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.
	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
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	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
	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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