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rfc:rfc1848

Network Working Group S. Crocker Request For Comments: 1848 CyberCash, Inc. Category: Standards Track N. Freed

                                          Innosoft International, Inc.
                                                             J. Galvin
                                                             S. Murphy
                                           Trusted Information Systems
                                                          October 1995
                   MIME Object Security Services

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Abstract

 This document defines MIME Object Security Services (MOSS), a
 protocol that uses the multipart/signed and multipart/encrypted
 framework [7] to apply digital signature and encryption services to
 MIME objects.  The services are offered through the use of end-to-end
 cryptography between an originator and a recipient at the application
 layer.  Asymmetric (public key) cryptography is used in support of
 the digital signature service and encryption key management.
 Symmetric (secret key) cryptography is used in support of the
 encryption service.  The procedures are intended to be compatible
 with a wide range of public key management approaches, including both
 ad hoc and certificate-based schemes.  Mechanisms are provided to
 support many public key management approaches.

Table of Contents

 1.  Introduction .............................................    3
 2.  Applying MIME Object Security Services ...................    4
 2.1  Digital Signature Service ...............................    4
 2.1.1  Canonicalization ......................................    5
 2.1.2  Digital Signature Control Information .................    7
 2.1.2.1  Version: ............................................    8
 2.1.2.2  Originator-ID: ......................................    8
 2.1.2.3  MIC-Info: ...........................................    8
 2.1.3  application/moss-signature Content Type Definition ....    9
 2.1.4  Use of multipart/signed Content Type ..................   10
 2.2  Encryption Service ......................................   11

Crocker, et al Standards Track [Page 1] RFC 1848 MIME Object Security Services October 1995

 2.2.1  Encryption Control Information ........................   12
 2.2.1.1  DEK-Info: ...........................................   13
 2.2.1.2  Recipient-ID: .......................................   14
 2.2.1.3  Key-Info: ...........................................   14
 2.2.2  application/moss-keys Content Type Definition .........   15
 2.2.3  Use of multipart/encrypted Content Type ...............   16
 3.  Removing MIME Object Security Services ...................   17
 3.1  Digital Signature Service ...............................   18
 3.1.1  Preparation ...........................................   18
 3.1.2  Verification ..........................................   19
 3.1.3  Results ...............................................   19
 3.2  Encryption Service ......................................   20
 3.2.1  Preparation ...........................................   20
 3.2.2  Decryption ............................................   20
 3.2.3  Results ...............................................   21
 4.  Identifying Originators, Recipients, and Their Keys ......   21
 4.1  Name Forms ..............................................   23
 4.1.1  Email Addresses .......................................   23
 4.1.2  Arbitrary Strings .....................................   23
 4.1.3  Distinguished Names ...................................   23
 4.2  Identifiers .............................................   24
 4.2.1  Email Address .........................................   25
 4.2.2  Arbitrary String ......................................   25
 4.2.3  Distinguished Name ....................................   26
 4.2.4  Public Key ............................................   26
 4.2.5  Issuer Name and Serial Number .........................   27
 5.  Key Management Content Types .............................   27
 5.1  application/mosskey-request Content Type Definition .....   28
 5.2  application/mosskey-data Content Type Definition ........   29
 6.  Examples .................................................   31
 6.1  Original Message Prepared for Protection ................   31
 6.2  Sign Text of Original Message ...........................   32
 6.3  Sign Headers and Text of Original Message ...............   32
 6.4  Encrypt Text of a Message ...............................   33
 6.5  Encrypt the Signed Text of a Message ....................   35
 6.6  Protecting Audio Content ................................   37
 6.6.1  Sign Audio Content ....................................   37
 6.6.2  Encrypt Audio Content .................................   37
 7.  Observations .............................................   38
 8.  Comparison of MOSS and PEM Protocols .....................   39
 9.  Security Considerations ..................................   41
 10.  Acknowledgements ........................................   41
 11.  References ..............................................   41
 12.  Authors' Addresses ......................................   43
   Appendix A: Collected Grammar ..............................   44
   Appendix B: Imported Grammar ...............................   47

Crocker, et al Standards Track [Page 2] RFC 1848 MIME Object Security Services October 1995

1. Introduction

 MIME [2], an acronym for "Multipurpose Internet Mail Extensions",
 defines the format of the contents of Internet mail messages and
 provides for multi-part textual and non-textual message bodies.  An
 Internet electronic mail message consists of two parts: the headers
 and the body.  The headers form a collection of field/value pairs
 structured according to STD 11, RFC 822 [1], whilst the body, if
 structured, is defined according to MIME.  MIME does not provide for
 the application of security services.
 PEM [3-6], an acronym for "Privacy Enhanced Mail", defines message
 encryption and message authentication procedures for text-based
 electronic mail messages using a certificate-based key management
 mechanism.  The specifications include several features that are
 easily and more naturally supported by MIME, for example, the
 transfer encoding operation, the Content-Domain header, and the
 support services specified by its Part IV [6].  The specification is
 limited by specifying the application of security services to text
 messages only.
 MOSS is based in large part on the PEM protocol as defined by RFC
 1421.  Many of PEMs features and most of its protocol specification
 are included here.  A comparison of MOSS and PEM may be found in
 Section 8.
 In order to make use of the MOSS services, a user (where user is not
 limited to being a human, e.g., it could be a process or a role) is
 required to have at least one public/private key pair.  The public
 key must be made available to other users with whom secure
 communication is desired.  The private key must not be disclosed to
 any other user.
 An originator's private key is used to digitally sign MIME objects; a
 recipient would use the originator's public key to verify the digital
 signature.  A recipient's public key is used to encrypt the data
 encrypting key that is used to encrypt the MIME object; a recipient
 would use the corresponding private key to decrypt the data
 encrypting key so that the MIME object can be decrypted.
 As long as the private keys are protected from disclosure, i.e., the
 private keys are accessible only to the user to whom they have been
 assigned, the recipient of a digitally signed message will know from
 whom the message was sent and the originator of an encrypted message
 will know that only the intended recipient is able to read it.  For
 assurance, the ownership of the public keys used in verifying digital
 signatures and encrypting messages should be verified.  A stored
 public key should be protected from modification.

Crocker, et al Standards Track [Page 3] RFC 1848 MIME Object Security Services October 1995

 The framework defined in [7] provides an embodiment of a MIME object
 and its digital signature or encryption keys.  When used by MOSS the
 framework provides digital signature and encryption services to
 single and multi-part textual and non-textual MIME objects.

2. Applying MIME Object Security Services

 The application of the MOSS digital signature service requires the
 following components.
 (1)  The data to be signed.
 (2)  The private key of the originator.
 The data to be signed is prepared according to the description below.
 The digital signature is created by generating a hash of the data and
 encrypting the hash value with the private key of the originator.
 The digital signature, some additional ancillary information
 described below, and the data are then embodied in a multipart/signed
 body part.  Finally, the multipart/signed body part may be
 transferred to a recipient or processed further, for example, it may
 be encrypted.
 The application of the MOSS encryption service requires the following
 components.
 (1)  The data to be encrypted.
 (2)  A data encrypting key to encrypt the data.
 (3)  The public key of the recipient.
 The data to be encrypted is prepared according to the description
 below.  The originator creates a data encrypting key and encrypts the
 data.  The recipient's public key is used to encrypt the data
 encrypting key.  The encrypted data, the encrypted data encrypting
 key, and some additional ancillary information described below are
 then embodied in a multipart/encrypted body part, ready to be
 transferred to a recipient or processed further, for example, it may
 be signed.
 The next two sections describe the digital signature and encryption
 services, respectively, in detail.

2.1. Digital Signature Service

 The MOSS digital signature service is applied to MIME objects,
 specifically a MIME body part.  The MIME body part is created

Crocker, et al Standards Track [Page 4] RFC 1848 MIME Object Security Services October 1995

 according to a local convention and then made available to the
 digital signature service.
 The following sequence of steps comprises the application of the
 digital signature service.
 (1)  The body part to be signed must be canonicalized.
 (2)  The digital signature and other control information must be gen-
      erated.
 (3)  The control information must be embodied in an appropriate MIME
      content type.
 (4)  The control information body part and the data body part must be
      embodied in a multipart/signed content type.
 Each of these steps is described below.

2.1.1. Canonicalization

 The body part must be converted to a canonical form that is uniquely
 and unambiguously representable in at least the environment where the
 digital signature is created and the environment where the digital
 signature will be verified, i.e., the originator and recipient's
 environment, respectively.  This is required in order to ensure that
 both the originator and recipient have the same data with which to
 calculate the digital signature; the originator needs to be able to
 create the digital signature value while the recipient needs to be
 able to compare a re-computed value with the received value.  If the
 canonical form is representable on many different host computers, the
 signed data may be forwarded by recipients to additional recipients,
 who will also be able to verify the original signature.  This service
 is called forwardable authentication.
 The canonicalization transformation is a two step process.  First,
 the body part must be converted to a form that is unambiguously
 representable on as many different host computers as possible.
 Second, the body part must have its line delimiters converted to a
 unique and unambiguous representation.
 The representation chosen to satisfy the first step is 7bit, as
 defined by MIME; the high order bit of each octet of the data to be

Crocker, et al Standards Track [Page 5] RFC 1848 MIME Object Security Services October 1995

 signed must be zero.  A MIME body part is comprised of two parts:
 headers and content.  Since the headers of body parts are already
 required to be represented in 7bit, this step does not require
 changes to the headers.  This step requires that if the content is
 not already 7bit then it must be encoded with an appropriate MIME
 content transfer encoding and a Content-Transfer-Encoding: header
 must be added to the headers.  For example, if the content to be
 signed contains 8bit or binary data, the content must be encoded with
 either the quoted-printable or base64 encoding as defined by MIME.
    IMPLEMENTORS NOTE: Since the MIME standard explicitly disallows
    nested content transfer encodings, i.e., the content types
    multipart and message may not themselves be encoded, the 7bit
    transformation requires each nested body part to be individually
    encoded in a 7bit representation.  Any valid MIME encoding, e.g.,
    quoted-printable or base64, may be used and, in fact, a different
    encoding may be used on each of the non-7bit body parts.
 Representing all content types in a 7bit format transforms them into
 text-based content types.  However, text-based content types present
 a unique problem.  In particular, the line delimiter used for a
 text-based content type is specific to a local environment; different
 environments use the single character carriage-return (<CR>), the
 single character line-feed (<LF>), or the two character sequence
 "carriage-return line-feed (<CR><LF>)".
 The application of the digital signature service requires that the
 same line delimiter be used by both the originator and the recipient.
 This document specifies that the two character sequence "<CR><LF>"
 must be used as the line delimiter.  Thus, the second step of the
 canonicalization transformation includes the conversion of the local
 line delimiter to the two character sequence "<CR><LF>".
 The conversion to the canonical line delimiter is only required for
 the purposes of computing the digital signature.  Thus, originators
 must apply the line delimiter conversion before computing the digital
 signature but must transfer the data without the line delimiter
 conversion.  Similarly, recipients must apply the line delimiter
 conversion before computing the digital signature.
    NOTE: An originator can not transfer the content with the line
    delimiter conversion intact because the conversion process is not
    idempotent.  In particular, SMTP servers may themselves convert
    the line delimiter to a local line delimiter, prior to the message
    being delivered to the recipient.  Thus, a recipient has no way of
    knowing if the conversion is present or not.  If the recipient
    applies the conversion to a content in which it is already
    present, the resulting content may have two line delimiters

Crocker, et al Standards Track [Page 6] RFC 1848 MIME Object Security Services October 1995

    present, which would cause the verification of the signature to
    fail.
    IMPLEMENTORS NOTE: Implementors should be aware that the
    conversion to a 7bit representation is a function that is required
    in a minimally compliant MIME user agent.  Further, the line
    delimiter conversion required here is distinct from the same
    conversion included in that function.  Specifically, the line
    delimiter conversion applied when a body part is converted to a
    7bit representation (transfer encoded) is performed prior to the
    application of the transfer encoding.  The line delimiter
    conversion applied when a body part is signed is performed after
    the body part is converted to 7bit (transfer encoded).  Both line
    delimiter conversions are required.

2.1.2. Digital Signature Control Information

 The application of the digital signature service generates control
 information which includes the digital signature itself.  The syntax
 of the control information is that of a set of RFC 822 headers,
 except that the folding of header values onto continuation lines is
 explicitly forbidden.  Each header and value pair generated by the
 digital signature service must be output on exactly one line.
 The complete set of headers generated by the digital signature
 service is as follows.
 Version:
    indicates which version of the MOSS protocol the remaining headers
    represent.
 Originator-ID:
    indicates the private key used to create the digital signature and
    the corresponding public key to be used to verify it.
 MIC-Info:
    contains the digital signature value.
 Each invocation of the digital signature service must emit exactly
 one Version: header and at least one pair of Originator-ID: and MIC-
 Info: headers.  The Version: header must always be emitted first.
 The Originator-ID: and MIC-Info: headers are always emitted in pairs
 in the order indicated.  This specification allows an originator to
 generate multiple signatures of the data, presumably with different
 signature algorithms, and to include them all in the control
 information.  The interpretation of the presence of multiple
 signatures is outside the scope of this specification except that a
 MIC-Info: header is always interpreted in the context of the

Crocker, et al Standards Track [Page 7] RFC 1848 MIME Object Security Services October 1995

 immediately preceding Originator-ID: header.

2.1.2.1. Version:

 The version header is defined by the grammar token <version> as
 follows.
    <version>  ::= "Version:" "5" CRLF
 Its value is constant and MOSS implementations compliant with this
 specification must recognize only this value and generate an error if
 any other value is found.

2.1.2.2. Originator-ID:

 The purpose of the originator header is two-fold: to directly
 identify the public key to be used to verify the digital signature
 and to indirectly identify the user who owns both it and its
 corresponding private key.  Typically, a recipient is less interested
 in the actual public key value, although obviously the recipient
 needs the value to verify the signature, and more interested in
 identifying its owner.  Thus, the originator header may convey either
 or both pieces of information:
    the public key to be used to verify the signature
    the name of the owner and which of the owner's public keys to use
    to verify the signature
 The decision as to what information to place in the value rests
 entirely with the originator.  The suggested value is to include
 both.  Recipients with whom the originator has previously
 communicated will have to verify that the information presented is
 consistent with what is already known.  New recipients will want all
 of the information, which they will need to verify prior to storing
 in their local database.
 The originator header is defined by the grammar token <origid> as
 follows.
    <origid>  ::= "Originator-ID:" <id> CRLF
 The grammar token <id> is defined in Section 4.

2.1.2.3. MIC-Info:

 The purpose of the Message Integrity Check (MIC) header is to convey
 the digital signature value.  Its value is a comma separated list of

Crocker, et al Standards Track [Page 8] RFC 1848 MIME Object Security Services October 1995

 three arguments: the hash (or MIC) algorithm identifier, the
 signature algorithm identifier, and the digital signature.
 The MIC header is defined by the grammar token <micinfo> as follows.
    <micinfo>  ::= "MIC-Info:" <micalgid> "," <ikalgid> ","
                   <asymsignmic> CRLF
 The grammar tokens for the MIC algorithms and identifiers
 (<micalgid>), signature algorithms and identifiers (<ikalgid>), and
 signed MIC formats (<asymsignmic>) are defined by RFC 1423.  They are
 also reprinted in Appendix B.
    IMPLEMENTORS NOTE: RFC 1423 is referenced by the PEM protocol,
    which includes support for symmetric signatures and key
    management.  As a result, some of the grammar tokens defined
    there, for example, <ikalgid>, will include options that are not
    legal for this protocol.  These options must be ignored and have
    not been included in the appendix.

2.1.3. application/moss-signature Content Type Definition

 (1)  MIME type name: application
 (2)  MIME subtype name: moss-signature
 (3)  Required parameters: none
 (4)  Optional parameters: none
 (5)  Encoding considerations: quoted-printable is always sufficient
 (6)  Security considerations: none
 The "application/moss-signature" content type is used on the second
 body part of an enclosing multipart/signed.  Its content is comprised
 of the digital signature of the data in the first body part of the
 enclosing multipart/signed and other control information required to
 verify that signature, as defined by Section 2.1.2.  The label
 "application/moss-signature" must be used as the value of the
 protocol parameter of the enclosing multipart/signed; the protocol
 parameter must be present.
 Part of the signature verification information will be the Message
 Integrity Check (MIC) algorithm(s) used during the signature creation
 process.  The MIC algorithm(s) identified in this body part must
 match the MIC algorithm(s) identified in the micalg parameter of the
 enclosing multipart/signed.  If it does (they do) not, a user agent

Crocker, et al Standards Track [Page 9] RFC 1848 MIME Object Security Services October 1995

 should identify the discrepancy to a user and it may choose to either
 halt or continue processing, giving precedence to the algorithm(s)
 identified in this body part.
 An application/moss-signature body part is constructed as follows:
    Content-Type: application/moss-signature
    <mosssig>
 where the grammar token <mosssig> is defined as follows.
    <mosssig>       ::= <version> ( 1*<origasymflds> )
    <version>       ::= "Version:" "5" CRLF
    <origasymflds>  ::= <origid> <micinfo>
    <origid>        ::= "Originator-ID:" <id> CRLF
    <micinfo>       ::= "MIC-Info:" <micalgid> "," <ikalgid> ","
                        <asymsignmic> CRLF
 The token <id> is defined in Section 4.  All other tokens are defined
 in Section 2.1.2.3.

2.1.4. Use of multipart/signed Content Type

 The definition of the multipart/signed content type in [7] specifies
 three steps for creating the body part.
 (1)  The body part to be digitally signed is created according to a
      local convention, for example, with a text editor or a mail user
      agent.
 (2)  The body part is prepared for the digital signature service
      according to the protocol parameter, in this case according to
      Section 2.1.1.
 (3)  The prepared body part is digitally signed according to the
      protocol parameter, in this case according to Section 2.1.2.
 The multipart/signed content type is constructed as follows.

Crocker, et al Standards Track [Page 10] RFC 1848 MIME Object Security Services October 1995

 (1)  The value of its required parameter "protocol" is set to
      "application/moss-signature".
 (2)  The signed body part becomes its first body part.
 (3)  Its second body part is labeled "application/moss-signature" and
      is filled with the control information generated by the digital
      signature service.
 (4)  The value of its required parameter "micalg" is set to the same
      value used in the MIC-Info: header in the control information.
      If there is more than one MIC-Info: header present the value is
      set to a comma separated list of values from the MIC-Info
      headers.  The interpretation of the order of the list of values
      is outside the scope of this specification.
 A multipart/signed content type with the MOSS protocol might look as
 follows:
    Content-Type: multipart/signed;
      protocol="application/moss-signature";
      micalg="rsa-md5"; boundary="Signed Message"
  1. -Signed Message

Content-Type: text/plain

    This is some example text.
  1. -Signed Message

Content-Type: application/moss-signature

    Version: 5
    Originator-ID: ID-INFORMATION
    MIC-Info: RSA-MD5,RSA,SIGNATURE-INFORMATION
    --Signed Message--
 where ID-INFORMATION and SIGNATURE-INFORMATION are descriptive of the
 content that would appear in a real body part.

2.2. Encryption Service

 The MOSS encryption service is applied to MIME objects, specifically
 a MIME body part.  The MIME body part is created according to a local
 convention and then made available to the encryption service.

Crocker, et al Standards Track [Page 11] RFC 1848 MIME Object Security Services October 1995

 The following sequence of steps comprises the application of the
 encryption service.
 (1)  The body part to be encrypted must be in MIME canonical form.
 (2)  The data encrypting key and other control information must be
      generated.
 (3)  The control information must be embodied in an appropriate MIME
      content type.
 (4)  The control information body part and the encrypted data body
      part must be embodied in a multipart/encrypted content type.
 The first step is defined by MIME.  The latter three steps are
 described below.

2.2.1. Encryption Control Information

 The application of the encryption service generates control
 information which includes the data encrypting key used to encrypt
 the data itself.  The syntax of the control information is that of a
 set of RFC 822 headers, except that the folding of header values onto
 continuation lines is explicitly forbidden.  Each header and value
 pair generated by the encryption service must be output on exactly
 one line.
 First, the originator must retrieve the public key of the recipient.
 The retrieval may be from a local database or from a remote service.
 The acquisition of the recipient's public key is outside the scope of
 the specification, although Section 5 defines one possible mechanism.
 With the public key, the originator encrypts the data encrypting key
 according to the Key-Info: header defined below.  The complete set of
 headers generated by the encryption service is as follows.
 Version:
    indicates which version of the MOSS protocol the remaining headers
    represent and is defined in Section 2.1.2.1.
 DEK-Info:
    indicates the algorithm and mode used to encrypt the data.

Crocker, et al Standards Track [Page 12] RFC 1848 MIME Object Security Services October 1995

 Recipient-ID:
    indicates the public key used to encrypt the data encrypting key
    that was used to encrypt the data.
 Key-Info:
    contains data encrypting key encrypted with the recipient's public
    key.
 Each invocation of the encryption service must emit exactly one
 Version: header, exactly one DEK-Info: header, and at least one pair
 of Recipient-ID: and Key-Info: headers.  Headers are always emitted
 in the order indicated.  The Recipient-ID: and Key-Info: headers are
 always emitted in pairs in the order indicated, one pair for each
 recipient of the encrypted data.  A Key-Info: header is always
 interpreted in the context of the immediately preceding Recipient-ID:
 header.
    IMPLEMENTORS NOTE: Implementors should always generate a
    Recipient-ID: and Key-Info header pair representing the originator
    of the encrypted data.  By doing so, if an originator sends a
    message to a recipient that is returned undelivered, the
    originator will be able to decrypt the message and determine an
    appropriate course of action based on its content.  If not, an
    originator will not be able to review the message that was sent.

2.2.1.1. DEK-Info:

 The purpose of the data encrypting key information header is to
 indicate the algorithm and mode used to encrypt the data, along with
 any cryptographic parameters that may be required, e.g.,
 initialization vectors.  Its value is either a single argument
 indicating the algorithm and mode or a comma separated pair of
 arguments where the second argument carries any cryptographic
 parameters required by the algorithm and mode indicated in the first
 argument.
 The data encrypting key information header is defined by the grammar
 token <dekinfo> as follows.
    <dekinfo>  ::= "DEK-Info" ":" <dekalgid>
                   [ "," <dekparameters> ] CRLF
 The grammar tokens for the encryption algorithm and mode identifier
 (<dekalgid>) and the optional cryptographic parameters
 (<dekparameters>) are defined by RFC 1423.  They are also reprinted
 in Appendix B.

Crocker, et al Standards Track [Page 13] RFC 1848 MIME Object Security Services October 1995

2.2.1.2. Recipient-ID:

 The purpose of the recipient header is to identify the private key
 that must be used to decrypt the data encrypting key that will be
 used to decrypt the data.  Presumably the recipient owns the private
 key and thus is less interested in identifying the owner of the key
 and more interested in the private key value itself.  Nonetheless,
 the recipient header may convey either or both pieces of information:
    the public key corresponding to the private key to be used to
    decrypt the data encrypting key
    the name of the owner and which of the owner's private keys to use
    to decrypt the data encrypting key
 The decision as to what information to place in the value rests
 entirely with the originator.  The suggested choice is to include
 just the public key.  However, some recipients may prefer that
 originators not include their public key.  How this preference is
 conveyed to and managed by the originator is outside the scope of
 this specification.
 The recipient header is defined by the grammar token <recipid> as
 follows.
    <recipid>  ::= "Recipient-ID:" <id> CRLF
 The grammar token <id> is defined in Section 4.

2.2.1.3. Key-Info:

 The purpose of the key information header is to convey the encrypted
 data encrypting key.  Its value is a comma separated list of two
 arguments: the algorithm and mode identifier in which the data
 encrypting key is encrypted and the encrypted data encrypting key.
 The key information header is defined by the grammar token
 <asymkeyinfo> as follows.
    <asymkeyinfo>  ::= "Key-Info" ":" <ikalgid> "," <asymencdek> CRLF
 The grammar tokens for the encryption algorithm and mode identifier
 (<ikalgid>) and the encrypted data encrypting key format
 (<asymsignmic>) are defined by RFC 1423.  They are also reprinted in
 Appendix B.
    IMPLEMENTORS NOTE: RFC 1423 is referenced by the PEM protocol,
    which includes support for symmetric signatures and key

Crocker, et al Standards Track [Page 14] RFC 1848 MIME Object Security Services October 1995

    management.  As a result, some of the grammar tokens defined
    there, for example, <ikalgid>, will include options that are not
    legal for this protocol.  These options must be ignored and have
    not been included in the appendix.

2.2.2. application/moss-keys Content Type Definition

 (1)  MIME type name: application
 (2)  MIME subtype name: moss-keys
 (3)  Required parameters: none
 (4)  Optional parameters: none
 (5)  Encoding considerations: quoted-printable is always sufficient
 (6)  Security considerations: none
 The "application/moss-keys" content type is used on the first body
 part of an enclosing multipart/encrypted.  Its content is comprised
 of the data encryption key used to encrypt the data in the second
 body part and other control information required to decrypt the data,
 as defined by Section 2.2.1.  The label "application/moss-keys" must
 be used as the value of the protocol parameter of the enclosing
 multipart/encrypted; the protocol parameter must be present.
 An application/moss-keys body part is constructed as follows:
    Content-Type: application/moss-keys
    <mosskeys>
 where the <mosskeys> token is defined as follows.
    <mosskeys>      ::= <version> <dekinfo> 1*<recipasymflds>
    <version>       ::= "Version:" "5" CRLF
    <dekinfo>       ::= "DEK-Info" ":" <dekalgid>
                        [ "," <dekparameters> ] CRLF
    <recipasymflds> ::= <recipid> <asymkeyinfo>
    <recipid>       ::= "Recipient-ID:" <id> CRLF
    <asymkeyinfo>   ::= "Key-Info" ":" <ikalgid> "," <asymencdek> CRLF

Crocker, et al Standards Track [Page 15] RFC 1848 MIME Object Security Services October 1995

 The token <id> is defined in Section 4.  The token <version> is
 defined in Section 2.1.2.1.  All other tokens are defined in Section
 2.2.1.3.

2.2.3. Use of multipart/encrypted Content Type

 The definition of the multipart/encrypted body part in [7] specifies
 three steps for creating the body part.
 (1)  The body part to be encrypted is created according to a local
      convention, for example, with a text editor or a mail user
      agent.
 (2)  The body part is prepared for encryption according to the
      protocol parameter, in this case the body part must be in MIME
      canonical form.
 (3)  The prepared body part is encrypted according to the protocol
      parameter, in this case according to Section 2.2.1.
 The multipart/encrypted content type is constructed as follows.
 (1)  The value of its required parameter "protocol" is set to
      "application/moss-keys".
 (2)  The first body part is labeled "application/moss-keys" and is
      filled with the control information generated by the encryption
      service.
 (3)  The encrypted body part becomes the content of its second body
      part, which is labeled "application/octet-stream".
 A multipart/encrypted content type with the MOSS protocol might look
 as follows:

Crocker, et al Standards Track [Page 16] RFC 1848 MIME Object Security Services October 1995

    Content-Type: multipart/encrypted;
      protocol="application/moss-keys";
      boundary="Encrypted Message"
  1. -Encrypted Message

Content-Type: application/moss-keys

    Version: 5
    DEK-Info: DES-CBC,DEK-INFORMATION
    Recipient-ID: ID-INFORMATION
    Key-Info: RSA,KEY-INFORMATION
  1. -Encrypted Message

Content-Type: application/octet-stream

    ENCRYPTED-DATA
    --Encrypted Message--
 where DEK-INFORMATION, ID-INFORMATION, and KEY-INFORMATION are
 descriptive of the content that would appear in a real body part.

3. Removing MIME Object Security Services

 The verification of the MOSS digital signature service requires the
 following components.
 (1)  A recipient to verify the digital signature.
 (2)  A multipart/signed body part with two body parts: the signed
      data and the control information.
 (3)  The public key of the originator.
 The signed data and control information of the enclosing
 multipart/signed are prepared according to the description below.
 The digital signature is verified by re-computing the hash of the
 data, decrypting the hash value in the control information with the
 originator's public key, and comparing the two hash values.  If the
 two hash values are equal, the signature is valid.
 The decryption of the MOSS encryption service requires the following
 components.

Crocker, et al Standards Track [Page 17] RFC 1848 MIME Object Security Services October 1995

 (1)  A recipient to decrypt the data.
 (2)  A multipart/encrypted body part with two body parts: the
      encrypted data and the control information.
 (3)  The private key of the recipient.
 The encrypted data and control information of the enclosing
 multipart/encrypted are prepared according to the description below.
 The data encrypting key is decrypted with the recipient's private key
 and used to decrypt the data.
 The next two sections describe the digital signature and encryption
 services in detail, respectively.

3.1. Digital Signature Service

 This section describes the processing steps necessary to verify the
 MOSS digital signature service.  The definition of the
 multipart/signed body part in [7] specifies three steps for receiving
 it.
 (1)  The digitally signed body part and the control information body
      part are prepared for processing.
 (2)  The prepared body parts are made available to the digital
      signature verification process.
 (3)  The results of the digital signature verification process are
      made available to the user and processing continues with the
      digitally signed body part, as returned by the digital signature
      verification process.
 Each of these steps is described below.

3.1.1. Preparation

 The digitally signed body part (the data) and the control information
 body part are separated from the enclosing multipart/signed body
 part.

Crocker, et al Standards Track [Page 18] RFC 1848 MIME Object Security Services October 1995

 The control information is prepared by removing any content transfer
 encodings that may be present.
 The digitally signed body part is prepared by leaving the content
 transfer encodings intact and canonicalizing the line delimiters
 according to Step 2 of Section 2.1.1.

3.1.2. Verification

 First, the recipient must obtain the public key of the originator.
 The public key may be contained in the control information or it may
 be necessary for the recipient to retrieve the public key based on
 information present in the control information.  The retrieval may be
 from a local database or from a remote service.  The acquisition of
 the originator's public key is outside the scope of the
 specification, although Section 5 defines one possible mechanism.
 With the public key, the recipient decrypts the hash value contained
 in the control information.  Then, a new hash value is computed over
 the body part purported to have been digitally signed.
 Finally, the two hash values are compared to determine the accuracy
 of the digital signature.

3.1.3. Results

 There are two required components of the results of the verification
 process.  The first is an indication as to whether a public key could
 be found that allows the hash values in the previous step to compare
 equal.  Such an indication verifies only that the data received is
 the same data that was digitally signed.
 The second indication identifies the owner of the public key who is
 presumably the holder of the private key that created the digital
 signature.  The indication must include a testament as to the
 accuracy of the owner identification.
 At issue is a recipient knowing who created the digital signature.
 In order for the recipient to know with certainty who digitally
 signed the message, the binding between the owner's name and the
 public key must have been verified by the recipient prior to the
 verification of the digital signature.  The verification of the
 binding may have been completed offline and stored in a trusted,
 local database or, if the owner's name and public key are embodied in
 a certificate, it may be possible to complete it in realtime.  See
 Section 5 for more information.

Crocker, et al Standards Track [Page 19] RFC 1848 MIME Object Security Services October 1995

3.2. Encryption Service

 This section describes the processing steps necessary to decrypt the
 MOSS encryption service.  The definition of the multipart/encrypted
 body part in [7] specifies three steps for receiving it.
 (1)  The encrypted body part and the control information body part
      are prepared for processing.
 (2)  The prepared body parts are made available to the decryption
      process.
 (3)  The results of the decryption process are made available to the
      user and processing continues with the decrypted body part, as
      returned by the decryption process.
 Each of these steps is described below.

3.2.1. Preparation

 The encrypted body part (the data) and the control information body
 part are separated from the enclosing multipart/encrypted body part.
 The body parts are prepared for the decryption process by removing
 any content transfer encodings that may be present.

3.2.2. Decryption

 First, the recipient must locate the encrypted data encrypting key in
 the control information.  Each Recipient-ID: header is checked in
 order to see if it identifies the recipient or a public key of the
 recipient.
 If it does, the immediately following Key-Info: header will contain
 the data encrypting key encrypted with the public key of the
 recipient.  The recipient must use the corresponding private key to
 decrypt the data encrypting key.
 The data is decrypted with the data encrypting key.  The decrypted
 data will be a MIME object, a body part, ready to be processed by a
 MIME agent.

Crocker, et al Standards Track [Page 20] RFC 1848 MIME Object Security Services October 1995

3.2.3. Results

 If the recipient is able to locate and decrypt a data encrypting key,
 from the point of view of MOSS the decryption should be considered
 successful.  An indication of the owner of the private key used to
 decrypt the data encrypting key must be made available to the user.
 Ultimately, the success of the decryption is dependent on the ability
 of a MIME agent to continue processing with the decrypted body part.

4. Identifying Originators, Recipients, and Their Keys

 In the PEM specifications, public keys are required to be embodied in
 certificates, an object that binds each public key with a
 distinguished name.  A distinguished name is a name form that
 identifies the owner of the public key.  The embodiment is issued by
 a certification authority, a role that is expected to be trustworthy
 insofar as the certification authority would have procedures to
 verify the identity of the owner prior to issuing the certificate.
 In MOSS, a user is not required to have a certificate.  The MOSS
 services require that the user have at least one public/private key
 pair.  The MOSS protocol requires the digital signature and
 encryption services to emit Originator-ID: and Recipient-ID: headers,
 as appropriate.  In the discussion above the actual value of these
 headers was omitted, having been relegated to this section.  Although
 the value of each of these headers serves a distinct purpose, for
 simplicity the single grammar token <id> represents the value that
 may be assigned to either header.
 One possible value for the Originator-ID: and Recipient-ID: headers
 is the public key values themselves.  However, while it is true that
 the public keys alone could be exchanged and used by users to
 communicate, the values are, in fact, large and cumbersome.  In
 addition, public keys would appear as a random sequence of characters
 and, as a result, would not be immediately consumable by human users.
    NOTE: It should be pointed out that a feature of being able to
    specify the public key explicitly is that it allows users to
    exchange encrypted, anonymous mail.  In particular, receiving
    users will always know a message comes from the same originating
    user even if the real identity of the originating user is unknown.
 Recognizing that the use of public keys is, in general, unsuitable
 for use by humans, MOSS allows other identifiers in Originator-ID:
 and Recipient-ID: headers.  These other identifiers are comprised of
 two parts: a name form and a key selector.

Crocker, et al Standards Track [Page 21] RFC 1848 MIME Object Security Services October 1995

 The name form is chosen and asserted by the user who owns the
 public/private key pair.  Three name forms are specified by this
 document.  The use of a distinguished name is retained for
 compatibility with PEM (and compatibility with the X.500 Directory
 should it become a ubiquitous service).  However, the Internet
 community has a great deal of experience with the use of electronic
 mail addresses as a name form.  Also, arbitrary strings are useful to
 identify the owners of public keys when private name forms are used.
 Hence, email addresses and arbitrary strings are included as name
 forms to increase flexibility.
 Since a user may have more than one public key and may wish to use
 the same name form for each public key, a name form is insufficient
 for uniquely identifying a public key.  A unique "key selector" must
 be assigned to each public key.  The combination of a name form and
 the key selector uniquely identifies a public key.  Throughout this
 document, this combination is called an identifier.  There are 5
 identifiers specified by this document.
    NOTE: In the simplest case, key selectors will be assigned by the
    owners of the public/private key pairs.  This works best when
    users generate their own key pairs for personal use, from which
    they distribute their public key to others asserting by
    declaration that the public key belongs to them.  When the
    assertion that the public key belongs to them is made by a third
    party, for example when a certification authority issues a
    certificate to a user according to [4], the key selector may be
    assigned by that third party.
 The value of the key selector must be unique with respect to the name
 form with which it forms an identifier.  Although the same key
 selector value may be used by more than one name form it must not be
 used for two different keys with the same name form.  When considered
 separately, neither a name form nor a key selector is sufficient for
 identifying the public key to be used.  Either could be used to
 determine a set of public keys that may be tried in turn until the
 desired public key is identified.
 With a public/private key pair for one's self and software that is
 MOSS aware, an originating user may digitally sign arbitrary data and
 send it to one or more recipients.  With the public keys of the
 recipients, a user may encrypt the data so that only the intended
 recipients can decrypt and read it.  With the name forms assigned to
 the public keys, originators and recipients can easily recognize
 their peers in a communication.
 In the next section the 3 name forms are described in detail.
 Following that is the specification of the 5 identifiers.

Crocker, et al Standards Track [Page 22] RFC 1848 MIME Object Security Services October 1995

4.1. Name Forms

 There are 3 name forms specified by this document: email addresses,
 distinguished names, and arbitrary strings.

4.1.1. Email Addresses

 The email address (grammar token <emailstr>) used must be a valid
 RFC822 address, which is defined in terms of one of the two grammar
 tokens <addr-spec> or <route-addr>.  The grammar for these two tokens
 is included in the Appendix as a convenience; the definitive source
 for these tokens is necessarily RFC822 [1].
    <emailstr>      ::= <addr-spec> / <route-addr>
                        ; an electronic mail address as defined by
                        ; one of these two tokens from RFC822
 For example, the strings "crocker@tis.com", "galvin@tis.com",
 "murphy@tis.com", and "ned@innosoft.com" are all email addresses.

4.1.2. Arbitrary Strings

 The arbitrary string (grammar token <string>) must have a length of
 at least 1.  There are no other restrictions on the value chosen.
    <string>        ::= ; a non-null sequence of characters
 For example, the string
    the SAAG mailing list maintainer
 is an arbitrary string.

4.1.3. Distinguished Names

 The distinguished name (grammar token <dnamestr>) must be constructed
 according to the guidelines of the X.500 Directory.  The actual
 syntax of the distinguished name is outside the scope of this
 specification.  However, RFC1422, for example, specifies syntactic
 restrictions based on its choice of a certification hierarchy for
 certificates.
 For the purposes of conveying a distinguished name from an originator
 to a recipient, it must be ASN.1 encoded and then printably encoded
 according to the base64 encoding defined by MIME.

Crocker, et al Standards Track [Page 23] RFC 1848 MIME Object Security Services October 1995

    <dnamestr>      ::= <encbin>
                        ; a printably encoded, ASN.1 encoded
                        ; distinguished name (as defined by the 'Name'
                        ; production specified in X.501 [8])
 For example,
    /Country Name=US
    /State or Province Name=MD
    /Organization Name=Trusted Information Systems
    /Organizational Unit Name=Glenwood
    /Common Name=James M. Galvin/
 is a distinguished name in a user friendly format (line breaks and
 leading spaces present only to improve readability).  When encoded,
 it would appear as follows (line breaks present only to improve
 readability):
    MG0xCzAJBgNVBAYTAlVTMQswCQYDVQQIEwJNRDEkMCIGA1UEChMbVHJ1c3RlZCBJ
    bmZvcm1hdGlvbiBTeXN0ZW1zMREwDwYDVQQLEwhHbGVud29vZDEYMBYGA1UEAxMP
    SmFtZXMgTS4gR2Fsdmlu

4.2. Identifiers

 There are 5 types of identifiers specified by this document:
    email address identifiers
    arbitrary string identifiers
    distinguished name identifiers
    the public keys themselves
    issuer name serial number pairs from a certificate
 All of these have approximately the same structure (except issuer
 name and serial number which has 'TYPE, STRING, KEYSEL' for
 historical reasons):
    TYPE, KEYSEL, STRING
 The TYPE field is a literal string chosen from the set "EN", "STR",
 "DN", "PK", and "IS", one for each of the possible identifiers.
 The KEYSEL field is used to distinguish between the multiple public
 keys that may be associated with the name form in the STRING field.
 Its value must be unique with respect to all other key selectors used

Crocker, et al Standards Track [Page 24] RFC 1848 MIME Object Security Services October 1995

 with the same name form.  An example would be to use a portion (low-
 order 16 or 32 bits) or all of the actual public key used.
 The STRING field is the name form and has a different syntax
 according to the value of the TYPE field.
 The identifier used in each of the originator and recipient fields is
 described by the following grammar.  The definition of the key
 selector token is included here since it used by several of the
 identifiers below.
    <id>            ::=   <id-email> / <id-string>    / <id-dname>
                        / <id-publickey> / <id-issuer>
    <keysel>        ::= 1*<hexchar>
                        ; hex dump of a non-null sequence of octets
 Each of the identifier name forms is described below.

4.2.1. Email Address

 The email address identifier has the following syntax.
    <id-email>      ::= "EN"  "," <keysel> "," <emailstr> CRLF
 The syntax of the token <emailstr> is defined in Section 4.1.1.
 For example:
    EN,1,galvin@tis.com
 is an email address identifier.

4.2.2. Arbitrary String

 The arbitrary string identifier has the following syntax.
    <id-string>     ::= "STR" "," <keysel> "," <string> CRLF
 The syntax of the token <string> is defined in Section 4.1.2.
 For example:
    STR,1,The SAAG mailing list maintainer
 is an arbitrary string identifier.

Crocker, et al Standards Track [Page 25] RFC 1848 MIME Object Security Services October 1995

4.2.3. Distinguished Name

 The distinguished name identifier has the following syntax.
    <id-dname>      ::= "DN"  "," <keysel> "," <dnamestr> CRLF
 The syntax of the token <dnamestr> is defined in Section 4.1.3.
 For example (line breaks present only to improve readability):
    DN,1,MG0xCzAJBgNVBAYTAlVTMQswCQYDVQQIEwJNRDEkMCIGA1UEChMbVHJ1c3R
    lZCBJbmZvcm1hdGlvbiBTeXN0ZW1zMREwDwYDVQQLEwhHbGVud29vZDEYMBYGA1U
    EAxMPSmFtZXMgTS4gR2Fsdmlu
 is a distinguished name identifier.

4.2.4. Public Key

 The public key identifier has the following syntax.
    <id-publickey>  ::= "PK"  "," <publickey> [ "," <id-subset> ] CRLF
    <publickey>     ::= <encbin>
                        ; a printably encoded, ASN.1 encoded public
                        ; key (as defined by the
                        ; 'SubjectPublicKeyInfo' production specified
                        ; in X.509 [9])
    <id-subset>     ::= <id-email> / <id-string> / <id-dname>
 The production SubjectPublicKeyInfo is imported from the X.500
 Directory from the certificate object.  It is currently the best
 choice for a general purpose public key encoding.
 For example, (line breaks present only to improve readability):
    PK,MHkwCgYEVQgBAQICAwADawAwaAJhAMAHQ45ywA357G4fqQ61aoC1fO6BekJmG
    4475mJkwGIUxvDkwuxe/EFdPkXDGBxzdGrW1iuh5K8kl8KRGJ9wh1HU4TrghGdhn
    0Lw8gG67Dmb5cBhY9DGwq0CDnrpKZV3cQIDAQAB
 is a public key identifier without the optional <id-subset>.
 In normal usage, the token <id-subset> is expected to be present.  It
 represents a mechanism by which an identifier (name form and key
 selector) can be associated with a public key.  Recipients of a
 public key identifier must take care to verify the accuracy of the
 purported association.  If they do not, it may be possible for a
 malicious originator to assert an identifier that accords the

Crocker, et al Standards Track [Page 26] RFC 1848 MIME Object Security Services October 1995

 originator unauthorized privileges.  See Section 5.2 for more
 details.
 For example, (line breaks present only to improve readability):
    PK,MHkwCgYEVQgBAQICAwADawAwaAJhAMAHQ45ywA357G4fqQ61aoC1fO6BekJmG
    4475mJkwGIUxvDkwuxe/EFdPkXDGBxzdGrW1iuh5K8kl8KRGJ9wh1HU4TrghGdhn
    0Lw8gG67Dmb5cBhY9DGwq0CDnrpKZV3cQIDAQAB,EN,2,galvin@tis.com
 is a public key identifier with the optional <id-subset>.

4.2.5. Issuer Name and Serial Number

 The issuer name and serial number identifier has the following
 syntax.
    <id-issuer>     ::= "IS"  "," <dnamestr>  "," <serial> CRLF
    <serial>        ::= 1*<hexchar>
                        ; hex dump of a certificate serial number
 The <id-issuer> identifier is included for compatibility with the
 ID-ASymmetric fields defined in [3] (and compatibility with X.500
 Directory certificates should they become ubiquitously available).
 Its syntax was chosen such that the older fields are easily converted
 to this new form by prefixing the old value with "IS" (and replacing
 the field name of [3] with an appropriate new ID field name).  For
 example, (line breaks present only to improve readability):
    IS,MFMxCzAJBgNVBAYTAlVTMQswCQYDVQQIEwJNRDEkMCIGA1UEChMbVHJ1c3
    RlZCBJbmZvcm1hdGlvbiBTeXN0ZW1zMREwDwYDVQQLEwhHbGVud29vZA==,02
 is an issuer name and serial number identifier according to MOSS,
 while
    MFMxCzAJBgNVBAYTAlVTMQswCQYDVQQIEwJNRDEkMCIGA1UEChMbVHJ1c3
    RlZCBJbmZvcm1hdGlvbiBTeXN0ZW1zMREwDwYDVQQLEwhHbGVud29vZA==,02
 is an issuer name and serial number identifier according to PEM.

5. Key Management Content Types

 This document defines two key management content types: one for
 requesting cryptographic key material and one for sending
 cryptographic key material.  Since MOSS depends only on the existence
 of public/private key pairs, these content types provide a means for
 conveying public keys and an assertion as to the identity of the
 owner.  In addition, in order to be compatible with the certificate-

Crocker, et al Standards Track [Page 27] RFC 1848 MIME Object Security Services October 1995

 base key management system proposed by RFC 1422, the content types
 may also be used to convey certificate and certificate revocation
 list material.
 The functions defined here are based on the exchange of body parts.
 In particular, a user would send a message containing at least one
 application/mosskey-request content, as defined below.  In response,
 a user would expect to receive a message containing at least one
 application/mosskey-data content, as defined below.  MIME provides a
 convenient framework for a user to send several request body parts
 and to receive several data (response) body parts in one message.

5.1. application/mosskey-request Content Type Definition

 (1)  MIME type name: application
 (2)  MIME subtype name: mosskey-request
 (3)  Required parameters: none
 (4)  Optional parameters: none
 (5)  Encoding considerations: quoted-printable is always sufficient
 (6)  Security Considerations: none
 The content of this body part corresponds to the following
 production.
    <request>       ::= <version>
                        ( <subject> / <issuer> / <certification> )
    <version>       ::= "Version:" "5" CRLF
    <subject>       ::= "Subject:" <id> CRLF
    <issuer>        ::= "Issuer:" <id> CRLF
    <certification> ::= "Certification:" <encbin> CRLF
 A user would use this content type to specify needed cryptographic
 key information.  The message containing this content type might be
 directed towards an automatic or manual responder, which may be
 mail-based, depending on the local implementation and environment.
 The application/mosskey-request content type is an independent body
 part because it is entirely independent of any other body part.

Crocker, et al Standards Track [Page 28] RFC 1848 MIME Object Security Services October 1995

 If the application/mosskey-request content contains a Certification:
 field it requests certification of the self-signed certificate in the
 field value.  If the content contains an Issuer: field it requests
 the Certificate Revocation List (CRL) chain beginning with the CRL of
 the issuer identified in the field value.  If the content contains a
 Subject: field it requests either the public key of the subject or a
 certificate chain beginning with the subject identified in the field
 value, or both if both exist.
 The Subject: and Issuer: fields each contain a value of type <id>,
 which is defined in Section 4.
 One possible response to receiving an application/mosskey-request
 body part is to construct and return an application/mosskey-data body
 part.  When returning public keys, certificate chains, and
 certificate revocation list chains, if there exists more than one,
 several application/mosskey-data body parts are to be returned in the
 reply message, one for each.

5.2. application/mosskey-data Content Type Definition

 The principal objective of this content type is to convey
 cryptographic keying material from a source to a destination.  This
 might be in response to the receipt of an application/mosskey-request
 content type or it might be in anticipation of receiving an
 application/mosskey-request if it is not sent, e.g., it may be
 combined with a multipart/signed object by an originator to ensure
 that a recipient has the cryptographic keying material necessary to
 verify the signature.  When combined with other content types, the
 processing by a recipient is enhanced if the application/mosskey-data
 content type is positioned in its enclosing content type prior to the
 content types that will make use of its cryptographic keying
 material.
 However, no explicit provision is made in this document for
 determining the authenticity or accuracy of the data being conveyed.
 In particular, when a public key and its identifier is conveyed,
 there is nothing to prevent the source or an interloper along the
 path from the source to the destination from substituting alternate
 values for either the public key or the identifier.
 It is incumbent upon a recipient to verify the authenticity and
 accuracy of the data received in this way prior to its use.  This
 problem can be addressed by the use of certificates, since a
 certification hierarchy is a well-defined mechanism that conveniently
 supports the automatic verification of the data.  Alternatively, the
 source of the application/mosskey-data body part could digitally sign
 it.  In this way, if the destination believes that a correct source's

Crocker, et al Standards Track [Page 29] RFC 1848 MIME Object Security Services October 1995

 public key is available locally and if the destination believes the
 source would convey accurate data, then the contents of the
 application/mosskey-data from the source could be believed to be
 accurate.
    NOTE: Insofar as a certificate represents a mechanism by which a
    third party vouches for the binding between a name and a public
    key, the signing of an application/mosskey-data body part is a
    similar mechanism.
 (1)  MIME type name: application
 (2)  MIME subtype name: mosskey-data
 (3)  Required parameters: none
 (4)  Optional parameters: none
 (5)  Encoding considerations: quoted-printable is always sufficient.
 (6)  Security Considerations: none
 The content of this body part corresponds to the following
 production.
    <mosskeydata>   ::= <version>
                        ( <publickeydata> / <certchain> / <crlchain> )
    <version>       ::= "Version:" "5" CRLF
    <publickeydata> ::= "Key:" "PK" "," <publickey> ","
                        <id-subset> CRLF
    <certchain>     ::= <cert> *( [ <crl> ] <cert> )
    <crlchain>      ::= 1*( <crl> [ <cert> ] )
    <cert>          ::= "Certificate:" <encbin> CRLF
    <crl>           ::= "CRL:" <encbin> CRLF
 This content type is used to transfer public keys, certificate
 chains, or Certificate Revocation List (CRL) chains.  The information
 in the body part is entirely independent of any other body part.
 (Note that the converse is not true: the validity of a protected body
 part cannot be determined without the proper public keys,
 certificates, or current CRL information.)  As such, the
 application/mosskey-data content type is an independent body part.

Crocker, et al Standards Track [Page 30] RFC 1848 MIME Object Security Services October 1995

 The <publickeydata> production contains exactly one public key.  It
 is used to bind a public key with its corresponding name form and key
 selector.  It is recommended that when responders are returning this
 information that the enclosing body part be digitally signed by the
 responder in order to protect the information.  The <id-subset> token
 is defined in Section 4.2.4.
 The <certchain> production contains one certificate chain.  A
 certificate chain starts with the requested certificate and continues
 with the certificates of subsequent issuers.  Each issuer certificate
 included must have issued the preceding certificate.  For each
 issuer, a CRL may be supplied.  A CRL in the chain belongs to the
 immediately following issuer.  Therefore, it potentially contains the
 immediately preceding certificate.
 The <crlchain> production contains one certificate revocation list
 chain.  The CRLs in the chain begin with the requested CRL and
 continue with the CRLs of subsequent issuers.  The issuer of each CRL
 is presumed to have issued a certificate for the issuer of the
 preceding CRL.  For each CRL, the issuer's certificate may be
 supplied.  A certificate in the chain must belong to the issuer of
 the immediately preceding CRL.
 The relationship between a certificate and an immediately preceding
 CRL is the same in both <certchain> and <crlchain>.  In a <certchain>
 the CRLs are optional.  In a <crlchain> the certificates are
 optional.

6. Examples

 Each example is included as a separate section for ease of reference.

6.1. Original Message Prepared for Protection

 Except as explicitly indicated, the following message is used as the
 message to be protected.
    To: Ned Freed <ned@innosoft.com>
    Subject: Hi Ned!
    How do you like the new MOSS?
    Jim

Crocker, et al Standards Track [Page 31] RFC 1848 MIME Object Security Services October 1995

6.2. Sign Text of Original Message

 When the text of the original message is signed, it will look like
 this, where lines with an ampersand '&' are digitally signed (note
 the use of the public key identifier with the included email name
 identifier, on the lines marked with an asterisk '*'):
      To: Ned Freed <ned@innosoft.com>
      Subject: Hi Ned!
      MIME-Version: 1.0
      Content-Type: multipart/signed;
        protocol="application/moss-signature";
        micalg="rsa-md5"; boundary="Signed Boundary"
  1. -Signed Boundary

& Content-Type: text/plain; charset="us-ascii"

    & Content-ID: <21436.785186814.2@tis.com>
    &
    & How do you like the new MOSS?
    &
    & Jim
  1. -Signed Boundary

Content-Type: application/moss-signature

      Content-ID: <21436.785186814.1@tis.com>
      Content-Transfer-Encoding: quoted-printable
      Version: 5
    * Originator-ID: PK,MHkwCgYEVQgBAQICAwADawAwaAJhAMAHQ45ywA357G4f=
    * qQ61aoC1fO6BekJmG4475mJkwGIUxvDkwuxe/EFdPkXDGBxzdGrW1iuh5K8kl8=
    * KRGJ9wh1HU4TrghGdhn0Lw8gG67Dmb5cBhY9DGwq0CDnrpKZV3cQIDAQAB,EN,=
    * 2,galvin@tis.com
      MIC-Info: RSA-MD5,RSA,PnEvyFV3sSyTSiGh/HFgWUIFa22jbHoTrFIMVERf=
      MZXUKzFsHbmKtIowJlJR56OoImo+t7WjRfzpMH7MOKgPgzRnTwk0T5dOcP/lfb=
      sOVJjleV7vTe9yoNp2P8mi/hs7
  1. -Signed Boundary–

6.3. Sign Headers and Text of Original Message

 If, instead, we choose to protect the headers with the text of the
 original message, it will look like this, where lines with an
 ampersand '&' are encrypted:

Crocker, et al Standards Track [Page 32] RFC 1848 MIME Object Security Services October 1995

      To: Ned Freed <ned@innosoft.com>
      Subject: Hi Ned!
      MIME-Version: 1.0
      Content-Type: multipart/signed;
        protocol="application/moss-signature";
        micalg="rsa-md5"; boundary="Signed Boundary"
  1. -Signed Boundary

& Content-Type: message/rfc822

    & Content-ID: <21468.785187044.2@tis.com>
    &
    & To:         Ned Freed <ned@innosoft.com>
    & Subject:    Hi Ned!
    &
    &
    & How do you like the new MOSS?
    &
    & Jim
  1. -Signed Boundary

Content-Type: application/moss-signature

      Content-ID: <21468.785187044.1@tis.com>
      Content-Transfer-Encoding: quoted-printable
      Version: 5
      Originator-ID: PK,MHkwCgYEVQgBAQICAwADawAwaAJhAMAHQ45ywA357G4f=
      qQ61aoC1fO6BekJmG4475mJkwGIUxvDkwuxe/EFdPkXDGBxzdGrW1iuh5K8kl8=
      KRGJ9wh1HU4TrghGdhn0Lw8gG67Dmb5cBhY9DGwq0CDnrpKZV3cQIDAQAB,EN,=
      2,galvin@tis.com
      MIC-Info: RSA-MD5,RSA,ctbDBgkYtFW1sisb5w4/Y/p94LftgQ0IrEn3d6WT=
      wjfxFBvAceVWfawsZPLijVKZUYtbIqJmjKtzTJlagBawfA/KhUsvTZdR6Dj+4G=
      d8dBBwMKvqMKTHAUxGXYxwNdbK
  1. -Signed Boundary–

6.4. Encrypt Text of a Message

 If we choose to encrypt the text of the following message, that is,
 encrypt the lines marked with asterisk '*':
      To: Jim Galvin <galvin@tis.com>
      Subject: an encrypted message
  • How do you like the new MOSS?
  • Jim

Crocker, et al Standards Track [Page 33] RFC 1848 MIME Object Security Services October 1995

 the message would look as follows (note the use of the email name
 identifier, on the line marked with an asterisk '*'):
      To: Jim Galvin <galvin@tis.com>
      Subject: an encrypted message
      MIME-Version: 1.0
      Content-Type: multipart/encrypted;
        protocol="application/moss-keys";
        boundary="Encrypted Boundary"
  1. -Encrypted Boundary

Content-Type: application/moss-keys

      Content-ID: <21535.785187667.1@tis.com>
      Content-Transfer-Encoding: quoted-printable
      Version: 5
      DEK-Info: DES-CBC,D488AAAE271C8159
    * Recipient-ID: EN,2,galvin@tis.com
      Key-Info: RSA,ISbC3IR01BrYq2rp493X+Dt7WrVq3V3/U/YXbxOTY5cmiy1/=
      7NvSqqXSK/WZq05lN99RDUQhdNxXI64ePAbFWQ6RGoiCrRs+Dc95oQh7EFEPoT=
      9P6jyzcV1NzZVwfp+u
  1. -Encrypted Boundary

Content-Type: application/octet-stream

      Content-Transfer-Encoding: base64
      AfR1WSeyLhy5AtcX0ktUVlbFC1vvcoCjYWy/yYjVj48eqzUVvGTGMsV6MdlynU
      d4jcJgRnQIQvIxm2VRgH8W8MkAlul+RWGu7jnxjp0sNsU562+RZr0f4F3K3n4w
      onUUP265UvvMj23RSTguZ/nl/OxnFM6SzDgV39V/i/RofqI=
  1. -Encrypted Boundary–

Crocker, et al Standards Track [Page 34] RFC 1848 MIME Object Security Services October 1995

6.5. Encrypt the Signed Text of a Message

 If, instead, we choose to sign the text before we encrypt it, the
 structure would be as follows, where lines with an asterisk '*' are
 digitally signed and lines with an ampersand '&' are encrypted:
        Content-Type: multipart/encrypted;
          protocol="application/moss-keys";
          boundary="Encrypted Boundary"
  1. -Encrypted Boundary

Content-Type: application/moss-keys

        KEY INFORMATION
  1. -Encrypted Boundary

Content-Type: application/octet-stream

    &   Content-Type: multipart/signed;
    &     protocol="application/moss-signature";
    &     micalg="rsa-md5"; boundary="Signed Boundary"
    &
    &   --Signed Boundary
    & * Content-Type: text/plain
    & *
    & * How do you like the new MOSS?
    & *
    & * Jim
    &
    &   --Signed Boundary
    &   Content-Type: application/moss-signature
    &
    &   SIGNATURE INFORMATION
    &
    &   --Signed Boundary--
  1. -Encrypted Boundary–
 where KEY INFORMATION and SIGNATURE INFORMATION are descriptive of
 the actual content that would appear in a real body part.  The actual
 message would be like this:

Crocker, et al Standards Track [Page 35] RFC 1848 MIME Object Security Services October 1995

    To: Jim Galvin <galvin@tis.com>
    Subject: an encrypted message
    MIME-Version: 1.0
    Content-Type: multipart/encrypted;
      protocol="application/moss-keys";
      boundary="Encrypted Boundary"
  1. -Encrypted Boundary

Content-Type: application/moss-keys

    Content-ID: <21546.785188458.1@tis.com>
    Content-Transfer-Encoding: quoted-printable
    Version: 5
    DEK-Info: DES-CBC,11CC89F8D90F1DFE
    Recipient-ID: EN,2,galvin@tis.com
    Key-Info: RSA,AZTtlEc6xm0vjkvtVUITUh7sz+nOuOwP0tsym6CQozD9IwVIJz=
    Y8+vIfbh5BpR0kS6prq3EGFBFR8gRMUvbgHtEKPD/4ICQ7b6ssZ7FmKhl/cJC5rV=
    jpb4EOUlwOXwRZ
  1. -Encrypted Boundary

Content-Type: application/octet-stream

    Content-Transfer-Encoding: base64
    ZvWvtosDzRBXJzkDFFRb9Qjrgm2nDWg3zotJ3ZpExpWUG/aRJ7Vwd+PWkSfrDPJ5
    2V/wkxwMrum6xJHZonrtyd0AvaztvriMm2zXTefzwpGG1i5zK47PBqreLA3HDTK2
    U6B13vzpE8wMSVefzaCTSpXRSCh08ceVEZrIYS53/CKZV2/Sga71pGNlux8MsJpY
    Lwdj5Q3NKocg1LMngMo8yrMAe+avMjfOnhui49Xon1Gft+N5XDH/+wI9qxI9fkQv
    NZVDlWIhCYEkxd5ke549tLkJjEqHQbgJW5C+K/uxdiD2dBt+nRCXcuO0Px3yKRyY
    g/9BgTf36padSHuv48xBg5YaqaEWpEzLI0Qd31vAyP23rqiPhfBn6sjhQ2KrWhiF
    2l3TV8kQsIGHHZUkaUbqkXJe6PEdWWhwsqCFPDdkpjzQRrTuJH6xleNUFg+CG1V+
    tL4IgMjQqm3KVojRXx8bG2auVN89NfwFswmoq4fXTrh3xyVS1VgxjKkcYI8SVVmk
    YjCxVviJP3zO2UzBvCoMfADtBVBz1njYETtVGDO97uT39MqL85uEgiF4E5TkOj/m
    04+88G0/vvN/RISKJiFQJ3FyVIB/ShX9Dixl8WCx3rxwN5g2QFLiyQVulzuNhimS
    D4ZxEo7smcTsAXUjwSLRtdjmTTutw2GmFESUaIrY81NcpQJRPNAvF0IkN6ddwL4q
    vzUS99vjQp15g9FUv82lHtHwhM18a9GokVG8xYOjBBsn9anp9abh4Tp/c/vpbunQ
    UqnpV29rF4wj+8OwUOMi9ymGabBXAjw7DhNH2RdRVr1upQO896OX81VWB0LsA0cp
    +ymxhTrEI+wCHcrsNMoRK/7zAeuAi0f1t9bN594EFlLoIrBnKEa1/OUAhMT7kG1f
    NkSRnc8BZswIoPyRetsTurQfD40nsVHvNwE9Jz7wbBo00gd6blPADOUYFxfW5zu6
    ubygBqJiKPM4II2fCdNj7CptfQcoRTeguKMVPLVmFg/EINuWBFm10GqlYT7p4zhf
    zysV/3r5LVZ1E8armTCRJ2GoYG5h+SKcytaQ0IT8S2nLPCZl1hzdajsrqHFe8omQ
  1. -Encrypted Boundary–

Crocker, et al Standards Track [Page 36] RFC 1848 MIME Object Security Services October 1995

6.6. Protecting Audio Content

 In addition to text, the MOSS services as defined here will protect
 arbitrary body parts, for example, the following audio body part:
    Content-Type: audio/basic
    AUDIO DATA HERE

6.6.1. Sign Audio Content

 When signed an audio content would appear as follows, where lines
 with an ampersand '&' are digitally signed:
      Content-Type: multipart/signed;
        protocol="application/moss-signature";
        micalg="rsa-md5"; boundary="Signed Boundary"
  1. -Signed Boundary

& Content-Type: audio/basic

    & Content-Transfer-Encoding: base64
    &
    & base64(AUDIO-DATA-HERE)
  1. -Signed Boundary

Content-Type: application/moss-signature

      SIGNATURE-INFORMATION-HERE
  1. -Signed Boundary–
 where AUDIO-DATA-HERE and SIGNATURE-INFORMATION-HERE are descriptive
 of the content that would appear in a real body part.

6.6.2. Encrypt Audio Content

 When encrypted an audio content would appear as follows, where lines
 with an ampersand '&' are encrypted:

Crocker, et al Standards Track [Page 37] RFC 1848 MIME Object Security Services October 1995

      Content-Type: multipart/encrypted;
        protocol="application/moss-keys";
        boundary="Encrypted Boundary"
  1. -Encrypted Boundary

Content-Type: application/moss-keys

      KEY-INFORMATION-HERE
  1. -Encrypted Boundary

Content-Type: application/octet-stream

      Content-Transfer-Encoding: base64
    & Content-Type: audio/basic
    &
    & base64(encrypted(AUDIO-DATA-HERE))
  1. -Encrypted Boundary–
 where KEY-INFORMATION-HERE and AUDIO-DATA-HERE are descriptive of the
 content that would appear in a real body part.

7. Observations

 The use of MIME and the framework defined by [7] exhibits several
 properties:
 (1)  It allows arbitrary content types to be protected, not just the
      body of an RFC822 message.
 (2)  It allows a message to contain several body parts which may or
      may not be protected.
 (3)  It allows the components of a multipart or message content to be
      protected with different services.
 The use of a MIME-capable user agent makes complex nesting of
 protected message body parts much easier.  For example, the user can
 separately sign and encrypt a message.  This allows complete
 separation of the confidentiality security service from the digital
 signature security service.  That is, different key pairs could be
 used for the different services and could be protected separately.

Crocker, et al Standards Track [Page 38] RFC 1848 MIME Object Security Services October 1995

 This is useful for at least two reasons.  First, some public key
 algorithms do not support both digital signatures and encryption; two
 key pairs would be required in this case.  Second, an employee's
 company could be given access to the (private) decryption key but not
 the (private) signature key, thereby granting the company the ability
 to decrypt messages addressed to the employee in emergencies without
 also granting the company the ability to sign messages as the
 employee.

8. Comparison of MOSS and PEM Protocols

 MOSS differs from PEM in the following ways.
 (1)  When using PEM, users are required to have certificates.  When
      using MOSS, users need only have a public/private key pair.
 (2)  MOSS broadens the allowable name forms that users may use to
      identify their public keys, including arbitrary strings, email
      addresses, or distinguished names.
 (3)  PEM currently only supports text-based electronic mail messages
      and the message text is required to be represented by the ASCII
      character set with "<CR><LF>" line delimiters.  These
      restrictions no longer apply.
 (4)  The PEM specification currently requires that encryption
      services be applied only to message bodies that have been
      signed.  By providing for each of the services separately, they
      may be applied in any order according to the needs of the
      requesting application.
 (5)  MIME includes transfer encoding operations to ensure the
      unmodified transfer of body parts.  Therefore, unlike PEM, MOSS
      does not need to include these functions.
 (6)  PEM specifies a Proc-Type: header field to identify the type of
      processing that was performed on the message.  This
      functionality is subsumed by the MIME Content-Type: headers.
      The Proc-Type: header also includes a decimal number that is
      used to distinguish among incompatible encapsulated header field
      interpretations which may arise as changes are made to the PEM
      standard.  This functionality is replaced by the Version: header

Crocker, et al Standards Track [Page 39] RFC 1848 MIME Object Security Services October 1995

      specified in this document.
 (7)  PEM specifies a Content-Domain: header, the purpose of which is
      to describe the type of the content which is represented within
      a PEM message's encapsulated text.  This functionality is
      subsumed by the MIME Content-Type: headers.
 (8)  The PEM specifications include a document that defines new types
      of PEM messages, specified by unique values used in the Proc-
      Type: header, to be used to request certificate and certificate
      revocation list information.  This functionality is subsumed by
      two new content types specified in this document:
      application/mosskey- request and application/mosskey-data.
 (9)  The header fields having to do with certificates (Originator-
      Certificate: and Issuer-Certificate:) and CRLs (CRL:) are
      relegated for use only in the application/mosskey-data and
      application/mosskey-request content types and are no longer
      allowed in the header portion of a PEM signed or encrypted
      message.  This separates key management services from the
      digital signature and encryption services.
 (10) The grammar specified here explicitly separates the header
      fields that may appear for the encryption and signature security
      services.  It is the intent of this document to specify a
      precise expression of the allowed header fields; there is no
      intent to disallow the functionality of combinations of
      encryption and signature security found in [3].
 (11) With the separation of the encryption and signature security
      services, there is no need for a MIC-Info: field in the headers
      associated with an encrypted message.
 (12) In [3], when asymmetric key management is used, an Originator-ID
      field is required in order to identify the private key used to
      sign the MIC argument in the MIC-Info: field.  Because no MIC-
      Info: field is associated with the encryption security service
      under asymmetric key management, there is no requirement in that
      case to include an Originator-ID field.
 (13) The protocol specified here explicitly excludes symmetric key

Crocker, et al Standards Track [Page 40] RFC 1848 MIME Object Security Services October 1995

      management.
 (14) This document requires all data that is to be digitally signed
      to be represented in 7bit form.

9. Security Considerations

 This entire document is about security.

10. Acknowledgements

 David H. Crocker suggested the use of a multipart structure for the
 MIME and PEM interaction, which has evolved into the MOSS protocol.
 The MOSS protocol is a direct descendant of the PEM protocol.  The
 authors gratefully acknowledge the editors of those specification,
 especially John Linn and Steve Kent.  This work would not have been
 possible had it not been for all of the PEM developers, users, and
 interested persons who are always present on the PEM developers
 mailing list and at PEM working group meetings at IETF meetings,
 especially, Amanda Walker, Bob Juenemann, Steve Dusse, Jeff Thomson,
 and Rhys Weatherly.

11. References

 [1] Crocker, D., "Standard for the Format of ARPA Internet Text
     Messages", STD 11, RFC 822, University of Delaware, August 1982.
 [2] Borenstein, N., and N. Freed, "MIME (Multipurpose Internet Mail
     Extension) Part One: Mechanisms for Specifying and Describing the
     Format of Internet Message Bodies", RFC 1521, Bellcore and
     Innosoft, September 1993.
 [3] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
     I: Message Encryption and Authentication Procedures", RFC 1421,
     IAB IRTF PSRG, IETF PEM WG, February 1993.
 [4] Kent, S., "Privacy Enhancement for Internet Electronic Mail: Part
     II: Certificate-Based Key Management", RFC 1422, BBN
     Communications, February 1993.
 [5] Balenson, D., "Privacy Enhancement for Internet Electronic Mail:
     Part III: Algorithms, Modes, and Identifiers", RFC 1423, Trusted
     Information Systems, February 1993.

Crocker, et al Standards Track [Page 41] RFC 1848 MIME Object Security Services October 1995

 [6] Kaliski, B., "Privacy Enhancement for Internet Electronic Mail:
     Part IV: Key Certification and Related Services", RFC 1424, RSA
     Laboratories, February 1993.
 [7] Galvin, J., Murphy, S., Crocker, S., and N. Freed, "Security
     Multiparts for MIME: Multipart/Signed and Multipart/Encrypted",
     RFC 1847, Trusted Information Systems and Innosoft, September
     1995.
 [8] The Directory -- Models.  X.501, 1988.  Developed in
     collaboration, and technically aligned, with ISO 9594-2.
 [9] The Directory -- Authentication Framework.  X.509, 1988.
     Developed in collaboration, and technically aligned, with ISO
     9594-8.

Crocker, et al Standards Track [Page 42] RFC 1848 MIME Object Security Services October 1995

12. Authors' Addresses

 Steve Crocker
 CyberCash, Inc.
 2086 Hunters Crest Way
 Vienna, VA 22181
 Phone: +1 703 620 1222
 Fax: +1 703 391 2651
 EMail:  crocker@cybercash.com
 James M. Galvin
 Trusted Information Systems
 3060 Washington Road
 Glenwood, MD  21738
 Phone: +1 301 854 6889
 Fax: +1 301 854 5363
 EMail:  galvin@tis.com
 Sandra Murphy
 Trusted Information Systems
 3060 Washington Road
 Glenwood, MD  21738
 Phone: +1 301 854 6889
 Fax: +1 301 854 5363
 EMail:  murphy@tis.com
 Ned Freed
 Innosoft International, Inc.
 1050 East Garvey Avenue South
 West Covina, CA 91790
 Phone: +1 818 919 3600
 Fax: +1 818 919 3614
 EMail:  ned@innosoft.com

Crocker, et al Standards Track [Page 43] RFC 1848 MIME Object Security Services October 1995

Appendix A: Collected Grammar

 The version of the grammar in this document is as follows:
    <version>       ::= "Version:" "5" CRLF
 The following grammar tokens are used throughout this specification:
    <encbin>        ::= 1*<encbingrp>
    <encbingrp>     ::= 4*4<encbinchar>
    <encbinchar>    ::= <ALPHA> / <DIGIT> / "+" / "/" / "="
    <hexchar>       ::= <DIGIT> / "A" / "B" / "C" / "D" / "E" / "F"
                        ; no lower case
 The content of an application/moss-signature body part is as follows:
    <mosssig>       ::= <version> ( 1*<origasymflds> )
    <version>       ::= "Version:" "5" CRLF
    <origasymflds>  ::= <origid> <micinfo>
    <origid>        ::= "Originator-ID:" <id> CRLF
    <micinfo>       ::= "MIC-Info:" <micalgid> "," <ikalgid> ","
                        <asymsignmic> CRLF
 The content of an application/moss-keys body part is as follows:
    <mosskeys>      ::= <version> <dekinfo> 1*<recipasymflds>
    <version>       ::= "Version:" "5" CRLF
    <dekinfo>       ::= "DEK-Info" ":" <dekalgid>
                        [ "," <dekparameters> ] CRLF
    <recipasymflds> ::= <recipid> <asymkeyinfo>
    <recipid>       ::= "Recipient-ID:" <id> CRLF
    <asymkeyinfo>   ::= "Key-Info" ":" <ikalgid> "," <asymencdek> CRLF

Crocker, et al Standards Track [Page 44] RFC 1848 MIME Object Security Services October 1995

 Identifiers are defined as follows:
    <id>            ::= <id-subset> / <id-publickey> / <id-issuer>
    <id-subset>     ::= <id-email> / <id-string> / <id-dname>
    <id-email>      ::= "EN"  "," <keysel> "," <emailstr> CRLF
    <id-string>     ::= "STR" "," <keysel> "," <string> CRLF
    <id-dname>      ::= "DN"  "," <keysel> "," <dnamestr> CRLF
    <id-publickey>  ::= "PK"  "," <publickey> [ "," <id-subset> ] CRLF
    <id-issuer>     ::= "IS"  "," <dnamestr>  "," <serial> CRLF
    <keysel>        ::= 1*<hexchar>
                        ; hex dump of a non-null sequence of octets
    <emailstr>      ::= <addr-spec> / <route-addr>
                        ; an electronic mail address as defined by
                        ; these two tokens from RFC822
    <string>        ::= ; a non-null sequence of characters
    <dnamestr>      ::= <encbin>
                        ; a printably encoded, ASN.1 encoded
                        ; distinguished name (as defined by the 'Name'
                        ; production specified in X.501 [8])
    <publickey>     ::= <encbin>
                        ; a printably encoded, ASN.1 encoded public
                        ; key (as defined by the
                        ; 'SubjectPublicKeyInfo' production specified
                        ; in X.509 [9])
    <serial>        ::= 1*<hexchar>
                        ; hex dump of a certificate serial number
 The content of an application/mosskey-request body part is as
 follows:
    <request>       ::= <version>
                        ( <subject> / <issuer> / <certification> )
    <version>       ::= "Version:" "5" CRLF

Crocker, et al Standards Track [Page 45] RFC 1848 MIME Object Security Services October 1995

    <subject>       ::= "Subject:" <id> CRLF
    <issuer>        ::= "Issuer:" <id> CRLF
    <certification> ::= "Certification:" <encbin> CRLF
 The content of an application/mosskey-data body part is as follows:
    <mosskeydata>   ::= <version>
                        ( <publickeydata> / <certchain> / <crlchain> )
    <version>       ::= "Version:" "5" CRLF
    <publickeydata> ::= "Key:" "PK" "," <publickey> ","
                        <id-subset> CRLF
    <certchain>     ::= <cert> *( [ <crl> ] <cert> )
    <crlchain>      ::= 1*( <crl> [ <cert> ] )
    <cert>          ::= "Certificate:" <encbin> CRLF
    <crl>           ::= "CRL:" <encbin> CRLF

Crocker, et al Standards Track [Page 46] RFC 1848 MIME Object Security Services October 1995

Appendix B: Imported Grammar

 Options normally present in the grammar reprinted here which are
 illegal in MOSS are excluded in this reprinting, for the convenience
 of the reader.
 The following productions are taken from [5].  The grammar presented
 in [5] remains the authoritative source for these productions; they
 are repeated here for the convenience of the reader.
    <dekalgid>         ::= "DES-CBC"
    <ikalgid>          ::= "RSA"
    <micalgid>         ::= "RSA-MD2" / "RSA-MD5"
    <dekparameters>    ::= <DESCBCparameters>
    <DESCBCparameters> ::= <IV>
    <IV>               ::= <hexchar16>
    <hexchar16>        ::= 16*16<hexchar>
    <asymsignmic>      ::= <RSAsignmic>
    <RSAsignmic>       ::= <encbin>
    <asymencdek>       ::= <RSAencdek>
    <RSAencdek>        ::= <encbin>
 The following productions are taken from [1].  The grammar presented
 in [1] remains the authoritative source for these productions; they
 are repeated here for the convenience of the reader.
    <route-addr>    ::= "<" [ <route> ] <addr-spec> ">"
    <route>         ::=  1# ( "@" <domain> ) ":" ; path-relative
    <addr-spec>     ::= <local-part> "@" <domain>; global address
    <local-part>    ::= <word> *( "." <word> )   ; uninterpreted
                                                 ; case-preserved
    <domain>        ::= <sub-domain> *( "." <sub-domain> )
    <sub-domain>    ::= <domain-ref> / <domain-literal>
    <domain-ref>    ::= <atom>                   ; symbolic
                                                 ; reference
    <domain-literal>::= "[" *( <dtext> / <quoted-pair> ) "]"

Crocker, et al Standards Track [Page 47] RFC 1848 MIME Object Security Services October 1995

    <dtext>         ::= <any CHAR excluding "[", "]",
                        "\" & <CR>, & including
                        linear-white-space>
                                                 ; => may be folded
    <word>          ::= <atom> / <quoted-string>
    <quoted-string> ::= """ *( <qtext> / <quoted-pair> ) """
    <qtext>         ::= (any <CHAR> excepting """, "\", and CR,
                         and including <linear-white-space>)
    <quoted-pair>   ::= "\" <CHAR>               ; may quote any
                                                 ; char
    <linear-white-space> ::= 1*( [ CRLF ] <LWSP-char> )
                                                 ; semantics = SPACE
                                                 ; CRLF => folding
    <LWSP-char>     ::= SPACE / HTAB             ; semantics = SPACE
    <atom>          ::= 1*(any <CHAR>
                        except <specials>, SPACE and <CTL>s)
    <CHAR>          ::= <any ASCII character>
    <CTL>           ::= <any ASCII control character and DEL>
    <specials>      ::= "(" / ")" / "<" / ">" / "@"
                        /  "," / ";" / ":" / "\" / <">
                        /  "." / "[" / "]"
                                                 ; Must be in quoted-
                                                 ; string, to use
                                                 ;  within a word.
    <ALPHA>         ::= <any ASCII alphabetic character>
                                                 ; (101-132, 65.-90.)
                                                 ; (141-172, 97.-122.)
    <DIGIT>         ::= <any ASCII decimal digit>; (60-71, 48.-57.)

Crocker, et al Standards Track [Page 48]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1848.txt · Last modified: 1995/10/02 19:50 by 127.0.0.1

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