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Versions: 05 06 07 rfc1848                                              
Network Working Group                                       Steve Crocker
INTERNET DRAFT                                                  Ned Freed
draft-ietf-pem-mime-05.txt                                     Jim Galvin
                                                             Sandy Murphy
                                                                June 1994


                     PEM Security Services and MIME



1.  Status of this Memo

This document is an Internet Draft.  Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas, and
its Working Groups.  Note that other groups may also distribute working
documents as Internet Drafts.

Internet Drafts are valid for a maximum of six months and may be
updated, replaced, or obsoleted by other documents at any time.  It is
inappropriate to use Internet Drafts as reference material or to cite
them other than as ``work in progress''.

To learn the current status of any Internet Draft, please check the
1id-abstracts.txt listing contained in one of the Internet Drafts Shadow
Directories on ds.internic.net (US East Coast), venera.isi.edu (US West
Coast), munnari.oz.au (Pacific Rim), or nic.nordu.net (Europe).

2.  Abstract

This document specifies how the services of MIME and PEM can be used in
a complementary fashion.  MIME, 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.  PEM, an acronym for "Privacy Enhanced Mail", provides message
authentication/integrity and message encryption services for Internet
mail messages.

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 RFC 822 [1], whilst the body, if structured, is
defined according to MIME [2].  MIME does not provide for the
application of security services.







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PEM [3-6] specifies how to apply encryption and authentication/integrity
services to the contents of a textual electronic mail message but does
not provide message structuring or type labelling facilities.  This
document specifies how to use PEM with the multipart/signed and
multipart/encrypted MIME content types to provide
authentication/integrity and encryption services.  We refer to the
authentication/integrity service as a digital signature service.

This document updates the message encryption and signature procedures
defined by [3] and obsoletes the key certification and related services
defined by [6].  The changes to [3] include the separation of the
encryption and signature services, the removal of the limitation to
enhance only text-based messages, the removal of the transfer encoding
operation, the deprecation of the Content-Domain: and Proc-Type:
headers, and the separation of certificate and certificate revocation
list transmission from the security enhancements.  These changes
represent a departure in mechanism, not in effect, and are detailed in
Section ??.

In addition, this document proposes three technical changes: in [3]
symmetric key management is deprecated, also in [3] the canonicalization
operation is generalized, and in [4] the allowable name forms for the
subjects of certificates is broadened to include arbitrary strings and
email addresses, and users may distribute their public keys directly in
lieu of certificates.

The key certification and related services document [6] is obsoleted by
the specification of two new MIME content types: application/key-request
and application/key-data.  These new content types are used to transmit
requests for key operations (retrieval, certification, revocation list
retrieval, etc.)  and the responses to those requests.  These two
content types are independent body parts and are not required to be
encapsulated in any other body part.  These changes represent a
departure in mechanism, not in effect, and are detailed in Section ??.

The relationship between MIME and PEM is described in terms of two
functions: message composition and message delivery.

3.  Applying PEM Security Services to MIME Body Parts

The next section describes the processing steps necessary to prepare a
MIME body part for the application of PEM security services.  The
succeeding two sections describe the content of the multipart/signed and
multipart/encrypted body parts resulting from the application of PEM
security services to MIME body parts.





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3.1.  PEM Processing Steps

The following three steps describe the preparation of outbound PEM
messages.  These steps may be repeated as necessary to prepare a message
for submission.

(1)  Local Form -- the content of the message is prepared in the native
     format of the user's local environment

(2)  Canonical Form -- the content of the message is transformed to a
     canonical form for the digital signature service; no
     canonicalization is required for the encryption service

(3)  Security Form -- either of the signature or encryption services may
     be applied

Each of these steps is described in detail below.  Their relationship to
message composition and delivery is described in Section ??.

3.1.1.  Step 1: Local Form

The message content is created in the native format of the user's local
environment.

3.1.2.  Step 2: Canonical Form

Prior to the application of the digital signature service, the content
must be in a canonical form.  No canonicalization is required for the
encryption service and therefore processing continues with the next
step.

Transforming the content to be signed into a canonical form is a
necessary and essential step in the digital signature process.  The
canonical form must satisfy the property that it is uniquely and
unambiguously representable on both the originator and recipient's local
environment.  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 include the
digital signature value when transferring the body part, while the
recipient needs to be able to compare a re-calculated value with the
received value.  Further, the canonical form should satisfy the property
that it is representable on as many different host computers as
possible.  By satisfying this property, 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.





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The canonical form of all content types is defined to be 7bit.  The data
to be signed must be represented as 7bit.  Since the MIME standard
explicitly disallows nested encodings, the body parts enclosed in a
multipart content type, for example, must be encoded in a 7bit
representation.  Any valid MIME encoding may be selected.

The 7bit representation of the data is transferred to the recipient.  As
may be required by MIME, an appropriate Content-Transfer-Encoding:
header is included with the data.  Upon receipt, a MIME implementation
would verify the signature of the data prior to decoding the data and
displaying it to the recipient.

Representing all complex content types as 7bit transforms them into
text-based content types.  However, text-based content types present a
unique problem.  In particular, there are far too many broken message
transfer agents that make arbitrary changes to text-based messages as
they are relayed, including adding, deleting, or changing TAB and SPACE
characters, and line delimiters are altered by message transfer agent
protocols.  These changes will make it impossible for recipients to
verify the signature on a message.

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 canonicalization transformation
is to transform the local line delimiter to the two character sequence
"<CR><LF>".

The transformation to the universal line delimiter is only required for
the purposes of computing the digital signature.  Thus, originators must
apply the universal line delimiter transformation before calculating the
digital signature but must transfer the data without the universal line
delimiter transformation.  Similarly, recipients must apply the
universal line delimiter transformation before calculating the digital
signature.

    NOTE: An originator can not transfer the content with the
    universal line delimiter transformation intact because the
    transformation process is not idempotent.  In particular, SMTP
    servers may themselves convert the universal line delimiter to a
    local line delimiter, prior to the message being delivered to
    the user.  Thus, a recipient has no way of knowing if the
    transformation is present or not.  Thus, if the recipient
    applies the transformation to a content in which it is already
    present, the resulting content may have two line delimiters





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    present, which would cause the verification of the signature to
    fail.


3.1.3.  Step 3: Security Form

Either of the digital signature or encryption services is applied to a
content.  The content to be protected is prepared by a MIME
implementation and made available to a PEM implementation according to a
local convention.  The PEM implementation must produce two outputs: the
data that has been protected and the control information necessary to
verify or remove the protection.  These outputs must be made available
to the MIME implementation which will construct a multipart/signed or
multipart/encrypted content, according to the service requested.  The
multipart content replaces the content that was selected for protection.

3.2.  Use of multipart/signed Content Type

When this content type is used, the value of the required parameter
"protocol" is "pem" and the value of the required parameter "hashalg" is
one of the valid choices from [5], for example:

    Content-Type: multipart/signed; protocol="pem"; hashalg="md5";
      boundary="Signed Message"

    --Signed Message
    Content-Type: text/plain

    This is some example text.

    --Signed Message
    Content-Type: application/signature

    <pemsig>
    --Signed Message--


where the <pemsig> token is defined as follows.












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    <pemsig>             ::= <version> (1*<origasymflds>)

    <version>            ::= "Version:" "5" CRLF

    <origasymflds>       ::= <origid> <micinfo>

    <origid>             ::= "Originator-ID:" <id> CRLF


The token <id> is defined in Section ??.

The only valid value for a Content-Transfer-Encoding: header, if
included, is "7bit".

3.3.  Use of multipart/encrypted Content Type

When this content type is used, the value of the required parameter
"protocol" is "pem", for example:

    Content-Type: multipart/encrypted; protocol="pem";
      boundary="Encrypted Message"

    --Encrypted Message
    Content-Type: application/keys

    <pemkeys>

    --Encrypted Message
    Content-Type: application/octet-stream

    <encrypted data>
    --Encrypted Message--


where the <pemkeys> token is defined as follows.

    <pemkeys>            ::= <version> <dekinfo> 1*<recipasymflds>

    <version>            ::= "Version:" "5" CRLF

    <recipasymflds>      ::= <recipid> <asymkeyinfo>

    <recipid>            ::= "Recipient-ID:" <id> CRLF

    <asymkeyinfo>        ::= "Key-Info" ":" <ikalgid> "," <asymencdek> CRLF





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The token <id> is defined in Section ??.

4.  Removing PEM Security Services from PEM Body Parts

Upon receipt of a multipart/signed or multipart/encrypted body part, the
PEM security services are removed by reversing the sequence of steps
specified in Section ??, modifying step 2 as follows.

(1)  All content types must have their line delimiters canonicalized
     prior to removing the PEM security services.

(2)  Outer layers of PEM security services must be processed prior to
     processing inner layers of PEM security services.  Processing
     includes a user choosing to display a content without removing the
     PEM security services.

5.  Definition of New Name Forms

    WARNING: This is the first draft of this section.  Although
    conceptually it represents a direction that will not change,
    while this document is an internet draft the details of the
    specification are subject to change at any time, without notice,
    owing to comments and implementation experience.  Implementors
    are encouraged to contact the authors for the current status.


Currently, [3] requires the use of certificates to specify the public
key used to create a PEM message.  Within certificates, [4] requires the
use of distinguished names as specified by the X.500 Series of
Recommendations.  However, the Internet community has a great deal more
experience with the use of electronic mail addresses as identifiers and
there is a desire to be able to use arbitrary strings to identify the
owners of public keys.  Hence, there is a need to support name forms
which do not conform to the expected usage of distinguished names.

In addition, users may distribute their public keys via mechanisms
outside the scope of the PEM specification, for example, in a file via
FTP as opposed to in a certificate.  As a result, it is desirable to be
able to explicitly specify the public key used rather than an identifier
of the public key.

The objective of the various Originator and Recipient fields specified
in [3] is to indicate which public key has been used or is required.
This document simplifies the set of fields by specifying exactly two:
Originator-ID: for originators and Recipient-ID: for recipients.  The





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value of each of these fields is indicated by the token <id>, which is
defined as follows.

    <id>           ::=   <id-email> / <id-string> / <id-dname>
                       / <id-publickey> / <id-issuer>

    <id-email>      ::= "EN"  "," <atstring>
                              "," <hashalgid> "," <hashpublickey>
    <id-string>     ::= "STR" "," <string>
                              "," <hashalgid> "," <hashpublickey>
    <id-dname>      ::= "DN"  "," <dname>
                              "," <hashalgid> "," <hashpublickey>
    <id-publickey>  ::= "PK"  ","
                              "," <pkalgid>   "," <publickey>
                              "," ( <string> / <atstring> )
    <id-issuer>     ::= "IS"  "," <dname>     "," <serial>

    <atstring>      ::= <encbin>
                        ; a printably encoded, ASN.1 encoded
                        ; string containing exactly one '@'
    <string>        ::= <encbin>
                        ; "a sequence of characters excluding '@'"
                        ; a printably encoded, ASN.1 value

    <hashalgid>     ::= "to be defined by RFC 1423"
    <hashpublickey> ::= 1*<hexchar>
                        ; hex dump of the <hashalgid> hash of the
                        ; public key

    <pkalgid>       ::= "to be defined by RFC 1423"
    <publickey>     ::= <encbin>
                        ; a printably encoded, ASN.1 encoded public key

    <dname>         ::= <encbin>
                        ; a printably encoded, ASN.1 encoded
                        ; distinguished name
    <serial>        ::= 1*<hexchar>
                        ; hex dump of the serial number of a certificate


The inclusion of the hash of the public key is intended to facilitate
the recognition of which public key among several that may be associated
with the string or distinguished name.







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The identifiers <id-email> and <id-string> are distinguished only by the
presence or absence of the character '@'.  In all other respects they
are equivalent and are encoded strings that are to be used as the
subject name in a certificate.  This distinguishing characteristic was
chosen as opposed to defining a new object identifier to represent email
addresses because of the perceived difficulty in distributing and
implementing the definition of a new object identifier.

The <id-publickey> identifier allows for the direct distribution and
indication of the public key that was or is to be used to process the
message.

The <id-issuer> identifier is included for backward compatibility with
the ID-ASymmetric fields defined in [3].  The older fields are easily
converted to this new form by prefixing the old value with "IS," and
replacing the field name with an appropriate new ID field.

6.  Definition of New Content Types

This document defines two new content types, the contents of which
comprise a replacement mechanism for [6].  The first content type is
application/key-request, which replaces the certification and CRL-
retrieval request messages.  The second content type is
application/key-data, which replaces the certification reply message,
the crl-storage request message, and the crl-retrieval reply message.
There were no requirements for a crl-storage reply message and none are
specified in this document.  This document includes a specification for
a certificate request message, which was previously undefined.

    NOTE: RFC1424 has some descriptive text, especially for
    certification messages, that should probably be included.


6.1.  application/key-request Content Type Definition

(1)  MIME type name: application

(2)  MIME subtype name: key-request

(3)  Required parameters: none

(4)  Optional parameters: none

(5)  Encoding considerations: quoted-printable is always sufficient






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(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



This content type is used to provide for some of the requests described
in [6].  The information in the body part is entirely independent of any
other body part.  As such, the application/key-request content type is
an independent body part.

The certification request, certificate-retrieval request and crl-
retrieval request are provided for directly.  If the 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 chain beginning with
the issuer identified in the field value.  If the content contains a
Subject: field it requests the certificate chain beginning with the
subject identified in the field value.

The Subject: and Issuer: fields each contain a value of type Name,
encoded according to the Basic Encoding Rules, then in ASCII, as for the
Originator-ID-Asymmetric: field of [3].

The crl-storage request is provided for by the application/key-data
content type described in the next section.

In each case, the response is transmitted in an application/key-data
content type.  When returning certificate and certificate revocation
list chains, if there exists more than one chain, several
application/key-data contents are to be returned in the reply message,
one for each chain.

6.2.  application/key-data Content Type Definition

(1)  MIME type name: application






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(2)  MIME subtype name: key-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.


    <certdata>           ::= <certchain> / <crlchain>
    <certchain>          ::= <version> <cert> *( [ <crl> ] <cert> )
    <crlchain>           ::= <version> 1*( <crl> [ <cert> ] )
    <cert>               ::= "Certificate:" <encbin> CRLF
    <crl>                ::= "CRL:" <encbin> CRLF
    <version>            ::= "Version:" "5" CRLF



This content type is used to transfer certificate or Certificate
Revocation List (CRL) information.  The information in the body part is
entirely independent of any particular privacy enhanced message.  (Note
that the converse is not true: the validity of a privacy enhanced
message cannot be determined without the proper certificates or current
CRL information.)  As such, the application/key-data content type is an
independent body part.

The <certchain> production contains one certificate chain.  A
certificate chain starts with a 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.






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The relationship between a certificate and an immediately preceding CRL
is the same in both cases.  In a <certchain> the crl's are optional.  In
a <crlchain> the certificates are optional.

7.  Message Processing

When a user composes a message, it is the responsibility of the user
agent to construct a valid MIME message.  In particular, Content-Type:
and Content-Transfer-Encoding: headers should be used wherever they are
appropriate.  This allows the receiving user agent to unambiguously
interpret the message body and process it accordingly.

Each block of content headers associated with either an RFC822 <message>
or with a MIME <body-part> represents a logical place where security
enhancement can be requested.  A security enhancement request associated
with a particular <message> or <body-part> content is taken to apply to
the entire content; it is not possible to security-enhance only a
portion of a body part.

The mechanism used to communicate security enhancement requests to the
pre-submission processor described below is strictly a local
implementation issue.  However, the interface between the message
composer and pre-submission processing MUST be trustworthy, since the
message composer relies on pre-submission processing to either perform
the requested security enhancement operation or return an error.
Regardless of the mechanism chosen, great care should be taken to
safeguard against both the release of information that has not received
the requested type of security enhancement as well as tampering with the
enhancement request itself.

7.1.  Pre-Submission Algorithm

The user agent first composes a MIME-compliant message and then applies
this algorithm:

(1)  If the content at this (initially top) level has NOT been selected
     for security enhancement, the user agent sees if the content is
     either multipart or message.  If so, it then recursively applies
     this algorithm to the encapsulated body parts; if not, it
     terminates processing for this content.

(2)  If the content at this level has been selected for security
     enhancement, then the content, including its headers, constitutes
     the object that is to be made available to the security enhancement
     process.  The headers at a minimum will include a Content-Type





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     header, either explicit or implicit.  The object will eventually be
     replaced with the multipart content that is produced by the
     security enhancement operation.

(3)  The selected security enhancement is performed.  This enhancement
     produces two data streams: the enhanced object and a control stream
     comprised of a set of headers as defined in the <pemsig> or
     <pemkeys> productions.

(4)  A new body part is then constructed, of content type
     multipart/signed or multipart/encrypted.  The new body part
     contains two body parts, whose content depends on the enhancement
     requested, which are constructed according to the specifications in
     this document.

(5)  This multipart content replaces the original object.

7.2.  Post-Delivery Algorithm

When a user receives a message containing a multipart content, the user
agent may transform the content back into its original form prior to
privacy-enhancement.  This operation, the post-delivery algorithm, is
performed by reversing the steps performed during the pre-submission
algorithm.

When the original content is reconstituted, it may use octet values
outside of the US-ASCII repertoire and may contain body parts without
line breaks.  If the user agent replaces the multipart content with the
original content, then it must select appropriate Content-Transfer-
Encodings for each body part and add corresponding Content-Transfer-
Encoding: headers.

Upon successful completion of the post-delivery algorithm for each
content, the type of enhancement that was in effect for that content
must be communicated to the user.  The mechanism used to do this is a
local implementation issue.  As with requests for enhancement to the
pre-submission algorithm, the path between post-delivery processing and
actual display of the message must be a trusted one, lest a message be
presented that purports to have undergone some form of enhancement it
did not in fact receive.

8.  Examples

    NOTE: To be included upon completion of implementation.






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9.  Observations

The use of the pre-submission and post-delivery algorithms to combine
PEM and MIME capabilities exhibits several properties:

(1)  It allows privacy-enhancement of an arbitrary content, not just the
     body of an RFC 822 message.

(2)  For a multipart or message content, it allows the user to specify
     different privacy enhancements to be applied to different
     components of the structure of the content.

(3)  It provides for messages containing several privacy enhanced
     contents, thereby removing the requirement for PEM software to be
     able to generate or interpret a single content which intermixes
     both unenhanced and enhanced components.

The use of a MIME-capable user agent makes complex nesting of enhanced
message body parts much easier.  For example, the user can separately
sign and encrypt a message.  This motivates a complete separation of the
confidentiality security service from the digital signature security
service.  That is, different keys could be used for the different
services and could be protected separately.  In the asymmetric case,
this means 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.

The use of two private keys requires the ability to maintain multiple
certificates for each user.

10.  Summary of Changes to PEM Specification

This document updates the message encryption and signature procedures
defined by [3] and obsoletes the key certification and related services
defined by [6].  The changes are enumerated below.

(1)  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
     recursively in any order according to the needs of the requesting
     application.







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(2)  PEM implementations are currently restricted to processing only
     text-based electronic mail messages.  In fact, the message text is
     required to be represented by the ASCII character set with
     "<CR><LF>" line delimiters.  This restriction no longer applies.

(3)  With the removal of the text restriction it is not possible to
     specify a universal canonical form.  However, canonicalization is
     required for the digital signature service, so the content of each
     body part must be transformed into a canonical form according to
     its type.

(4)  MIME includes transfer encoding operations to ensure the unmodified
     transfer of body parts, which obviates these services in PEM.

(5)  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 included a decimal number that was 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 specified in this
     document.

(6)  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.

(7)  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.

(8)  The header fields having to do with certificates (Originator-
     Certificate: and Issuer-Certificate:) and CRLs (CRL:) are relegated
     for use only in the application/key-data and application/key-
     request content types and are no longer allowed in the header
     portion of a PEM signed or encrypted message.

(9)  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 reduce the
     functionality of combinations of encryption and signature security





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     from those of [3].

(10) 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 under asymmetric key
     management.

(11) 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 managment, there is no requirement in that case to
     include an Originator-ID field.

These changes represent a departure in mechanism, not in effect, from
those specified in [3] and [6].  The following technical changes to [3]
and [4] are also specified by this document.

(1)  The grammar specified here explicitly excludes symmetric key
     management.  Currently, there are no generally available
     implementations of symmetric key management nor are there any known
     plans for implementing it.  As a result, the IETF standards process
     will require this feature to be dropped when the documents are
     promoted to draft standard status from proposed standard status.

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

(3)  This document relaxes the syntax of distinguished names.  In
     particular, distinguished names are not constrained to conform to
     the X.500 Series of Recommendations.  Instead users may use
     arbitrary strings and email addresses as their name.  Further,
     users may distribute their public key directly in lieu of using
     certificates.  In support of this change the Originator-ID-
     ASymmetric: and Recipient-ID-ASymmetric: fields are deprecated in
     favor of Originator-ID: and Recipient-ID: fields, respectively.

11.  Collected Grammar

The following is a summary of the grammar presented in this document.

(1)  Signature headers








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         <pemsig>             ::= <version> (1*<origasymflds>)

         <version>            ::= "Version:" "5" CRLF

         <origasymflds>       ::= <origid> <micinfo>

         <origid>             ::= "Originator-ID:" <id> CRLF


(2)  Encryption Headers


         <pemkeys>            ::= <version> <dekinfo> 1*<recipasymflds>

         <version>            ::= "Version:" "5" CRLF

         <recipasymflds>      ::= <recipid> <asymkeyinfo>

         <recipid>            ::= "Recipient-ID:" <id> CRLF

         <asymkeyinfo>        ::= "Key-Info" ":" <ikalgid> "," <asymencdek> CRLF


(3)  Request Headers (certificate, certification, etc.)


         <request>            ::= <version>
                                  ( <subject> / <issuer> / <certification> )
         <version>            ::= "Version:" "5" CRLF
         <subject>            ::= "Subject:" <id> CRLF
         <issuer>             ::= "Issuer:" <id> CRLF
         <certification>      ::= "Certification:" <encbin> CRLF


(4)  Certificate Headers (certificate, certification revocation list)

         <certdata>           ::= <certchain> / <crlchain>
         <certchain>          ::= <version> <cert> *( [ <crl> ] <cert> )
         <crlchain>           ::= <version> 1*( <crl> [ <cert> ] )
         <cert>               ::= "Certificate:" <encbin> CRLF
         <crl>                ::= "CRL:" <encbin> CRLF
         <version>            ::= "Version:" "5" CRLF








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12.  Security Considerations

    NOTE: to be done


13.  Acknowledgements

David H. Crocker suggested the use of a multipart structure for MIME-PEM
interaction.

14.  References

[1]  David H. Crocker.  Standard for the Format of ARPA Internet Text
     Messages.  RFC 822, University of Delaware, August 1982.

[2]  Nathaniel Borenstein and Ned 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.  Obsoletes RFC 1341.

[3]  John Linn.  Privacy Enhancement for Internet Electronic Mail: Part
     I: Message Encryption and Authentication Procedures.  RFC 1421,
     February 1993.  Obsoletes RFC 1113.

[4]  Steve Kent.  Privacy Enhancement for Internet Electronic Mail: Part
     II: Certificate-Based Key Management.  RFC 1422, BBN
     Communications, February 1993.

[5]  David M. Balenson.  Privacy Enhancement for Internet Electronic
     Mail: Part III: Algorithms, Modes, and Identifiers.  RFC 1423,
     Trusted Information Systems, February 1993.

[6]  Burton S. Kaliski.  Privacy Enhancement for Internet Electronic
     Mail: Part IV: Key Certification and Related Services.  RFC 1424,
     RSA Laboratories, February 1993.

[7]  David Crocker.  Multipart/Family Content Types.  Work in progress.

[8]  James Galvin.  Security Multiparts for MIME: Multipart/Signed and
     Multipart/Encrypted.  Work in progress.

[9]  Jon Postel.  Simple Mail Transfer Protocol. RFC 821, ISI, August
     1982.







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15.  Authors' Addresses

    Steve Crocker
    Trusted Information Systems
    3060 Washington Road
    Glenwood, MD  21738
    Tel:    +1 301 854 6889
    FAX:    +1 301 854 5363
    email:  crocker@tis.com



    Ned Freed
    Innosoft International, Inc.
    250 West First Street, Suite 240
    Claremont, CA 91711
    Tel:    +1 909 624 7907
    FAX:    +1 909 621 5319
    email:  ned@innosoft.com



    James M. Galvin
    Trusted Information Systems
    3060 Washington Road
    Glenwood, MD  21738
    Tel:    +1 301 854 6889
    FAX:    +1 301 854 5363
    email:  galvin@tis.com



    Sandra Murphy
    Trusted Information Systems
    3060 Washington Road
    Glenwood, MD  21738
    Tel:    +1 301 854 6889
    FAX:    +1 301 854 5363
    email:  murphy@tis.com











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16.  Appendix: Imported Grammar

The following productions are taken from [3].  The grammar presented in
[3] remains the authoritative source for these productions; they are
repeated here for the convenience of the reader.

    <dekinfo>    ::= "DEK-Info" ":" <dekalgid> [ "," <dekparameters> ] CRLF

    <micinfo>    ::= "MIC-Info" ":" <micalgid> "," <ikalgid> ","
                     <asymsignmic> CRLF

    <encbin>     ::= 1*<encbingrp>
    <encbingrp>  ::= 4*4<encbinchar>
    <encbinchar> ::= ALPHA / DIGIT / "+" / "/" / "="


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>          ::= "DES-EDE" / "DES-ECB" / "RSA"
    <micalgid>         ::= "RSA-MD2" / "RSA-MD5"

    <dekparameters>    ::= <DESCBCparameters>
    <DESCBCparameters> ::= <IV>
    <IV>               ::= <hexchar16>

    <asymsignmic>      ::= <RSAsignmic>
    <RSAsignmic>       ::= <encbin>

    <asymencdek>       ::= <RSAencdek>
    <RSAencdek>        ::= <encbin>

    <hexchar16>        ::= 16*16<hexchar>
    <hexchar>          ::= DIGIT / "A" / "B" / "C" / "D" / "E" / "F"
                                                        ; no lower case













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Table of Contents


1 Status of this Memo .............................................    1
2 Abstract ........................................................    1
3 Applying PEM Security Services to MIME Body Parts ...............    2
3.1 PEM Processing Steps ..........................................    3
3.1.1 Step 1: Local Form ..........................................    3
3.1.2 Step 2: Canonical Form ......................................    3
3.1.3 Step 3: Security Form .......................................    5
3.2 Use of multipart/signed Content Type ..........................    5
3.3 Use of multipart/encrypted Content Type .......................    6
4 Removing PEM Security Services from PEM Body Parts ..............    7
5 Definition of New Name Forms ....................................    7
6 Definition of New Content Types .................................    9
6.1 application/key-request Content Type Definition ...............    9
6.2 application/key-data Content Type Definition ..................   10
7 Message Processing ..............................................   12
7.1 Pre-Submission Algorithm ......................................   12
7.2 Post-Delivery Algorithm .......................................   13
8 Examples ........................................................   13
9 Observations ....................................................   14
10 Summary of Changes to PEM Specification ........................   14
11 Collected Grammar ..............................................   16
12 Security Considerations ........................................   18
13 Acknowledgements ...............................................   18
14 References .....................................................   18
15 Authors' Addresses .............................................   19
16 Appendix: Imported Grammar .....................................   20





















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