Cisco Systems, Inc Cisco Systems, Inc
170 W. Tasman Drive 170 W. Tasman Drive
San Jose, CA 95070 San Jose, CA 95070
USA USA
Email: agarwaso@cisco.com Email: agarwaso@cisco.com
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