Network Working Group M. Blinov

Network Working Group M. Blinov
Request for Comments: 4212 Guardeonic Solutions
Category: Informational C. Adams
University of Ottawa
October 2005

Alternative Certificate Formats for the
Public-Key Infrastructure Using X.509 (PKIX)
Certificate Management Protocols

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2005).

IESG Note

This document is not a candidate for any level of Internet Standard.
The IETF disclaims any knowledge of the fitness of this document for
any purpose, and in particular notes that it has not had IETF review
for such things as security, congestion control, or inappropriate
interaction with deployed protocols. The RFC Editor has chosen to
publish this document at its discretion. Readers of this document
should exercise caution in evaluating its value for implementation
and deployment.

Abstract

The Public-Key Infrastructure using X.509 (PKIX) Working Group of the
Internet Engineering Task Force (IETF) has defined a number of
certificate management protocols. These protocols are primarily
focused on X.509v3 public-key certificates. However, it is sometimes
desirable to manage certificates in alternative formats as well.
This document specifies how such certificates may be requested using
the Certificate Request Message Format (CRMF) syntax that is used by
several different protocols. It also explains how alternative
certificate formats may be incorporated into such popular protocols
as PKIX Certificate Management Protocol (PKIX-CMP) and Certificate
Management Messages over CMS (CMC).

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1. Introduction

Full certificate life-cycle management in a Public-Key Infrastructure
(PKI) requires protocol support in order to achieve automated
processing and end user transparency. Such protocols require
standardization in order to allow more than one vendor to supply
various pieces -- End Entity (EE), Certification Authority (CA),
Registration Authority (RA) -- in the PKI deployment of a single
organization, or to allow multiple, independently-deployed PKIs to be
interconnected usefully.

The IETF PKIX (Public-Key Infrastructure using X.509) Working Group
currently has several certificate management protocols and
certificate request syntax specifications on the standards track.
Although these specifications are primarily focused on X.509v3
public-key certificates, some of them can be easily extended to
handle certificates in alternative formats as well.

This document focuses on a popular certificate request syntax called
CRMF (Certificate Request Message Format) [CRMF]. Although the
original specification of CRMF is X.509-specific, extensions have
already been proposed to allow for alternative certificate templates
[CMP]. However, those extensions have only defined a framework; they
did not define the exact format to be used for various certificate
types.

This document builds on top of the framework mentioned above and
defines how CRMF can be used to request certificates of the following
types:

- X.509 attribute certificates [ATTCERT]

- OpenPGP certificates [OPENPGP]

The CRMF syntax is used by such popular protocols as PKIX-CMP (PKIX
Certificate Management Protocol) [CMP] and CMC (Certificate
Management Messages over CMS) [CMC]. This means that CRMF extensions
proposed in this document enable these protocols to request
certificates of the above types. However, it is not enough to be
able to request a certificate. The protocol should be prepared to
handle certificates of a particular type and, for example, return
them to the user.

This document proposes extensions to the PKIX-CMP and CMC protocols
that are required to manage certificates in alternative formats.

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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2. Certificate Template

One of the features of the CRMF format is its use of the CertTemplate
construct, which allows a requester (EE, or RA acting on behalf of an
EE) to specify as much or as little as they wish regarding the
content of the requested certificate. It is explicitly noted that
the CA has final authority over the actual certificate content; that
is, the CA may alter certificate fields or may add, delete, or alter
extensions according to its operating policy (if the resulting
certificate is unacceptable to the EE or RA, then that certificate
may be rejected and/or revoked prior to any publication/use).

A similar flexibility in the request must be available for
alternative certificate types as well. For this purpose, an
AltCertTemplate extension was introduced in [CMP] as follows (where
id-regCtrl = {1 3 6 1 5 5 7 5 1}, as defined in [CRMF]).

CertRequest ::= SEQUENCE {
certReqId INTEGER,
certTemplate CertTemplate,
controls Controls OPTIONAL }

-- If certTemplate is an empty SEQUENCE (i.e., all fields
-- omitted), then controls MAY contain the
-- id-regCtrl-altCertTemplate control, specifying a template
-- for a certificate other than an X.509v3 public-key
-- certificate. Conversely, if certTemplate is not empty
-- (i.e., at least one field is present), then controls
-- MUST NOT contain id-regCtrl-altCertTemplate. The new
-- control is defined as follows:
id-regCtrl-altCertTemplate OBJECT IDENTIFIER ::= {id-regCtrl 7}
AltCertTemplate ::= AttributeTypeAndValue

In this section, an AltCertTemplate is specified for each of the
alternative certificate types defined in Section 1.

2.1. X.509 Attribute Certificate CertTemplate

A CertTemplate for an X.509 attribute certificate can be used by
simply defining an object identifier (OID) and corresponding value
for use in the id-regCtrl-altCertTemplate control. These are
specified as follows.

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OID:

id-acTemplate OBJECT IDENTIFIER ::=
{id-regCtrl-altCertTemplate 1}

Value:

AttCertTemplate ::= SEQUENCE {
version AttCertVersion OPTIONAL,
holder Holder OPTIONAL,
issuer AttCertIssuer OPTIONAL,
signature AlgorithmIdentifier OPTIONAL,
serialNumber CertificateSerialNumber OPTIONAL,
attrCertValidityPeriod OptionalAttCertValidity OPTIONAL,
attributes SEQUENCE OF Attribute OPTIONAL,
issuerUniqueID UniqueIdentifier OPTIONAL,
extensions Extensions OPTIONAL
}
OptionalAttCertValidity ::= SEQUENCE {
notBeforeTime GeneralizedTime OPTIONAL,
notAfterTime GeneralizedTime OPTIONAL
} -- at least one must be present

2.2. OpenPGP Certificate CertTemplate

Similar to certificate templates defined above, a CertTemplate for an
OpenPGP certificate can be used by defining an object identifier
(OID) and corresponding value for use in the
id-regCtrl-altCertTemplate control. These are specified as follows:

OID:

id-openPGPCertTemplateExt OBJECT IDENTIFIER ::=
{id-regCtrl-altCertTemplate 2}

Value:

OpenPGPCertTemplateExtended ::= SEQUENCE {
nativeTemplate OpenPGPCertTemplate,
controls Controls OPTIONAL }

OpenPGPCertTemplate ::= OCTET STRING
-- contains the OpenPGP CertTemplate data structure defined
-- below (binary format without Radix-64 conversions)
-- encoded as an ASN.1 OCTET STRING

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2.2.1. OpenPGP CertTemplate Data Structure

Similar to the X.509 CertTemplate, the OpenPGP CertTemplate is an
OpenPGP certificate (OpenPGP Transferable Public Key) [OPENPGP] with
all fields optional. The essential elements of an OpenPGP
CertTemplate are:

- Zero or one Public Key packet.

- Zero or more Direct Key Self Signature packets.

- Zero or more Certification Signature packets (only if no User ID
packets are present).

- Zero or more User ID packets.

- After each User ID packet, zero or more Certification Signature
packets.

- Zero or more Subkey packets.

- After each Subkey packet, zero or one Subkey Binding Signature
packet.

Each packet in the OpenPGP CertTemplate MUST be a syntactically
correct OpenPGP packet. This will enable conformant implementations
to use existing PGP libraries for building and parsing OpenPGP
CertTemplates.

The following implications of this rule should be explicitly noted:

- Fields for which the OpenPGP specification defines a set of
permitted values (e.g., the signature type or the public key
algorithm fields of the Signature packet) MUST have a value from
the defined set. Even if the requester does not have any
particular preferences for, for example, the signature algorithm,
it MUST choose one value that is the most desirable.

Rationale: An alternative solution could be to define extra "any"
values, but this would be a modification of the OpenPGP syntax,
which is not considered appropriate in this document.

- All subpackets of the Signature packet defined by the OpenPGP
specification as mandatory (e.g., the creation time and the
issuer's key id subpackets) MUST be present even though they do not
make much sense in the context of a certificate request.

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- The number of MPIs at the end of the Key Material and the Signature
packets MUST match the number defined by the OpenPGP specification
for the given algorithm (the algorithm is controlled by the value
of the "algorithm" field). For example, there should be 2 MPIs for
DSA signatures. Note that the OpenPGP specification does not
define validation rules for the content of those MPIs.

Though it is not considered appropriate here to define extra "any"
values for fields of enumerated types, such values can still be
defined for some other fields where the OpenPGP specification is not
that strict.

The following extra values are defined in the context of the OpenPGP
CertTemplate. Note that these definitions do not modify the syntax
of OpenPGP packets, and existing PGP libraries can still be used to
generate and parse them.

- For fields representing time (e.g., signature creation time): the
value of zero means "any time".

- For fields holding key IDs: the value of 0xFFFFFFFFFFFFFFFF means
"any key id".

- For signature fields: the "any signature" value is encoded as a
sequence of MPIs such that:

* the number of MPIs matches the number of MPIs defined by the
OpenPGP specification for the given algorithm, and

* the value of each MPI is 0xFF.

A Signature packet with the "any" value in the signature fields is
called a Signature Template.

Example: The "any signature" value for a DSA signature would look
like [00 08 FF 00 08 FF]

- For key material fields: the "any key" value is encoded as a
sequence of MPIs such that:

* the number of MPIs matches the number of MPIs defined by the
OpenPGP specification for the given algorithm, and

* the value of at least one of the MPIs is a bit string with all
its bits set to 1.

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A Key Material packet with the "any" value in the key material
fields is called a Key Template. (See Key Template section for
further details.)

Example: The "any key" value for a DSA public key may look like
[00 08 FF 00 10 FF FF 00 10 85 34 00 08 FF]

The following rules apply to the sequence of packets within the
OpenPGP CertTemplate:

- If the Public Key packet is omitted from the OpenPGP CertTemplate,
then this CertTemplate does not constrain the value of the public
key (i.e., it refers to "any" public key).

- The order of Signature packets following a User ID packet and the
order of User ID packets within the CertTemplate are not important.

- If an OpenPGP CertTemplate does not contain any User ID packets,
then it refers to "any" user IDs that are relevant to a given
request.

2.2.2. OpenPGP CertTemplate in Certificate Requests

Since an OpenPGP certificate can have several certification
signatures, the OpenPGP CertTemplate uses Signature Templates to
define where certification signatures should occur. The values of
the fields of the Signature Templates define the parameters of the
new certification signatures. The following rules apply:

- A Signature Template that is present in the list of signatures
following a User ID packet requests that the CA certify this User
ID and the public key and replace the Signature Template with the
new certification signature. The Signature Template does not
mandate the exact place of the certification signature within the
list. The certification signature may be inserted at any position
within the list of signatures (following the certified User ID
packet).

- A Signature Template may be present in the OpenPGP CertTemplate
without any preceding User ID packet. In this case, it is assumed
that the CA knows the ID(s) of the user by some other means. A
Signature Template without a preceding User ID requests that the CA
insert all known User IDs of the user into the OpenPGP certificate
and certify each of them. The Signature Template defines the
parameters of these certification signatures.

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- If an OpenPGP CertTemplate contains no Signature Templates, then
the CA is requested to certify all User IDs that are present in the
OpenPGP CertTemplate. Such a CertTemplate does not define
parameters of the certification signatures explicitly, but the CA
SHOULD use parameters of the certification self-signatures (if
present in the CertTemplate) as a guide (e.g., key flags fields).

- If neither Signature Templates nor User IDs are present in the
OpenPGP CertTemplate, then the CA is expected to know the ID(s) of
the user by some other means. In this case, the CertTemplate
requests that the CA insert these User IDs into the OpenPGP
certificate and certify each of them. The parameters of the
certification signatures are left to the CA.

If several certification signatures have to be produced according to
an OpenPGP CertTemplate, and any of them cannot be granted (even with
modifications) for whatever reason, then the whole request with this
OpenPGP CertTemplate MUST be rejected.

The client SHOULD provide enough information in its request that the
CA could produce a complete OpenPGP certificate. For example, the
client SHOULD include in the template all relevant subkeys with their
binding signatures so that the CA can include them in the resultant
OpenPGP certificate as well. Rationale: In some environments, the
CA/RA is responsible for publishing certificates.

2.2.3. Key Templates and Central Key Generation

The OpenPGP CertTemplate can also be used to request certification of
centrally-generated keys. This is accomplished by using Key
Templates.

If the Public Key packet of an OpenPGP CertTemplate is a Key
Template, then this OpenPGP CertTemplate requests that the CA/RA
generate the key pair prior to certifying it. Fields of the Key
Template define parameters of the new key pair as follows (see
examples in the Appendix):

- The "public key algorithm" field specifies the algorithm to be used
for the key generation.

- MPI fields with the value of 0xFF ([00 08 FF]) specify that no
constraint is placed on the corresponding part of the key.

- MPI fields that contain any other bit strings in which all bits are
set to 1, specify that the corresponding part of the key should be
of the same length as the length of the MPI (e.g., the length of
the public modulus n of the RSA key).

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- MPI fields that contain any other values specify that the
corresponding part of the key should be of the given value (key
generation parameters).

In order to return a complete OpenPGP certificate, in addition to
certifying the new key and the User ID, the CA (or RA) SHOULD also
create a self-signature (i.e., sign the new public key and the User
ID with the new private key) and include it after the User ID packet.
This SHOULD be done for all User IDs certified by the CA.

If a Subkey packet of an OpenPGP CertTemplate is a Key Template, then
this OpenPGP CertTemplate requests that the CA/RA generate a subkey.
Fields of the Key Template define parameters of the new subkey. The
new subkey obviously does not have to be certified. However, the
CA/RA SHOULD produce the binding signature and include it after the
subkey, if the CA/RA knows the user's primary private key (e.g., it
was centrally generated as well). Note that if the CA/RA does not
know the user's primary private key, then the resultant OpenPGP
certificate returned from the CA/RA to the client will be incomplete
(i.e., there will be no binding signature for the subkey). It will
be the responsibility of the client to produce and add the binding
signature and to publish the final OpenPGP certificate.

If an OpenPGP CertTemplate contains neither PublicKey/Subkey packets
nor Key Template packets, then it requests that the CA generate
keys/subkeys according to the CA's policies.

2.2.4. OpenPGPCertTemplateExtended

The OpenPGPCertTemplateExtended structure enables additional
extensions and controls to be added to the basic OpenPGP
CertTemplate.

2.2.5. OpenPGP CertTemplate Required Profile

A conformant implementation is REQUIRED to support OpenPGP
CertTemplates that are valid OpenPGP certificates, i.e., that have
the following structure (see examples in the Appendix):

- One Public Key packet (not a Key Template).

- Zero or more Direct Key Self Signature packets (without Signature
Templates).

- One or more User ID packets.

- After each User ID packet, zero or more Certification Signature
packets (without Signature Templates).

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- Zero or more Subkey packets (without Key Templates).

- After each Subkey packet, one Subkey Binding Signature packet (not
a Signature Template).

A conformant implementation is REQUIRED to recognise Key Templates
and Signature Templates and is REQUIRED to either support them or
reject requests containing them if it does not.

3. Proof-of-Possession

A CRMF request includes a Proof-of-Possession (POP) field that
contains proof that an End Entity has possession of the private key
corresponding to the public key for which a certificate is requested.

The following rule applies to this field (with modifications from
[CMP]):

* NOTE: If CertReqMsg certReq certTemplate (or the
* altCertTemplate control) contains the subject and
* publicKey values, then poposkInput MUST be omitted
* and the signature MUST be computed on the DER-encoded
* value of CertReqMsg certReq (or the DER-encoded value
* of AltCertTemplate).

An OpenPGP CertTemplate is considered to satisfy the conditions of
this note if it has a Public Key packet (not a Key Template) and at
least one User ID packet.

4. Protocol-specific Issues

This section explains how alternative certificate formats may be
incorporated into such popular protocols as PKIX-CMP and CMC.

4.1. PKIX-CMP

In PKIX-CMP, the ASN.1 [ASN1] construct, and corresponding comment
for a certificate is given as follows.

CMPCertificate ::= CHOICE {
x509v3PKCert Certificate
}

-- This syntax, while bits-on-the-wire compatible with the
-- standard X.509 definition of "Certificate", allows the
-- possibility of future certificate types (such as X.509
-- attribute certificates, WAP WTLS certificates, or
-- other kinds of certificates) within this certificate

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-- management protocol, should a need ever arise to support
-- such generality.

Building on this framework, this document expands the above CHOICE
construct as follows.

CMPCertificate ::= CHOICE {
x509v3PKCert Certificate,
x509v2AttCert [0] AttributeCertificate,
-- defined in [ATTCERT]
openPGPCert [2] OpenPGPCert
}

OpenPGPCert ::= OCTET STRING
-- contains the OpenPGP certificate (OpenPGP Transferable
-- Public Key) data structure from the OpenPGP specification
-- [OPENPGP] (binary format without Radix-64 conversions),
-- encoded as an ASN.1 OCTET STRING

Expanding the CHOICE construct as above allows X.509 attribute
certificates and OpenPGP certificates to be used within the PKIX-CMP
management messages. In the future, this construct may be expanded
further (in subsequent revisions of this document) to accommodate
other certificate types, if this is found to be necessary.

4.2. CMC

The CMC protocol uses the CMS (Cryptographic Message Syntax) syntax
[CMS], which defines the certificate type as

CertificateChoices ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
v1AttrCert [1] IMPLICIT AttributeCertificateV1, -- Obsolete
v2AttrCert [2] IMPLICIT AttributeCertificateV2 }

Similar to PKIX-CMP, this CHOICE can be extended to include
additional types of certificates as follows.

CertificateChoices ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate, -- Obsolete
v1AttrCert [1] IMPLICIT AttributeCertificateV1, -- Obsolete
v2AttrCert [2] IMPLICIT AttributeCertificateV2,
openPGPCert [3] IMPLICIT OpenPGPCert }

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This allows both X.509 attribute certificates and OpenPGP
certificates to be used within the CMC management messages. In the
future, this construct may be expanded further (in subsequent
revisions of this document) to accommodate other certificate types,
if this is found to be necessary.

The CMC specification defines certain constraints on the subject and
publicKey fields of the CRMF's CertTemplate structure. The same
constraints should apply to the AltCertTemplate structure if
alternative certificate types are used. For example, the CMC
specification mandates that

When CRMF message bodies are used in the Full Enrollment Request
message, each CRMF message MUST include both the subject and
publicKey fields in the CertTemplate.

If alternative certificate types are used, this should be extended as

When CRMF message bodies are used in the Full Enrollment Request
message, each CRMF message MUST include both the subject and
publicKey fields in the CertTemplate (or in the altCertTemplate
control).

5. Security Considerations

5.1. Protection of Alternative Certificate Templates

This document defines extensions to the CRMF format, so security
considerations from the CRMF specification [CRMF] apply here as well.
In particular, the security of alternative certificate templates
relies upon the security mechanisms of the protocol or process used
to communicate with CAs.

Exact security requirements depend on a particular PKI deployment,
but integrity protection and message origin authentication are
typically required for certification requests. The CMP and CMC
certificate management protocols mentioned in this document provide
both integrity protection and message origin authentication for
request messages (which includes certificate templates as well).

Confidentiality may also be required where alternative certificate
templates contain subscriber-sensitive information. The CMC protocol
allows the content of request messages to be encrypted. CMP does not
include confidentiality mechanisms for certification requests, but if
confidentiality is needed, it can be achieved with a lower-layer
security protocol (e.g., TLS or IPsec).

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5.2. Request Authorisation

In order to make a decision as to whether a request should be
accepted, a CA should normally be able to compare the (authenticated)
name of the sender of the request with the request subject name.

For example, an End Entity may be allowed to request additional
certificates for himself/herself. In this case, the CA will accept a
request if the Sender is equal to the Subject (of course, other
conditions will have to be checked as well before the certificate is
granted).

If a PGP certificate is requested using the extensions proposed here,
the Sender field of the request will be encoded as an ASN.1
GeneralName (in both CMP and CMC), while the Subject will be
represented as a PGP UserID. Since the PGP UserID is effectively an
unrestricted octet string, it is not always trivial to compare these
two types. It is possible that an attacker may try to submit
requests with specially crafted UserIDs (e.g., that include obscure
characters) in order to trick the CA comparison algorithm and obtain
a PGP certificate with a UserID that belongs to someone else.

In these circumstances, it is safer for the CA, when building the PGP
certificate's UserID, to completely rebuild the UserID based on the
content of the authenticated Sender name rather than take the UserID
from the request. To achieve this, additional information about the
End Entity may be required at the CA (e.g., the EE's email address).

5.3. PGP Parser

Software components that implement the proposed extensions (e.g., CMP
or CMC servers) will necessarily increase in complexity. If a
"standard" server is expected to be able to parse ASN.1 streams, the
"extended" server is required to be able to parse PGP streams as
well. A PGP parser code may introduce new security vulnerabilities
that can be exploited by an attacker to mount a DoS attack or gain
access to the server.

In order to reduce the consequences of a successful attack, it is
recommended that the CMP or CMC servers be run on a separate machine
from the main CA server. These protocol servers should not have
access to the main CA key and should not have write access to the CA
store.

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Appendix A. Examples of OpenPGP CertTemplates

This Appendix presents examples of OpenPGP CertTemplates that are
used for requesting OpenPGP certificates from a CA.

A1. Simple Certificate Request

Alice requests an OpenPGP certificate for her public key accompanied
by a subkey.

The content of the OpenPGP CertTemplate in the request is as follows.
This CertTemplate conforms to the OpenPGP CertTemplate Required
Profile.

0000: 99 01 A2 === Pub Key packet ===
0003: 04 3C 58 27 A2 11 ver 4, created 30 Jan 2002, DSA
0009: 00 E3 FB 9D .. 2B EF DSA prime p
008B: 00 A0 FF 7E .. BA 71 DSA group order q
00A1: 03 FF 68 BC .. 56 71 DSA group generator g
0123: 03 FE 38 1F .. F2 63 DSA public key value y
01A5: B4 19 === User ID packet ===
01A7: 41 6C .. 6D 3E "Alice <[email protected]>"
01C0: 89 00 49 === Signature packet (self-signature) ===
01C3: 04 10 11 02 ver 4, gen cert, DSA, SHA1
01C7: 00 09 05 02 3C 58 27 A2 02 1B 03
created 30 Jan 2002, key usage:
sign data and certify other keys
01D2: 00 0A 09 10 43 5C .. 06 77 issuer key id
01DE: 5A C2 left 16 bits of signed hash value
01E0: 00 A0 EB 00 .. 1B 75 DSA value r
01F6: 00 A0 F4 E4 .. A8 3D DSA value s
020C: B9 02 0D === Public Subkey packet ===
020F: 04 3C 58 27 A2 10 ver 4, created 30 Jan 2002,
Elgamal (encrypt-only) algorithm
0215: 08 00 F6 42 .. 0B 3B Elgamal prime p
0317: 00 02 02 Elgamal group generator g
031A: 07 FE 37 BA .. DF 21 Elgamal public key value y
041C: 89 00 49 === Signature packet (subkey binding) ===
041F: 04 18 11 02 ver 4, subkey binding, DSA, SHA1
0423: 00 09 05 02 3C 58 27 A2 02 1B 0C
created 30 Jan 2002, key usage:
encrypt communications and storage
042E: 00 0A 09 10 43 5C .. 06 77 issuer key id
043A: C7 DE left 16 bits of signed hash value
043C: 00 9E 21 33 .. 39 1B DSA value r
0452: 00 9F 64 D7 .. 63 08 DSA value s
0468:

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CA certifies Alice's User ID and the public key and creates the
following OpenPGP certificate:

0000: 99 01 A2 === Pub Key packet ===
0003: <the same as in the request>
01A5: B4 19 === User ID packet ===
01A7: <the same as in the request>
01C0: 89 00 49 === Signature packet (self-signature) ===
01C3: <the same as in the request>
020C: 89 00 49 === Signature packet (certification) ===
020F: 04 13 11 02 ver 4, positive cert, DSA, SHA1
0213: 00 09 05 02 3C 58 28 1A 02 1B 03
created 30 Jan 2002, key usage:
sign data and certify other keys
021E: 00 0A 09 10 F0 0D .. 1F CA issuer key id
022A: 06 DF left 16 bits of signed hash value
022C: 00 9F 57 2D .. 26 E3 DSA value r
0242: 00 A0 B3 02 .. CE 65 DSA value s
0258: B9 02 0D === Public Subkey packet ===
025B: <the same as in the request>
0468: 89 00 49 === Signature packet (subkey binding) ===
046B: <the same as in the request>
04B4:

A2. Certificate Request with Central Key Generation

Alice requests that the CA generate an RSA key pair that will be used
for signing, an RSA key pair that will be used for encryption, and
requests that the CA certify these keys. The RSA keys are requested
to be 2048 bits long with the public exponent 65537.

The content of the OpenPGP CertTemplate in the request is as follows:

0000: 99 01 0D === Pub Key packet (Template) ===
0003: 04 FF FF FF FF 01 ver 4, any creation date, RSA
0009: 08 00 FF FF .. FF FF RSA public modulus n - given length
010B: 00 11 01 00 01 RSA public exponent e
0110: B4 19 === User ID packet ===
0112: 41 6C .. 6D 3E "Alice <[email protected]>"
012B: 89 00 23 === Signature packet (Template) ===
012E: 04 10 11 02 ver 4, gen cert, DSA, SHA1
0132: 00 09 05 02 FF FF FF FF 02 1B 03
any creation date, key usage:
sign data and certify other keys
013D: 00 0A 09 10 FF FF .. FF FF issuer key id - any
0149: 05 3A left 16 bits of signed hash value
014B: 00 08 FF DSA value r - any
014E: 00 08 FF DSA value s - any

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0151: 99 01 0D === Public Subkey packet (Template) ===
0154: 04 FF FF FF FF 01 ver 4, any creation date, RSA
015A: 08 00 FF FF .. FF FF RSA public modulus n - given length
025C: 00 11 01 00 01 RSA public exponent e
0261: 89 00 20 === Signature packet (Template) ===
0264: 04 18 01 02 ver 4, subkey binding, RSA, SHA1
0268: 00 09 05 02 FF FF FF FF 02 1B 0C
any creation date, key usage:
encrypt communications and storage

0273: 00 0A 09 10 FF FF .. FF FF issuer key id - any
027F: 12 E6 left 16 bits of signed hash value
0281: 00 08 FF RSA signature value - any
0284:

CA generates keys, certifies Alice's User ID and the public key, and
creates the following OpenPGP certificate:

0000: 99 01 0D === Pub Key packet ===
0003: 04 3C 5A A5 BB 01 ver 4, created 01 Feb 2002, RSA
0009: 08 00 C7 21 .. 5B EB RSA public modulus n
010B: 00 11 01 00 01 RSA public exponent e
0110: B4 19 === User ID packet ===
0112: 41 6C .. 6D 3E "Alice <[email protected]>"
012B: 89 01 1F === Signature packet (self-signature) ===
012E: 04 10 01 02 ver 4, gen cert, RSA, SHA1
0132: 00 09 05 02 3C 5A A5 BB 02 1B 03
created 01 Feb 2002, key usage:
sign data and certify other keys
014D: 00 0A 09 10 8E AF .. 1A 18 issuer key id
0149: 3B 21 left 16 bits of signed hash value
014B: 07 FE 2F 1D .. C0 81 RSA signature value
024D: 89 00 49 === Signature packet (certification) ===
0250: 04 13 11 02 ver 4, positive cert, DSA, SHA1
0254: 00 09 05 02 3C 5A A5 DC 02 1B 03
created 01 Feb 2002, key usage:
sign data and certify other keys
025F: 00 0A 09 10 F0 0D .. 1F CA issuer key id
026B: BA C2 left 16 bits of signed hash value
026D: 00 9F 5E 58 .. 30 B3 DSA value r
0283: 00 A0 D1 D7 .. 5A AF DSA value s
0299: 99 01 0D === Public Subkey packet ===
029C: 04 3C 5A A5 C5 01 ver 4, created 01 Feb 2002, RSA
02A2: 08 00 C3 03 .. 8C 53 RSA public modulus n
03A4: 00 11 01 00 01 RSA public exponent e
03A9: 89 01 1F === Signature packet (subkey binding) ===
03AC: 04 18 01 02 ver 4, subkey binding, RSA, SHA1

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RFC 4212 Alternative Certificate Formats October 2005

03B0: 00 09 05 02 3C 5A A5 C5 05 1B 0C
created 01 Feb 2002, key usage:
encrypt communications and storage
03BB: 00 0A 09 10 8E AF .. 1A 18 issuer key id
03C7: C8 44 left 16 bits of signed hash value
03C9: 07 FB 04 D7 .. 75 BE RSA signature value
04CB:

Normative References

[ASN1] CCITT Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1), 1988.

[ATTCERT] Farrell, S. and R. Housley, "An Internet Attribute
Certificate Profile for Authorization", RFC 3281, April
2002.

[CMC] Myers, M., Liu, X., Schaad, J., and J. Weinstein,
"Certificate Management Messages over CMS", RFC 2797, April
2000.

[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004.

[CMP] Adams, C., Farrell, S., Kause, T., and T. Mononen,
"Internet X.509 Public Key Infrastructure: Certificate
Management Protocol (CMP)", RFC 4210, September 2005.

[CRMF] Schaad, J., "Internet X.509 Public Key Infrastructure:
Certificate Request Message Format (CRMF)", RFC 4211,
September 2005.

[OPENPGP] Callas, J., Donnerhacke, L., Finney, H., and R. Thayer,
"OpenPGP Message Format", RFC 2440, November 1998.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

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RFC 4212 Alternative Certificate Formats October 2005

Authors' Addresses

Mikhail Blinov
Guardeonic Solutions
Fitzwilliam Court, Leeson Close
Dublin 2, Ireland

EMail: [email protected]

Carlisle Adams
School of Information Technology and Engineering (SITE)
University of Ottawa
800 King Edward Avenue
P.O. Box 450, Stn A
Ottawa, Ontario, Canada K1N 6N5

EMail: [email protected]

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RFC 4212 Alternative Certificate Formats October 2005

Full Copyright Statement

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