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Network Working Group                                           S. DusseRequest for Comments: 2312                             RSA Data SecurityCategory: Informational                                       P. Hoffman                                                Internet Mail Consortium                                                             B. Ramsdell                                                               Worldtalk                                                            J. Weinstein                                                                Netscape                                                              March 1998S/MIME Version 2 Certificate HandlingStatus 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].Dusse, et. al.               Informational                      [Page 1]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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/MIMEAppendix 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.Dusse, et. al.               Informational                      [Page 2]

RFC 2312        S/MIME Version 2 Certificate Handling         March 19982. 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 insection 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.Dusse, et. al.               Informational                      [Page 3]

RFC 2312        S/MIME Version 2 Certificate Handling         March 19982.3 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.Dusse, et. al.               Informational                      [Page 4]

RFC 2312        S/MIME Version 2 Certificate Handling         March 19983. Distinguished Names in Certificates3.1 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 inRFC 822 [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 haveDusse, et. al.               Informational                      [Page 5]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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   inSection 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   EmailAddressDusse, et. al.               Informational                      [Page 6]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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].Dusse, et. al.               Informational                      [Page 7]

RFC 2312        S/MIME Version 2 Certificate Handling         March 19984.1 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.Dusse, et. al.               Informational                      [Page 8]

RFC 2312        S/MIME Version 2 Certificate Handling         March 19984.3 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.Dusse, et. al.               Informational                      [Page 9]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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 Requests5.1 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.Dusse, et. al.               Informational                     [Page 10]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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.Dusse, et. al.               Informational                     [Page 11]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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 #10Dusse, et. al.               Informational                     [Page 12]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998   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 inSection 4.Dusse, et. al.               Informational                     [Page 13]

RFC 2312        S/MIME Version 2 Certificate Handling         March 19986. 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.Dusse, et. al.               Informational                     [Page 14]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998A. Object Identifiers and Syntax   Sections A.1 through A.4 are adopted from [SMIME-MSG].A.5 Name AttributesemailAddress 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 AttributespostalAddress 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}Dusse, et. al.               Informational                     [Page 15]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998unstructuredAddress OBJECT IDENTIFIER ::=     {iso(1) member-body(2) US(840) rsadsi(113549) pkcs(1) pkcs-9(9) 8}A.7 X.509 V3 Certificate ExtensionsbasicConstraints 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)}Dusse, et. al.               Informational                     [Page 16]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998B. 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,RFC 2119, March 1997.   [PKCS-1] Kaliski, B., "PKCS #1: RSA Encryption Version 1.5",RFC2313, March 1998.   [PKCS-7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax Version   1.5",RFC 2315, March 1998.   [PKCS-10] Kaliski, B., "PKCS #10: Certification Request Syntax   Version 1.5",RFC 2314, March 1998.   [RFC-822] Crocker, D., "Standard For The Format Of ARPA Internet Text   Messages", STD 11,RFC 822, August 1982.   [SMIME-MSG] Dusse, S., Hoffman, P., Ramsdell, R., Lundblade, L., and   L. Repka, "S/MIME Version 2 Message Specification",RFC 2311, 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.Dusse, et. al.               Informational                     [Page 17]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998C. 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.Dusse, et. al.               Informational                     [Page 18]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998E. 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.comDusse, et. al.               Informational                     [Page 19]

RFC 2312        S/MIME Version 2 Certificate Handling         March 1998F.  Full Copyright Statement   Copyright (C) The Internet Society (1998).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   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   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Dusse, et. al.               Informational                     [Page 20]