PKIX Working Group J. Schaad
Internet Draft Soaring Hawk Consulting
M. Myers
February 2005 TraceRoute Security
Expires: August 2005 X. Liu
Cisco
J. Weinstein
Certificate Management Messages over CMS
draft-ietf-pkix-2797-bis-02.txt
Status of this Memo
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all provisions of Section 10 of RFC2026.
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Abstract
This document defines the base syntax for CMC, a Certificate
Management protocol using CMS (Cryptographic Message Syntax). This
protocol addresses two immediate needs within the Internet PKI
community:
1. The need for an interface to public key certification products
and services based on CMS and PKCS #10 (Public Key Crytpography
Standard), and
2. The need in S/MIME (Secure MIME) for a certificate enrollment
protocol for DSA-signed certificates with Diffie-Hellman public
keys.
CMC also requires the use of the transport document and the
requirements usage document along with this document for a full
definition.
1. Introduction
This document defines the base syntax for CMC, a Certificate
Management protocol using CMS (Cryptographic Message Syntax). This
protocol addresses two immediate needs within the Internet PKI
community:
1. The need for an interface to public key certification products
and services based on CMS and the PKCS #10 (Public Key
Cryptography Standard), and
2. The need in S/MIME (Secure MIME) for a certificate enrollment
protocol for DSA-signed certificates with Diffie-Hellman public
keys.
A small number of additional services are defined to supplement the
core certificate request service.
Throughout this specification the term CMS is used to refer to both
[CMS] and [PKCS7]. For both signedData and envelopedData, CMS is a
superset of the PKCS7. In general, the use of PKCS7 in this document
is aligned to the Cryptographic Message Syntax [CMS] that provides a
superset of the PKCS7 syntax. The term CMC refers to this
specification.
1.1 Protocol Requirements
- The protocol is to be based as much as possible on the existing
CMS, PKCS#10 and CRMF specifications.
- The protocol must support the current industry practice of a
PKCS#10 request followed by a PKCS#7 response as a subset of the
protocol.
- The protocol needs to easily support the multi-key enrollment
protocols required by S/MIME and other groups.
- The protocol must supply a way of doing all operations in a
single-round trip. When this is not possible the number of round
trips is to be minimized.
- The protocol will be designed such that all key generation can
occur on the client.
- The mandatory algorithms must superset the required algorithms
for S/MIME.
- The protocol will contain POP methods. Optional provisions for
multiple-round trip POP will be made if necessary.
- The protocol will support deferred and pending responses to
certificate request for cases where external procedures are
required to issue a certificate.
- The protocol needs to support arbitrary chains of local
registration authorities as intermediaries between certificate
requesters and issuers.
1.2 Notation
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].
2. Protocol Overview
An enrollment transaction in this specification is generally
composed of a single round trip of messages. In the simplest case
an enrollment request is sent from the client to the server and an
enrollment response is then returned from the server to the client.
In some more complicated cases, such as delayed certificate issuance
and polling for responses, more than one round trip is required.
This specification supports two different request messages and two
different response messages.
Public key certification requests can be based on either the PKCS10
or CRMF object. The two different request messages are (a) the bare
PKCS10 (in the event that no other services are needed), and (b) the
PKCS10 or CRMF message wrapped in a CMS encapsulation as part of a
PKIData object.
Public key certification responses are based on the CMS signedData
object. The response may be either (a) a degenerate CMS signedData
object (in the event no other services are needed), or (b) a
ResponseBody object wrapped in a CMS signedData object.
No special services are provided for doing either renewal (new
certificates with the same key) or re-keying (new certificates on
new keys) of clients. Instead a renewal/re-key message looks the
same as any enrollment message, with the identity proof being
supplied by existing certificates from the CA.
No special services are provided to distinguish between doing a re-
keying operation and obtaining a new certificate (generally for a
new purpose). A control to unpublish a certificate would normally
be included in a replacement operation, and be omitted if a new
certificate was desired. CAs or other publishing agents are also
expected to have policies for removing certificates from publication
either based on new certificates being added or the expiration or
revocation of a certificate.
A provision exists for Local Registration Authorities (LRAs) to
participate in the protocol by taking client enrollment messages,
wrapping them in a second layer of enrollment message with
additional requirements or statements from the LRA and then passing
this new expanded request on to the Certification Authority.
This specification makes no assumptions about the underlying
transport mechanism. The use of CMS is not meant to imply an email-
based transport.
Optional services available through this specification are
transaction management, replay detection (through nonces), deferred
certificate issuance, certificate revocation requests and
certificate/CRL retrieval.
2.1 Terminology
There are several different terms, abbreviations and acronyms used
in this document that we define here for convenience and consistency
of usage:
"End-Entity" (EE) refers to the entity that owns a key pair and for
whom a certificate is issued.
"LRA" or "RA" refers to a (Local) Registration Authority. A
registration authority acts as an intermediary between an End-Entity
and a Certification Authority. Multiple RAs can exist between the
End-Entity and the Certification Authority.
"CA" refers to a Certification Authority. A Certification Authority
is the entity that performs the actual issuance of a certificate.
"Client" refers to an entity that creates a PKI request. In this
document both RAs and End-Entities can be clients.
"Server" refers to the entities that process PKI requests and create
PKI responses. CAs and RAs can be servers in this document.
"PKCS#10" refers the Public Key Cryptography Standard #10. This is
one of a set of standards defined by RSA Laboratories in the 1980s.
PKCS#10 defines a Certificate Request Message syntax.
"CRMF" refers to the Certificate Request Message Format RFC [CRMF].
We are using certificate request message format defined in this
document as part of our management protocol.
"CMS" refers to the Cryptographic Message Syntax RFC [CMS]. This
document provides for basic cryptographic services including
encryption and signing with and without key management.
"POP" is an acronym for "Proof of Possession". POP refers to a
value that can be used to prove that the private key corresponding
to a public key is in the possession and can be used by an end-
entity.
"Transport wrapper" refers to the outermost CMS wrapping layer.
2.2 Protocol Flow Charts
Figure 1 shows the Simple Enrollment Request and Response messages.
The contents of these messages are detailed in Sections 4.1 and 4.3
below.
Simple PKI Request Simple PKI Response
------------------------- --------------------------
+----------+ +------------------+
| PKCS #10 | | CMS "certs-only" |
+----------+--------------+ | message |
| | +------------------+------+
| Certificate Request | | |
| | | CMS Signed Data, |
| Subject Name | | no signerInfo |
| Subject Public Key Info | | |
| (K_PUB) | | signedData contains one |
| Attributes | | or more certificates in |
| | | the "certificates" |
+-----------+-------------+ | portion of the |
| signed with | | signedData. |
| matching | | |
| K_PRIV | | encapsulatedContentInfo |
+-------------+ | is empty. |
| |
+--------------+----------+
| unsigned |
+----------+
Figure 1: Simple PKI Request and Response Messages
Full PKI Request Full PKI Response
----------------------- ------------------------
+----------------+ +----------------+
| CMS signedData | | CMS signedData |
| object | | object |
+----------------+--------+ +----------------+--------+
| | | |
| PKIData object | | ResponseBody object |
| | | |
| Sequence of: | | Sequence of: |
| <enrollment attribute>* | | <enrollment attribute>* |
| <certification request>*| | <CMS object>* |
| <CMS objects>* | | <other message>* |
| <other message>* | | |
| | | where * == zero or more |
| where * == zero or more | | |
| | | All certificates issued |
| Certificate requests | | as part of the response |
| are CRMF or PKCS#10 | | are included in the |
| objects. Attributes are | | "certificates" portion |
| (OID, ANY defined by | | of the signedData. |
| OID) pairs. | | Relevant CA certs and |
| | | CRLs can be included as |
+-------+-----------------+ | well. |
| signed (keypair | | |
| used may be pre-| +---------+---------------+
| existing or | | signed by the |
| identified in | | CA or an LRA |
| the request) | +---------------+
+-----------------+
Figure 2: Full PKI Request and Response Messages
Figure 2 shows the Full Enrollment Request and Response messages.
The contents of these messages are detailed in Sections 4.2 and 4.4
below.
3. Protocol Elements
This section covers each of the different elements that may be used
to construct enrollment request and enrollment response messages.
Section 4 will cover how to build the enrollment request and
response messages.
3.1 PKIData Object
The new content object PKIData has been defined for this protocol.
This new object is used as the body of the full PKI request message.
The new body is identified by:
id-cct-PKIData ::= {id-pkix id-cct(12) 2 }
The ASN.1 structure corresponding to this new content type is:
PKIData ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
reqSequence SEQUENCE SIZE(0..MAX) OF TaggedRequest,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
-- controlSequence consists of a sequence of control attributes.
The control attributes defined in this document are found in section
5. As control sequences are defined by OIDs, other parties can
define additional control attributes. Unrecognized OIDs MUST result
in no part of the request being successfully processed.
-- reqSequence consists of a sequence of requests. The requests can
be a CertificateRequest (PKCS10 request), a CertReqMsg or an
externally defined request (orm). Details on the first two request
types are found in sections 3.3.1 and 3.3.2 respectively. If an
externally defined request message is present, but the server does
not understand the request (or will not process it), a CMCStatus of
noSupport MUST be returned for the request item and no requests
processed.
-- cmsSequence consists of a sequence of [CMS] message objects.
This protocol uses EnvelopedData, SignedData, EncryptedData and
AuthenticatedData. See section 3.6 for more details.
-- otherMsgSequence allows for other arbitrary data items to be
placed into the enrollment protocol. The {OID, any} pair of values
allows for arbitrary definition of material. Data objects are
placed here while control objects are placed in the controlSequence
field. See section 3.7 for more details.
Processing of this object by a recipient is as follows:
1. All control attributes should be examined and processed in an
appropriate manner. The appropriate processing may be either to
do complete processing at this time, ignore the control
attribute or to place the control attribute on a to-do list for
later processing.
2. An implicit control attribute is then processed for each item in
the reqSequence. Again this may be either immediate processing
or addition to a to-do list for later processing.
No processing is required for cmsSequence or otherMsgSequence
members of the element. If items are present and are not referenced
by a control sequence, they are to be ignored.
3.2 ResponseBody Object
The new content object ResponseBody has been defined for this
protocol. This new object is used as the body of the full PKI
response message. The new body is identified by:
id-cct-PKIResponse ::= {id-pkix id-cct(12) 3 }
The ASN.1 structure corresponding to this body content type is:
ResponseBody ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
-- controlSequence consists of a sequence of control attributes.
The control attributes defined in this document are found in section
3.5. Other parties can define additional control attributes.
-- cmsSequence consists of a sequence of [CMS] message objects.
This protocol only uses EnvelopedData, SignedData, EncryptedData and
AuthenticatedData. See section 3.6 for more details.
-- otherMsgSequence allows for other arbitrary items to be placed
into the enrollment protocol. The {OID, any} pair of values allows
for arbitrary definition of material. Data objects are placed here
while control objects are placed in the controlSequence field. See
section 3.7 for more details.
Processing of this object by a recipient is as follows:
1. All control attributes should be examined and processed in an
appropriate manner. The appropriate processing may be either to
do complete processing at this time, ignore the control
attribute or to place the control attribute on a to-do list for
later processing.
2. Additional processing of non-element items includes the saving
of certificates and CRLs present in wrapping layers. This type
of processing is based on the consumer of the element and should
not be relied on by generators.
No processing is required for cmsSequence or otherMsgSequence
members of the element. If items are present and are not referenced
by a control sequence, they are to be ignored.
3.3 Certification Requests (PKCS10/CRMF)
Certification Requests are based on either PKCS10 or CRMF messages.
Section 3.3.1 specifies mandatory and optional requirements for
clients and servers dealing with PKCS10 request messages. Section
3.3.2 specifies mandatory and optional requirements for clients and
servers dealing with CRMF request messages.
All certificate requests directly encoded into a single PKIData
object SHOULD be for the same identity. RAs that batch processing
are expected to place the signed PKIData sequences received into the
cmsSequence of the PKIData object it generates.
3.3.1 PKCS10 Request Body
Servers MUST be able to understand and process PKCS10 request
bodies. Clients MUST produce a PKCS10 request body when using the
Simple Enrollment Request message. Clients MAY produce a PKCS10
request body when using the Full Enrollment Request message.
When producing a PKCS10 request body, clients MUST produce a PKCS10
message body containing a subject name and public key. Some
certification products are operated using a central repository of
information to assign subject names upon receipt of a public key for
certification. To accommodate this mode of operation, the subject
name in a CertificationRequest MAY be NULL, but MUST be present.
CAs that receive a CertificationRequest with a NULL subject name MAY
reject such requests. If rejected and a response is returned, the
CA MUST respond with the failInfo attribute of badRequest.
The client MAY incorporate one or more standard X.509 v3 extensions
in any PKCS10 request as an ExtensionReq attribute. An ExtensionReq
attribute is defined as
ExtensionReq ::= SEQUENCE OF Extension
where Extension is imported from [PKIXCERT] and ExtensionReq is
identified by {pkcs-9 14}.
Servers MUST be able to process all extensions defined, but not
prohibited, in [PKIXCERT]. Servers are not required to be able to
process other V3 X.509 extensions transmitted using this protocol,
nor are they required to be able to process other, private
extensions. Servers are not required to put all client-requested
extensions into a certificate. Servers are permitted to modify
client-requested extensions. Servers MUST NOT alter an extension so
as to invalidate the original intent of a client-requested
extension. (For example, changing key usage from key exchange to
signing.) If a certification request is denied due to the inability
to handle a requested extension and a response is returned, the
server MUST respond with the failInfo attribute of unsupportedExt.
3.3.2 CRMF Request Body
Servers MUST be able to understand and process CRMF request body.
Clients MAY produce a CRMF message body when using the Full
Enrollment Request message.
This memo imposes the following additional changes on the
construction and processing of CRMF messages:
- 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. As in the case of PKCS10
requests, the subject may be encoded as NULL, but MUST be
present.
- When both CRMF and CMC controls exist with equivalent
functionality, the CMC control SHOULD be used. The CMC control
MUST override the CRMF control.
- The regInfo field MUST NOT be used on a CRMF message. Equivalent
functionality is provided in the regInfo control attribute
(section 5.12).
- The indirect method of proving POP is not supported in this
protocol. One of the other methods (including the direct method
described in this document) MUST be used instead if POP is
desired. The value of encrCert in SubsequentMessage MUST NOT be
used.
- Since the subject and publicKeyValues are always present, the
POPOSigningKeyInput MUST NOT be used when computing the value for
POPSigningKey.
A server is not required to use all of the values suggested by the
client in the certificate template. Servers MUST be able to process
all extensions defined, but not prohibited in [PXIXCERT]. Servers
are not required to be able to process other V3 X.509 extension
transmitted using this protocol, nor are they required to be able to
process other, private extensions. Servers are permitted to modify
client-requested extensions. Servers MUST NOT alter an extension so
as to invalidate the original intent of a client-requested
extension. (For example change key usage from key exchange to
signing.) If a certificate request is denied due to the inability
to handle a requested extension, the server MUST respond with a
failInfo attribute of unsupportedExt.
3.3.3 Production of Diffie-Hellman Public Key Certification Requests
Part of a certification request is a signature over the request;
Diffie-Hellman is a key agreement algorithm and cannot be used to
directly produce the required signature object. [DH-POP] provides
two ways to produce the necessary signature value. This document
also defines a signature algorithm that does not provide a POP
value, but can be used to produce the necessary signature value.
3.3.3.1 No-Signature Signature Mechanism
Key management (encryption/decryption) private keys cannot always be
used to produce some type of signature value as they can be in a
decrypt only device. Certification requests require that the
signature field be populated. This section provides a signature
algorithm specifically for that purposes. The following object
identifier and signature value are used to identify this signature
type:
id-alg-noSignature OBJECT IDENTIFIER ::= {id-pkix id-alg(6) 2}
NoSignatureValue ::= OCTET STRING
The parameters for id-alg-noSignature MUST be present and MUST be
encoded as NULL. NoSignatureValue contains the hash of the
certification request. It is important to realize that there is no
security associated with this signature type. If this signature
type is on a certification request and the Certification Authority
policy requires proof-of-possession of the private key, the POP
mechanism defined in section 5.7 MUST be used.
3.3.3.2 Diffie-Hellman POP Discrete Logarithm Signature
CMC compliant implementations MUST support section 4 of [DH-POP].
3.3.3.3 Diffie-Hellman MAC signature
CMC compliant implementations MAY support section 3 of [DH-POP].
3.4 Body Part Identifiers
Each element of a PKIData or PKIResponse message has an associated
body part identifier. The Body Part Identifier is a 4-octet integer
encoded in the certReqIds field for CertReqMsg objects (in a
TaggedRequest) or in the bodyPartID field of the other objects. The
Body Part Identifier MUST be unique within a single PKIData or
PKIResponse object. Body Part Identifiers can be duplicated in
different layers (for example a CMC message embedded within
another). The Body Part Id of zero is reserved to designate the
current PKIData object. This value is used in control attributes
such as the Add Extensions Control in the pkiDataReference field to
refer to a request in the current PKIData object.
Some control attribute, such as the CMC Status Info attribute, will
also use Body Part Identifiers to refer to elements in the previous
message. This allows an error to be explicit about the attribute or
request to which the error applies.
3.5 Control Attributes
The overall control flow of how a message is processed in this
document is based on the control attributes. Each control attribute
consists of an object identifier and a value based on the object
identifier.
Servers MUST fail the processing of an entire PKIData message if any
included control attribute is not recognized. The response MUST be
the error badRequest and bodyList MUST contain the bodyPartID of the
invalid or unrecognized control attribute(s).
The syntax of a control attribute is
TaggedAttribute ::= SEQUENCE {
bodyPartID BodyPartID,
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue
}
-- bodyPartID is a unique integer that is used to reference this
control attribute. The id of 0 is reserved for use as the reference
to the current PKIData object.
-- attrType is the OID defining the associated data in attrValues
-- attrValues contains the set of data values used in processing
the control attribute.
The set of control attributes that are defined by this memo are
found in section 5.
3.6 Content Info objects
The cmsSequence field of the PKIRequest and PKIResponse messages
contains zero or more tagged content info objects. The syntax for
this structure is
TaggedContentInfo ::= SEQUENCE {
bodyPartID BodyPartID,
contentInfo ContentInfo
}
-- bodyPartID is a unique integer that is used to reference this
content info object. The id of 0 is reserved for use as the
reference to the current PKIData object.
-- contentInfo contains a ContentInfo object (defined in [CMS]).
The four contents used in this location are SignedData,
EnvelopedData, AuthenticatedData and Data.
EnvelopedData provides for shrouding of data. Data allows for
general transport of unstructured data.
The SignedData object from [CMS] is also used in this specification
to provide for authentication as well as serving as the general
transport wrapper of requests and responses.
AuthenticatedData provides a method of doing pass phrase based
validation of data being sent between two parties. Unlike
SignedData it does not specify which party actually generated the
information.
3.6.1 Signed Data
The signedData object is used in two different locations when
constructing enrollment messages. The signedData object is used as
a wrapper for a PKIData as part of the enrollment request message.
The signedData object is also used as the outer part of an
enrollment response message.
As part of processing a message the signature(s) MUST be verified.
If the signature does not verify, and the body contains anything
other than a status response, a new message containing a status
response MUST be returned using a CMCFailInfo with a value of
badMessageCheck and a bodyPart of 0.
For the enrollment response the signedData wrapper allows the server
to sign the returning data, if any exists, and to carry the
certificates and CRLs for the enrollment request. If no data is
being returned beyond the certificates, no signerInfo objects are
placed in the signedData object.
3.6.2 Enveloped Data
EnvelopedData is the primary method of providing confidentiality for
sensitive information in this protocol. The protocol currently uses
EnvelopedData to provide encryption of an entire request (see
section 4.5). The envelopedData object would also be used to wrap
private key material for key archival. If the decryption on an
envelopedData failes, the response is a CMCFailInfo with a value of
badMessageCheck and a bodyPart of 0.
Servers MUST implement envelopedData according to [CMS]. There is
an ambiguity (about encrypting content types other than id-data) in
the PKCS7 specification that has lead to non-interoperability.
3.6.3 Authenticated Data
AuthenticatedData is used for providing origination authentication
in those circumstances where a shared-secret exists, but a PKI trust
anchor has not yet been established. This is currently only used
for the id-cmc-authData control (section 5.2.16). This control is
uses the PKIData body so that new controls with additional policy
type information could be included as well.
3.7 Other Message Bodies
The other message body portion of the message allows for arbitrary
data objects to be carried as part of a message. This is intended
to contain data that is not already wrapped in a CMS contentInfo
object. The data is ignored unless a control attribute references
the data by bodyPartID.
OtherMsg ::= SEQUENCE {
bodyPartID BodyPartID,
otherMsgType OBJECT IDENTIFIER,
otherMsgValue ANY DEFINED BY otherMsgType }
-- bodyPartID contains the unique id of this object
-- otherMsgType contains the OID defining both the usage of this
body part and the syntax of the value associated with this body part
-- otherMsgValue contains the data associated with the message body
part.
3.8 Unsigned Attributes
There is sometimes a need to include data in an enrollment message
designed to be removed during processing. An example of this is the
inclusion of an encrypted private key, where a key archive agent
removes the encrypted private key before sending it on to the CA.
One side effect of this desire is the fact that every RA which
encapsulates this information needs to move the data so that it is
not covered by the RA signature. (A client request, encapsulated by
an RA cannot have the unsigned attribute removed by the key archive
agent without breaking the RA's signature.) This attribute
addresses that problem.
This attribute is used to contain the information that is not
directly signed by a user. When an RA finds a message that has this
attribute in the unsigned or unauthenticated attribute fields of the
CMS objects it is aggregating, they are removed from the embedded
CMS objects and propagated up to the RA CMS object.
id-aa-cmc-unsignedData OBJECT IDENTIFIER ::= {id-aa 34}
CMCUnsignedData ::= SEQUENCE {
bodyPartPath SEQUENCE SIZE (1..MAX) OF BodyPartID,
identifier OBJECT IDENTIFIER,
content ANY DEFINED BY identifier
}
There MUST be at most one CMCUnsignedData attribute in the
UnsignedAttribute sequence of a SignerInfo structure. The attribute
can have any number of attribute values greater than zero. If the
attribute appears in one SignerInfo in a sequence, it MUST appear
the same in all SignerInfo items and MUST have the same value(s).
4. PKI Messages
This section discusses the details of putting together the different
enrollment request and response messages.
4.1 Simple Enrollment Request
The simplest form of an enrollment request is a plain PKCS10
message. If this form of enrollment request is used for a private
key that is capable of generating a signature, the PKCS10 MUST be
signed with that private key. If this form of the enrollment
request is used for a D-H key, then the D-H POP mechanism described
in [DH-POP] MUST be used.
Servers MUST support the Simple Enrollment Request message. If the
Simple Enrollment Request message is used, servers MUST return the
Simple Enrollment Response message (see Section 4.3) if the
enrollment request is granted. If the enrollment request fails, the
Full Enrollment Response MAY be returned or no response MAY be
returned.
The Simple Enrollment Request message MUST NOT be used if a proof-
of-identity needs to be included.
Many advanced services specified in this memo are not supported by
the Simple Enrollment Request message.
4.2 Full PKI Request
The Full Enrollment Request provides the most functionality and
flexibility. Clients SHOULD use the Full Enrollment Request message
when enrolling. Servers MUST support the Full Enrollment Request
message. An enrollment response (full or simple as appropriate)
MUST be returned to all Full Enrollment Requests.
The Full Enrollment Request message consists of a PKIData object
wrapped in a signedData CMS object. The objects in the PKIData are
ordered as follows:
1. All Control Attributes,
2. All certification requests,
3. All CMS objects,
4. All other messages.
Each object in the PKIData sequence is identified by a Body Part
Identifier. If duplicate ids are found, the server MUST return the
error badRequest with a bodyPartID of 0.
The signedData object wrapping the PKIData may be signed either by
the private key material of the signature certification request, or
by a previously certified signature key. If the private key of a
signature certification request is being used, then:
a) the certification request containing the corresponding public key
MUST include a Subject Key Identifier extension,
b) the subjectKeyIdentifier form of signerInfo MUST be used, and
c) the value of the subjectKeyIdentifier form of signerInfo MUST be
the Subject Key Identifier specified in the corresponding
certification request.
(The subjectKeyIdentifier form of signerInfo is used here because no
certificates have yet been issued for the signing key.) If the
request key is used for signing, there MUST be only one signerInfo
object in the signedData object.
When creating a message to renew a certificate, the following should
be taken into consideration:
1. The identification and identityProof control statements are not
required. The same information is provided by the use of an
existing certificate from the CA when signing the enrollment
message.
2. CAs and LRAs may impose additional restrictions on the signing
certificate used. They may require that the most recently issued
signing certificate for an entity be used.
3. A renewal message may occur either by creating a new set of keys,
or by re-using an existing set of keys. Some CAs may prevent re-
use of keys by policy. In this case the CA MUST return
NOKEYREUSE as the failure code.
4.3 Simple Enrollment Response
Servers SHOULD use the simple enrollment response message whenever
possible. Clients MUST be able to process the simple enrollment
response message. The simple enrollment response message consists
of a signedData object with no signerInfo objects on it. The
certificates requested are returned in the certificate bag of the
signedData object.
Clients MUST NOT assume the certificates are in any order. Servers
SHOULD include all intermediate certificates needed to form complete
chains to one or more self-signed certificates, not just the newly
issued certificate(s). The server MAY additionally return CRLs in
the CRL bag. Servers MAY include the self-signed certificates.
Clients MUST NOT implicitly trust included self-signed
certificate(s) merely due to its presence in the certificate bag. In
the event clients receive a new self-signed certificate from the
server, clients SHOULD provide a mechanism to enable the user to
explicitly trust the certificate.
4.4 Full PKI Response
Servers MUST return full PKI response messages if a) a full PKI
request message failed or b) additional services other than
returning certificates are required. Servers MAY return full PKI
responses with failure information for simple PKI requests.
Following section 4.3 above, servers returning only certificates and
a success status to the client SHOULD use the simple PKI response
message.
Clients MUST be able to process a full PKI response message.
The full enrollment response message consists of a signedData object
encapsulating a responseBody object. In a responseBody object all
Control Attributes MUST precede all CMS objects. The certificates
granted in an enrollment response are returned in the certificates
field of the immediately encapsulating signedData object.
Clients MUST NOT assume the certificates are in any order. Servers
SHOULD include all intermediate certificates needed to form complete
chains one or more self-signed certificates, not just the newly
issued certificate(s). The server MAY additionally return CRLs in
the CRL bag. Servers MAY include the self-signed certificates.
Clients MUST NOT implicitly trust included self-signed
certificate(s) merely due to its presence in the certificate bag. In
the event clients receive a new self-signed certificate from the
server, clients SHOULD provide a mechanism to enable the user to
explicitly trust the certificate. (The publish trust root control
exists for the purpose of allowing for distribution of root
certificates. If a trusted root publishes a new trusted root, this
is one case where automated trust of the new root could be allowed.)
4.5 Application of Encryption to a PKI Message
There are occasions where a PKI request or response message must be
encrypted in order to prevent any information about the enrollment
from being accessible to unauthorized entities. This section
describes the means used to encrypt a PKI message. This section is
not applicable to a simple enrollment message.
Confidentiality is provided by wrapping the PKI message (a
signedData object) in a CMS EnvelopedData object. The nested
content type in the EnvelopedData is id-signedData. Note that this
is different from S/MIME where there is a MIME layer placed between
the encrypted and signed data objects. It is recommended that if an
enveloped data layer is applied to a PKI message, a second signing
layer be placed outside of the enveloped data layer. The following
figure shows how this nesting would be done:
Normal Option 1 Option 2
------ -------- --------
SignedData EnvelopedData SignedData
PKIData SignedData EnvelopedData
PKIData SignedData
PKIData
Options 1 and 2 provide the benefit of preventing leakage of
sensitive data by encrypting the information. LRAs can remove the
enveloped data wrapping, and replace or forward without further
processing. Section 6 contains more information about LRA
processing.
PKI Messages MAY be encrypted or transmitted in the clear. Servers
MUST provided support for all three versions.
Alternatively, an authenticated, secure channel could exist between
the parties requiring encryption. Clients and servers MAY use such
channels instead of the technique described above to provide secure,
private communication of PKI request and response messages.
5. Control Attributes
Control attributes are carried as part of both PKI requests and
responses. Each control attribute is encoded as a unique Object
Identifier followed by that data for the control attribute. The
encoding of the data is based on the control attribute object
identifier. Processing systems would first detect the OID and
process the corresponding attribute value prior to processing the
message body.
The following table lists the names, OID and syntactic structure for
each of the control attributes documented in this memo.
Control Attribute OID Syntax
----------------- ---------- --------------
id-cmc-statusInfo id-cmc 1 CMCStatusInfo
id-cmc-identification id-cmc 2 UTF8String
id-cmc-identityProof id-cmc 3 OCTET STRING
id-cmc-dataReturn id-cmc 4 OCTET STRING
id-cmc-transactionId id-cmc 5 INTEGER
id-cmc-senderNonce id-cmc 6 OCTET STRING
id-cmc-recipientNonce id-cmc 7 OCTET STRING
id-cmc-addExtensions id-cmc 8 AddExtensions
id-cmc-encryptedPOP id-cmc 9 EncryptedPOP
id-cmc-decryptedPOP id-cmc 10 DecryptedPOP
id-cmc-lraPOPWitness id-cmc 11 LraPOPWitness
id-cmc-getCert id-cmc 15 GetCert
id-cmc-getCRL id-cmc 16 GetCRL
id-cmc-revokeRequest id-cmc 17 RevokeRequest
id-cmc-regInfo id-cmc 18 OCTET STRING
id-cmc-responseInfo id-cmc 19 OCTET STRING
id-cmc-QueryPending id-cmc 21 OCTET STRING
id-cmc-idPOPLinkRandom id-cmc 22 OCTET STRING
id-cmc-idPOPLinkWitness id-cmc 23 OCTET STRING
id-cmc-idConfirmCertAcceptance id-cmc 24 CMCCertId
id-cmc-statusInfoExt id-cmc 25 CMCStatusInfoExt
id-cmc-trustRoots id-cmc 27 PublishTrustRoots
id-cmc-authData id-cmc 27 AuthPublish
id-cmc-batchRequests id-cmc 28 BodyPartList
id-cmc-batchResponses id-cmc 29 BodyPartList
id-cmc-publishCertificate id-cmc 30 CMCPublicationInfo
id-cmc-modCertTemplate id-cmc 31 CertTemplate
5.1 CMC Status Info Control Attributes
The CMC status info control is used in full PKI Response messages to
return information about the processing of a client request. Two
controls are described in this section. The first is the preferred
control; the second is included for backwards compatibility with RFC
2797.
Servers MAY emit multiple CMC status info controls referring to a
single body part. Clients MUST be able to deal with multiple CMC
status info controls in a response message. Servers MUST use the
CMCStatusInfoExt control, but MAY additionally use the CMCStatusInfo
control. Clients MUST be able to process the CMCStatusInfoExt
control.
5.1.1 Extended CMC Status Info Control Attribute
This control uses the following ASN.1 definition:
CMCStatusInfoExt ::= SEQUENCE {
CMCStatus CMCStatus,
BodyList SEQUENCE SIZE (1..MAX) OF
BodyPartReference,
StatusString UTF8String OPTIONAL,
OtherInfo CHOICE {
FailInfo CMCFailInfo,
PendInfo PendInfo,
ExtendedFailInfo SEQUENCE {
FailInfoOID OBJECT IDENTIFIER,
FailInfoValue AttributeValue
}
}
}
BodyPartReference ::= CHOICE {
bodyPartID BodyPartID,
bodyPartPath SEQUENCE SIZE (1..MAX) OF BodyPartID
}
PendInfo ::= SEQUENCE {
pendToken OCTET STRING,
pendTime GeneralizedTime
}
-- cMCStatus is described in section 5.1.3
-- bodyList contains the list of references to body parts in the
request message to which this status information applies. If an
error is being returned for a simple enrollment message, body list
will contain a single integer of value '1'.
-- statusString contains a string with additional description
information. This string is human readable.
-- failInfo is described in section 5.1.4. It provides a detailed
error on what the failure was. This choice is present only if
cMCStatus is failed.
-- extendedFailInfo is provided for other users of the enrollment
protocol to provided their own error codes. This choice is present
only if cMCStatus is failed. Caution should be used in defining new
values as they may not be correctly recognized by all clients and
servers. The failInfo value of internalCA error may be assumed if
the extended error is not recognized.
-- pendToken is the token to be used in the queryPending control
attribute.
-- pendTime contains the suggested time the server wants to be
queried about the status of the request.
If the cMCStatus field is success, the CMC Status Info Control MAY
be omitted unless it is only item in the response message. If no
status exists for a certificate request or other item requiring
processing, then the value of success is to be assumed.
5.1.2 CMC Status Info Control Attribute
The CMC status info control is used in full PKI Response messages to
return information on a client request. Servers MAY emit multiple
CMC status info controls referring to a single body part. Clients
MUST be able to deal with multiple CMC status info controls in a
response message. This statement uses the following ASN.1
definition:
CMCStatusInfo ::= SEQUENCE {
cMCStatus CMCStatus,
bodyList SEQUENCE SIZE (1..MAX) OF BodyPartID,
statusString UTF8String OPTIONAL,
otherInfo CHOICE {
failInfo CMCFailInfo,
pendInfo PendInfo } OPTIONAL
}
-- cMCStatus is described in section 5.1.3
-- bodyList contains the list of body parts in the request
message to which this status information applies. If an error is
being returned for a simple enrollment message, body list will
contain a single integer of value '1'.
-- statusString contains a string with additional description
information. This string is human readable.
-- failInfo is described in section 5.1.4. It provides a detailed
error on what the failure was. This choice is present only if
cMCStatus is failed.
If the cMCStatus field is success, the CMC Status Info Control MAY
be omitted unless it is only item in the response message. If no
status exists for a certificate request or other item requiring
processing, then the value of success is to be assumed.
5.1.3 CMCStatus values
CMCStatus is a field in the CMCStatusInfo structure. This field
contains a code representing the success or failure of a specific
operation. CMCStatus has the ASN.1 structure of:
CMCStatus ::= INTEGER {
success (0),
-- request was granted
-- reserved (1),
-- not used, defined where the original structure was
defined
failed (2),
-- you don't get what you want, more information elsewhere
in the message
pending (3),
-- the request body part has not yet been processed,
-- requester is responsible to poll back on this
-- pending may only be return for certificate request
operations.
noSupport (4),
-- the requested operation is not supported
confirmRequired (5),
-- conformation using the idConfirmCertAcceptance control is
required
-- before use of certificate
popRequired (6)
-- A certificate requires an indirect POP operation.
-- Info for the indirect POP in this message.
}
5.1.4 CMCFailInfo
CMCFailInfo conveys information relevant to the interpretation of a
failure condition. The CMCFailInfo has the following ASN.1
structure:
CMCFailInfo ::= INTEGER {
badAlg (0)
-- Unrecognized or unsupported algorithm
badMessageCheck (1)
-- integrity check failed
badRequest (2)
-- transaction not permitted or supported
badTime (3)
-- Message time field was not sufficiently close to the
system time
badCertId (4)
-- No certificate could be identified matching the provided
criteria
unsuportedExt (5)
-- A requested X.509 extension is not supported by the
recipient CA.
mustArchiveKeys (6)
-- Private key material must be supplied
badIdentity (7)
-- Identification Attribute failed to verify
popRequired (8)
-- Server requires a POP proof before issuing certificate
popFailed (9)
-- POP processing failed
noKeyReuse (10)
-- Server policy does not allow key re-use
internalCAError (11)
tryLater (12)
authDataFail (13)
-- Failure occurred during processing of authenticated data
}
Additional failure reasons MAY be defined for closed environments
with a need.
5.2 Identification and IdentityProof Control Attributes
Some CAs and LRAs require that a proof of identity be included in a
certification request. Many different ways of doing this exist with
different degrees of security and reliability. Most people are
familiar with the request of a bank to provide your mother's maiden
name as a form of identity proof.
CMC provides one method of proving the client's identity based on a
shared secret between the certificate requestor and the verifying
authority. If clients support full request messages, clients MUST
implement this method of identity proof. Servers MUST provide this
method and MAY also have bilateral methods of similar strength
available.
The CMC method starts with an out-of-band transfer of a token (the
shared secret). The shared-secret should be generated in a random
manner. The distribution of this token is beyond the scope of this
document. The client then uses this token for an identity proof as
follows:
1. The reqSequence field of the PKIData object (encoded exactly as
it appears in the request message including the sequence type and
length) is the value to be validated.
2. A SHA1 hash of the token is computed.
3. An HMAC-SHA1 value is then computed over the value produced in
Step 1, as described in [HMAC], using the hash of the token from
Step 2 as the shared secret value.
4. The 160-bit HMAC-SHA1 result from Step 3 is then encoded as the
value of the identityProof attribute.
When the server verifies the identityProof attribute, it computes
the HMAC-SHA1 value in the same way and compares it to the
identityProof attribute contained in the enrollment request.
If a server fails the verification of an identityProof attribute and
the server returns a response message, the failInfo attribute MUST
be present in the response and MUST have a value of badIdentity.
Reuse of the shared-secret on enrollment retries makes it easier for
the client and to prevent getting out of sync. However, reuse of
the shared-secret can potentially open the door for some types of
attacks.
Optionally, servers MAY require the inclusion of the unprotected
identification attribute with an identification attribute. The
identification attribute is intended to contain either a text string
or a numeric quantity, such as a random number, which assists the
server in locating the shared secret needed to validate the contents
of the identityProof attribute. Numeric values MUST be converted to
text string representations prior to encoding as UTF8-STRINGs in
this attribute. If the identification control attribute is included
in the message, the derivation of the shared secret in step 2 is
altered so that the hash of the concatenation of the token and the
UTF8 encoded (without the type and length bytes) identity value are
hashed rather than just the token.
5.2.1 Hardware Shared Secret Token Generation
The shared secret between the end-entity and the identity verify is
sometimes transferred using a hardware device that generates a
series of tokens based on some shared secret value. The user can
therefore prove their identity by transferring this token in plain
text along with a name string. The above protocol can be used with
a hardware shared-secret token generation device by the following
modifications:
1. The identification attribute MUST be included and MUST contain
the hardware-generated token.
2. The shared secret value used above is the same hardware-generated
token.
3. All certification requests MUST have a subject name and the
subject name MUST contain the fields required to identify the
holder of the hardware token device.
5.3 Linking Identity and POP Information
In a PKI Full Request message identity information about the
creator/author of the message is carried in the signature of the CMS
SignedData object containing all of the certificate requests. Proof-
of-possession information for key pairs requesting certification,
however, is carried separately for each PKCS#10 or CRMF message.
(For keys capable of generating a digital signature, the POP is
provided by the signature on the PKCS#10 or CRMF request. For
encryption-only keys the controls described in Section 5.7 below are
used.) In order to prevent substitution-style attacks we must
guarantee that the same entity generated both the POP and proof-of-
identity information.
This section describes two mechanisms for linking identity and POP
information: witness values cryptographically derived from the
shared-secret (Section 5.3.1) and shared-secret/subject DN matching
(Section 5.3.2). Clients and servers MUST support the witness value
technique. Clients and servers MAY support shared-secret/subject DN
matching or other bilateral techniques of similar strength. The
idea behind both mechanisms is to force the client to sign some data
into each certificate request that can be directly associated with
the shared-secret; this will defeat attempts to include certificate
requests from different entities in a single Full PKI Request
message.
5.3.1 Witness values derived from the shared-secret
The first technique for doing identity-POP linking works by forcing
the client to include a piece of information cryptographically-
derived from the shared-secret token as a signed extension within
each certificate request (PKCS#10 or CRMF) message. This technique
is useful if null subject DNs are used (because, for example, the
server can generate the subject DN for the certificate based only on
the shared secret). Processing begins when the client receives the
shared-secret token out-of-band from the server. The client then
computes the following values:
1. The client generates a random byte-string, R, which SHOULD be at
least 512 bits in length.
2. A SHA1 hash of the token is computed.
3. An HMAC-SHA1 value is then computed over the random value
produced in Step 1, as described in [HMAC], using the hash of the
token from Step 2 as the shared secret.
4. The random value produced in Step 1 is encoded as the value of an
idPOPLinkRandom control attribute. This control attribute MUST
be included in the Full PKI Request message.
5. The 160-bit HMAC-SHA1 result from Step 3 is encoded as the value
of an idPOPLinkWitness extension to the certificate request.
a. For CRMF, idPOPLinkWitness is included in the controls
section of the CertRequest structure.
b. For PKCS#10, idPOPLinkWitness is included in the attributes
section of the CertificationRequest structure.
Upon receipt, servers MUST verify that each certificate request
contains a copy of the idPOPLinkWitness and that its value was
derived in the specified manner from the shared secret and the
random string included in the idPOPLinkRandom control attribute.
5.3.2 Shared-secret/subject DN matching
The second technique for doing identity-POP linking is to link a
particular subject distinguished name (subject DN) to the shared-
secrets that are distributed out-of-band and to require that clients
using the shared-secret to prove identity include that exact subject
DN in every certificate request. It is expected that many client-
server connections using shared-secret based proof-of-identity will
use this mechanism. (It is common not to omit the subject DN
information from the certificate request messages.)
When the shared secret is generated and transferred out-of-band to
initiate the registration process (Section 5.2), a particular
subject DN is also associated with the shared secret and
communicated to the client. (The subject DN generated MUST be
unique per entity in accordance with CA policy; a null subject DN
cannot be used. A common practice could be to place the
identification value as part of the subject DN.) When the client
generates the Full PKI Request message, it MUST use these two pieces
of information as follows:
1. The client MUST include the specific subject DN that it received
along with the shared secret as the subject name in every
certificate request (PKCS#10 and/or CRMF) in the Full PKI
Request. The subject names in the requests MUST NOT be null.
2. The client MUST include the identityProof control attribute
(Section 5.2), derived from the shared secret, in the Full PKI
Request.
The server receiving this message MUST (a) validate the
identityProof control attribute and then, (b) check that the subject
DN included in each certificate request matches that associated with
the shared secret. If either of these checks fails the certificate
request MUST be rejected.
5.3.3 Renewal and Re-Key Messages
In a renewal or re-key message, the subject DN in (a) the
certificate referenced by the CMS SignerInfo object, and (b) all
certificate requests within the request message MUST match according
to the standard name match rules described in [PKIXCERT].
5.4 Data Return Control Attribute
The data return control attribute allows clients to send arbitrary
data (usually some type of internal state information) to the server
and to have the data returned as part of the enrollment response
message. Data placed in a data return statement is considered to be
opaque to the server. The same control is used for both requests
and responses. If the data return statement appears in an
enrollment message, the server MUST return it as part of the
enrollment response message.
In the event that the information in the data return statement needs
to be confidential, it is expected that the client would apply some
type of encryption to the contained data, but the details of this
are outside the scope of this specification.
An example of using this feature is for a client to place an
identifier marking the exact source of the private key material.
This might be the identifier of a hardware device containing the
private key.
5.5 RA Certificate Modification Controls
These extensions exist for RAs/LRAs to be able to modify the
contents of a requestors certificate. This might be necessary for
various reasons. The addition of extensions dealing with policies
and correcting naming information for subject and alternative
subject names are two such reasons.
Two controls exist for this purpose. The first Modify Certificate
Template has the full control for allowing modification of any field
in the certificate. The second Add Extensions control only allows
for the addition of extensions.
5.5.1 Modify Certificate Request Control
The Modify Certificate Request control is used by LRAs/RAs in order
to change various fields in an EE requested certificate. This
control allows for the specification of fields in the certificate
other than extensions. This attribute uses the following ASN.1
definition:
ModCertTemplate ::= SEQUENCE {
pkiDataReference BodyPartList,
certReferences SEQUENCE OF BodyPartID,
replace BOOLEAN DEFAULT TRUE,
certTemplate CertTemplate
}
-- pkiDataReference field contains the list of body part ids that
define the path of the embedded request message.
-- certReferences field is a list of references to one or more of
the payloads contained within a PKIData element. Each element of
the certReferences sequence MUST be equal to either the bodyPartID
of a TaggedCertificationRequest or the certReqId of the CertRequest
within a CertReqMsg. By definition, the listed extensions are to
be applied to every element referenced in the certReferences
sequence. If a request corresponding to bodyPartID cannot be found,
the error badRequest is returned referencing this control attribute.
-- replace specifies if the data is to be replace with what is
here, or if the fields in the original certificate request are to be
removed. If replace is FALSE, any field defined in the certTemplate
field is removed from proposed certificate. For the extensions
field, only those extensions which are defined in the template
certificate are removed. The use of the replace field set to FALSE
is be considered to be a rare event as generally the field would
just be replaced with a correct value.
-- certTemplate contains a certificate template object. Items
are to be omitted from the certificate template unless the value
present is to replace the value found the in the requested
certificate template. If a field is present in the extensions field
of the template, that extension would either replace the same
existing extension or be added to the set of extensions in the
requested certificate.
Servers MUST be able to process all extensions defined, but not
prohibited, in [PKIXCERT]. Servers are not required to be able to
process every V3 X.509 extension transmitted using this protocol,
nor are they required to be able to process other, private
extensions. Servers are not required to put all LRA-requested
extensions into a certificate. Servers are permitted to modify LRA-
requested extensions. Servers MUST NOT alter an extension so as to
reverse the meaning of a client-requested extension If a
certification request is denied due to the inability to handle a
requested extension and a response is returned, the server MUST
return a failInfo attribute with the value of unsupportedExt.
If multiple Modify Certificate Template controls exist in an
enrollment message, the exact behavior is left up to the certificate
issuer policy. However it is recommended that the following policy
be used. These rules would be applied to individual extensions
within an Add Extensions control attribute (as opposed to an "all or
nothing" approach).
1. If the conflict is within a single PKIData object, the
certificate request would be rejected with an error of
badRequest.
2. If the conflict is between different PKIData objects, the
outermost version of the extension would be used (allowing an LRA
to override the extension requested by the end-entity).
5.5.2 Add Extensions Control
The Add Extensions control has been depreciated in favor of the
Modify Certificate Template control. It was replaced so that fields
in the certificate template other than extensions could be modified.
The Add Extensions control attribute is used by LRAs in order to
specify additional extensions that are to be placed on certificates.
This attribute uses the following ASN.1 definition:
AddExtensions ::= SEQUENCE {
pkiDataReference BodyPartID
certReferences SEQUENCE OF BodyPartID,
extensions SEQUENCE OF Extension
}
-- pkiDataReference field contains the body part id of the
embedded request message.
-- certReferences field is a list of references to one or more of
the payloads contained within a PKIData. Each element of the
certReferences sequence MUST be equal to either the bodyPartID of a
TaggedCertificationRequest or the certReqId of the CertRequest
within a CertReqMsg. By definition, the listed extensions are to
be applied to every element referenced in the certReferences
sequence. If a request corresponding to bodyPartID cannot be found,
the error badRequest is returned referencing this control attribute.
-- extensions field contains the sequence of extensions to be
applied to the referenced certificate requests.
Servers MUST be able to process all extensions defined, but not
prohibited, in [PKIXCERT]. Servers are not required to be able to
process every V3 X.509 extension transmitted using this protocol,
nor are they required to be able to process other, private
extensions. Servers are not required to put all LRA-requested
extensions into a certificate. Servers are permitted to modify LRA-
requested extensions. Servers MUST NOT alter an extension so as to
reverse the meaning of a client-requested extension If a
certification request is denied due to the inability to handle a
requested extension and a response is returned, the server MUST
return a failInfo attribute with the value of unsupportedExt.
If multiple Add Extensions statements exist in an enrollment
message, the exact behavior is left up to the certificate issuer
policy. However it is recommended that the following policy be used.
These rules would be applied to individual extensions within an Add
Extensions control attribute (as opposed to an "all or nothing"
approach).
1. If the conflict is within a single PKIData object, the
certificate request would be rejected with an error of
badRequest.
2. If the conflict is between different PKIData objects, the
outermost version of the extension would be used (allowing an LRA
to override the extension requested by the end-entity).
5.6 Transaction Management Control Attributes
Transactions are identified and tracked using a transaction
identifier. If used, clients generate transaction identifiers and
retain their value until the server responds with a message that
completes the transaction. Servers correspondingly include received
transaction identifiers in the response.
The transactionId attribute identifies a given transaction. It is
used between client and server to manage the state of an operation.
Clients MAY include a transactionID attribute in request messages.
If the original request contains a transactionID attribute, all
subsequent request and response messages MUST include the same
transactionID attribute. A server MUST use only transactionIds in
the outermost PKIdata object. TransactionIds on inner PKIdata
objects are for intermediate entities.
Replay protection can be supported through the use of sender and
recipient nonces. If nonces are used, in the first message of a
transaction, no recipientNonce is transmitted; a senderNonce is
instantiated by the message originator and retained for later
reference. The recipient of a sender nonce reflects this value back
to the originator as a recipientNonce and includes it's own
senderNonce. Upon receipt by the transaction originator of this
message, the originator compares the value of recipientNonce to its
retained value. If the values match, the message can be accepted
for further security processing. The received value for senderNonce
is also retained for inclusion in the next message associated with
the same transaction.
The senderNonce and recipientNonce attribute can be used to provide
application-level replay prevention. Clients MAY include a
senderNonce in the initial request message. Originating messages
include only a value for senderNonce. If a message includes a
senderNonce, the response MUST include the transmitted value of the
previously received senderNonce as recipientNonce and include new
value for senderNonce. A server MUST use only nonces in the
outermost PKIdata object. Nonces on inner PKIdata objects are for
intermediate entities.
5.7 Proof-of-possession (POP) for encryption-only keys
Everything described in this section is optional to implement, for
both servers and clients. Servers MAY require this POP method be
used only if another POP method is unavailable. Servers SHOULD
reject all requests contained within a PKIData if any required POP
is missing for any element within the PKIData.
Many servers require proof that an entity requesting a certificate
for a public key actually possesses the corresponding private
component of the key pair. For keys that can be used as signature
keys, signing the certification request with the private key serves
as a POP on that key pair. With keys that can only be used for
encryption operations, POP MUST be performed by forcing the client
to decrypt a value. See Section 5 of [CRMF] for a detailed
discussion of POP.
By necessity, POP for encryption-only keys cannot be done in one
round-trip, since there are four distinct phases:
1. Client tells the server about the public component of a new
encryption key pair.
2. Server sends the client a POP challenge, encrypted with the
presented public encryption key, which the client must decrypt.
3. Client decrypts the POP challenge and sends it back to the
server.
4. Server validates the decrypted POP challenge and continues
processing the certificate request.
CMC defines two different attributes. The first deals with the
encrypted challenge sent from the server to the user in step 2. The
second deals with the decrypted challenge sent from the client to
the server in step 3.
The encryptedPOP attribute is used to send the encrypted challenge
from the server to the client. As such, it is encoded as a tagged
attribute within the controlSequence of a ResponseBody. (Note that
we assume that the message sent in Step 1 above is an enrollment
request and that the response in step 2 is a Full Enrollment
Response including a failureInfo specifying that a POP is explicitly
required, and providing the POP challenge in the encryptedPOP
attribute.)
EncryptedPOP ::= SEQUENCE {
request TaggedRequest,
cms contentInfo,
thePOPAlgID AlgorithmIdentifier,
witnessAlgID AlgorithmIdentifier,
witness OCTET STRING
}
DecryptedPOP ::= SEQUENCE {
bodyPartID BodyPartID,
thePOPAlgID AlgorithmIdentifier,
thePOP OCTET STRING
}
The encrypted POP algorithm works as follows:
1. The server generates a random value y and associates it with the
request.
2. The server returns the encrypted pop with the following fields
set:
a. request is the certificate request in the original request
message (it is included here so the client need not key a
copy of the request),
b. cms is an EnvelopedData object, the content type being id-
data and the content being the value y. If the certificate
request contains a subject key identifier (SKI) extension,
then the recipient identifier SHOULD be the SKI. If the
issuerAndSerialNumber form is used, the IsserName MUST be
encoded as NULL and the SerialNumber as the bodyPartID of
the certificate request,
c. thePOPAlgID contains the algorithm to be used in computing
the return POP value,
d. witnessAlgID contains the hash algorithm used on y to create
the field witness,
e. witness contains the hashed value of y.
3. The client decrypts the cms field to obtain the value y. The
client computes H(y) using the witnessAlgID and compares to the
value of witness. If the values do not compare or the decryption
is not successful, the client MUST abort the enrollment process.
The client aborts the process by sending a request message
containing a CMCStatusInfo control attribute with failInfo value
of popFailed.
4. The client creates the decryptedPOP as part of a new PKIData
message. The fields in the decryptedPOP are:
a. bodyPartID refers to the certificate request in the new
enrollment message,
b. thePOPAlgID is copied from the encryptedPOP,
c. thePOP contains the possession proof. This value is
computed by thePOPAlgID using the value y and request
referenced in (4a).
5. The server then re-computes the value of thePOP from its cached
value of y and the request and compares to the value of thePOP.
If the values do not match, the server MUST NOT issue the
certificate. The server MAY re-issue a new challenge or MAY fail
the request altogether.
When defining the algorithms for thePOPAlgID and witnessAlgID care
must be taken to ensure that the result of witnessAlgID is not a
useful value to shortcut the computation with thePOPAlgID. Clients
MUST implement SHA-1 for witnessAlgID. Clients MUST implement HMAC-
SHA1 for thePOPAlgID. The value of y is used as the secret value in
the HMAC algorithm and the request referenced in (4a) is used as the
data. If y is greater than 64 bytes, only the first 64 bytes of y
are used as the secret.
One potential problem with the algorithm above is the amount of
state that a CA needs to keep in order to verify the returned POP
value. This describes one of many possible ways of addressing the
problem by reducing the amount of state kept on the CA to a single
(or small set) of values.
1. Server generates random seed x, constant across all requests.
(The value of x would normally be altered on a regular basis and
kept for a short time afterwards.)
2. For certificate request R, server computes y = F(x,R). F can be,
for example, HMAC-SHA1(x,R). All that's important for
statelessness is that y be consistently computable with only
known state constant x and function F, other inputs coming from
the cert request structure. y should not be predictable based on
knowledge of R, thus the use of a OWF like HMAC-SHA1.
5.8 LRA POP Witnesses Control Attribute
In an enrollment scenario involving an LRAs the CA may allow (or
require) the LRA to perform the POP protocol with the entity
requesting certification. In this case the LRA needs a way to
inform the CA it has done the POP. This control attribute has been
created to address this issue.
The ASN.1 structure for the LRA POP witness is as follows:
LraPopWitness ::= SEQUENCE {
pkiDataBodyid BodyPartID,
bodyIds SEQUENCE of BodyPartID
}
-- pkiDataBodyid field contains the body part id of the nested CMS
body object containing the client's full request message.
pkiDataBodyid is set to 0 if the request is in the current
PKIRequest body.
-- bodyIds contains a list of certificate requests for which the LRA
has performed an out-of-band authentication. The method of
authentication could be archival of private key material, challenge-
response or other means.
If a certificate server does not allow for an LRA to do the POP
verification, it returns an error of POPFAILURE. The CA MUST NOT
start a challenge-response to re-verify the POP itself.
5.9 Get Certificate Control Attribute
Everything described in this section is optional to implement.
The get certificate control attribute is used to retrieve previously
issued certificates from a repository of certificates. A
Certificate Authority, an LRA or an independent service may provide
this repository. The clients expected to use this facility are
those operating in a resource-constrained environment. (An example
of a resource-constrained client would be a low-end IP router that
does not retain its own certificate in non-volatile memory.)
The get certificate control attribute has the following ASN.1
structure:
GetCert ::= SEQUENCE {
issuerName GeneralName,
serialNumber INTEGER }
The service responding to the request will place the requested
certificate in the certificates field of a SignedData object. If
the get certificate attribute is the only control in a Full PKI
Request message, the response would be a Simple Enrollment Response.
5.10 Get CRL Control Attribute
Everything described in this section is optional to implement.
The get CRL control attribute is used to retrieve CRLs from a
repository of CRLs. A Certification Authority, an LRA or an
independent service may provide this repository. The clients
expected to use this facility are those where a fully deployed
directory is either infeasible or undesirable.
The get CRL control attribute has the following ASN.1 structure:
GetCRL ::= SEQUENCE {
issuerName Name,
cRLName GeneralName OPTIONAL,
time GeneralizedTime OPTIONAL,
reasons ReasonFlags OPTIONAL }
The fields in a GetCRL have the following meanings:
-- issuerName is the name of the CRL issuer.
-- cRLName may be the value of CRLDistributionPoints in the subject
certificate or equivalent value in the event the certificate does
not contain such a value.
-- time is used by the client to specify from among potentially
several issues of CRL that one whose thisUpdate value is less than
but nearest to the specified time. In the absence of a time
component, the CA always returns with the most recent CRL.
-- reasons is used to specify from among CRLs partitioned by
revocation reason. Implementers should bear in mind that while a
specific revocation request has a single CRLReason code--and
consequently entries in the CRL would have a single CRLReason code
value--a single CRL can aggregate information for one or more
reasonFlags.
A service responding to the request will place the requested CRL in
the crls field of a SignedData object. If the get CRL attribute is
the only control in a full enrollment message, the response would be
a simple enrollment response.
5.11 Revocation Request Control Attribute
The revocation request control attribute is used to request that a
certificate be revoked.
The revocation request control attribute has the following ASN.1
syntax:
RevRequest ::= SEQUENCE {
issuerName Name,
serialNumber INTEGER,
reason CRLReason,
invalidityDate GeneralizedTime OPTIONAL,
sharedSecret OCTET STRING OPTIONAL,
comment UTF8string OPTIONAL }
-- issuerName contains the issuerName of the certificate to be
revoked.
-- serialNumber contains the serial number of the certificate to be
revoked
-- reason contains the suggested CRLReason code for why the
certificate is being revoked. The CA can use this value at its
discretion in building the CRL.
-- invalidityDate contains the suggested value for the Invalidity
Date CRL Extension. The CA can use this value at its discretion in
building the CRL.
-- sharedSecret contains a secret value registered by the EE when
the certificate was obtained to allow for revocation of a
certificate in the event of key loss.
-- comment contains a human readable comment.
For a revocation request to become a reliable object in the event of
a dispute, a strong proof of originator authenticity is required.
However, in the instance when an end-entity has lost use of its
signature private key, it is impossible for the end-entity to
produce a digital signature (prior to the certification of a new
signature key pair). The RevRequest provides for the optional
transmission from the end-entity to the CA of a shared secret that
may be used as an alternative authenticator in the instance of loss
of use. The acceptability of this practice is a matter of local
security policy.
(Note that in some situations a Registration Authority may be
delegated authority to revoke certificates on behalf of some
population within its scope control. In these situations the CA
would accept the LRA's digital signature on the request to revoke a
certificate, independent of whether the end entity still had access
to the private component of the key pair.)
Clients MUST provide the capability to produce a digitally signed
revocation request control attribute. Clients SHOULD be capable of
producing an unsigned revocation request containing the end-entity's
shared secret. (The unsigned message consisting of a CMS signedData
object with no signatures.) If a client provides shared secret
based self-revocation, the client MUST be capable of producing a
revocation request containing the shared secret. Servers MUST be
capable of accepting both forms of revocation requests.
The structure of an unsigned, shared secret based revocation request
is a matter of local implementation. The shared secret does not
need to be encrypted when sent in a revocation request. The shared
secret has a one-time use, that of causing the certificate to be
revoked, and public knowledge of the shared secret after the
certificate has been revoked is not a problem. Clients need to
inform users that the same shared secret SHOULD NOT be used for
multiple certificates.
A full response message MUST be returned for a revocation request.
5.12 Registration and Response Information Control Attributes
The regInfo control attribute is for clients and LRAs to pass
additional information as part a PKI request. The regInfo control
attribute uses the ASN.1 structure:
RegInfo ::= OCTET STRING
The content of this data is based on bilateral agreement between the
client and server.
If a server (or LRA) needs to return information back to a requestor
in response to data submitted in a regInfo attribute, then that data
is returned as a responseInfo control attribute. The content of the
OCTET STRING for response information is based on bilateral
agreement between the client and server.
5.13 Query Pending Control Attribute
In some environments, process requirements for manual intervention
or other identity checking can cause a delay in returning the
certificate related to a certificate request. The query pending
attribute allows for a client to query a server about the state of a
pending certificate request. The server returns a token as part of
the CMCStatusInfo attribute (in the otherInfo field). The client
puts the token into the query pending attribute to identify the
correct request to the server. The server can also return a
suggested time for the client to query for the state of a pending
certificate request.
The ASN.1 structure used by the query pending control attribute is:
QueryPending ::= OCTET STRING
If a server returns a pending state (the transaction is still
pending), the otherInfo MAY be omitted. If it is not omitted then
the same value MUST be returned (the token MUST NOT change during
the request).
5.14 Confirm Certificate Acceptance
Some Certification Authorities require that clients give a positive
conformation that the certificates issued to it are acceptable. The
Confirm Certificate Acceptance control attribute is used for that
purpose. If the CMCStatusInfo on a certificate response is
confirmRequired, then the client MUST return a Confirm Certificate
attribute contained in a full enrollment response message.
Clients SHOULD wait for the response from the server that the
conformation has been received before using the certificate for any
purpose.
The confirm certificate acceptance structure is:
CMCCertId ::= IssuerAndSerialNumber
-- CMCCertId contains the issuer and serial number of the
certificate being accepted.
Servers MUST return a full enrollment response for a confirm
certificate acceptance control.
Note that if the Certification Authority includes this attribute,
there will be two full round trips of messages.
1. The client sends the request to the CA.
2. The CA returns the certificate and this attribute.
3. The client sends a response message to the CA with a
CMCStatusInfoExt control either accepting or rejecting the
certificate.
4. The CA sends a response message to the client with a
CMCStatusInfoExt of success.
5.15 Publish Trust Roots
This control allows for distribution of trust roots from a central
authority to an end-entity.
What is included in the control as data is the set of certificates
that are to be treated as trusted roots, and a set of certificates
that are no longer to be treated as trusted roots.
Prior to accepting the change in trust roots, a client MUST do the
at least following: Validate the signature on the message to a
current trusted root, check with policy to ensure that the signer is
permitted to use the attribute, validate that the authenticated
publish time in the signature is near to the current time and
validate the sequence number is greater than the previously used
one.
This attribute uses the following ASN.1 definition:
PublishTrustRoots ::= SEQUENCE {
seqNumber INTEGER,
rootHashes SEQUENCE OF OCTET STRING
}
-- seqNumber contains an increasing integer specifying where in the
sequence of updates this item is.
-- rootHashes contains the hashes for the certificates that are to
be treated as trust roots by the client.
While it is recommended that the sender places the certificates that
are to be trusted in the message, it is not required as the
certificates should be obtainable using normal discovery techniques.
In the event that multiple agents publish a set of trust lists, it
is up to local policy to determine how the different trust lists
should be combined. Clients SHOULD be able to handle the update of
trust lists multiple trust list independently.
NOTE: Clients which handle this attribute must use extreme care in
validating that the operation is permissible. Incorrect handling of
this attribute allows for an attacker to change the set of trusted
roots on the client.
5.16 Provide Autenticated Data
This control allows for an authority to provide data back to the
user in an authenticated manner. In general, one would expect that
the same passphrase used in the identity proof operation. This
attribute uses the following ASN.1 definition:
AuthPublish ::= BodyPartID
The bodyPartID refers to a member of the cmsSequence either a
ResponseBody or PKIData sequence. The element within the is an
AuthenticatedData structure with a id-cct-PKIData content. Only the
id-Publish-Roots control is currently expected to be in this
sequence.
If the authentication operation fails, the error authDataFail is
returned.
5.17 Batch Process Identification
With the processing rules on message bodies, items which have been
batched together must be identified as such. Additionally the
returned batched responses must also be identified as such.
The batchRequests control attribute is used to identify the elements
in the cmsSequence section that contain batched up requests to be
processed.
The batchResponses control attribute is used to identify the set of
elements in the cmsSequence which correspond to batched responses.
When a server processes a batchRequests control, it may return the
items being processed either as individual messages or in a batched
response (identifying the elements with a batchResponses control).
The preferable behavior is to batch the responses back to the client
submitting the batched request. If only partial responses can be
generated at this time, the server SHOULD generate a batchResponse
with complete responses where available and QueryPending responses
where a complete response is not ready. A QueryPending responses on
the entire request SHOULD only be returned if processing based on
the top level message itself (or on the status of the requestor) is
involved in the pending processing.
5.18 Publication Information Control
This control allows for modifying publication of already issued
certificates, both for publishing and removal from publication. A
common usage for this control is to remove an existing certificate
from publication during a re-key operation. This control should
always be processed after the issuance of new certificates and
revocation requests. This control should not be processed if a
certificate failed to be issued.
The attribute uses the following ASN.1 definition:
id-cmc-publishCert = 30
CMCPublicationInfo ::= SEQUENCE {
certHashes SEQUENCE of OCTET STRING,
pubInfo PKIPublicationInfo
}
-- certHashes contains the hashes of the certificates for which
publication is to change
-- pubInfo contains the information how where and how the
certificates should be published. The action dontPublish has the
added connotation of remove from publication if the certificate is
already published.
A single certificate SHOULD NOT appear in more than one
CMCPublicationInfo attribute. The behavior is undefined in the
event that it does.
The PKIPublicationInfo control is used to control publication of
certificates at the time of issue.
6. Local Registration Authorities
This specification permits the use of Local Registration Authorities
(LRAs). An LRA sits between the end-entity and the Certification
Authority. From the end-entity's perspective, the LRA appears to be
the Certification Authority and from the server the LRA appears to
be a client. LRAs receive the enrollment messages, perform local
processing and then forward onto Certificate Authorities. Some of
the types of local processing that an LRA can perform include:
- batching multiple enrollment messages together,
- challenge/response POP proofs,
- addition of private or standardized certificate extensions to all
requests,
- archival of private key material,
- routing of requests to different CAs.
When an LRA receives an enrollment message it has three options: it
may forward the message without modification, it may add a new
wrapping layer to the message, or it may remove one or more existing
layers and add a new wrapping layer.
When an LRA adds a new wrapping layer to a message it creates a new
PKIData object. The new layer contains any control attributes
required (for example if the LRA does the POP proof for an
encryption key or the addExtension control attribute to modify an
enrollment request) and the client enrollment message. The client
enrollment message is placed in the cmsSequence if it is a Full
Enrollment message and in the reqSequence if it is a Simple
Enrollment message. If an LRA is batching multiple client messages
together, then each client enrollment message is placed into the
appropriate location in the LRA's PKIData object along with all
relevant control attributes.
(If multiple LRAs are in the path between the end-entity and the
Certification Authority, this will lead to multiple wrapping layers
on the message.)
In processing an enrollment message, an LRA MUST NOT alter any
certificate request body (PKCS #10 or CRMF) as any alteration would
invalidate the signature on the request and thus the POP for the
private key.
An example of how this would look is illustrated by the following
figure:
SignedData (by LRA)
PKIData
controlSequence
LRA added control statements
reqSequence
Zero or more Simple CertificationRequests from clients
cmsSequence
Zero or more Full PKI messages from clients
SignedData (by client)
PKIData
Under some circumstances an LRA is required to remove wrapping
layers. The following sections look at the processing required if
encryption layers and signing layers need to be removed.
6.1 Encryption Removal
There are two cases that require an LRA to remove or change
encryption in an enrollment message. In the first case the
encryption was applied for the purposes of protecting the entire
enrollment request from unauthorized entities. If the CA does not
have a recipient info entry in the encryption layer, the LRA MUST
remove the encryption layer. The LRA MAY add a new encryption layer
with or without adding a new signing layer.
The second change of encryption that may be required is to change
the encryption inside of a signing layer. In this case the LRA MUST
remove all signing layers containing the encryption. All control
statements MUST be merged according to local policy rules as each
signing layer is removed and the resulting merged controls MUST be
placed in a new signing layer provided by the LRA. If the signing
layer provided by the end-entity needs to be removed to the LRA can
remove the layer.
6.2 Signature Layer Removal
Only two instances exist where an LRA should remove a signature
layer on a Full Enrollment message. If an encryption needs to be
modified within the message, or if a Certificate Authority will not
accept secondary delegation (i.e. multiple LRA signatures). In all
other situations LRAs SHOULD NOT remove a signing layer from a
message.
If an LRA removes a signing layer from a message, all control
statements MUST be merged according to local policy rules. The
resulting merged control statements MUST be placed in a new signing
layer provided by the LRA.
7. Security Considerations
Initiation of a secure communications channel between an end-entity
and a CA or LRA (and, similarly, between an LRA and another LRA or
CA) necessarily requires an out-of-band trust initiation mechanism.
For example, a secure channel may be constructed between the end-
entity and the CA via IPSEC or TLS. Many such schemes exist and the
choice of any particular scheme for trust initiation is outside the
scope of this document. Implementers of this protocol are strongly
encouraged to consider generally accepted principles of secure key
management when integrating this capability within an overall
security architecture.
Mechanisms for thwarting replay attacks may be required in
particular implementations of this protocol depending on the
operational environment. In cases where the CA maintains significant
state information, replay attacks may be detectable without the
inclusion of the optional nonce mechanisms. Implementers of this
protocol need to carefully consider environmental conditions before
choosing whether or not to implement the senderNonce and
recipientNonce attributes described in section 5.6. Developers of
state-constrained PKI clients are strongly encouraged to incorporate
the use of these attributes.
Under no circumstances should a signing key be archived. Doing so
allows the archiving entity to potentially use the key for forging
signatures.
Due care must be taken prior to archiving keys. Once a key is given
to an archiving entity, the archiving entity could use the keys in a
way not conducive to the archiving entity. Users should be made
especially aware that proper verification is made of the certificate
used to encrypt the private key material.
Clients and servers need to do some checks on cryptographic
parameters prior to issuing certificates to make sure that weak
parameters are not used. A description of the small subgroup attack
is provided in [X942]. Methods of avoiding the small subgroup
attack can be found in [SMALL-GROUP]. CMC implementations ought to
be aware of this attack when doing parameter validations.
When using a shared-secret for authentication purposes, the shared-
secret should be generated using good random number techniques.
User selection of the secret allows for dictionary attacks to be
mounted.
Extreme care must be used when processing the Publish Trust Roots
attribute. Incorrect processing can lead to the practice of
slamming where an attacker changes the set of trusted roots in order
to weaken security.
8. Acknowledgments
The authors would like to thank Brian LaMacchia for his work in
developing and writing up many of the concepts presented in this
document. The authors would also like to thank Alex Deacon and Barb
Fox for their contributions.
9. References
9.1 Normative References
[CMS] Housley, R., "Cryptographic Message Syntax", RFC 3852,
July 2004.
[CRMF] Schaad, J., "Internet X.509 Certificate Request Message
Format", <draft-ietf-pkix-crmf-04.txt>
[DH-POP] H. Prafullchandra, J. Schaad, "Diffie-Hellman Proof-of-
Possession Algorithms", RFC 2875, June 2000.
[HMAC] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[PKIXCERT] Housley, R., Ford, W., Polk, W. and D. Solo "Internet
X.509 Public Key Infrastructure Certificate and CRL
Profile", RFC 3280, April 2002.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2 Informational References.
[DH] B. Kaliski, "PKCS 3: Diffie-Hellman Key Agreement v1.4"
[PKCS1] Kaliski, B., "PKCS #1: RSA Encryption, Version 1.5", RFC
2313, March 1998.
[PKCS7] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
v1.5", RFC 2315, October 1997.
[PKCS8] RSA Laboratories, "PKCS#8: Private-Key Information Syntax
Standard, Version 1.2", November 1, 1993.
[PKCS10] Kaliski, B., "PKCS #10: Certification Request Syntax
v1.5", RFC 2314, October 1997.
[SMALL-GROUP] Zuccherato, R., "Methods for Avoiding the "Small-
Subgroup" Attacks on the Diffie-Hellman Key Agreement
Method for S/MIME", RFC 2785, March 2000.
[SMIMEV2] Dusse, S., Hoffman, P., Ramsdell, B., Lundblade, L. and
L. Repka, "S/MIME Version 2 Message Specification",
RFC 2311, March 1998.
[SMIMEV3] Ramsdell, B., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, July 2004.
[X942] Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC
2631, June 1999.
10. Authors' Addresses
Jim Schaad
Soaring Hawk Consulting
EMail: jimsch@exmsft.com
Michael Myers
TraceRoute Security, Inc.
EMail: myers@coastside.net
Xiaoyi Liu
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
Phone: (480) 526-7430
EMail: xliu@cisco.com
Jeff Weinstein
EMail: jsw@meer.net
Appendix A ASN.1 Module
EnrollmentMessageSyntax
{ iso(1) identified-organization(3) dod(4) internet(1)
security(5) mechansims(5) pkix(7) id-mod(0) id-mod-cmc2002(23) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS All --
-- The types and values defined in this module are exported for use
-- in the other ASN.1 modules. Other applications may use them for
-- their own purposes.
IMPORTS
-- PKIX Part 1 - Implicit From [PKIXCERT]
CertificateSerialNumber, GeneralName, CRLReason, ReasonFlags
FROM PKIX1Implicit88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-implicit-88(19)}
-- PKIX Part 1 - Explicit From [PKIXCERT]
AlgorithmIdentifier, Extension, Name
FROM PKIX1Explicit88 {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit-88(18)}
-- Cryptographic Message Syntax FROM [CMS]
ContentInfo, Attribute
FROM CryptographicMessageSyntax { 1 2 840 113549 1 9 16 0 1}
-- CRMF FROM [CRMF]
CertReqMsg, PKIPublicationInfo
FROM PKIXCRMF {iso(1) identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-crmf(5)};
-- Global Types
UTF8String ::= [UNIVERSAL 12] IMPLICIT OCTET STRING
-- The content of this type conforms to RFC 2279.
id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) }
id-cmc OBJECT IDENTIFIER ::= {id-pkix 7} -- CMC controls
id-cct OBJECT IDENTIFIER ::= {id-pkix 12} -- CMC content types
-- The following controls have the type OCTET STRING
id-cmc-identityProof OBJECT IDENTIFIER ::= {id-cmc 3}
id-cmc-dataReturn OBJECT IDENTIFIER ::= {id-cmc 4}
id-cmc-regInfo OBJECT IDENTIFIER ::= {id-cmc 18}
id-cmc-responseInfo OBJECT IDENTIFIER ::= {id-cmc 19}
id-cmc-queryPending OBJECT IDENTIFIER ::= {id-cmc 21}
id-cmc-popLinkRandom OBJECT IDENTIFIER ::= {id-cmc 22}
id-cmc-popLinkWitness OBJECT IDENTIFIER ::= {id-cmc 23}
-- The following controls have the type UTF8String
id-cmc-identification OBJECT IDENTIFIER ::= {id-cmc 2}
-- The following controls have the type INTEGER
id-cmc-transactionId OBJECT IDENTIFIER ::= {id-cmc 5}
id-cmc-senderNonce OBJECT IDENTIFIER ::= {id-cmc 6}
id-cmc-recipientNonce OBJECT IDENTIFIER ::= {id-cmc 7}
-- This is the content type used for a request message in the
protocol
id-cct-PKIData OBJECT IDENTIFIER ::= { id-cct 2 }
PKIData ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
reqSequence SEQUENCE SIZE(0..MAX) OF TaggedRequest,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
bodyIdMax INTEGER ::= 4294967295
BodyPartID ::= INTEGER(0..bodyIdMax)
TaggedAttribute ::= SEQUENCE {
bodyPartID BodyPartID,
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue
}
AttributeValue ::= ANY
TaggedRequest ::= CHOICE {
tcr [0] TaggedCertificationRequest,
crm [1] CertReqMsg,
orm [2] SEQUENCE {
bodyPartID BodyPartID,
requestMessageType OBJECT IDENTIFIER,
requestMessageValue ANY DEFINED BY requestMessageType
}
}
TaggedCertificationRequest ::= SEQUENCE {
bodyPartID BodyPartID,
certificationRequest CertificationRequest
}
CertificationRequest ::= SEQUENCE {
certificationRequestInfo SEQUENCE {
version INTEGER,
subject Name,
subjectPublicKeyInfo SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING },
attributes [0] IMPLICIT SET OF Attribute },
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING
}
TaggedContentInfo ::= SEQUENCE {
bodyPartID BodyPartID,
contentInfo ContentInfo
}
OtherMsg ::= SEQUENCE {
bodyPartID BodyPartID,
otherMsgType OBJECT IDENTIFIER,
otherMsgValue ANY DEFINED BY otherMsgType }
-- This defines the response message in the protocol
id-cct-PKIResponse OBJECT IDENTIFIER ::= { id-cct 3 }
ResponseBody ::= SEQUENCE {
controlSequence SEQUENCE SIZE(0..MAX) OF TaggedAttribute,
cmsSequence SEQUENCE SIZE(0..MAX) OF TaggedContentInfo,
otherMsgSequence SEQUENCE SIZE(0..MAX) OF OtherMsg
}
-- Used to return status state in a response
id-cmc-statusInfo OBJECT IDENTIFIER ::= {id-cmc 1}
CMCStatusInfo ::= SEQUENCE {
cMCStatus CMCStatus,
bodyList SEQUENCE SIZE (1..MAX) OF BodyPartID,
statusString UTF8String OPTIONAL,
otherInfo CHOICE {
failInfo CMCFailInfo,
pendInfo PendInfo } OPTIONAL
}
PendInfo ::= SEQUENCE {
pendToken OCTET STRING,
pendTime GENERALIZEDTIME
}
CMCStatus ::= INTEGER {
success (0),
-- you got exactly what you asked for
-- reserved (1), -- use is deprecated.
failed (2),
-- you don't get it, more information elsewhere in the message
pending (3),
-- the request body part has not yet been processed,
-- requester is responsible to poll back on this
noSupport (4),
-- the requested operation is not supported
confirmRequired (5),
-- confirmation using the idConfirmCertAcceptance control is
-- required
popRequired (6)
-- A certificate request requires an indirect POP operation.
-- Info for the indirect POP in this message.
}
CMCFailInfo ::= INTEGER {
badAlg (0),
-- Unrecognized or unsupported algorithm
badMessageCheck (1),
-- integrity check failed
badRequest (2),
-- transaction not permitted or supported
badTime (3),
-- Message time field was not sufficiently close to the
systemtime
badCertId (4),
-- No certificate could be identified matching the provided
criteria
unsuportedExt (5),
-- A requested X.509 extension is not supported by the recipient
CA.
mustArchiveKeys (6),
-- Private key material must be supplied
badIdentity (7),
-- Identification Attribute failed to verify
popRequired (8),
-- Server requires a POP proof before issuing certificate
popFailed (9),
-- Server failed to get an acceptable POP for the request
noKeyReuse (10),
-- Server policy does not allow key re-use
internalCAError (11),
tryLater (12),
authDataFail (13)
-- Failure occurred during processing of authenticated data
}
-- Used for LRAs to add extensions to certificate requests
id-cmc-addExtensions OBJECT IDENTIFIER ::= {id-cmc 8}
AddExtensions ::= SEQUENCE {
pkiDataReference BodyPartID,
certReferences SEQUENCE OF BodyPartID,
extensions SEQUENCE OF Extension
}
id-cmc-encryptedPOP OBJECT IDENTIFIER ::= {id-cmc 9}
id-cmc-decryptedPOP OBJECT IDENTIFIER ::= {id-cmc 10}
EncryptedPOP ::= SEQUENCE {
request TaggedRequest,
cms ContentInfo,
thePOPAlgID AlgorithmIdentifier,
witnessAlgID AlgorithmIdentifier,
witness OCTET STRING
}
DecryptedPOP ::= SEQUENCE {
bodyPartID BodyPartID,
thePOPAlgID AlgorithmIdentifier,
thePOP OCTET STRING
}
id-cmc-lraPOPWitness OBJECT IDENTIFIER ::= {id-cmc 11}
LraPopWitness ::= SEQUENCE {
pkiDataBodyid BodyPartID,
bodyIds SEQUENCE OF BodyPartID
}
--
id-cmc-getCert OBJECT IDENTIFIER ::= {id-cmc 15}
GetCert ::= SEQUENCE {
issuerName GeneralName,
serialNumber INTEGER }
id-cmc-getCRL OBJECT IDENTIFIER ::= {id-cmc 16}
GetCRL ::= SEQUENCE {
issuerName Name,
cRLName GeneralName OPTIONAL,
time GeneralizedTime OPTIONAL,
reasons ReasonFlags OPTIONAL }
id-cmc-revokeRequest OBJECT IDENTIFIER ::= {id-cmc 17}
RevRequest ::= SEQUENCE {
issuerName Name,
serialNumber INTEGER,
reason CRLReason,
invalidityDate GeneralizedTime OPTIONAL,
passphrase OCTET STRING OPTIONAL,
comment UTF8String OPTIONAL }
id-cmc-confirmCertAcceptance OBJECT IDENTIFIER ::= {id-cmc 24}
CMCCertId ::= IssuerAndSerialNumber
-- The following is used to request V3 extensions be added to a
certificate
id-ExtensionReq OBJECT IDENTIFIER ::= {iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) 14}
ExtensionReq ::= SEQUENCE OF Extension
-- The following exists to allow Diffie-Hellman Certificate Requests
Messages to be
-- well-formed
id-alg-noSignature OBJECT IDENTIFIER ::= {id-pkix id-alg(6) 2}
NoSignatureValue ::= OCTET STRING
-- Unauthenticated attribute to carry removable data.
-- This will be used in the key archive draft among others.
id-aa OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) id-aa(2)}
id-aa-cmc-unsignedData OBJECT IDENTIFIER ::= {id-aa 34}
CMCUnsignedData ::= SEQUENCE {
bodyPartPath SEQUENCE SIZE (1..MAX) OF BodyPartID,
identifier OBJECT IDENTIFIER,
content ANY DEFINED BY identifier
}
-- Replaces CMC Status Info
--
id-cmc-statusInfoEx OBJECT IDENTIFIER ::= {id-cmc 25}
CMCStatusInfoExt ::= SEQUENCE {
CMCStatus CMCStatus,
BodyList SEQUENCE SIZE (1..MAX) OF
BodyPartReference,
StatusString UTF8String OPTIONAL,
OtherInfo CHOICE {
FailInfo CMCFailInfo,
PendInfo PendInfo,
ExtendedFailInfo SEQUENCE {
FailInfoOID OBJECT IDENTIFIER,
FailInfoValue AttributeValue
}
}
}
BodyPartReference ::= CHOICE {
BodyPartID BodyPartID,
BodyPartPath SEQUENCE SIZE (1..MAX) OF BodyPartID
}
-- Allow for distribution of trust roots
--
id-cmc-trustedRoots OBJECT IDENTIFIER ::= {id-cmc 26}
PublishTrustRoots ::= SEQUENCE {
seqNumber INTEGER,
rootHashes SEQUENCE OF OCTET STRING
}
id-cmc-authData OBJECT IDENTIFIER ::= {id-cmc 27}
AuthPublish ::= BodyPartID
-- These two items use BodyPartList
id-cmc-batchRequests OBJECT IDENTIFIER ::= {id-cmc 28}
id-cmc-batchResponses OBJECT IDENTIFIER ::= {id-cmc 29}
BodyPartList ::= SEQUENCE OF BodyPartID
--
id-cmc-publishCert OBJECT IDENTIFIER ::= {id-cmc 30}
CMCPublicationInfo ::= SEQUENCE {
certHashes SEQUENCE of OCTET STRING,
pubInfo PKIPublicationInfo
}
id-cmc-modCertTemplate OBJECT IDENTIFIER ::= {id-cmc XX}
ModCertTemplate ::= SEQUENCE {
pkiDataReference BodyPartList,
certReferences SEQUENCE OF BodyPartID,
replace BOOLEAN DEFAULT TRUE,
certTemplate CertTemplate
}
END
Appendix B. Enrollment Message Flows
This section is informational. The purpose of this section is to
present, in an abstracted version, the messages that would flow
between the client and server for several different common cases.
B.1 Request of a Signing Certificate
This section looks at the messages that would flow in the event that
an enrollment is occurring for a signing only key. If the
certificate was designed for both signing and encryption, the only
difference would be the key usage extension in the certificate
request.
Message from client to server:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-identityProof, computed value}
{103, id-cmc-senderNonce, 10001}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = My Proposed DN
publicKey = My Public Key
extensions
{id-ce-subjectPublicKeyIdentifier, 1000}
{id-ce-keyUsage, digitalSignature}
SignedData.SignerInfos
SignerInfo
sid.subjectKeyIdentifier = 1000
Response from server to client:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-cMCStatusInfoEx, {success, 201}}
{103, id-cmc-senderNonce, 10005}
{104, id-cmc-recipientNonce, 10001}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
B.2 Single Certificate Request, But Modified by RA
This section looks at the messages that would flow in the event that
an enrollment is has one RA in the middle of the data flow. That RA
will modify the certificate request before passing it on the CA.
Message from client to RA:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-identityProof, computed value}
{103, id-cmc-senderNonce, 10001}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = My Proposed DN
publicKey = My Public Key
extensions
{id-ce-subjectPublicKeyIdentifier, 1000}
{id-ce-keyUsage, digitalSignature}
SignedData.SignerInfos
SignerInfo
sid.subjectKeyIdentifier = 1000
Message from RA to CA:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{ 102, id-cmc-batchRequests, { 1, 2} }
{ 103, id-cmc-addExtensions,
{ {1, 201, {id-ce-certificatePolicies, anyPolicy}}
{1, 201, {id-ce-subjectAltName, {extension data}}
{2, XXX, {id-ce-subjectAltName, {extension data}}}
cmsSequence
{ 1, <Message from client to RA #1> }
{ 2, <Message from client to RA #2> }
SignedData.SignerInfos
SignerInfo
sid = RA key.
Response from the CA to the RA:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-BatchResponse, {999, 998}}
{102, id-cmc-CMCStatusInfoEx, {failed, 2, badIdentity}}
cmsSequence
{ bodyPartID = 999
contentInfo
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-cMCStatusInfoEx, {success, 201}}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
}
{ bodyPartID = 998,
contentInfo
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-cMCStatusInfoEx, {failure, badAlg}}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
}
SignedData.SignerInfos
Signed by CA
Response from RA to client:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{102, id-cmc-cMCStatusInfoEx, {success, 201}}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
B.3 Indirect POP for an RSA certificate
This section looks at the messages that would flow in the event that
an enrollment is done for an encryption only certificate using an
indirect POP method. For simplicity it is assumed that the
certificate requestor already has a signing only certificate
The fact that a second round trip is required is implicit rather
than explicit. The server determines this based on fact that no
other POP exists for the certificate request.
Message #1 from client to server:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-transactionID, 10132985123483401}
{103, id-cmc-senderNonce, 10001}
{104, id-cmc-dataRetrun, <packet of binary data identifying
where the key in question is.>}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = <My DN from my signing cert>
publicKey = My Public Key
extensions
{id-ce-keyUsage, keyEncipherment}
popo
keyEncipherment
subsequentMessage
SignedData.SignerInfos
SignerInfo
Signed by requestor's signing cert
Response #1 from server to client:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{101, id-cmc-cMCStatusInfoEx, {failed, 201, popRequired}}
{102, id-cmc-transactionID, 10132985123483401}
{103, id-cmc-senderNonce, 10005}
{104, id-cmc-recipientNonce, 10001}
{105, id-cmc-encryptedPOP, {
request {
certRequest
certReqId = 201
certTemplate
subject = <My DN from my signing cert>
publicKey = My Public Key
extensions
{id-ce-keyUsage, keyEncipherment}
popo
keyEncipherment
subsequentMessage
}
cms
contentType = id-envelopedData
content
recipipentInfos.riid.issuerSerialNumber = <NULL, 201>
encryptedContentInfo
eContentType = id-data
eContent = <Encrypted value of 'y'>
thePOPAlgID = HMAC-SHA1
witnessAlgID = SHA-1
witness <hashed value of 'y'>}}
{106, id-cmc-dataReturn, <packet of binary data identifying
where the key in question is.>}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIData
eContent
controlSequence
{102, id-cmc-transactionID, 10132985123483401}
{103, id-cmc-senderNonce, 100101}
{104, id-cmc-dataRetrun, <packet of binary data identifying
where the key in question is.>}
{105, id-cmc-recipientNonce, 10005}
{107, id-cmc-decryptedPOP, {
bodyPartID 201,
thePOPAlgID HMAC-SHA1,
thePOP <HMAC computed value goes here> }}
reqSequence
certRequest
certReqId = 201
certTemplate
subject = <My DN from my signing cert>
publicKey = My Public Key
extensions
{id-ce-keyUsage, keyEncipherment}
popo
keyEncipherment
subsequentMessage
SignedData.SignerInfos
SignerInfo
Signed by requestor's signing cert
Response from server to client:
ContentInfo.contentType = id-SignedData
ContentInfo.content
SignedData.encapContentInfo
eContentType = id-ct-PKIResponse
eContent
controlSequence
{101, id-cmc-transactionID, 10132985123483401}
{102, id-cmc-cMCStatusInfoEx, {success, 201}}
{103, id-cmc-senderNonce, 10019}
{104, id-cmc-recipientNonce, 100101}
{104, id-cmc-dataReturn, <packet of binary data identifying
where the key in question is.>}
certificates
Newly issued certificate
Other certificates
SignedData.SignerInfos
Signed by CA
Appendix C. Change History
RFC 27XX to -00
1. Addition of CMCStatusInfoExt
From -00 to -01
1. Removal of Transport section to a new document.
2. Removal of Compliance section to a new document.
From -01 to -02
1. Add processing rules for PKIData and PKIResponse processing.
2. Add unsigned attribute for holding data (to be used by key
archival).
3. Add trust root identification control.
4. Add Server to Client identity proof method.
5. Add controls to identify batch processing, needed by rules added
in item 1.
From -02 to -03
1. Add unpublish control
2. Added use of AuthenticatedData structure from CMS
3. Insert Appendix B - Enrollment Message Flows
4. Add Modify Certificate Request control
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights."
This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Datatracker
draft-ietf-pkix-2797-bis-02
Internet-Draft
