< draft-ietf-smime-3850bis-05.txt		draft-ietf-smime-3850bis-06.txt >
	S/MIME WG Blake Ramsdell, SendMail		S/MIME WG Blake Ramsdell, Brute Squad Labs
	Internet Draft Sean Turner, IECA		Internet Draft Sean Turner, IECA
	Intended Status: Standard Track August 20, 2008		Intended Status: Standard Track September 18, 2008
	Obsoletes: 3850 (once approved)		Obsoletes: 3850 (once approved)
	Expires: February 20, 2009		Expires: March 18, 2009
	Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2		Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2
	Certificate Handling		Certificate Handling
	draft-ietf-smime-3850bis-05.txt		draft-ietf-smime-3850bis-06.txt
	Status of this Memo		Status of this Memo
	By submitting this Internet-Draft, each author represents that any		By submitting this Internet-Draft, each author represents that any
	applicable patent or other IPR claims of which he or she is aware		applicable patent or other IPR claims of which he or she is aware
	have been or will be disclosed, and any of which he or she becomes		have been or will be disclosed, and any of which he or she becomes
	aware will be disclosed, in accordance with Section 6 of BCP 79.		aware will be disclosed, in accordance with Section 6 of BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF), its areas, and its working groups. Note that		Task Force (IETF), its areas, and its working groups. Note that
	skipping to change at page 1, line 35 ¶		skipping to change at page 1, line 35 ¶
	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."
	The list of current Internet-Drafts can be accessed at		The list of current Internet-Drafts can be accessed at
	http://www.ietf.org/ietf/1id-abstracts.txt		http://www.ietf.org/ietf/1id-abstracts.txt
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	This Internet-Draft will expire on February 20, 2008.		This Internet-Draft will expire on March 18, 2008.
	Copyright Notice		Copyright Notice
	Copyright (C) The IETF Trust (2008).		Copyright (C) The IETF Trust (2008).
	Abstract		Abstract
	This document specifies conventions for X.509 certificate usage by		This document specifies conventions for X.509 certificate usage by
	Secure/Multipurpose Internet Mail Extensions (S/MIME) agents. S/MIME		Secure/Multipurpose Internet Mail Extensions (S/MIME) agents. S/MIME
	provides a method to send and receive secure MIME messages, and		provides a method to send and receive secure MIME messages, and
	skipping to change at page 2, line 25 ¶		skipping to change at page 2, line 25 ¶
	for the mailing list at <http://www.imc.org/ietf-smime/>.		for the mailing list at <http://www.imc.org/ietf-smime/>.
	Table of Contents		Table of Contents
	1. Introduction...................................................2		1. Introduction...................................................2
	1.1. Definitions...............................................3		1.1. Definitions...............................................3
	1.2. Conventions used in this document.........................4		1.2. Conventions used in this document.........................4
	1.3. Compatibility with Prior Practice S/MIME..................4		1.3. Compatibility with Prior Practice S/MIME..................4
	1.4. Changes From S/MIME v3 to S/MIME v3.1.....................4		1.4. Changes From S/MIME v3 to S/MIME v3.1.....................4
	1.5. Changes Since S/MIME v3.1.................................5		1.5. Changes Since S/MIME v3.1.................................5
	2. CMS Options....................................................5		2. CMS Options....................................................6
	2.1. Certificate Revocation Lists..............................6		2.1. Certificate Revocation Lists..............................6
	2.2. Certificate Choices.......................................6		2.2. Certificate Choices.......................................6
	2.2.1. Historical Note About CMS Certificates...............6		2.2.1. Historical Note About CMS Certificates...............6
	2.3. CertificateSet............................................7		2.3. CertificateSet............................................7
	3. Using Distinguished Names For Internet Mail....................8		3. Using Distinguished Names For Internet Mail....................8
	4. Certificate Processing.........................................9		4. Certificate Processing.........................................9
	4.1. Certificate Revocation Lists.............................10		4.1. Certificate Revocation Lists.............................10
	4.2. Certificate Path Validation..............................10		4.2. Certificate Path Validation..............................10
	4.3. Certificate and CRL Signing Algorithms and Key Sizes.....11		4.3. Certificate and CRL Signing Algorithms and Key Sizes.....11
	4.4. PKIX Certificate Extensions..............................11		4.4. PKIX Certificate Extensions..............................12
	5. IANA Considerations...........................................14		5. IANA Considerations...........................................14
	6. Security Considerations.......................................14		6. Security Considerations.......................................14
	7. References....................................................16		7. References....................................................16
	7.1. Normative References.....................................16		7.1. Normative References.....................................16
	7.2. Informative References...................................17		7.2. Informative References...................................17
	Appendix A. Moving S/MIME v2 Certificate Handling to Historic		Appendix A. Moving S/MIME v2 Certificate Handling to Historic
	Status...............................................19		Status...............................................20
	Appendix B. Acknowledgements.....................................19		Appendix B. Acknowledgements.....................................20
	1. Introduction		1. Introduction
	S/MIME (Secure/Multipurpose Internet Mail Extensions), described in		S/MIME (Secure/Multipurpose Internet Mail Extensions), described in
	[SMIME-MSG], provides a method to send and receive secure MIME		[SMIME-MSG], provides a method to send and receive secure MIME
	messages. Before using a public key to provide security services,		messages. Before using a public key to provide security services,
	the S/MIME agent MUST verify that the public key is valid. S/MIME		the S/MIME agent MUST verify that the public key is valid. S/MIME
	agents MUST use PKIX certificates to validate public keys as		agents MUST use PKIX certificates to validate public keys as
	described in the Internet X.509 Public Key Infrastructure (PKIX)		described in the Internet X.509 Public Key Infrastructure (PKIX)
	Certificate and CRL Profile [KEYM]. S/MIME agents MUST meet the		Certificate and CRL Profile [KEYM]. S/MIME agents MUST meet the
	skipping to change at page 4, line 37 ¶		skipping to change at page 4, line 37 ¶
	time, it is reasonable to expect that if a future revision of a		time, it is reasonable to expect that if a future revision of a
	document alters the status of a MUST- requirement, it will remain		document alters the status of a MUST- requirement, it will remain
	at least a SHOULD or a SHOULD-.		at least a SHOULD or a SHOULD-.
	1.3. Compatibility with Prior Practice S/MIME		1.3. Compatibility with Prior Practice S/MIME
	S/MIME version 3.2 agents should attempt to have the greatest		S/MIME version 3.2 agents should attempt to have the greatest
	interoperability possible with agents for prior versions of S/MIME.		interoperability possible with agents for prior versions of S/MIME.
	S/MIME version 2 is described in RFC 2311 through RFC 2315 inclusive		S/MIME version 2 is described in RFC 2311 through RFC 2315 inclusive
	[SMIMEv2], S/MIME version 3 is described in RFC 2630 through RFC 2634		[SMIMEv2], S/MIME version 3 is described in RFC 2630 through RFC 2634
	inclusive [SMIMEv3], and S/MIME version 3.1 is described in RFC 3850		inclusive and RFC 5035 [SMIMEv3], and S/MIME version 3.1 is described
	through RFC 3852 and RFC 2634 [SMIMEv3.1]. RFC 2311 also has		in RFC 3850, RFC 3851, RFC 3852, RFC 2634, RFC4853, and RFC 5035
	historical information about the development of S/MIME.		[SMIMEv3.1]. RFC 2311 also has historical information about the
			development of S/MIME.
	1.4. Changes From S/MIME v3 To S/MIME v3.1		1.4. Changes From S/MIME v3 To S/MIME v3.1
	Version 1 and Version 2 CRLs MUST be supported.		Version 1 and Version 2 CRLs MUST be supported.
	Multiple CA certificates with the same subject and public key, but		Multiple CA certificates with the same subject and public key, but
	with overlapping validity periods, MUST be supported.		with overlapping validity periods, MUST be supported.
	Version 2 attribute certificates SHOULD be supported, and version 1		Version 2 attribute certificates SHOULD be supported, and version 1
	attributes certificates MUST NOT be used.		attributes certificates MUST NOT be used.
	skipping to change at page 5, line 33 ¶		skipping to change at page 5, line 33 ¶
	Conventions Used in This Document: Moved to section 1.2. Added		Conventions Used in This Document: Moved to section 1.2. Added
	definitions for SHOULD+, SHOULD-, and MUST-.		definitions for SHOULD+, SHOULD-, and MUST-.
	Sec 1.2: Updated ASN.1 definition and reference.		Sec 1.2: Updated ASN.1 definition and reference.
	Sec 1.3: Added text about v3.1 RFCs.		Sec 1.3: Added text about v3.1 RFCs.
	Sec 3: Updated note to indicate emailAddress IA5String upper bound is		Sec 3: Updated note to indicate emailAddress IA5String upper bound is
	255 characters.		255 characters.
			Sec 4.2: Added text to indicate how S/MIME agents locate the correct
			user certificate.
	Sec 4.3: RSA with SHA-256 (PKCS #1 v1.5) added as MUST, DSA with SHA-		Sec 4.3: RSA with SHA-256 (PKCS #1 v1.5) added as MUST, DSA with SHA-
	256 added as SHOULD, RSA with SHA-1 changed to SHOULD-, DSA with SHA-		256 added as SHOULD+, RSA with SHA-1 changed to SHOULD-, DSA with
	1, and RSA with MD5 changed to SHOULD-, and RSA-PSS with SHA-256.		SHA-1, and RSA with MD5 changed to SHOULD-, and RSA-PSS with SHA-256
	Updated key sizes and changed pointer from [KEYM] to [KEYMALG].		added as SHOULD+. Updated key sizes and changed pointer from [KEYM]
			to [KEYMALG].
	Sec 4.4.1: Clarified which extension is used to constrain EEs from		Sec 4.4.1: Aligned with PKIX on use of basic constraints extension in
	using their keys to perform issuing authority operations.		CA certificates. Clarified which extension is used to constrain EEs
			from using their keys to perform issuing authority operations.
			Sec 6: Updated security considerations.
	Sec 7: Moved references from Appendix B to section 7. Updated the		Sec 7: Moved references from Appendix B to section 7. Updated the
	references.		references.
	Appendix A: Moved Appendix A to Appendix B. Added Appendix A to move		Appendix A: Moved Appendix A to Appendix B. Added Appendix A to move
	S/MIME v2 Certificate Handling to Historic Status.		S/MIME v2 Certificate Handling to Historic Status.
	2. CMS Options		2. CMS Options
	The CMS message format allows for a wide variety of options in		The CMS message format allows for a wide variety of options in
	skipping to change at page 6, line 24 ¶		skipping to change at page 6, line 33 ¶
	All agents MUST be capable of performing revocation checks using CRLs		All agents MUST be capable of performing revocation checks using CRLs
	as specified in [KEYM]. All agents MUST perform revocation status		as specified in [KEYM]. All agents MUST perform revocation status
	checking in accordance with [KEYM]. Receiving agents MUST recognize		checking in accordance with [KEYM]. Receiving agents MUST recognize
	CRLs in received S/MIME messages.		CRLs in received S/MIME messages.
	Agents SHOULD store CRLs received in messages for use in processing		Agents SHOULD store CRLs received in messages for use in processing
	later messages.		later messages.
	2.2. Certificate Choices		2.2. Certificate Choices
	Receiving agents MUST support v1 X.509 and v3 X.509 identity		Receiving agents MUST support v1 X.509 and v3 X.509 certificates as
	certificates as profiled in [KEYM]. End entity certificates MAY		profiled in [KEYM]. End entity certificates MAY include an Internet
	include an Internet mail address, as described in section 3.		mail address, as described in section 3.
	Receiving agents SHOULD support X.509 version 2 attribute		Receiving agents SHOULD support X.509 version 2 attribute
	certificates. See [ACAUTH] for details about the profile for		certificates. See [ACAUTH] for details about the profile for
	attribute certificates.		attribute certificates.
	2.2.1. Historical Note About CMS Certificates		2.2.1. Historical Note About CMS Certificates
	The CMS message format supports a choice of certificate formats for		The CMS message format supports a choice of certificate formats for
	public key content types: PKIX, PKCS #6 Extended Certificates [PKCS6]		public key content types: PKIX, PKCS #6 Extended Certificates [PKCS6]
	and PKIX Attribute Certificates.		and PKIX Attribute Certificates.
	skipping to change at page 7, line 35 ¶		skipping to change at page 7, line 40 ¶
	certificate distribution. Receiving S/MIME agents SHOULD be able to		certificate distribution. Receiving S/MIME agents SHOULD be able to
	handle messages without certificates using a database or directory		handle messages without certificates using a database or directory
	lookup scheme.		lookup scheme.
	A sending agent SHOULD include at least one chain of certificates up		A sending agent SHOULD include at least one chain of certificates up
	to, but not including, a Certificate Authority (CA) that it believes		to, but not including, a Certificate Authority (CA) that it believes
	that the recipient may trust as authoritative. A receiving agent		that the recipient may trust as authoritative. A receiving agent
	MUST be able to handle an arbitrarily large number of certificates		MUST be able to handle an arbitrarily large number of certificates
	and chains.		and chains.
	Agents MAY send CA certificates, that is, certificates which can be		Agents MAY send CA certificates, that is, cross-certificates, self-
	considered the "root" of other chains, and which MAY be self-signed.		issued certificates, and self-signed certificates. Note that
	Note that receiving agents SHOULD NOT simply trust any self-signed		receiving agents SHOULD NOT simply trust any self-signed certificates
	certificates as valid CAs, but SHOULD use some other mechanism to		as valid CAs, but SHOULD use some other mechanism to determine if
	determine if this is a CA that should be trusted. Also note that		this is a CA that should be trusted. Also note that when
	when certificates contain DSA public keys the parameters may be		certificates contain DSA public keys the parameters may be located in
	located in the root certificate. This would require that the		the root certificate. This would require that the recipient possess
	recipient possess both the end-entity certificate as well as the root		both the end-entity certificate as well as the root certificate to
	certificate to perform a signature verification, and is a valid		perform a signature verification, and is a valid example of a case
	example of a case where transmitting the root certificate may be		where transmitting the root certificate may be required.
	required.
	Receiving agents MUST support chaining based on the distinguished		Receiving agents MUST support chaining based on the distinguished
	name fields. Other methods of building certificate chains MAY be		name fields. Other methods of building certificate chains MAY be
	supported.		supported.
	Receiving agents SHOULD support the decoding of X.509 attribute		Receiving agents SHOULD support the decoding of X.509 attribute
	certificates included in CMS objects. All other issues regarding the		certificates included in CMS objects. All other issues regarding the
	generation and use of X.509 attribute certificates are outside of the		generation and use of X.509 attribute certificates are outside of the
	scope of this specification. One specification that addresses		scope of this specification. One specification that addresses
	attribute certificate use is defined in [SECLABEL].		attribute certificate use is defined in [SECLABEL].
	skipping to change at page 8, line 49 ¶		skipping to change at page 9, line 6 ¶
	are present in the certificate. A receiving agent SHOULD provide		are present in the certificate. A receiving agent SHOULD provide
	some explicit alternate processing of the message if this comparison		some explicit alternate processing of the message if this comparison
	fails, which may be to display a message that shows the recipient the		fails, which may be to display a message that shows the recipient the
	addresses in the certificate or other certificate details.		addresses in the certificate or other certificate details.
	A receiving agent SHOULD display a subject name or other certificate		A receiving agent SHOULD display a subject name or other certificate
	details when displaying an indication of successful or unsuccessful		details when displaying an indication of successful or unsuccessful
	signature verification.		signature verification.
	All subject and issuer names MUST be populated (i.e., not an empty		All subject and issuer names MUST be populated (i.e., not an empty
	SEQUENCE) in S/MIME-compliant X.509 identity certificates, except		SEQUENCE) in S/MIME-compliant X.509 certificates, except that the
	that the subject DN in a user's (i.e., end-entity) certificate MAY be		subject DN in a user's (i.e., end-entity) certificate MAY be an empty
	an empty SEQUENCE in which case the subjectAltName extension will		SEQUENCE in which case the subjectAltName extension will include the
	include the subject's identifier and MUST be marked as critical.		subject's identifier and MUST be marked as critical.
	4. Certificate Processing		4. Certificate Processing
	A receiving agent needs to provide some certificate retrieval		S/MIME agents need to provide some certificate retrieval mechanism in
	mechanism in order to gain access to certificates for recipients of		order to gain access to certificates for recipients of digital
	digital envelopes. There are many ways to implement certificate		envelopes. There are many ways to implement certificate retrieval
	retrieval mechanisms. X.500 directory service is an excellent		mechanisms. [X.500] directory service is an excellent example of a
	example of a certificate retrieval-only mechanism that is compatible		certificate retrieval-only mechanism that is compatible with classic
	with classic X.500 Distinguished Names. Another method under		X.500 Distinguished Names. Another method under consideration by the
	consideration by the IETF is to provide certificate retrieval		IETF is to provide certificate retrieval services as part of the
	services as part of the existing Domain Name System (DNS). Until		existing Domain Name System (DNS). Until such mechanisms are widely
	such mechanisms are widely used, their utility may be limited by the		used, their utility may be limited by the small number of the
	small number of the correspondent's certificates that can be		correspondent's certificates that can be retrieved. At a minimum, for
	retrieved. At a minimum, for initial S/MIME deployment, a user agent		initial S/MIME deployment, a user agent could automatically generate
	could automatically generate a message to an intended recipient		a message to an intended recipient requesting the recipient's
	requesting the recipient's certificate in a signed return message.		certificate in a signed return message.
	Receiving and sending agents SHOULD also provide a mechanism to allow		Receiving and sending agents SHOULD also provide a mechanism to allow
	a user to "store and protect" certificates for correspondents in such		a user to "store and protect" certificates for correspondents in such
	a way so as to guarantee their later retrieval. In many		a way so as to guarantee their later retrieval. In many
	environments, it may be desirable to link the certificate		environments, it may be desirable to link the certificate
	retrieval/storage mechanisms together in some sort of certificate		retrieval/storage mechanisms together in some sort of certificate
	database. In its simplest form, a certificate database would be		database. In its simplest form, a certificate database would be
	local to a particular user and would function in a similar way as an		local to a particular user and would function in a similar way as an
	"address book" that stores a user's frequent correspondents. In this		"address book" that stores a user's frequent correspondents. In this
	way, the certificate retrieval mechanism would be limited to the		way, the certificate retrieval mechanism would be limited to the
	skipping to change at page 11, line 7 ¶		skipping to change at page 11, line 11 ¶
	procedure in two ways: a) incoming messages, and b) certificate and		procedure in two ways: a) incoming messages, and b) certificate and
	CRL retrieval mechanisms. Certificates and CRLs in incoming messages		CRL retrieval mechanisms. Certificates and CRLs in incoming messages
	are not required to be in any particular order nor are they required		are not required to be in any particular order nor are they required
	to be in any way related to the sender or recipient of the message		to be in any way related to the sender or recipient of the message
	(although in most cases they will be related to the sender). Incoming		(although in most cases they will be related to the sender). Incoming
	certificates and CRLs SHOULD be cached for use in path validation and		certificates and CRLs SHOULD be cached for use in path validation and
	optionally stored for later use. This temporary certificate and CRL		optionally stored for later use. This temporary certificate and CRL
	cache SHOULD be used to augment any other certificate and CRL		cache SHOULD be used to augment any other certificate and CRL
	retrieval mechanisms for path validation on incoming signed messages.		retrieval mechanisms for path validation on incoming signed messages.
			When verifying a signature and the certificates are included in the
			message, if a signingCertificate or a signingCertificateV2 attribute
			is found in an S/MIME message, it SHALL be used to identify the
			signer's certificate. Otherwise, the certificate is identified in an
			S/MIME message, either using the issuerAndSerialNumber which
			identifies the signer's certificate by the issuer's distinguished
			name and the certificate serial number, or the subjectKeyIdentifier
			which identifies the signer's certificate by a key identifier.
			When decrypting an encrypted message, if a
			SMIMEEncryptionKeyPreference attribute is found in an encapsulating
			SignedData, it SHALL be used to identify the originator's certificate
			found in OriginatorInfo. Otherwise, a) for DH encrypted messages the
			certificate is identified by the KeyAgreeRecipientInfo originator
			field using either the issuer and serial number or subject public key
			identifier choice or the certificate is omitted and the originator's
			public key is included in originatorKey b) for RSA encrypted messages
			the originator's certificate is not required for decryption.
	4.3. Certificate and CRL Signing Algorithms and Key Sizes		4.3. Certificate and CRL Signing Algorithms and Key Sizes
	Certificates and Certificate Revocation Lists (CRLs) are signed by		Certificates and Certificate Revocation Lists (CRLs) are signed by
	the certificate issuer. Receiving agents:		the certificate issuer. Receiving agents:
	- MUST support RSA with SHA-256, as specified in [CMS-SHA2]		- MUST support RSA with SHA-256, as specified in [CMS-SHA2]
	- SHOULD+ support DSA with SHA-256, as specified in [CMS-SHA2]		- SHOULD+ support DSA with SHA-256, as specified in [CMS-SHA2]
	- SHOULD+ support RSA-PSS with SHA-256, as specified in [RSAPSS]		- SHOULD+ support RSA-PSS with SHA-256, as specified in [RSAPSS]
	- SHOULD- support RSA with SHA-1, as specified in [CMSALG]		- SHOULD- support RSA with SHA-1, as specified in [CMSALG]
	- SHOULD- support DSA with SHA-1, as specified in [CMSALG]		- SHOULD- support DSA with SHA-1, as specified in [CMSALG]
	- SHOULD- support RSA with MD5, as specified in [CMSALG]		- SHOULD- support RSA with MD5, as specified in [CMSALG]
	The following are the RSA key size requirements for S/MIME receiving		The following are the RSA key size requirements for S/MIME receiving
	agents during certificate and CRL signature verification:		agents during certificate and CRL signature verification:
	0 < key size < 512 : MAY (see Section 6 [SMIME-MSG])		0 < key size < 512 : MAY (see Section 6)
	512 <= key size <= 4096 : MUST (see Section 6 [SMIME-MSG])		512 <= key size <= 4096 : MUST (see Section 6)
	4096 < key size : MAY (see Section 6 [SMIME-MSG])		4096 < key size : MAY (see Section 6)
	The following are the RSA key size requirements for S/MIME receiving		The following are the DSA key size requirements for S/MIME receiving
	agents during certificate and CRL signature verification:		agents during certificate and CRL signature verification:
	512 <= key size <= 1024 : MAY (see Section 6 [SMIME-MSG])		512 <= key size <= 1024 : MAY (see Section 6)
	4.4. PKIX Certificate Extensions		4.4. PKIX Certificate Extensions
	PKIX describes an extensible framework in which the basic certificate		PKIX describes an extensible framework in which the basic certificate
	information can be extended and describes how such extensions can be		information can be extended and describes how such extensions can be
	used to control the process of issuing and validating certificates.		used to control the process of issuing and validating certificates.
	The PKIX Working Group has ongoing efforts to identify and create		The PKIX Working Group has ongoing efforts to identify and create
	extensions which have value in particular certification environments.		extensions which have value in particular certification environments.
	Further, there are active efforts underway to issue PKIX certificates		Further, there are active efforts underway to issue PKIX certificates
	for business purposes. This document identifies the minimum required		for business purposes. This document identifies the minimum required
	skipping to change at page 12, line 32 ¶		skipping to change at page 13, line 17 ¶
	The basic constraints extension serves to delimit the role and		The basic constraints extension serves to delimit the role and
	position that an issuing authority or end-entity certificate plays in		position that an issuing authority or end-entity certificate plays in
	a certification path.		a certification path.
	For example, certificates issued to CAs and subordinate CAs contain a		For example, certificates issued to CAs and subordinate CAs contain a
	basic constraint extension that identifies them as issuing authority		basic constraint extension that identifies them as issuing authority
	certificates. End-entity certificates contain the key usage		certificates. End-entity certificates contain the key usage
	extension which restrains EEs from using the key to performing		extension which restrains EEs from using the key to performing
	issuing authority operations (see Section 4.4.2).		issuing authority operations (see Section 4.4.2).
	Certificates SHOULD contain a basicConstraints extension in CA		As per [KEYM], Certificates MUST contain a basicConstraints extension
	certificates, and SHOULD NOT contain that extension in end entity		in CA certificates, and SHOULD NOT contain that extension in end
	certificates.		entity certificates.
	4.4.2. Key Usage Certificate Extension		4.4.2. Key Usage Certificate Extension
	The key usage extension serves to limit the technical purposes for		The key usage extension serves to limit the technical purposes for
	which a public key listed in a valid certificate may be used. Issuing		which a public key listed in a valid certificate may be used. Issuing
	authority certificates may contain a key usage extension that		authority certificates may contain a key usage extension that
	restricts the key to signing certificates, certificate revocation		restricts the key to signing certificates, certificate revocation
	lists and other data.		lists and other data.
	For example, a certification authority may create subordinate issuer		For example, a certification authority may create subordinate issuer
	skipping to change at page 15, line 29 ¶		skipping to change at page 16, line 14 ¶
	certificate, or cause an improper result when checking the Validity		certificate, or cause an improper result when checking the Validity
	field of a certificate.		field of a certificate.
	In addition to the Security Considerations identified in [KEYM],		In addition to the Security Considerations identified in [KEYM],
	caution should be taken when processing certificates which have not		caution should be taken when processing certificates which have not
	first been validated to a trust anchor. Certificates could be		first been validated to a trust anchor. Certificates could be
	manufactured by untrusted sources for the purpose of mounting denial		manufactured by untrusted sources for the purpose of mounting denial
	of service or other attacks. For example, keys selected to require		of service or other attacks. For example, keys selected to require
	excessive cryptographic processing, or extensive lists of CDP and/or		excessive cryptographic processing, or extensive lists of CDP and/or
	AIA addresses in the certificate, could be used to mount denial of		AIA addresses in the certificate, could be used to mount denial of
	service attacks. Similarly, originator-specified CDP and/or AIA		service attacks. Similarly, attacker-specified CRL Distribution
	addresses could be inserted into bogus certificates to allow the		Point (CRLDP) and/or Authority Information Access (AIA) addresses
	originator to detect receipt of the message even if signature		could be included in fake certificates to allow the originator to
	verification fails.		detect receipt of the message even if signature verification fails.
	In addition to the Security Considerations identified in [KEYM],		The 4096-bit RSA key size requirement for certificate and CRL
	caution should be taken when processing certificates which have not		verification is larger than the 2048-bit RSA key sizes for message
	first been validated to a trust anchor. Certificates could be		signature generation/verification or message encryption/decryption in
	manufactured by untrusted sources for the purpose of mounting denial		[SMIME-MSG] because many Root CAs included in certificate stores have
	of service or other attacks. For example, keys selected to require		already issued Root certificates with 4096-bit key. The standard
	excessive cryptographic processing, or extensive lists of CDP and/or		that defines comparable key sizes for DSA is not yet available. In
	AIA addresses in the certificate, could be used to mount denial of		particular, [FIPS186-3] only defines DSA key sizes up to 1024 bits.
	service attacks. Similarly, attacker-specified CRL distribution		A revision to support larger key sizes is being developed, and once
	point and/or authority information access addresses could be included		it is available, implementors ought to support DSA key sizes
	into fake certificates to allow the originator to detect receipt of		comparable to the RSA key sizes recommended in this specification.
	the message even if signature verification fails.
			Today, 512-bit RSA and DSA keys are considered by many experts to be
			cryptographically insecure.
	7. References		7. References
	7.1. Normative References		7.1. Normative References
	[ACAUTH] Farrell, S. and R. Housley, "An Internet Attribute		[ACAUTH] Farrell, S. and R. Housley, "An Internet Attribute
	Certificate Profile for Authorization", RFC 3281, April		Certificate Profile for Authorization", RFC 3281, April
	2002.		2002.
	[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC		[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
	3852, July 2004.		3852, July 2004.
	Housley, R., "Cryptographic Message Syntax (CMS)		Housley, R., "Cryptographic Message Syntax (CMS)
	Multiple Signer Clarification", RFC 4852, April 2007.		Multiple Signer Clarification", RFC 4852, April 2007.
	[CMSALG] Housley, R., "Cryptographic Message Syntax (CMS)		[CMSALG] Housley, R., "Cryptographic Message Syntax (CMS)
	Algorithms", RFC 3370, August 2002.		Algorithms", RFC 3370, August 2002.
	[CMS-SHA2] Turner. S., "Using SHA2 Algorithms with Cryptographic		[CMS-SHA2] Turner. S., "Using SHA2 Algorithms with Cryptographic
	Message Syntax", work in progress.		Message Syntax", draft-ietf-smime-sha2, work-in-
			progress.
			[FIPS186-3] National Institute of Standards and Technology (NIST),
			"Digital Signature Standard (DSS)", FIPS Publication
			186-3, March 2006.
	[KEYM] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.		[KEYM] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.
	Housley, R., and W. Polk, "Internet X.509 Public Key		Housley, R., and W. Polk, "Internet X.509 Public Key
	Infrastructure Certificate and Certificate Revocation		Infrastructure Certificate and Certificate Revocation
	List (CRL) Profile", RFC 5280, May 2008.		List (CRL) Profile", RFC 5280, May 2008.
	[KEYMALG] Bassham, L., Polk, W., and R. Housley, "Algorithms and		[KEYMALG] Bassham, L., Polk, W., and R. Housley, "Algorithms and
	Identifiers for the Internet X.509 Public Key		Identifiers for the Internet X.509 Public Key
	Infrastructure Certificate and Certificate Revocation		Infrastructure Certificate and Certificate Revocation
	List (CRL) Profile", RFC 3279, April 2002.		List (CRL) Profile", RFC 3279, April 2002.
	skipping to change at page 16, line 50 ¶		skipping to change at page 17, line 38 ¶
	November 2000.		November 2000.
	[IMF] Resnick, P., "Internet Message Format", work-in-		[IMF] Resnick, P., "Internet Message Format", work-in-
	progress.		progress.
	[RSAPSS] Schaad, J., "Use of RSASA-PSS Signature Algorithm in		[RSAPSS] Schaad, J., "Use of RSASA-PSS Signature Algorithm in
	Cryptographic Message Syntax (CMS)", RFC 4056, June		Cryptographic Message Syntax (CMS)", RFC 4056, June
	2005.		2005.
	[SMIME-MSG] Ramsdell, B., and S. Turner, "S/MIME Version 3.2		[SMIME-MSG] Ramsdell, B., and S. Turner, "S/MIME Version 3.2
	Message Specification", work in progress.		Message Specification", draft-ietf-smime-3851bis, work-
			in-progress.
	[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-		[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-
	1:2002. Information Technology - Abstract Syntax		1:2002. Information Technology - Abstract Syntax
	Notation One (ASN.1): Specification of basic notation.		Notation One (ASN.1): Specification of basic notation.
	7.2. Informative References		7.2. Informative References
	[PKCS6] RSA Laboratories, "PKCS #6: Extended-Certificate Syntax		[PKCS6] RSA Laboratories, "PKCS #6: Extended-Certificate Syntax
	Standard", November 1993.		Standard", November 1993.
	skipping to change at page 17, line 33 ¶		skipping to change at page 18, line 24 ¶
	"S/MIME Version 2 Certificate Handling", RFC 2312,		"S/MIME Version 2 Certificate Handling", RFC 2312,
	March 1998.		March 1998.
	Kaliski, B., "PKCS #1: RSA Encryption Version 1.5", RFC		Kaliski, B., "PKCS #1: RSA Encryption Version 1.5", RFC
	2313, March 1998.		2313, March 1998.
	Kaliski, B., "PKCS #10: Certificate Request Syntax		Kaliski, B., "PKCS #10: Certificate Request Syntax
	Version 1.5", RFC 2314, March 1998.		Version 1.5", RFC 2314, March 1998.
	Kaliski, B., "PKCS #7: Certificate Message Syntax		Kaliski, B., "PKCS #7: Certificate Message Syntax
	Version 1.5", RFC 2314, March 1998.		Version 1.5", RFC 2315, March 1998.
	[SMIMEv3] Housley, R., "Cryptographic Message Syntax", RFC 2630,		[SMIMEv3] Housley, R., "Cryptographic Message Syntax", RFC 2630,
	June 1999.		June 1999.
	Rescorla, E., "Diffie-Hellman Key Agreement Method",		Rescorla, E., "Diffie-Hellman Key Agreement Method",
	RFC 2631, June 1999.		RFC 2631, June 1999.
	Ramsdell, B., "S/MIME Version 3 Certificate Handling",		Ramsdell, B., "S/MIME Version 3 Certificate Handling",
	RFC 2632, June 1999.		RFC 2632, June 1999.
	Ramsdell, B., "S/MIME Version 3 Message Specification",		Ramsdell, B., "S/MIME Version 3 Message Specification",
	RFC 2633, June 1999.		RFC 2633, June 1999.
	Hoffman, P., "Enhanced Security Services for S/MIME",		Hoffman, P., "Enhanced Security Services for S/MIME",
	RFC 2634, June 1999.		RFC 2634, June 1999.
			Schaad, J., "ESS Update: Adding CertID Algorithm
			Agility", RFC 5035, August 2007.
	[SMIMEv3.1] Housley, R., "Cryptographic Message Syntax", RFC 3852,		[SMIMEv3.1] Housley, R., "Cryptographic Message Syntax", RFC 3852,
	July 2004.		July 2004.
			Housley, R., "Cryptographic Message Syntax (CMS)
			Multiple Signer Clarification", RFC 4853, April 2007.
	Ramsdell, B., "S/MIME Version 3.1 Certificate		Ramsdell, B., "S/MIME Version 3.1 Certificate
	Handling", RFC 3850, July 2004.		Handling", RFC 3850, July 2004.
	Ramsdell, B., "S/MIME Version 3.1 Message		Ramsdell, B., "S/MIME Version 3.1 Message
	Specification", RFC 3851, July 2004.		Specification", RFC 3851, July 2004.
	Hoffman, P., "Enhanced Security Services for S/MIME",		Hoffman, P., "Enhanced Security Services for S/MIME",
	RFC 2634, June 1999.		RFC 2634, June 1999.
			Schaad, J., "ESS Update: Adding CertID Algorithm
			Agility", RFC 5035, August 2007.
	[X.500] ITU-T Recommendation X.500 (1997) | ISO/IEC 9594-		[X.500] ITU-T Recommendation X.500 (1997) | ISO/IEC 9594-
	1:1997, Information technology - Open Systems		1:1997, Information technology - Open Systems
	Interconnection - The Directory: Overview of concepts,		Interconnection - The Directory: Overview of concepts,
	models and services.		models and services.
	[X.501] ITU-T Recommendation X.501 (1997) | ISO/IEC 9594-
	2:1997, Information technology - Open Systems
	Interconnection - The Directory: Models.
	[X.509] ITU-T Recommendation X.509 (1997) | ISO/IEC 9594-
	8:1997, Information technology - Open Systems
	Interconnection - The Directory: Authentication
	Framework.
	[X.520] ITU-T Recommendation X.520 (1997) | ISO/IEC 9594-
	6:1997, Information technology - Open Systems
	Interconnection - The Directory: Selected Attribute
	Types.
	Appendix A. Moving S/MIME v2 Certificate Handling to Historic Status		Appendix A. Moving S/MIME v2 Certificate Handling to Historic Status
	The S/MIME v3 [SMIMEv3], v3.1 [SMIMEv3.1], and v3.2 (this document)		The S/MIME v3 [SMIMEv3], v3.1 [SMIMEv3.1], and v3.2 (this document)
	Certificate Handling documents are backwards S/MIME v2 Message		are backwards compatible with the S/MIME v2 Certificate Handling
	Specification RFC 2312 [SMIMEv2], with the exception of the		Specification [SMIMEv2], with the exception of the algorithms
	algorithms (dropped RC2/40 requirement and added DSA and RSA-PSS		(dropped RC2/40 requirement and added DSA and RSA-PSS requirements).
	requirements). Therefore, it is recommended that RFC 2312 [SMIMEv2]		Therefore, it is recommended that RFC 2312 [SMIMEv2] be moved to
	be moved to Historic status.		Historic status.
	Appendix B. Acknowledgements		Appendix B. Acknowledgements
	Many thanks go out to the other authors of the S/MIME v2 RFC: Steve		Many thanks go out to the other authors of the S/MIME v2 RFC: Steve
	Dusse, Paul Hoffman and Jeff Weinstein. Without v2, there wouldn't		Dusse, Paul Hoffman and Jeff Weinstein. Without v2, there wouldn't
	be a v3, v3.1 or v3.2.		be a v3, v3.1 or v3.2.
	A number of the members of the S/MIME Working Group have also worked		A number of the members of the S/MIME Working Group have also worked
	very hard and contributed to this document. Any list of people is		very hard and contributed to this document. Any list of people is
	doomed to omission and for that I apologize. In alphabetical order,		doomed to omission and for that I apologize. In alphabetical order,
	the following people stand out in my mind due to the fact that they		the following people stand out in my mind due to the fact that they
	made direct contributions to this document.		made direct contributions to this document.
	Bill Flanigan, Trevor Freeman, Elliott Ginsburg, Alfred Hoenes, Paul		Bill Flanigan, Trevor Freeman, Elliott Ginsburg, Alfred Hoenes, Paul
	Hoffman, Russ Housley, David P. Kemp, Michael Myers, John Pawling,		Hoffman, Russ Housley, David P. Kemp, Michael Myers, John Pawling,
	Denis Pinkas, and Jim Schaad.		Denis Pinkas, and Jim Schaad.
	Author's Addresses		Author's Addresses
	Blake Ramsdell		Blake Ramsdell
	SendMail		Brute Squad Labs, Inc.
	Email: blake@sendmail.com		Email: blaker@gmail.com
	Sean Turner		Sean Turner
	IECA, Inc.		IECA, Inc.
	3057 Nutley Street, Suite 106		3057 Nutley Street, Suite 106
	Fairfax, VA 22031		Fairfax, VA 22031
	USA		USA
	Email: turners@ieca.com		Email: turners@ieca.com
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