RFC2312 - S/MIME Version 2 Certificate Handling

Network Working Group S. Dusse
Request for Comments: 2312 RSA Data Security
Category: Informational P. Hoffman
Internet Mail Consortium
B. Ramsdell
Worldtalk
J. Weinstein
Netscape
March 1998
S/MIME Version 2 Certificate Handling
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
1. Overview
S/MIME (Secure/Multipurpose Internet Mail Extensions), described in
[SMIME-MSG], provides a method to send and receive secure MIME
messages. In order to validate the keys of a message sent to it, an
S/MIME agent needs to certify that the key is valid. This memo
describes the mechanisms S/MIME uses to create and validate keys
using certificates.
This specification is compatible with PKCS #7 in that it uses the
data types defined by PKCS #7. It also inherits all the varieties of
architectures for certificate-based key management supported by PKCS
#7. Note that the method S/MIME messages make certificate requests
is defined in [SMIME-MSG].
In order to handle S/MIME certificates, an agent has to follow
specifications in this memo, as well as some of the specifications
listed in the following documents:
- "PKCS #1: RSA Encryption", [PKCS-1].
- "PKCS #7: Cryptographic Message Syntax", [PKCS-7]
- "PKCS #10: Certification Request Syntax", [PKCS-10].
Please note: The information in this document is historical material
being published for the public record. It is not an IETF standard.
The use of the Word "standard" in this document indicates a standard
for adopters of S/MIME version 2, not an IETF standard.
1.1 Definitions
For the purposes of this memo, the following definitions apply.
ASN.1: Abstract Syntax Notation One, as defined in CCITT X.208.
BER: Basic Encoding Rules for ASN.1, as defined in CCITT X.209.
Certificate: A type that binds an entity"s distinguished name to a
public key with a digital signature. This type is defined in CCITT
X.509 [X.509]. This type also contains the distinguished name of the
certificate issuer (the signer), an issuer-specific serial number,
the issuer"s signature algorithm identifier, and a validity period.
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, and a list of certificate serial
numbers and their associated revocation times. The CRL is signed by
the issuer. The type intended by this specification is the one
defined in [KEYM].
DER: Distinguished Encoding Rules for ASN.1, as defined in CCITT
X.509.
1.2 Compatibility with Prior Practice of S/MIME
Appendix C contains important information about how S/MIME agents
following this specification should act in order to have the greatest
interoperability with earlier implementations of S/MIME.
1.3 Terminology
Throughout this memo, the terms MUST, MUST NOT, SHOULD, and SHOULD
NOT are used in capital letters. This conforms to the definitions in
[MUSTSHOULD]. [MUSTSHOULD] defines the use of these key words to
help make the intent of standards track documents as clear as
possible. The same key words are used in this document to help
implementors achieve interoperability.
2. PKCS #7 Options
The PKCS #7 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 PKCS #7 format for S/MIME messages is defined in [SMIME-MSG].
2.1 CertificateRevocationLists
Receiving agents MUST support for 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.
All agents MUST validate CRLs and check certificates against CRLs, if
available, in accordance with [KEYM]. All agents SHOULD check the
nextUpdate field in the CRL against the current time. If the current
time is later than the nextUpdate time, the action that the agent
takes is a local decision. For instance, it could warn a human user,
it could retrieve a new CRL if able, and so on.
Receiving agents MUST recognize CRLs in received S/MIME messages.
Clients MUST use revocation information included as a CRL in an
S/MIME message when verifying the signature and certificate path
validity in that message. Clients SHOULD store CRLs received in
messages for use in processing later messages.
Clients MUST handle multiple valid Certificate Authority (CA)
certificates containing the same subject name and the same public
keys but with overlapping validity intervals.
2.2 ExtendedCertificateOrCertificate
Receiving agents MUST support X.509 v1 and X.509 v3 certificates. See
[KEYM] for details about the profile for certificate formats. End
entity certificates MUST include an Internet mail address, as
described in section 3.1.
2.2.1 Historical Note About PKCS #7 Certificates
The PKCS #7 message format supports a choice of certificate two
formats for public key content types: X.509 and PKCS #6 Extended
Certificates. The PKCS #6 format is not in widespread use. In
addition, proposed revisions of X.509 certificates address mUCh of
the same functionality and flexibility as was intended in the PKCS
#6. Thus, sending and receiving agents MUST NOT use PKCS #6 extended
certificates.
2.3 ExtendedCertificateAndCertificates
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
SHOULD be able to handle an arbitrarily large number of certificates
and chains.
Clients MAY send CA certificates, that is, certificates that are
self-signed and can be considered the "root" of other chains. 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.
Receiving agents MUST support chaining based on the distinguished
name fields. Other methods of building certificate chains may be
supported but are not currently recommended.
3. Distinguished Names in Certificates
3.1 Using Distinguished Names for Internet Mail
The format of an X.509 certificate includes fields for the subject
name and issuer name. The subject name identifies the owner of a
particular public key/private key pair while the issuer name is meant
to identify the entity that "certified" the subject (that is, who
signed the subject"s certificate). The subject name and issuer name
are defined by X.509 as Distinguished Names.
Distinguished Names are defined by a CCITT standard X.501 [X.501]. A
Distinguished Name is broken into one or more Relative Distinguished
Names. Each Relative Distinguished Name is comprised of one or more
Attribute-Value Assertions. Each Attribute-Value Assertion consists
of a Attribute Identifier and its corresponding value information,
such as CountryName=US. Distinguished Names were intended to identify
entities in the X.500 directory tree [X.500]. Each Relative
Distinguished Name can be thought of as a node in the tree which is
described by some collection of Attribute-Value Assertions. The
entire Distinguished Name is some collection of nodes in the tree
that traverse a path from the root of the tree to some end node which
represents a particular entity.
The goal of the directory was to provide an infrastructure to
uniquely name every communications entity everywhere. However,
adoption of a global X.500 directory infrastructure has been slower
than eXPected. Consequently, there is no requirement for X.500
directory service provision in the S/MIME environment, although such
provision would almost undouBTedly be of great value in facilitating
key management for S/MIME.
The use of Distinguished Names in accordance with the X.500 directory
is not very widespread. By contrast, Internet mail addresses, as
described in RFC822 [RFC-822], are used almost exclusively in the
Internet environment to identify originators and recipients of
messages. However, Internet mail addresses bear no resemblance to
X.500 Distinguished Names (except, perhaps, that they are both
hierarchical in nature). Some method is needed to map Internet mail
addresses to entities that hold public keys. Some people have
suggested that the X.509 certificate format should be abandoned in
favor of other binding mechanisms. Instead, S/MIME keeps the X.509
certificate and Distinguished Name mechanisms while tailoring the
content of the naming information to suit the Internet mail
environment.
End-entity certificates MUST contain an Internet mail address as
described in [RFC-822]. The address must be an "addr-spec" as defined
in Section 6.1 of that specification.
Receiving agents MUST recognize email addresses in the subjectAltName
field. Receiving agents MUST recognize email addresses in the
Distinguished Name field.
Sending agents SHOULD make the address in the From 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 header of a
mail message matches an Internet mail address in the signer"s
certificate. A receiving agent MUST provide some explicit alternate
processing of the message if this comparison fails, which may be to
reject the message.
3.2 Required Name Attributes
Receiving agents MUST support parsing of zero, one, or more instances
of each of the following set of name attributes within the
Distinguished Names in certificates.
Sending agents MUST include the Internet mail address during
Distinguished Name creation. Guidelines for the inclusion, omission,
and ordering of the remaining name attributes during the creation of
a distinguished name will most likely be dictated by the policies
associated with the certification service which will certify the
corresponding name and public key.
CountryName
StateOrProvinceName
Locality
CommonName
Title
Organization
OrganizationalUnit
StreetAddress
PostalCode
PhoneNumber
EmailAddress
All attributes other than EmailAddress are described in X.520
[X.520]. EmailAddress is an IA5String that can have multiple
attribute values.
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. The PKIX Working Group is
investigating other mechanisms. 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 a "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 PKCS #7 certs-only
message. This allows for import and export of full certificate chains
as opposed to just a single certificate. This is described in
[SMIME-MSG].
4.1 Certificate Revocation Lists
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 certificate
chains. 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. However, it is always better to get the latest information
from the CA than to get information stored away from incoming
messages.
Receiving and sending agents SHOULD retrieve and utilize CRL
information every time a certificate is verified as part of a
certificate chain 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
memo but may be governed by the policies associated with particular
certificate hierarchies.
4.2 Certificate Chain Validation
In creating a user agent for secure messaging, certificate, CRL, and
certificate chain validation SHOULD be highly automated while still
acting in the best interests of the user. Certificate, CRL, and chain
validation MUST be performed when validating a correspondent"s public
key. This is necessary when a) verifying a signature from a
correspondent and, b) creating a digital envelope with the
correspondent as the intended recipient.
Certificates and CRLs are made available to the chain 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 chain 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 chain validation on incoming signed
messages.
4.3 Certificate and CRL Signing Algorithms
Certificates and Certificate-Revocation Lists (CRLs) are signed by
the certificate issuer. A receiving agent MUST be capable of
verifying the signatures on certificates andCRLs made with
md5WithRSAEncryption and sha-1WithRSAEncryption signature algorithms
with key sizes from 512 bits to 2048 bits described in [SMIME-MSG]. A
receiving agent SHOULD be capable of verifying the signatures on
certificates and CRLs made with the md2WithRSAEncryption signature
algorithm with key sizes from 512 bits to 2048 bits.
4.4 X.509 Version 3 Certificate Extensions
The X.509 v3 standard 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. As such, there is still a fair amount of profiling work
to be done before there is widespread agreement on which v3
extensions will be used. Further, there are active efforts underway
to issue X.509 v3 certificates for business purposes. This memo
identifies the minumum required set of certificate extensions which
have the greatest value in the S/MIME environment. The
basicConstraints, and keyUsage extensions are defined in [X.509].
Sending and receiving agents MUST correctly handle the v3 Basic
Constraints Certificate Extension, the Key Usage Certificate
Extension, authorityKeyID, subjectKeyID, and the subjectAltNames when
they appear in end-user certificates. Some mechanism SHOULD exist to
handle the defined v3 certificate extensions when they appear in
intermediate or CA certificates.
Certificates issued for the S/MIME environment SHOULD NOT contain any
critical extensions 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.
4.4.1 Basic Constraints Certificate Extension
The basic constraints extension serves to delimit the role and
position of an issuing authority or end-user certificate plays in a
chain of certificates.
For example, certificates issued to CAs and subordinate CAs contain a
basic constraint extension that identifies them as issuing authority
certificates. End-user subscriber certificates contain an extension
that constrains the certificate from being an issuing authority
certificate.
Certificates SHOULD contain a basicContstraints extension.
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 keyUsage extension which specifies that
the corresponding public key can be used to sign end user certs and
sign CRLs.
5. Generating Keys and Certification Requests
5.1 Binding Names and Keys
An S/MIME agent or some related administrative utility or function
MUST be capable of generating a certification request given a user"s
public key and associated name information. In most cases, the user"s
public key/private key pair will be generated simultaneously.
However, there are cases where the keying information may be
generated by an external process (such as when a key pair is
generated on a cryptographic token or by a "key recovery" service).
There SHOULD NOT be multiple valid (that is, non-expired and non-
revoked) certificates for the same key pair bound to different
Distinguished Names. Otherwise, a security flaw exists where an
attacker can substitute one valid certificate for another in such a
way that can not be detected by a message recipient. If a users
wishes to change their name (or create an alternate name), the user
agent SHOULD generate a new key pair. If the user wishes to reuse an
existing key pair with a new or alternate name, the user SHOULD first
have any valid certificates for the existing public key revoked.
In general, it is possible for a user to request certification for
the same name and different public key from the same or different
certification authorities. This is acceptable both for end-entity
and issuer certificates and can be useful in supporting a change of
issuer keys in a smooth fashion.
CAs that re-use their own name with distinct keys MUST include the
AuthorityKeyIdentifier extension in certificates that they issue, and
MUST have the SubjectKeyIdentifier extension in their own
certificate. CAs SHOULD use these extensions uniformly.
Clients SHOULD handle multiple valid CA certificates that certify
different public keys but contain the same subject name (in this
case, that CA"s name).
When selecting an appropriate issuer"s certificate to use to verify a
given certificate, clients SHOULD process the AuthorityKeyIdentifier
and SubjectKeyIdentifier extensions.
5.2 Using PKCS #10 for Certification Requests
PKCS #10 is a flexible and extensible message format for representing
the results of cryptographic operations on some data. The choice of
naming information is largely dictated by the policies and procedures
associated with the intended certification service.
In addition to key and naming information, the PKCS #10 format
supports the inclusion of optional attributes, signed by the entity
requesting certification. This allows for information to be conveyed
in a certification request which may be useful to the request
process, but not necessarily part of the Distinguished Name being
certified.
Receiving agents MUST support the identification of an RSA key with
the rsa defined in X.509 and the rsaEncryption OID. Certification
authorities MUST support sha-1WithRSAEncryption and
md5WithRSAEncryption and SHOULD support MD2WithRSAEncryption for
verification of signatures on certificate requests as described in
[SMIME-MSG].
For the creation and submission of certification-requests, RSA keys
SHOULD be identified with the rsaEncryption OID and signed with the
sha-1WithRSAEncryption signature algorithm. Certification-requests
MUST NOT be signed with the md2WithRSAEncryption signature algorithm.
Certification requests MUST include a valid Internet mail address,
either as part of the certificate (as described in 3.2) or as part of
the PKCS #10 attribute list. Certification authorities MUST check
that the address in the "From:" header matches either of these
addresses. CAs SHOULD allow the CA operator to configure processing
of messages whose addresses do not match.
Certification authorities SHOULD support parsing of zero or one
instance of each of the following set of certification-request
attributes on incoming messages. Attributes that a particular
implementation does not support may generate a warning message to the
requestor, or may be silently ignored. Inclusion of the following
attributes during the creation and submission of a certification-
request will most likely be dictated by the policies associated with
the certification service which will certify the corresponding name
and public key.
postalAddress
challengePassword
unstructuredAddress
postalAddress is described in [X.520].
5.2.1 Challenge Password
The challenge-password attribute type specifies a password by which
an entity may request certificate revocation. The interpretation of
the password is intended to be specified by the issuer of the
certificate; no particular interpretation is required. The
challenge-password attribute type is intended for PKCS #10
certification requests.
Challenge-password attribute values have ASN.1 type ChallengePassword:
ChallengePassword ::= CHOICE {
PrintableString, T61String }
A challenge-password attribute must have a single attribute value.
It is expected that if UCS becomes an ASN.1 type
(e.g., UNIVERSAL STRING),
ChallengePassword will become a CHOICE type:
ChallengePassword ::= CHOICE {
PrintableString, T61String, UNIVERSAL STRING }
5.2.2 Unstructured Address
The unstructured-address attribute type specifies the address or
addresses of the subject of a certificate as an unstructured ASCII or
T.61 string. The interpretation of the addresses is intended to be
specified by the issuer of the certificate; no particular
interpretation is required. A likely interpretation is as an
alternative to the X.520 postalAddress attribute type. The
unstructured-address attribute type is intended for PKCS #10
certification requests.
Unstructured-address attribute values have
ASN.1 type UnstructuredAddress:
UnstructuredAddress ::= CHOICE {
PrintableString, T61String }
An unstructured-address attribute can have multiple attribute values.
Note: T.61"s newline character (hexadecimal code 0d) is recommended
as a line separator in multi-line addresses.
It is expected that if UCS becomes an ASN.1 type (e.g., UNIVERSAL
STRING), UnstructuredAddress will become a CHOICE type:
UnstructuredAddress ::= CHOICE {
PrintableString, T61String, UNIVERSAL STRING }
5.3 Fulfilling a Certification Request
Certification authorities SHOULD use the sha-1WithRSAEncryption
signature algorithms when signing certificates.
5.4 Using PKCS #7 for Fulfilled Certificate Response
[PKCS-7] supports a degenerate case of the SignedData content type
where there are no signers on the content (and hence, the content
value is "irrelevant"). This degenerate case is used to convey
certificate and CRL information. Certification authorities MUST use
this format for returning certificate information resulting from the
successful fulfillment of a certification request. At a minimum, the
fulfilled certificate response MUST include the actual subject
certificate (corresponding to the information in the certification
request). The response SHOULD include other certificates which link
the issuer to higher level certification authorities and
corresponding certificate-revocation lists. Unrelated certificates
and revocation information is also acceptable.
Receiving agents MUST parse this degenerate PKCS #7 message type and
handle the certificates and CRLs according to the requirements and
recommendations in Section 4.
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 noticable 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 match the sender of a
message
- 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.
A. Object Identifiers and Syntax
Sections A.1 through A.4 are adopted from [SMIME-MSG].
A.5 Name Attributes
emailAddress OBJECT IDENTIFIER ::=
{iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1) pkcs-9(9) 1}
CountryName OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 6}
StateOrProvinceName OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 8}
locality OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 7}
CommonName OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 3}
Title OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 12}
Organization OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 10}
OrganizationalUnit OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 11}
StreetAddress OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 9}
Postal Code OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 17}
Phone Number OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 20}
A.6 Certification Request Attributes
postalAddress OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) attributeType(4) 16}
challengePassword OBJECT IDENTIFIER ::=
{iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1) pkcs-9(9) 7}
unstructuredAddress OBJECT IDENTIFIER ::=
{iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1) pkcs-9(9) 8}
A.7 X.509 V3 Certificate Extensions
basicConstraints OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) 29 19 }
The ASN.1 definition of basicConstraints certificate extension is:
basicConstraints basicConstraints EXTENSION ::= {
SYNTAX BasicConstraintsSyntax
IDENTIFIED BY { id-ce 19 } }
BasicConstraintsSyntax ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER (0..MAX) OPTIONAL }
keyUsage OBJECT IDENTIFIER ::=
{joint-iso-ccitt(2) ds(5) 29 15 }
The ASN.1 definition of keyUsage certificate extension is:
keyUsage EXTENSION ::= {
SYNTAX KeyUsage
IDENTIFIED BY { id-ce 15 }}
KeyUsage ::= BIT STRING {
digitalSignature (0),
nonRepudiation (1),
keyEncipherment (2),
dataEncipherment (3),
keyAgreement (4),
keyCertSign (5),
cRLSign (6)}
B. References
[KEYM] PKIX Part 1. At the time of this writing, PKIX is a Work in
Progress, but it is expected that there will be standards-track RFCs
at some point in the future.
[MUSTSHOULD] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 1l4, RFC2119, March 1997.
[PKCS-1] Kaliski, B., "PKCS #1: RSA Encryption Version 1.5", RFC
2313, March 1998.
[PKCS-7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax Version
1.5", RFC2315, March 1998.
[PKCS-10] Kaliski, B., "PKCS #10: Certification Request Syntax
Version 1.5", RFC2314, March 1998.
[RFC-822] Crocker, D., "Standard For The Format Of ARPA Internet Text
Messages", STD 11, RFC822, August 1982.
[SMIME-MSG] Dusse, S., Hoffman, P., Ramsdell, R., Lundblade, L., and
L. Repka, "S/MIME Version 2 Message Specification", RFC2311, March
1998.
[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.
C. Compatibility with Prior Practice in S/MIME
S/MIME was originally developed by RSA Data Security, Inc. Many
developers implemented S/MIME agents before this document was
published. All S/MIME receiving agents SHOULD make every attempt to
interoperate with these earlier implementations of S/MIME.
D. Acknowledgements
Significant contributions to the content of this memo were made by
many people, including David Solo, Anil Gangolli, Jeff Thompson, and
Lisa Repka.
E. Authors" Addresses
Steve Dusse
RSA Data Security, Inc.
100 Marine Parkway, #500
Redwood City, CA 94065 USA
Phone: (415) 595-8782
EMail: spock@rsa.com
Paul Hoffman
Internet Mail Consortium
127 Segre Place
Santa Cruz, CA 95060
Phone: (408) 426-9827
EMail: phoffman@imc.org
Blake Ramsdell
Worldtalk
13122 NE 20th St., Suite C
Bellevue, WA 98005
Phone: (425) 882-8861
EMail: blaker@deming.com
Jeff Weinstein
Netscape Communications Corporation
501 East Middlefield Road
Mountain View, CA 94043
Phone: (415) 254-1900
EMail: jsw@netscape.com
F. Full Copyright Statement
Copyright (C) The Internet Society (1998). All Rights Reserved.
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or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
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included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
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English.
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