One document matched: draft-ietf-smime-3850bis-01.txt
Differences from draft-ietf-smime-3850bis-00.txt
S/MIME WG Blake Ramsdell, SendMail
Internet Draft Sean Turner, IECA
Intended Status: Standard Track February 21, 2008
Obsoletes: 3850 (once approved)
Expires: August 21, 2008
Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2
Certificate Handling
draft-ietf-smime-3850bis-01.txt
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document specifies conventions for X.509 certificate usage by
Secure/Multipurpose Internet Mail Extensions (S/MIME) agents. S/MIME
provides a method to send and receive secure MIME messages, and
certificates are an integral part of S/MIME agent processing. S/MIME
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agents validate certificates as described in RFC 3280bis, the
Internet X.509 Public Key Infrastructure Certificate and CRL Profile.
S/MIME agents must meet the certificate processing requirements in
this document as well as those in RFC 3280bis. This document
obsoletes RFC 3850.
Conventions used in this document
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 [MUSTSHOULD].
We define some additional terms here:
SHOULD+ This term means the same as SHOULD. However, it is likely
that an algorithm marked as SHOULD+ will be promoted at some
future time to be a MUST.
SHOULD- This term means the same as SHOULD. However, an algorithm
marked as SHOULD- may be deprecated to a MAY in a future version
of this document.
MUST- This term means the same as MUST. However, we expect at some
point that this algorithm will no longer be a MUST in a future
document. Although its status will be determined at a later
time, it is reasonable to expect that if a future revision of a
document alters the status of a MUST- algorithm, it will remain
at least a SHOULD or a SHOULD-.
Discussion
This draft is being discussed on the 'ietf-smime' mailing list. To
subscribe, send a message to ietf-smime-request@imc.org with the
single word subscribe in the body of the message. There is a Web site
for the mailing list at <http://www.imc.org/ietf-smime/>.
Table of Contents
1. Introduction...................................................3
1.1. Definitions...............................................3
1.2. Compatibility with Prior Practice S/MIME..................4
1.3. Changes Since S/MIME V3.1 (RFC 3850)......................4
2. CMS Options....................................................5
2.1. Certificate Revocation Lists..............................5
2.2. Certificate Choices.......................................5
2.2.1. Historical Note About CMS Certificates...............5
2.3. CertificateSet............................................6
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3. Using Distinguished Names For Internet Mail....................7
4. Certificate Processing.........................................8
4.1. Certificate Revocation Lists..............................9
4.2. Certificate Path Validation...............................9
4.3. Certificate and CRL Signing Algorithms...................10
4.4. PKIX Certificate Extensions..............................10
4.4.1. Basic Constraints...................................11
4.4.2. Key Usage Certificate Extension.....................11
4.4.3. Subject Alternative Name............................12
4.4.4. Extended Key Usage Extension........................12
5. IANA Considerations...........................................12
6. Security Considerations.......................................13
1. Introduction
S/MIME (Secure/Multipurpose Internet Mail Extensions), described in
[SMIME-MSG], provides a method to send and receive secure MIME
messages. Before using a public key to provide security services,
the S/MIME agent MUST verify that the public key is valid. S/MIME
agents MUST use PKIX certificates to validate public keys as
described in the Internet X.509 Public Key Infrastructure (PKIX)
Certificate and CRL Profile [KEYM]. S/MIME agents MUST meet the
certificate processing requirements documented in this document in
addition to those stated in [KEYM].
This specification is compatible with the Cryptographic Message
Syntax [CMS] in that it uses the data types defined by CMS. It also
inherits all the varieties of architectures for certificate-based key
management supported by CMS.
1.1. Definitions
For the purposes of this document, the following definitions apply.
ASN.1: Abstract Syntax Notation One, as defined in ITU-T X.208
[X.208-88].
Attribute Certificate (AC): An X.509 AC is a separate structure from
a subject's public key X.509 Certificate. A subject may have
multiple X.509 ACs associated with each of its public key X.509
Certificates. Each X.509 AC binds one or more Attributes with one of
the subject's public key X.509 Certificates. The X.509 AC syntax is
defined in [ACAUTH].
Certificate: A type that binds an entity's name to a public key with
a digital signature. This type is defined in the Internet X.509
Public Key Infrastructure (PKIX) Certificate and CRL Profile [KEYM].
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This type also contains the distinguished name of the certificate
issuer (the signer), an issuer-specific serial number, the issuer's
signature algorithm identifier, a validity period, and extensions
also defined in that document.
Certificate Revocation List (CRL): A type that contains information
about certificates whose validity an issuer has prematurely revoked.
The information consists of an issuer name, the time of issue, the
next scheduled time of issue, a list of certificate serial numbers
and their associated revocation times, and extensions as defined in
[KEYM]. The CRL is signed by the issuer. The type intended by this
specification is the one defined in [KEYM].
Receiving agent: Software that interprets and processes S/MIME CMS
objects, MIME body parts that contain CMS objects, or both.
Sending agent: Software that creates S/MIME CMS objects, MIME body
parts that contain CMS objects, or both.
S/MIME agent: User software that is a receiving agent, a sending
agent, or both.
1.2. Compatibility with Prior Practice S/MIME
S/MIME version 3.2 agents should attempt to have the greatest
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 3 is described in RFC 2630 through RFC 2634 inclusive,
and S/MIME version 3.1 is described in RFC 3850 through 3851
inclusive and RFC 2634. RFC 2311 also has historical information
about the development of S/MIME.
1.3. Changes Since S/MIME V3.1 (RFC 3850)
Conventions Used in This Document: Added definitions for SHOULD+,
SHOULD-, and MUST-.
Sec 1.2: Added text about v3.1 RFCs.
Sec 3: Updated note to indicate emailAddress IA5String upper bound is
255 characters.
Sec 4.3: RSA with SHA-256 (PKCS #1 v1.5) added as MUST, RSA with SHA-
1 changed to MUST-, DSA with SHA-1, and RSA with MD5 changed to
SHOULD-, and RSA-PS with SHA-256. Updated key sizes.
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Sec A.1: Updated references to latest versions of PKIX profile and
S/MIME Message Specification.
Sec A.1: Changed reference from KEYMALG to KEYM.
2. CMS Options
The CMS message format allows for a wide variety of options in
content and algorithm support. This section puts forth a number of
support requirements and recommendations in order to achieve a base
level of interoperability among all S/MIME implementations. Most of
the CMS format for S/MIME messages is defined in [SMIME-MSG].
2.1. Certificate Revocation Lists
Receiving agents MUST support the Certificate Revocation List (CRL)
format defined in [KEYM]. If sending agents include CRLs in outgoing
messages, the CRL format defined in [KEYM] MUST be used. In all
cases, both v1 and v2 CRLs MUST be supported.
All agents MUST be capable of performing revocation checks using CRLs
as specified in [KEYM]. All agents MUST perform revocation status
checking in accordance with [KEYM]. Receiving agents MUST recognize
CRLs in received S/MIME messages.
Agents SHOULD store CRLs received in messages for use in processing
later messages.
2.2. Certificate Choices
Receiving agents MUST support v1 X.509 and v3 X.509 identity
certificates as profiled in [KEYM]. End entity certificates MAY
include an Internet mail address, as described in section 3.
Receiving agents SHOULD support X.509 version 2 attribute
certificates. See [ACAUTH] for details about the profile for
attribute certificates.
2.2.1. Historical Note About CMS Certificates
The CMS message format supports a choice of certificate formats for
public key content types: PKIX, PKCS #6 Extended Certificates [PKCS6]
and PKIX Attribute Certificates.
The PKCS #6 format is not in widespread use. In addition, PKIX
certificate extensions address much of the same functionality and
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flexibility as was intended in the PKCS #6. Thus, sending and
receiving agents MUST NOT use PKCS #6 extended certificates.
X.509 version 1 attribute certificates are also not widely
implemented, and have been superseded with version 2 attribute
certificates. Sending agents MUST NOT send version 1 attribute
certificates.
2.3. CertificateSet
Receiving agents MUST be able to handle an arbitrary number of
certificates of arbitrary relationship to the message sender and to
each other in arbitrary order. In many cases, the certificates
included in a signed message may represent a chain of certification
from the sender to a particular root. There may be, however,
situations where the certificates in a signed message may be
unrelated and included for convenience.
Sending agents SHOULD include any certificates for the user's public
key(s) and associated issuer certificates. This increases the
likelihood that the intended recipient can establish trust in the
originator's public key(s). This is especially important when
sending a message to recipients that may not have access to the
sender's public key through any other means or when sending a signed
message to a new recipient. The inclusion of certificates in
outgoing messages can be omitted if S/MIME objects are sent within a
group of correspondents that has established access to each other's
certificates by some other means such as a shared directory or manual
certificate distribution. Receiving S/MIME agents SHOULD be able to
handle messages without certificates using a database or directory
lookup scheme.
A sending agent SHOULD include at least one chain of certificates up
to, but not including, a Certificate Authority (CA) that it believes
that the recipient may trust as authoritative. A receiving agent
MUST be able to handle an arbitrarily large number of certificates
and chains.
Agents MAY send CA certificates, that is, certificates which can be
considered the "root" of other chains, and which MAY be self-signed.
Note that receiving agents SHOULD NOT simply trust any self-signed
certificates as valid CAs, but SHOULD use some other mechanism to
determine if this is a CA that should be trusted. Also note that
when certificates contain DSA public keys the parameters may be
located in the root certificate. This would require that the
recipient possess both the end-entity certificate as well as the root
certificate to perform a signature verification, and is a valid
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example of a case where transmitting the root certificate may be
required.
Receiving agents MUST support chaining based on the distinguished
name fields. Other methods of building certificate chains MAY be
supported.
Receiving agents SHOULD support the decoding of X.509 attribute
certificates included in CMS objects. All other issues regarding the
generation and use of X.509 attribute certificates are outside of the
scope of this specification. One specification that addresses
attribute certificate use is defined in [SECLABEL].
3. Using Distinguished Names For Internet Mail
End-entity certificates MAY contain an Internet mail address as
described in [RFC-2822]. The address must be an "addr-spec" as
defined in Section 3.4.1 of that specification. The email address
SHOULD be in the subjectAltName extension, and SHOULD NOT be in the
subject distinguished name.
Receiving agents MUST recognize and accept certificates that contain
no email address. Agents are allowed to provide an alternative
mechanism for associating an email address with a certificate that
does not contain an email address, such as through the use of the
agent's address book, if available. Receiving agents MUST recognize
email addresses in the subjectAltName field. Receiving agents MUST
recognize email addresses in the Distinguished Name field in the PKCS
#9 [PKCS9] emailAddress attribute:
pkcs-9-at-emailAddress OBJECT IDENTIFIER ::=
{iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) 1 }
Note that this attribute MUST be encoded as IA5String and has an
upper bounds of 255 characters.
Sending agents SHOULD make the address in the From or Sender header
in a mail message match an Internet mail address in the signer's
certificate. Receiving agents MUST check that the address in the
From or Sender header of a mail message matches an Internet mail
address, if present, in the signer's certificate, if mail addresses
are present in the certificate. A receiving agent SHOULD provide
some explicit alternate processing of the message if this comparison
fails, which may be to display a message that shows the recipient the
addresses in the certificate or other certificate details.
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A receiving agent SHOULD display a subject name or other certificate
details when displaying an indication of successful or unsuccessful
signature verification.
All subject and issuer names MUST be populated (i.e., not an empty
SEQUENCE) in S/MIME-compliant X.509 identity certificates, except
that the subject DN in a user's (i.e., end-entity) certificate MAY be
an empty SEQUENCE in which case the subjectAltName extension will
include the subject's identifier and MUST be marked as critical.
4. Certificate Processing
A receiving agent needs to provide some certificate retrieval
mechanism in order to gain access to certificates for recipients of
digital envelopes. There are many ways to implement certificate
retrieval mechanisms. X.500 directory service is an excellent
example of a certificate retrieval-only mechanism that is compatible
with classic X.500 Distinguished Names. Another method under
consideration by the IETF is to provide certificate retrieval
services as part of the existing Domain Name System (DNS). Until
such mechanisms are widely used, their utility may be limited by the
small number of correspondent's certificates that can be retrieved.
At a minimum, for initial S/MIME deployment, a user agent could
automatically generate a message to an intended recipient requesting
that recipient's certificate in a signed return message.
Receiving and sending agents SHOULD also provide a mechanism to allow
a user to "store and protect" certificates for correspondents in such
a way so as to guarantee their later retrieval. In many
environments, it may be desirable to link the certificate
retrieval/storage mechanisms together in some sort of certificate
database. In its simplest form, a certificate database would be
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
way, the certificate retrieval mechanism would be limited to the
certificates that a user has stored (presumably from incoming
messages). A comprehensive certificate retrieval/storage solution
may combine two or more mechanisms to allow the greatest flexibility
and utility to the user. For instance, a secure Internet mail agent
may resort to checking a centralized certificate retrieval mechanism
for a certificate if it can not be found in a user's local
certificate storage/retrieval database.
Receiving and sending agents SHOULD provide a mechanism for the
import and export of certificates, using a CMS certs-only message.
This allows for import and export of full certificate chains as
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opposed to just a single certificate. This is described in [SMIME-
MSG].
Agents MUST handle multiple valid Certification Authority (CA)
certificates containing the same subject name and the same public
keys but with overlapping validity intervals.
4.1. Certificate Revocation Lists
In general, it is always better to get the latest CRL information
from a CA than to get information stored away from incoming messages.
A receiving agent SHOULD have access to some certificate revocation
list (CRL) retrieval mechanism in order to gain access to certificate
revocation information when validating certification paths. A
receiving or sending agent SHOULD also provide a mechanism to allow a
user to store incoming certificate revocation information for
correspondents in such a way so as to guarantee its later retrieval.
Receiving and sending agents SHOULD retrieve and utilize CRL
information every time a certificate is verified as part of a
certification path validation even if the certificate was already
verified in the past. However, in many instances (such as off-line
verification) access to the latest CRL information may be difficult
or impossible. The use of CRL information, therefore, may be
dictated by the value of the information that is protected. The
value of the CRL information in a particular context is beyond the
scope of this specification but may be governed by the policies
associated with particular certification paths.
All agents MUST be capable of performing revocation checks using CRLs
as specified in [KEYM]. All agents MUST perform revocation status
checking in accordance with [KEYM]. Receiving agents MUST recognize
CRLs in received S/MIME messages.
4.2. Certificate Path Validation
In creating a user agent for secure messaging, certificate, CRL, and
certification path validation SHOULD be highly automated while still
acting in the best interests of the user. Certificate, CRL, and path
validation MUST be performed as per [KEYM] when validating a
correspondent's public key. This is necessary before using a public
key to provide security services such as: verifying a signature;
encrypting a content-encryption key (ex: RSA); or forming a pairwise
symmetric key (ex: Diffie-Hellman) to be used to encrypt or decrypt a
content-encryption key.
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Certificates and CRLs are made available to the path validation
procedure in two ways: a) incoming messages, and b) certificate and
CRL retrieval mechanisms. Certificates and CRLs in incoming messages
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
(although in most cases they will be related to the sender). Incoming
certificates and CRLs SHOULD be cached for use in path validation and
optionally stored for later use. This temporary certificate and CRL
cache SHOULD be used to augment any other certificate and CRL
retrieval mechanisms for path validation on incoming signed messages.
4.3. Certificate and CRL Signing Algorithms
Certificates and Certificate Revocation Lists (CRLs) are signed by
the certificate issuer. Receiving agents:
- MUST support RSA with SHA-256, as specified in [CMS-SHA2]
- MUST- support RSA with SHA-1, as specified in [CMSALG]
- SHOULD+ support RSA-PSS with SHA-256, as specified in [RSAPSS]
- SHOULD- support DSA with SHA-1, as specified in [CMSALG].
- SHOULD- support RSA with MD5, as specified in [CMSALG].
Key sizes from 1024 bits to 2048 bits MUST be supported.
4.4. PKIX Certificate Extensions
PKIX describes an extensible framework in which the basic certificate
information can be extended and how such extensions can be used to
control the process of issuing and validating certificates. The PKIX
Working Group has ongoing efforts to identify and create extensions
which have value in particular certification environments. Further,
there are active efforts underway to issue PKIX certificates for
business purposes. This document identifies the minimum required set
of certificate extensions which have the greatest value in the S/MIME
environment. The syntax and semantics of all the identified
extensions are defined in [KEYM].
Sending and receiving agents MUST correctly handle the basic
constraints, key usage, authority key identifier, subject key
identifier, and subject alternative names certificate extensions when
they appear in end-entity and CA certificates. Some mechanism SHOULD
exist to gracefully handle other certificate extensions when they
appear in end-entity or CA certificates.
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Certificates issued for the S/MIME environment SHOULD NOT contain any
critical extensions (extensions that have the critical field set to
TRUE) other than those listed here. These extensions SHOULD be
marked as non-critical unless the proper handling of the extension is
deemed critical to the correct interpretation of the associated
certificate. Other extensions may be included, but those extensions
SHOULD NOT be marked as critical.
Interpretation and syntax for all extensions MUST follow [KEYM],
unless otherwise specified here.
4.4.1. Basic Constraints
The basic constraints extension serves to delimit the role and
position that an issuing authority or end-entity certificate plays in
a certification path.
For example, certificates issued to CAs and subordinate CAs contain a
basic constraint extension that identifies them as issuing authority
certificates. End-entity certificates contain an extension that
constrains the certificate from being an issuing authority
certificate.
Certificates SHOULD contain a basicConstraints extension in CA
certificates, and SHOULD NOT contain that extension in end entity
certificates.
4.4.2. Key Usage Certificate Extension
The key usage extension serves to limit the technical purposes for
which a public key listed in a valid certificate may be used. Issuing
authority certificates may contain a key usage extension that
restricts the key to signing certificates, certificate revocation
lists and other data.
For example, a certification authority may create subordinate issuer
certificates which contain a key usage extension which specifies that
the corresponding public key can be used to sign end user
certificates and sign CRLs.
If a key usage extension is included in a PKIX certificate, then it
MUST be marked as critical.
S/MIME receiving agents MUST NOT accept the signature of a message if
it was verified using a certificate which contains the key usage
extension without either the digitalSignature or nonRepudiation bit
set. Sometimes S/MIME is used as a secure message transport for
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applications beyond interpersonal messaging. In such cases, the
S/MIME-enabled application can specify additional requirements
concerning the digitalSignature or nonRepudiation bits within this
extension.
If the key usage extension is not specified, receiving clients MUST
presume that the digitalSignature and nonRepudiation bits are set.
4.4.3. Subject Alternative Name
The subject alternative name extension is used in S/MIME as the
preferred means to convey the RFC-2822 email address(es) that
correspond(s) to the entity for this certificate. Any RFC-2822 email
addresses present MUST be encoded using the rfc822Name CHOICE of the
GeneralName type. Since the SubjectAltName type is a SEQUENCE OF
GeneralName, multiple RFC-2822 email addresses MAY be present.
4.4.4. Extended Key Usage Extension
The extended key usage extension also serves to limit the technical
purposes for which a public key listed in a valid certificate may be
used. The set of technical purposes for the certificate therefore
are the intersection of the uses indicated in the key usage and
extended key usage extensions.
For example, if the certificate contains a key usage extension
indicating digital signature and an extended key usage extension
which includes the email protection OID, then the certificate may be
used for signing but not encrypting S/MIME messages. If the
certificate contains a key usage extension indicating digital
signature, but no extended key usage extension then the certificate
may also be used to sign but not encrypt S/MIME messages.
If the extended key usage extension is present in the certificate
then interpersonal message S/MIME receiving agents MUST check that it
contains either the emailProtection or the anyExtendedKeyUsage OID as
defined in [KEYM]. S/MIME uses other than interpersonal messaging
MAY require the explicit presence of the extended key usage extension
or other OIDs to be present in the extension or both.
5. IANA Considerations
None: All identifiers are already registered. Please remove this
section prior to publication as an RFC.
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6. Security Considerations
All of the security issues faced by any cryptographic application
must be faced by a S/MIME agent. Among these issues are protecting
the user's private key, preventing various attacks, and helping the
user avoid mistakes such as inadvertently encrypting a message for
the wrong recipient. The entire list of security considerations is
beyond the scope of this document, but some significant concerns are
listed here.
When processing certificates, there are many situations where the
processing might fail. Because the processing may be done by a user
agent, a security gateway, or other program, there is no single way
to handle such failures. Just because the methods to handle the
failures has not been listed, however, the reader should not assume
that they are not important. The opposite is true: if a certificate
is not provably valid and associated with the message, the processing
software should take immediate and noticeable steps to inform the end
user about it.
Some of the many places where signature and certificate checking
might fail include:
- no Internet mail addresses in a certificate matches the sender of
a message, if the certificate contains at least one mail address
- no certificate chain leads to a trusted CA
- no ability to check the CRL for a certificate
- an invalid CRL was received
- the CRL being checked is expired
- the certificate is expired
- the certificate has been revoked
There are certainly other instances where a certificate may be
invalid, and it is the responsibility of the processing software to
check them all thoroughly, and to decide what to do if the check
fails.
At the Selected Areas in Cryptography '95 conference in May 1995,
Rogier and Chauvaud presented an attack on MD2 that can nearly find
collisions [RC95]. Collisions occur when one can find two different
messages that generate the same message digest. A checksum operation
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in MD2 is the only remaining obstacle to the success of the attack.
For this reason, the use of MD2 for new applications is discouraged.
It is still reasonable to use MD2 to verify existing signatures, as
the ability to find collisions in MD2 does not enable an attacker to
find new messages having a previously computed hash value.
It is possible for there to be multiple unexpired CRLs for a CA. If
an agent is consulting CRLs for certificate validation, it SHOULD
make sure that the most recently issued CRL for that CA is consulted,
since an S/MIME message sender could deliberately include an older
unexpired CRL in an S/MIME message. This older CRL might not include
recent revoked certificates, which might lead an agent to accept a
certificate that has been revoked in a subsequent CRL.
When determining the time for a certificate validity check, agents
have to be careful to use a reliable time. Unless it is from a
trusted agent, this time MUST NOT be the SigningTime attribute found
in an S/MIME message. For most sending agents, the SigningTime
attribute could be deliberately set to direct the receiving agent to
check a CRL that could have out-of-date revocation status for a
certificate, or cause an improper result when checking the Validity
field of a certificate.
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Appendix A. References
A.1. Normative References
[ACAUTH] Farrell, S. and R. Housley, "An Internet Attribute
Certificate Profile for Authorization", RFC 3281, April
2002.
[CMS] Housely, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004.
Housley, R., "Cryptographic Message Syntax (CMS)
Multiple Signer Clarification", RFC 4852, April 2007.
[CMSALG] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
[CMS-SHA2] Turner. S., "Using SHA2 Algorithms with Cryptographic
Message Syntax", work in progress.
[KEYM] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", work in progress.
[MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[PKCS9] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
Classes and Attribute Types Version 2.0", RFC 2985,
November 2000.
[RFC-2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[RSAPSS] Schaad, J., "Use of RSASA-PSS Signature Algorithm in
Cryptographic Message Syntax (CMS)", RFC 4056, June
2005.
[SMIME-MSG] Ramsdell, B., and S. Turner, "S/MIME Version 3.2
Message Specification", work in progress.
[X.208-88] ITU-T. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988.
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A.2. Informative References
[PKCS6] RSA Laboratories, "PKCS #6: Extended-Certificate Syntax
Standard", November 1993.
[RC95] Rogier, N. and Chauvaud, P., "The compression function
of MD2 is not collision free," Presented at Selected
Areas in Cryptography '95, May 1995.
[SECLABEL] Nicolls, W., "Implementing Company Classification
Policy with the S/MIME Security Label", RFC 3114, May
2002.
[X.500] ITU-T Recommendation X.500 (1997) | ISO/IEC 9594-
1:1997, Information technology - Open Systems
Interconnection - The Directory: Overview of concepts,
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.
Ramsdell & Turner Expires August 21, 2008 [Page 16]
Internet-Draft S/MIME 3.2 Certificate Handling February 2008
Appendix B. Acknowledgements
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
be a v3.
A number of the members of the S/MIME Working Group have also worked
very hard and contributed to v3 of this document. Any list of people
is 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 made direct contributions to this document.
Bill Flanigan, Trevor Freeman, Elliott Ginsburg, Paul Hoffman, Russ
Housley, David P. Kemp, Michael Myers, John Pawling, Denis Pinkas,
Jim Schaad.
Author's Addresses
Blake Ramsdell
SendMail
Email: ramsdell@sendmail.com
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
Email: turners@ieca.com
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Internet-Draft S/MIME 3.2 Certificate Handling February 2008
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