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


                     PEM Security Services and MIME



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).

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 RFC822 [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 specifies a number of changes to the message encryption
and signature procedures of PEM and broadens the name forms that may be
used to identify public keys.  Many of the changes represent a departure
in mechanism, not in effect.

1.  Introduction

This document updates the message encryption and signature procedures
defined by [3] and replaces 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 8.

In addition, this document specifies four technical changes to PEM:
symmetric key management in [3] is deprecated, the canonicalization
operation in [3] is generalized, the allowable name forms for the
identification of public keys 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 are replaced 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 (storage, 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 8.

In order to make use of the PEM services, a user is required to have at
least one public/private key pair.  Prior to this specification, the
public key was required to be embodied in a certificate, an object that





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binds a public key with a distinguished name, a name form that
identified the owner of the public key.  The embodiment was issued by a
certification authority, a role that was expected to be trustworthy
insofar as it verified the identity of the owner prior to issuing the
certificate.  However, the deployment of certificates and the creation
of the hierarchy of certification authorities has been problematic.

Instead, this specification bases the PEM services on a public/private
key pair.  Each key pair is required to belong to a user (where user is
not limited to being a human, e.g., it could be a process or a role)
which has a name.  There are 3 name forms specified by this document.
For backward compatibility (and forward compatibility if the X.500
Directory becomes a ubiquitous service) one of the name forms is a
distinguished name.  In addition, email addresses and arbitrary strings
are allowed.

Since a user may have more than one key pair, a name form is
insufficient for uniquely identifying a key pair.  A unique key selector
must be assigned to each key pair.  The combination of a name form and a
key selector uniquely identifies a key pair and each key pair is
uniquely identified by a name form and key selector combination.
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 key pairs.  This works best when users
    generate their own key pairs for personal use, which they
    distribute 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.


With a key pair for one's self and software that is both MIME and PEM
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.  This specification separates these two services so
that an originator may apply either or both, in either order.

The name forms and identifiers are described in detail in the next
section.  Succeeding sections specify how PEM and MIME are used together
and other ancillary details.






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2.  Name Forms and Identifiers

Currently, [3] requires the use of certificates to create and receive
PEM messages.  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 a name form 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.

When receiving PEM messages it is necessary to be able to uniquely
identify the key pair used to create the message.  A certificate is one
mechanism that accomplishes this, since it is uniquely identified by the
combination of its issuer's distinguished name and its serial number.
In any case, an identifier is required that consists of both a name form
and key selector.

In addition, users may distribute their public keys via mechanisms
outside the scope of the PEM specification, for example, in a file via
FTP.  Users receiving such keys will probably assign name forms to them
to be displayed when receiving messages created with them.  As a result,
it is desirable to be able to explicitly specify the public key used
rather than an identifier of the public key.

    NOTE:  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.


The principal objective of the various Originator and Recipient fields
specified in [3] is to identify which public key has been used or is
required.  This document reduces the set of fields by specifying exactly
two: Originator-ID: for originators and Recipient-ID: for recipients.
This specification defines 5 identifiers with which the public key used
may be indicated in each of these fields.

In the next section the 3 name forms are described in detail.  Following
that is the specification of the 5 identifiers.

2.1.  Name Forms

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





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2.1.1.  Email Addresses

The email address (grammar token <emailstr>) used must be a valid RFC822
address, which is defined in terms of the two grammar tokens <addr-spec>
and <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
                        ; 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.

2.1.2.  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

    Jim "the SAAG mailing list maintainer" Galvin

is an arbitrary string.

2.1.3.  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
a particular 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.

    <dnamestr>      ::= <encbin>
                        ; a printably encoded, ASN.1 encoded
                        ; distinguished name (as defined by the 'Name'
                        ; production specified in X.501)






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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


2.2.  Identifiers

There are 5 types of identifiers specified by this document: email
address identifiers, arbitrary string identifiers, distinguished name
identifiers, the public keys themselves, and 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, 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 distinct from all other KEYSELs assigned by whomever
assigned this KEYSEL.  A suggested value is 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





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below.

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

    <keysel>        ::= <encbin>
                        ; a printably encoded non-null sequence of octets

Each of the identifier name forms is described below.

2.2.1.  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 2.1.1.

2.2.2.  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 2.1.2.

2.2.3.  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 2.1.3.

2.2.4.  Public Key

The public key identifier has the following syntax.










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    <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)

    <id-subset>     ::= <id-email> / <id-string> / <id-dname>


The object 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.

In normal usage, the token <id-subset> is expected to be absent.  When
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 not, it may be possible for a malicious
originator to assert an identifier that accords the originator
unauthorized privileges.  See Section 5.2 for more details.

2.2.5.  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 the serial number of a certificate


The <id-issuer> identifier is included for backward compatibility (and
forward compatibility if X.500 Directory certificates become
ubiquitously available) with the ID-ASymmetric fields defined in [3].
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 with an appropriate new ID field name.

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





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security services to MIME body parts.

3.1.  PEM Processing Steps

The definition of the multipart/signed and multipart/encrypted body
parts in [7] specifies three steps for creating both body parts.

(1)  The body part to be protected is created according to a local
     convention.

(2)  The body part is prepared for protection according to the protocol
     parameter.

(3)  The prepared body part is protected according to the protocol
     parameter.

This specification makes no changes to step one in the sequence.  For
step two, there is no preparation necessary for the encryption service.
For the digital signature service, the body part must be canonicalized
as described below.  This specification makes no changes to step three
in the sequence.

Prior to the application of the digital signature service, the body part
must be in a canonical form.  Transforming the body part 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 in 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-computed 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.

The canonicalization transformation is a two step process.  First, the
body part must be converted to a form that is uniquely and unambiguously
representable on as many different host computers as possible.  Second,
the body part must have its line delimiters converted to a unique and
unambigous representation prior to computing the digital signature and
prior to each verification of the digital signature.






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The representation of all body parts in the first step is specified to
be 7bit, as defined by [2].  Since the headers of body parts are already
required to be representable in 7bit, this step requires that if the
data to be signed is not already 7bit then it must be encoded with an
appropriate MIME content transfer encoding.  Note: since the MIME
standard explicitly disallows nested content transfer encodings, i.e.,
the content types multipart and message may not themselves be encoded,
body parts enclosed within, for example, a multipart content type must
be encoded in a 7bit representation.  Any valid MIME encoding may be
selected for encoding the content of each of the non-7bit body parts.

As may be required by MIME, an appropriate Content-Transfer-Encoding:
header is added and included with the data to be signed.  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, 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 user.  Thus, a recipient has
    no way of knowing if the conversion is present or not.  Thus, if
    the recipient applies the conversion to a content in which it is





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    already present, the resulting content may have two line
    delimiters 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
    available 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 is performed prior to application of
    the transfer encoding.  The line delimiter conversion applied
    when a body part is signed is performed after the body is
    converted to 7bit.


3.2.  Use of multipart/signed Content Type

Using this content type requires the specification of a control
information content type, the label of which is used as the value for
the required protocol parameter.  Section 3.4 defines the control
information content type of application/pem-signature.  The value of the
required parameter "protocol" is "application/pem-signature" and the
value of the required parameter "micalg" is one of the valid choices
from [5], for example:

    Content-Type: multipart/signed; protocol="application/pem-signature";
      micalg="rsa-md5"; boundary="Signed Message"

    --Signed Message
    Content-Type: text/plain

    This is some example text.

    --Signed Message
    Content-Type: application/pem-signature

    SIGNATURE INFORMATION
    --Signed Message--


where SIGNATURE INFORMATION is descriptive of the content that would
appear in a real body part.






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3.3.  Use of multipart/encrypted Content Type

Using this content type requires the specification of a control
information content type, the label of which is used as the value for
the required protocol parameter.  Section 3.5 defines the control
information content type of application/pem-keys.  The value of the
required parameter "protocol" is "application/pem-keys", for example:

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

    --Encrypted Message
    Content-Type: application/pem-keys

    KEY DATA

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

    ENCRYPTED DATA WOULD BE HERE
    --Encrypted Message--


3.4.  application/pem-signature Content Type Definition

(1)  MIME type name: application

(2)  MIME subtype name: pem-signature

(3)  Required parameters: none

(4)  Optional parameters: none

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

(6)  Security considerations: none

This content type is used on the second body part of an enclosing
multipart/signed when the protocol used is PEM.  It is comprised of the
digital signature of the data, which is the first body part of the
enclosing multipart/signed, and the information required to verify that
signature.  The label application/pem-signature is used as the value of
the protocol parameter of the enclosing multipart/signed.  It is an
error for the protocol parameter to be missing from the enclosing
multipart/signed body part or for its value to be different from





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application/pem-signature when this body part is used.

Included in the signature verification information will be the Message
Integrity Check (MIC) algorithm used during the signature creation
process.  The MIC algorithm identified in this body part must match the
MIC algorithm identified in the micalg parameter of the enclosing
multipart/signed.  If it does not, a user agent should identify the
discrepancy to a user and may choose to either halt or continue
processing, giving precedence to the algorithm identified in this body
part.

An application/pem-signature body part is constructed as follows:

    Content-Type: application/pem-signature

    <pemsig>


where the <pemsig> token is defined as follows.

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

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

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

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


The token <id> is defined in Section 2.2.

3.5.  application/pem-keys Content Type Definition

(1)  MIME type name: application

(2)  MIME subtype name: pem-keys

(3)  Required parameters: none

(4)  Optional parameters: none

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

(6)  Security considerations: none






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This content type is used on the first body part of an enclosing
multipart/encrypted.  It is comprised of the data encryption key used to
encrypt the data, located in the second body part of the enclosing
multipart/encrypted, and the information required to perform the
decryption.  The label application/pem-keys is used as the value of the
protocol parameter of the enclosing multipart/encrypted.  It is an error
for the protocol parameter to be missing in the enclosing
multipart/encrypted body part or for its value to be different from
application/pem-keys when this body part is used.

An application/pem-keys body part is constructed as follows:

    Content-Type: application/pem-keys

    <pemkeys>


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


The token <id> is defined in Section 2.2.

4.  Removing PEM Security Services from PEM Body Parts

This section describes the processing steps necessary to verify or
decrypt the PEM security services that have been applied to MIME body
parts.  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.

The definition of the multipart/signed and multipart/encrypted body
parts in [7] specifies three steps for receiving both body parts.







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(1)  The protected body part and the control information body part are
     prepared for processing.

(2)  The prepared body parts are made available to the protection
     removal process.

(3)  The results of the protection removal process are made available to
     the user and processing continues with the unprotected body part,
     as returned by the protection removal process.

For step one, the preparation for digitally signed and encrypted body
parts is different, as described below.  No changes are required to
steps two and three in the sequence.

For multipart/signed body parts, 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 converting the line delimiters according to Step 2
of Section 3.1.

Multipart/encrypted body parts are prepared by removing the content
transfer encodings, if present, from both the control information and
the encrypted body part.

5.  Key Management Content Types

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

5.1.  application/pemkey-request Content Type Definition

(1)  MIME type name: application

(2)  MIME subtype name: pemkey-request

(3)  Required parameters: none






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(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



This content type is used to provide for some of the request messages
described in [6].  The information in the body part is entirely
independent of any other body part.  As such, the application/pemkey-
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 (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 2.2.

The crl-storage request is provided for by the application/pemkey-data
content type described in the Section 5.2.

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






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5.2.  application/pemkey-data Content Type Definition

The principal objective of this content type is to convey cryptographic
keying material from a source to a destination.  However, no explicit
provision is made 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, thus setting up the destination such that when the data is
used sensitive information may be intercepted and disclosed
inappropriately.

It is incumbent upon a recipient to verify the authenticity and accuracy
of the data received prior to its use.  The problem is 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 application/key-data body part could be
digitally signed by the source.  In this way, if the destination
believes that a correct source's public key is available locally and if
the destination believes the source would convey accurate data, then the
key data received from the source can be believed.

    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/pemkey-data body part is a
    similar mechanism.


(1)  MIME type name: application

(2)  MIME subtype name: pemkey-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.








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    <keydata>       ::= <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/pemkey-data content type is
an independent body part.

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 2.2.4.

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.

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.






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6.  Examples

Given the following email message prepared for submission:

    To: Ned Freed <ned@innosoft.com>
    Subject: Hi Ned!

    How do you like the new MIME/PEM?

    Jim


When the text of the message is signed, it will look like this (note the
use of the public key identifier with the included email name
identifier):

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

    --Signed Boundary
    Content-Type: text/plain; charset="us-ascii"
    Content-ID: <21436.785186814.2@tis.com>

    How do you like the new MIME/PEM?

    Jim

    --Signed Boundary
    Content-Type: application/pem-signature
    Content-ID: <21436.785186814.1@tis.com>
    Content-Transfer-Encoding: quoted-printable

    Version: 5
    Originator-ID: PK,MHkwCgYEVQgBAQICAwADawAwaAJhAMAHQ45ywA357G4fqQ61aoC1fO6B=
    ekJmG4475mJkwGIUxvDkwuxe/EFdPkXDGBxzdGrW1iuh5K8kl8KRGJ9wh1HU4TrghGdhn0Lw8g=
    G67Dmb5cBhY9DGwq0CDnrpKZV3cQIDAQAB,EN,2,galvin@tis.com
    MIC-Info: RSA-MD5,RSA,PnEvyFV3sSyTSiGh/HFgWUIFa22jbHoTrFIMVERfMZXUKzFsHbmK=
    tIowJlJR56OoImo+t7WjRfzpMH7MOKgPgzRnTwk0T5dOcP/lfbsOVJjleV7vTe9yoNp2P8mi/h=
    s7

    --Signed Boundary--






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If, instead, we choose to protect the headers with the text, it will
look like this:

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

    --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 MIME/PEM?

    Jim

    --Signed Boundary
    Content-Type: application/pem-signature
    Content-ID: <21468.785187044.1@tis.com>
    Content-Transfer-Encoding: quoted-printable

    Version: 5
    Originator-ID: PK,MHkwCgYEVQgBAQICAwADawAwaAJhAMAHQ45ywA357G4fqQ61aoC1fO6B=
    ekJmG4475mJkwGIUxvDkwuxe/EFdPkXDGBxzdGrW1iuh5K8kl8KRGJ9wh1HU4TrghGdhn0Lw8g=
    G67Dmb5cBhY9DGwq0CDnrpKZV3cQIDAQAB,EN,2,galvin@tis.com
    MIC-Info: RSA-MD5,RSA,ctbDBgkYtFW1sisb5w4/Y/p94LftgQ0IrEn3d6WTwjfxFBvAceVW=
    fawsZPLijVKZUYtbIqJmjKtzTJlagBawfA/KhUsvTZdR6Dj+4Gd8dBBwMKvqMKTHAUxGXYxwNd=
    bK

    --Signed Boundary--


If we choose to encrypt the text of the following message, that is,
encrypt the lines marked with asterick (*):











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    To: Jim Galvin <galvin@tis.com>
    Subject: an encrypted message

    * How do you like the new MIME/PEM?
    *
    * Jim


the message would look as follows (note the use of the email name
identifier):

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

    --Encrypted Boundary
    Content-Type: application/pem-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/WZ=
    q05lN99RDUQhdNxXI64ePAbFWQ6RGoiCrRs+Dc95oQh7EFEPoT9P6jyzcV1NzZVwfp+u

    --Encrypted Boundary
    Content-Type: application/octet-stream
    Content-Transfer-Encoding: base64

    AfR1WSeyLhy5AtcX0ktUVlbFC1vvcoCjYWy/yYjVj48eqzUVvGTGMsV6MdlynUd4jcJgRnQIQvIx
    m2VRgH8W8MkAlul+RWGu7jnxjp0sNsU562+RZr0f4F3K3n4wonUUP265UvvMj23RSTguZ/nl/Oxn
    FM6SzDgV39V/i/RofqI=

    --Encrypted Boundary--


If, instead, we choose to sign the text before we encrypt it, the
structure would be as follows (where lines with an asterick '*' are
digitally signed and lines with an ampersand '&' are encrypted):








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    Content-Type: multipart/encrypted; boundary="Encrypted Boundary"

    --Encrypted Boundary
    Content-Type: application/pem-keys

    KEY INFORMATION

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

    & Content-Type: multipart/signed; boundary="Signed Boundary"
    &
    & --Signed Boundary
    & * Content-Type: text/plain
    & *
    & * How do you like the new MIME/PEM?
    & *
    & * Jim
    &
    & --Signed Boundary
    & Content-Type: application/pem-signature
    &
    & SIGNATURE INFORMATION
    &
    & --Signed Boundary--

    --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:


















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

    --Encrypted Boundary
    Content-Type: application/pem-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+nOuOwP0tsym6CQozD9IwVIJzY8+vIfbh5B=
    pR0kS6prq3EGFBFR8gRMUvbgHtEKPD/4ICQ7b6ssZ7FmKhl/cJC5rVjpb4EOUlwOXwRZ

    --Encrypted Boundary
    Content-Type: application/octet-stream
    Content-Transfer-Encoding: base64

    ZvWvtosDzRBXJzkDFFRb9Qjrgm2nDWg3zotJ3ZpExpWUG/aRJ7Vwd+PWkSfrDPJ52V/wkxwMrum6
    xJHZonrtyd0AvaztvriMm2zXTefzwpGG1i5zK47PBqreLA3HDTK2U6B13vzpE8wMSVefzaCTSpXR
    SCh08ceVEZrIYS53/CKZV2/Sga71pGNlux8MsJpYLwdj5Q3NKocg1LMngMo8yrMAe+avMjfOnhui
    49Xon1Gft+N5XDH/+wI9qxI9fkQvNZVDlWIhCYEkxd5ke549tLkJjEqHQbgJW5C+K/uxdiD2dBt+
    nRCXcuO0Px3yKRyYg/9BgTf36padSHuv48xBg5YaqaEWpEzLI0Qd31vAyP23rqiPhfBn6sjhQ2Kr
    WhiF2l3TV8kQsIGHHZUkaUbqkXJe6PEdWWhwsqCFPDdkpjzQRrTuJH6xleNUFg+CG1V+tL4IgMjQ
    qm3KVojRXx8bG2auVN89NfwFswmoq4fXTrh3xyVS1VgxjKkcYI8SVVmkYjCxVviJP3zO2UzBvCoM
    fADtBVBz1njYETtVGDO97uT39MqL85uEgiF4E5TkOj/m04+88G0/vvN/RISKJiFQJ3FyVIB/ShX9
    Dixl8WCx3rxwN5g2QFLiyQVulzuNhimSD4ZxEo7smcTsAXUjwSLRtdjmTTutw2GmFESUaIrY81Nc
    pQJRPNAvF0IkN6ddwL4qvzUS99vjQp15g9FUv82lHtHwhM18a9GokVG8xYOjBBsn9anp9abh4Tp/
    c/vpbunQUqnpV29rF4wj+8OwUOMi9ymGabBXAjw7DhNH2RdRVr1upQO896OX81VWB0LsA0cp+ymx
    hTrEI+wCHcrsNMoRK/7zAeuAi0f1t9bN594EFlLoIrBnKEa1/OUAhMT7kG1fNkSRnc8BZswIoPyR
    etsTurQfD40nsVHvNwE9Jz7wbBo00gd6blPADOUYFxfW5zu6ubygBqJiKPM4II2fCdNj7CptfQco
    RTeguKMVPLVmFg/EINuWBFm10GqlYT7p4zhfzysV/3r5LVZ1E8armTCRJ2GoYG5h+SKcytaQ0IT8
    S2nLPCZl1hzdajsrqHFe8omQ

    --Encrypted Boundary--


In addition to text, the PEM services as defined here will protect
arbitrary body parts, for example, the following audio body part:








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    Content-Type: audio/basic

    AUDIO DATA HERE


when signed would appear as follows:

    Content-Type: multipart/signed; protocol="application/pem-signature";
            micalg="rsa-md5"; boundary="Signed Boundary"

    --Signed Boundary
    Content-Type: audio/basic
    Content-Transfer-Encoding: base64

    base64(AUDIO DATA HERE)

    --Signed Boundary
    Content-Type: application/pem-signature

    SIGNATURE INFORMATION HERE


and when encrypted would appear as follows:

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

    --Encrypted Boundary
    Content-Type: application/pem-keys

    KEY INFORMATION HERE

    --Encrypted Boundary
    Content-Type: application/octet-stream
    Content-Transfer-Encoding: base64

    base64(encrypted(AUDIO DATA HERE))

    --Encrypted Boundary--


7.  Observations

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





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(1)  It allows privacy-enhancement of an arbitrary content, not just the
     body of an RFC822 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 key pairs could be used for the different
services and could be protected separately.

This is useful for at least two reasons.  First, some public key
algorithms do not support both digital signatures and encryption, for
example, the way that the RSA algorithm does; 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.  Summary of Changes to PEM Specification

This document updates the message encryption and signature procedures
defined by [3] and replaces 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.

(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.






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

(4)  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.

(5)  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.

(6)  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.

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

(8)  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].

(9)  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.

(10) 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





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     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 broadens the allowable name forms that users may use
     to identify their public keys.  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.

9.  Collected Grammar

The version of the grammar in this document is as follows:

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


The content of an application/pem-signature body part is as follows:

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

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

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


The content of an application/pem-keys body part is as follows:









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

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

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

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


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>        ::= <encbin>
                        ; a printably encoded 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

    <publickey>     ::= <encbin>
                        ; a printably encoded, ASN.1 encoded
                        ; subjectPublicKeyInfo

    <serial>        ::= 1*<hexchar>
                        ; hex dump of the serial number of a certificate






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The content of an application/pemkey-request body part is as follows:

    <request>       ::= <version>
                        ( <subject> / <issuer> / <certification> )

    <subject>       ::= "Subject:" <id> CRLF

    <issuer>        ::= "Issuer:" <id> CRLF

    <certification> ::= "Certification:" <encbin> CRLF


The content of an application/pemkey-data body part is as follows:

    <keydata>       ::= <version>
                        ( <publickeydata> / <certchain> / <crlchain> )

    <publickeydata> ::= "Key:" "PK" "," <publickey> "," <id-subset> CRLF

    <certchain>     ::= <cert> *( [ <crl> ] <cert> )

    <crlchain>      ::= 1*( <crl> [ <cert> ] )

    <cert>          ::= "Certificate:" <encbin> CRLF

    <crl>           ::= "CRL:" <encbin> CRLF


10.  Security Considerations

This entire document is about security.

11.  Acknowledgements

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

12.  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





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     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]  James Galvin, Sandy Murphy, Steve Crocker, and Ned Freed.  Security
     Multiparts for MIME: Multipart/Signed and Multipart/Encrypted.
     RFC XXXX, Trusted Information Systems and Innosoft, XXXX 1994.

13.  Authors' Addresses

    Steve Crocker
    email:  crocker@tis.com

    James M. Galvin
    email:  galvin@tis.com

    Sandra Murphy
    email:  murphy@tis.com

    Trusted Information Systems
    3060 Washington Road
    Glenwood, MD  21738
    Tel:    +1 301 854 6889
    FAX:    +1 301 854 5363












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    Ned Freed
    Innosoft International, Inc.
    1050 East Garvey Avenue South
    West Covina, CA 91790
    Tel:    +1 818 919 3600
    FAX:    +1 818 919 3614
    email:  ned@innosoft.com











































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14.  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


The following productions are taken from [1].  The grammar presented in
[1] remains the authorative source for these productions; they are
repeated here for the convenience of the reader.








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    <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

    <route-addr>    ::= "<" [ <route> ] <addr-spec> ">"

    <route>         ::=  1# ( "@" <domain> ) ":"         ; path-relative



    <word>          ::= <atom> / <quoted-string>

    <quoted-string> ::= """ *( <qtext> / <quoted-pair> ) """

    <qtext>         ::= (any <CHAR> excepting """, "
                         and including <linear-white-space>)

    <quoted-pair>   ::= "

    <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-
                         /  "," / ";" / ":" / "
                         /  "." / "[" / "]"              ;  within a word.









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Table of Contents


  Status of this Memo .............................................    1
  Abstract ........................................................    1
1  Introduction ...................................................    2
2  Name Forms and Identifiers .....................................    4
2.1  Name Forms ...................................................    4
2.1.1  Email Addresses ............................................    5
2.1.2  Arbitrary Strings ..........................................    5
2.1.3  Distinguished Names ........................................    5
2.2  Identifiers ..................................................    6
2.2.1  Email Address ..............................................    7
2.2.2  Arbitrary String ...........................................    7
2.2.3  Distinguished Name .........................................    7
2.2.4  Public Key .................................................    7
2.2.5  Issuer Name and Serial Number ..............................    8
3  Applying PEM Security Services to MIME Body Parts ..............    8
3.1  PEM Processing Steps .........................................    9
3.2  Use of multipart/signed Content Type .........................   11
3.3  Use of multipart/encrypted Content Type ......................   12
3.4  application/pem-signature Content Type Definition ............   12
3.5  application/pem-keys Content Type Definition .................   13
4  Removing PEM Security Services from PEM Body Parts .............   14
5  Key Management Content Types ...................................   15
5.1  application/pemkey-request Content Type Definition ...........   15
5.2  application/pemkey-data Content Type Definition ..............   17
6  Examples .......................................................   19
7  Observations ...................................................   24
8  Summary of Changes to PEM Specification ........................   25
9  Collected Grammar ..............................................   27
10  Security Considerations .......................................   29
11  Acknowledgements ..............................................   29
12  References ....................................................   29
13  Authors' Addresses ............................................   30
14  Appendix: Imported Grammar ....................................   32














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