draft-ietf-lamps-ocsp-nonce-04.txt		draft-ietf-lamps-ocsp-nonce-05.txt
	LAMPS M. Sahni, Ed.		LAMPS M. Sahni, Ed.
	Internet-Draft Palo Alto Networks		Internet-Draft Palo Alto Networks
	Updates: 6960 (if approved) September 2, 2020		Updates: 6960 (if approved) September 10, 2020
	Intended status: Standards Track		Intended status: Standards Track
	Expires: March 6, 2021		Expires: March 14, 2021
	OCSP Nonce Extension		OCSP Nonce Extension
	draft-ietf-lamps-ocsp-nonce-04		draft-ietf-lamps-ocsp-nonce-05
	Abstract		Abstract
	This document specifies the updated format of the Nonce extension in		This document specifies the updated format of the Nonce extension in
	Online Certificate Status Protocol (OCSP) request and response		the Online Certificate Status Protocol (OCSP) request and response
	messages. OCSP is used to check the status of a certificate and the		messages. OCSP is used to check the status of a certificate and the
	Nonce extension is used in the OCSP request and response messages to		Nonce extension is used to cryptographically bind an OCSP response
	avoid replay attacks. This document updates the RFC 6960.		message to a particular OCSP request message. This document updates
			RFC 6960.
	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-
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	This Internet-Draft will expire on March 6, 2021.		This Internet-Draft will expire on March 14, 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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	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
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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
	1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2		1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
	2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 3		2. OCSP Extensions . . . . . . . . . . . . . . . . . . . . . . . 2
	2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3		2.1. Nonce Extension . . . . . . . . . . . . . . . . . . . . . 3
	3. Security Considerations . . . . . . . . . . . . . . . . . . . 4		3. Security Considerations . . . . . . . . . . . . . . . . . . . 3
	3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4		3.1. Replay Attack . . . . . . . . . . . . . . . . . . . . . . 4
	3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4		3.2. Nonce Collision . . . . . . . . . . . . . . . . . . . . . 4
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
	5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 5		5. Changes to Appendix B. of RFC 6960 . . . . . . . . . . . . . 4
	5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax . . 5		5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax . . 4
	5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . . 5		5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax . . . 5
	6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	6.1. Normative References . . . . . . . . . . . . . . . . . . 5		6.1. Normative References . . . . . . . . . . . . . . . . . . 5
	6.2. Informative References . . . . . . . . . . . . . . . . . 6		6.2. Informative References . . . . . . . . . . . . . . . . . 5
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
	1. Introduction		1. Introduction
	This document updates the usage and format of the Nonce extension		This document updates the usage and format of the Nonce extension
	used in OCSP request and response messages. This extension was		used in OCSP request and response messages. This extension was
	previously defined in section 4.4.1 of [RFC6960]. The [RFC6960] does		previously defined in section 4.4.1 of [RFC6960]. [RFC6960] does not
	not mention any minimum and maximum length of the nonce extension.		mention any minimum and maximum length of nonce in the Nonce
	Due to not having an upper or lower limit of the length of the Nonce		extension. Lacking limits on the length of nonce in the Nonce
	extension, the OCSP responders that follow [RFC6960] may be		extension, an OCSP responders that follow [RFC6960] may be vulnerable
	vulnerable to various attacks like Denial of Service attacks		to various attacks like Denial of Service attacks [RFC4732], chosen
	[RFC4732], chosen prefix attacks to get a desired signature from the		prefix attacks to get a desired signature, and possible evasions
	OCSP responder and possible evasions that can use the Nonce extension		using the Nonce extension data. This document specifies a lower
	data for evasion. This document specifies a lower limit of 1 and an		limit of 1 and an upper limit of 32 to the length of nonce in the
	upper limit of 32 to the length of the Nonce extension. This		Nonce extension. This document updates [RFC6960].
	document updates the [RFC6960].
	1.1. Terminology		1.1. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	2. OCSP Extensions		2. OCSP Extensions
	The message format for the OCSP request and response is defined in		The message format for OCSP request and response is defined in
	the [RFC6960]. [RFC6960] also defines the standard extensions for		[RFC6960]. [RFC6960] also defines the standard extensions for OCSP
	OCSP messages based on the extension model employed in X.509 version		messages based on the extension model employed in X.509 version 3
	3 certificates (see [RFC5280]). The following is a list of standard		certificates (see [RFC5280]). This document only specifies the new
	extensions that can be used in the OCSP messages by the OCSP		format for Nonce extension and does not change specification of any
	responder and OCSP client.		of the other standard extensions defined in [RFC6960].
	* Nonce
	* CRL References
	* Acceptable Response Types
	* Archive Cutoff
	* CRL Entry Extensions
	* Service Locator
	* Preferred Signature Algorithms
	* Extended Response Definition
	This document only specifies the new format for Nonce extension and
	does not change the specification of any of the other standard
	extensions.
	2.1. Nonce Extension		2.1. Nonce Extension
	This section replaces the entirety of the Section 4.4.1 of [RFC6960]		This section replaces the entirety of the Section 4.4.1 of [RFC6960]
	which describes the OCSP Nonce extension.		which describes the OCSP Nonce extension.
	The nonce cryptographically binds a request and a response to prevent		The nonce cryptographically binds a request and a response to prevent
	replay attacks. The nonce is included as one of the		replay attacks. The nonce is included as one of the
	requestExtensions in requests, while in responses it would be		requestExtensions in requests, while in responses it would be
	included as one of the responseExtensions. In both the request and		included as one of the responseExtensions. In both the request and
	the response, the nonce will be identified by the object identifier		the response, the nonce will be identified by the object identifier
	id-pkix-ocsp-nonce, while the extnValue is the value of the nonce.		id-pkix-ocsp-nonce, while the extnValue is the value of the nonce.
	If Nonce extension is present then the length of nonce MUST be at		If Nonce extension is present then the length of nonce MUST be at
	least 1 octet and can be up to 32 octets.		least 1 octet and can be up to 32 octets.
	A server MUST reject any OCSP request having a Nonce extension with		A server MUST reject any OCSP request having a nonce in the Nonce
	length of 0 octets or more than 32 octets with the malformedRequest		extension with length of 0 octets or more than 32 octets with the
	OCSPResponseStatus as described in section 4.2.1 of [RFC6960].		malformedRequest OCSPResponseStatus as described in section 4.2.1 of
			[RFC6960].
	The value of the nonce MUST be generated using a cryptographically		The value of the nonce MUST be generated using a cryptographically
	strong pseudorandom number generator (see [RFC4086]). The OCSP		strong pseudorandom number generator (see [RFC4086]). The minimum
	clients SHOULD use a length of 32 octets for the Nonce extension.		nonce length of 1 octet is defined to provide backward compatibility
	The minimum nonce length of 1 octet is defined to provide the		with older clients that follow [RFC6960]. Newer OCSP clients that
	backward compatibility with older clients following [RFC6960]		support this document MUST use a length of 32 octets for the nonce in
	however, the newer OCSP clients MUST use a length of at least 16		Nonce extension. OCSP responders MUST accept lengths of at least 16
	octets for Nonce extension. The OCSP responder MAY choose to ignore		octets, and MAY choose to ignore the Nonce extension for requests
	Nonce extension for the requests where length of the Nonce extension		where the length of the nonce is less than 16 octets
	is less than 16 octets.
	id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp }		id-pkix-ocsp OBJECT IDENTIFIER ::= { id-ad-ocsp }
	id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }		id-pkix-ocsp-nonce OBJECT IDENTIFIER ::= { id-pkix-ocsp 2 }
	Nonce ::= OCTET STRING(SIZE(1..32))		Nonce ::= OCTET STRING(SIZE(1..32))
	3. Security Considerations		3. Security Considerations
	The security considerations of OCSP, in general, are described in the		The security considerations of OCSP, in general, are described in
	[RFC6960]. The Nonce extension is used to avoid replay attacks		[RFC6960]. During the interval in which the previous OCSP response
	during the interval in which the previous OCSP response for a		for a certificate is not expired but the responder has a changed
	certificate is not expired but the responder has a changed status for		status for that certificate, a copy of that OCSP response can be used
	that certificate. Including client's Nonce value in the OCSP		to indicate that the status of the certificate is still valid.
	response makes sure that the response is the latest response from the		Including client's Nonce value in the OCSP response makes sure that
	server and not an old copy.		the response is the latest response from the server and not an old
			copy.
	3.1. Replay Attack		3.1. Replay Attack
	The Nonce extension is used to avoid replay attacks. Since the OCSP		The Nonce extension is used to avoid replay attacks. Since the OCSP
	responder may choose to not send the Nonce extension in the OCSP		responder may choose to not send the Nonce extension in the OCSP
	response even if the client has sent the Nonce extension in the		response even if the client has sent the Nonce extension in the
	request [RFC5019], an on-path attacker can intercept the OCSP request		request [RFC5019], an on-path attacker can intercept the OCSP request
	and respond with an earlier response from the server without the		and respond with an earlier response from the server without the
	Nonce extension. This can be mitigated by configuring the server to		Nonce extension. This can be mitigated by configuring the server to
	use a short time interval between thisUpdate and nextUpdate fields in		use a short time interval between the thisUpdate and nextUpdate
	the OCSP response.		fields in the OCSP response.
	3.2. Nonce Collision		3.2. Nonce Collision
	If the value of the nonce used by a client in OCSP request is not		If the value of nonce used by a client in OCSP request is
	random enough, then an attacker may prefetch responses with the		predictable, then an attacker may prefetch responses with the
	predicted nonce and can replay them, thus defeating the purpose of		predicted nonce and can replay them, thus defeating the purpose of
	using nonce. Therefore the value of Nonce extension in the OCSP		using nonce. Therefore the value of Nonce extension in the OCSP
	request MUST contain cryptographically strong randomness and MUST be		request MUST contain cryptographically strong randomness and MUST be
	freshly generated at the time of creating the OCSP request. Also if		freshly generated at the time of creating the OCSP request. Also if
	the length of the nonce extension is too small e.g. 1 octet then an		the length of nonce is too small e.g. 1 octet then an on-path
	on-path attacker can prefetch responses with all the possible values		attacker can prefetch responses with all the possible values of nonce
	of the nonce and replay a matching nonce.		and replay a matching nonce.
	4. IANA Considerations		4. IANA Considerations
	This document does not call for any IANA actions.		This document does not call for any IANA actions.
	5. Changes to Appendix B. of RFC 6960		5. Changes to Appendix B. of RFC 6960
	This section updates the ASN.1 definitions of the OCSP Nonce		This section updates the ASN.1 definitions of the OCSP Nonce
	extension in the Appendix B.1 and Appendix B.2 of the [RFC6960] The		extension in Appendix B.1 and Appendix B.2 of [RFC6960] The
	Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2		Appendix B.1 defines OCSP using ASN.1 - 1998 Syntax and Appendix B.2
	defines OCSP using ASN.1 - 2008 Syntax		defines OCSP using ASN.1 - 2008 Syntax
	5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax		5.1. Changes to Appendix B.1. OCSP in ASN.1 - 1998 Syntax
	OLD Syntax:		OLD Syntax:
	The definition of OCSP Nonce Extension is not provided in the		The definition of OCSP Nonce Extension is not provided in
	Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax.		Appendix B.1 of [RFC6960] for the ASN.1 - 1998 Syntax.
	NEW Syntax:		NEW Syntax:
	Nonce ::= OCTET STRING(SIZE(1..32))		Nonce ::= OCTET STRING(SIZE(1..32))
	5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax		5.2. Changes to Appendix B.2 OCSP in ASN.1 - 2008 Syntax
	OLD Syntax:		OLD Syntax:
End of changes. 20 change blocks.
	68 lines changed or deleted		56 lines changed or added
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