draft-ietf-smime-certdist-01.txt   draft-ietf-smime-certdist-02.txt 
Internet Draft Jim Schaad Internet Draft Jim Schaad
draft-ietf-smime-certdist-01.txt Microsoft draft-ietf-smime-certdist-02.txt Microsoft
July 6, 1998 October 12, 1998
Expires in six months Expires in six months
Certificate Distribution Specification Certificate Distribution Specification
Status of this memo Status of this memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
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ftp.isi.edu (US West Coast). ftp.isi.edu (US West Coast).
Abstract Abstract
Current methods of publishing certificates in directory services are Current methods of publishing certificates in directory services are
restricted to just certificates. This document provides a method of restricted to just certificates. This document provides a method of
publishing certificates with secondary support information such as the publishing certificates with secondary support information such as the
SMimeCapabilities attribute (containing bulk algorithm support) in a SMimeCapabilities attribute (containing bulk algorithm support) in a
way that is both authenticated and bound to a given certificate. way that is both authenticated and bound to a given certificate.
This draft is being discussed on the "ietf-smime" mailing list. To This draft is being discussed on the 'ietf-smime' mailing list. To
join the list, send a message to <ietf-smime-request@imc.org> with the join the list, send a message to <ietf-smime-request@imc.org> with the
single word "subscribe" in the body of the message. Also, there is a single word 'subscribe' in the body of the message. Also, there is a
Web site for the mailing list at <http://www.imc.org/ietf-smime>. Web site for the mailing list at <http://www.imc.org/ietf-smime>.
1. Introduction 1. Introduction
This document discusses a new method of publishing certificates in a This document discusses a new method of publishing certificates in a
directory to provide authenticated attributes as part of the directory to provide authenticated attributes as part of the
certificate publishing process. This allows for the addition of certificate publishing process. This allows for the addition of
information such as the SMimeCapabilities attribute from [SMIME] which information such as the SMimeCapabilities attribute from [SMIME] which
contains information about the bulk encryption algorithms supported by contains information about the bulk encryption algorithms supported by
the End-Entity's cryptography module. the End-Entity's cryptography module.
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encryption certificates to the other party. This attribute is a encryption certificates to the other party. This attribute is a
sequence so that more than one encryption certificate can be sequence so that more than one encryption certificate can be
identified in a single SignerInfo object. Each certificate is then identified in a single SignerInfo object. Each certificate is then
given a set of capabilities so senders can identify the correct given a set of capabilities so senders can identify the correct
certificate to use for specific capabilities. certificate to use for specific capabilities.
The structure and OID for the SMimeEncryptionCerts attribute are: The structure and OID for the SMimeEncryptionCerts attribute are:
id-aa-smimeEncryptionCerts OBJECT IDENTIFIER ::= { iso(1) id-aa-smimeEncryptionCerts OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) <TBD> } rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-aa(2) 13 }
SMimeEncryptionCert ::= SEQUENCE { SMimeEncryptionCert ::= SEQUENCE {
hash Hash, hash Hash,
capabilities SMIMECapabilities capabilities SMIMECapabilities
} }
SMimeEncryptionCerts ::= SEQUENCE OF SmimeEncryptionCert SMimeEncryptionCerts ::= SEQUENCE OF SMimeEncryptionCert
Hash ::= OCTET STRING - SHA1 hash of the certificate Hash ::= OCTET STRING - SHA1 hash of the certificate
When a certificate appears in an SMimeEncryptionCerts attribute, the When a certificate appears in an SMimeEncryptionCerts attribute, the
certificate MUST be included SignedData object. The order of certificate MUST be included SignedData object. The order of
certificates in the SMimeEncryptionCerts attribute is the preferred certificates in the SMimeEncryptionCerts attribute is the preferred
order of use by the sender. It is expected that the preferred order of use by the sender. It is expected that the preferred
certificate in the SMIMEEncrpytionKeyPreference would be the first certificate in the SMIMEEncrpytionKeyPreference would be the first
certificate in the SMimeEncryptionCerts attribute. certificate in the SMimeEncryptionCerts attribute.
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4.1 Signed Content 4.1 Signed Content
The SMimeCertificatePublish object is explicitly designed to carry no The SMimeCertificatePublish object is explicitly designed to carry no
body content. All information is carried in the signed attribute body content. All information is carried in the signed attribute
section of the SignerInfo. section of the SignerInfo.
The following object identifier is used to distinguish the content of The following object identifier is used to distinguish the content of
a SMimeCertificatePublish: a SMimeCertificatePublish:
id-ct-publishCert OBJECT IDENTIFIER ::= { iso(1) member-body(2) id-ct-publishCert OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-ct(1) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-ct(1) 3 }
<TBD>)
When creating a SMimeCertificatePublish object, the eContent of the When creating a SMimeCertificatePublish object, the eContent of the
Signed-Data object is omitted and the eContentType OID is set to id-ct- Signed-Data object is omitted and the eContentType OID is set to
publishCert. Note this is different from an empty content, which id-ct-publishCert. Note this is different from an empty content,
would be represented as an octet string containing zero bytes. The which would be represented as an octet string containing zero bytes.
hash of the body (used in the id-message-digest attribute) is set to The hash of the body (used in the id-message-digest attribute) is set
the initialization value of the hash function. (This is expected to to the initialization value of the hash function. (This is expected
provide the same result as if you had hashed a body containing exactly to provide the same result as if you had hashed a body containing
0 bytes.) exactly 0 bytes.)
4.2 Signed Attributes 4.2 Signed Attributes
The signed attributes section MUST be present in the SignerInfo The signed attributes section MUST be present in the SignerInfo
object, and the following signed attributes MUST be present: The object, and the following signed attributes MUST be present: The
signing-time attribute (from [CMS]), the SMimeCapabilities and signing-time attribute (from [CMS]), the SMimeCapabilities and
SMIMEEncryptionKeyPreference (from [SMIME]). SMIMEEncryptionKeyPreference (from [SMIME]).
4.3 CertificateSet 4.3 CertificateSet
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certificate found to the address matching the directory look-up. The certificate found to the address matching the directory look-up. The
validation SHOULD match the address used to look up the certificate validation SHOULD match the address used to look up the certificate
with one of the names found in the certificate. Thus if an RFC822 with one of the names found in the certificate. Thus if an RFC822
name was used to do the directory look-up, the RFC822 name would be in name was used to do the directory look-up, the RFC822 name would be in
the SubjectAltName extension on the certificate. the SubjectAltName extension on the certificate.
The steps for extracting the encryption certificate from a The steps for extracting the encryption certificate from a
SMimeCertificatePublish object are as follows: SMimeCertificatePublish object are as follows:
1. Verify that the SMimeCertificatePublish object contains a valid 1. Verify that the SMimeCertificatePublish object contains a valid
signature and the certificate used to sign the message can be validated. signature and the certificate used to sign the message can be
validated.
a) Certificate validates -- goto 2.
b) Certificate fails validation -- stop.
2. Does the certificate used to sign the SMimeCertificatePublish 2. Does the certificate used to sign the SMimeCertificatePublish
object "match" the intended recipient of the encryption object. If so, object "match" the intended recipient of the encryption object.
proceed to step 6 else step 3. a) "Match" found -- goto step 6.
b) No "Match" found -- stop.
3. Does the certificate referenced in the SMIMEEncryptionKeyPreference 3. Does the certificate referenced in the SMIMEEncryptionKeyPreference
attribute "match" the intended recipient of the encryption object? If attribute "match" the intended recipient of the encryption object?
so, proceed to step 4, else stop. a) "Match" found -- goto step 4.
b) No "Match" found -- stop.
4. Validate the reference encryption certificate. 4. Validate the reference encryption certificate.
a) Validation succeedes -- goto step 5
b) Validation fails -- stop.
5. Compare the signing certificate to the set of certificates used to 5. Compare the signing certificate to the set of certificates used to
verify the encryption certificate. Is the signing certificate in the verify the encryption certificate. Is the signing certificate in
set of verification certificates? If yes then the encryption the set of verification certificates? If yes then the encryption
certificate has been located. If no, no encryption certificate was certificate has been located. If no, no encryption certificate was
found. found.
6. Locate the encryption certificate using the 6. Locate the encryption certificate using the
SMIMEEncryptionKeyPreference attribute in the signed attributes of the SMIMEEncryptionKeyPreference attribute in the signed attributes of
SMimeCertificatePublish object. the SMimeCertificatePublish object.
In all cases, once an encryption certificate has been obtained, the In all cases, once an encryption certificate has been obtained, the
standard methods of validating signatures on the certificate and standard methods of validating signatures on the certificate and
checking for revocation MUST be followed. checking for revocation MUST be followed.
4.5 LDAP Schema 4.5 LDAP Schema
After a SignedData object has been produced, it needs to be published After a SignedData object has been produced, it needs to be published
into one or more directories. This section describes the LDAP schema into one or more directories. This section describes the LDAP schema
used to support this. used to support this.
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smimeUserCapabilities in the published object. smimeUserCapabilities in the published object.
4.6 MIME Encoding 4.6 MIME Encoding
The application/pkcs7-mime-publish type is used to carry The application/pkcs7-mime-publish type is used to carry
SMimeCertificatePublish objects as mime objects. The optional "name" SMimeCertificatePublish objects as mime objects. The optional "name"
parameter SHOULD be emitted as part of the Content-Type field. The parameter SHOULD be emitted as part of the Content-Type field. The
file extension for the file name SHOULD be ". p7p". file extension for the file name SHOULD be ". p7p".
A. ASN Module A. ASN Module
To be supplied
CertPublish DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
Cryptographic Message Syntax (CMS)
ContentInfo
FROM CryptographicMessageSyntax { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) CMS(1) };
SMIMECapability ::= SEQUENCE {
capabilityID OBJECT IDENTIFIER,
parameters ANY DEFINED BY capabilityID OPTIONAL }
SMIMECapabilities ::= SEQUENCE OF SMIMECapability
id-aa-smimeEncryptionCerts OBJECT IDENTIFIER ::= { iso(1)
member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16)
id-aa(2) 13 }
SMimeEncryptionCert ::= SEQUENCE {
hash Hash,
capabilities SMIMECapabilities
}
SMimeEncrpytionCerts ::= SEQUENCE OF SMimeEncryptionCert
Hash ::= OCTET STRING -- SHA1 hash of a certificate
SMimeCertificatePublish ::= ContentInfo
id-ct-publishCert OBJECT IDENTIFIER ::= {iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) id-ct(1) 3 }
END
B. Backwards Compatibility B. Backwards Compatibility
The SMimeCertificatePublish object is based on work previously done at The SMimeCertificatePublish object is based on work previously done at
both Microsoft and Netscape. both Microsoft and Netscape.
Both of these companies have implemented a version of Both of these companies have implemented a version of
userSMimeCertificate in their mail LDAP directory structures. userSMimeCertificate in their mail LDAP directory structures.
Microsoft has also put the property into its MAPI based directory Microsoft has also put the property into its MAPI based directory
schema. schema.
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File extension (s): p7p File extension (s): p7p
Macintosh File Type Code (s): - Macintosh File Type Code (s): -
Person and email address to contact for further information: Person and email address to contact for further information:
Jim Schaad, jimsch@microsoft.com Jim Schaad, jimsch@microsoft.com
Intended usage: COMMON Intended usage: COMMON
D. Open Issues D. Open Issues
- Currently SMimeCertificatePublish objects contain no content. One - There are no current open issues.
could make a case that some content, such as a vCard should be allowed.
I don't see a big win for this as we are talking about publishing in
directories and the additional information could be carried in the
directory itself.
- I would like to allow RAs to publish SMimeCertificatePublish
objects into a directory as well. I don't however see a way (short of
adding an extension to a certificate) which allows one to distinguish
between the case of an RA signing and publishing the
SMimeCertificatePublish object and an arbitrary agent doing so.
E. Changes E. Changes
Add SMimeEncryptionCerts attribute to identify multiple encryption As stated at the August IETF Working group meeting, I now consider the
certificates and their capabilities. issue on content for an SMimeCertificatePublish object to be closed.
Allow multiple SignerInfos to be in a single SignedData object when There has been no communications about this being a desired goal or
publishing certificates. suggesting what should be included here.
Clarify that encryption certificates must still be validated after one
is found. All attempts to allow for RAs to do publishing of
SMimeCertificatePublish objects on behalf of the end-user are being
terminated. The reason for this is two-fold.
1) There appears to be no good way of identifying which RA
certificates would be allowed to do the publishing without the
introduction of a new certificate extension specifically for that
purpose. This is something that I just cannot think of as good at
this point in time.
2) Allowing CAs to either directly or indirectly (through an RA
certificate) do the publishing seems must to liberal. If this was
to continue then a good set of restrictions would need to be
developed as part of the change.
References References
CMS "Cryptographic Message Syntax", Internet Draft ietf-draft- CMS "Cryptographic Message Syntax", Internet Draft ietf-draft-
smime-cms smime-cms
MUSTSHOULD "Key words for use in RFCs to Indicate Requirement Levels", MUSTSHOULD "Key words for use in RFCs to Indicate Requirement Levels",
RFC 2119 RFC 2119
LDAPV3 "Lightweight Directory Access Protocol (v3): Attribute Syntax LDAPV3 "Lightweight Directory Access Protocol (v3): Attribute Syntax
Definitions", RFC 2252 Definitions", RFC 2252
SMIME "S/MIME Version 3 Message Specification", Internet Draft ietf- SMIME "S/MIME Version 3 Message Specification", Internet Draft ietf-
draft-smime-msg draft-smime-msg
 End of changes. 

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