Clarification of Enrollment over
Secure Transport (EST): Transfer Encodings and ASN.1
Sandelman Software Works
mcr+ietf@sandelman.ca
Siemens
thomas-werner@siemens.com
Huawei Technologies
william.panwei@huawei.com
Internet
LAMPS Working Group
This document updates RFC 7030: Enrollment over Secure Transport
to resolve some errata that were reported and that have proven to
cause interoperability issues when RFC 7030 was extended.
This document deprecates the specification of
"Content-Transfer-Encoding" headers for Enrollment over Secure Transport
(EST) endpoints. This document
fixes some syntactical errors in ASN.1 that were present.
Introduction
Enrollment over Secure Transport (EST) is defined in . The EST specification defines a
number of HTTP endpoints for certificate enrollment and management. The
details of the transaction were defined in terms of MIME headers, as
defined in , rather than in
terms of the HTTP protocol, as defined in and .
and later have text
specifically deprecating Content-Transfer-Encoding. However, incorrectly uses this header.
Any updates to to bring it
in line with HTTP processing risk changing the on-wire protocol in a way
that is not backwards compatible. However, reports from implementers
suggest that many implementations do not send the
Content-Transfer-Encoding, and many of them ignore it. The consequence
is that simply deprecating the header would remain compatible with
current implementations.
extends ,
adding new functionality. Interop testing of the protocol has
revealed that unusual processing called out in causes confusion.
EST is currently specified as part of and is widely used in government, utilities, and
financial markets today.
This document, therefore, revises to reflect the field reality, deprecating the
extraneous field.
This document deals with errata numbers , , , and .
This document deals with
and in . is dealt with in . is
closed by correcting the ASN.1 Module in .
Terminology
The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
Changes to EST Endpoint Processing
Sections (CA Certificates Response, /cacerts), and (Full CMC,
/fullcmc),
(Server-Side Key Generation, /serverkeygen), and (CSR Attributes, /csrattrs) of
specify the use of base64 encoding with a Content-Transfer-Encoding for
requests and responses.
This document updates to
require the POST request and payload response of all endpoints using
base64 encoding, as specified in . In both cases, the Distinguished
Encoding Rules (DER) are used to
produce the input for the base64 encoding routine. This format is to
be used regardless of any Content-Transfer-Encoding header, and any
value in such a header MUST be ignored.
White Space Processing
Note that "base64" as used in the HTTP does not permit CRLF, while the "base64" used in
MIME does. This
specification clarifies that despite what says, white space including CR, LF, spaces (ASCII
32), and tabs (ASCII 9) SHOULD be tolerated by
receivers. Senders are not required to insert any kind of white space.
Changes to Section 4 of RFC 7030
Section 4.1.3
Replace:
A successful response MUST be a certs-only CMC Simple PKI Response,
as defined in , containing the certificates described in the
following paragraph. The HTTP content-type of
"application/pkcs7-mime" is used. The Simple PKI Response is sent
with a Content-Transfer-Encoding of "base64" .
with:
A successful response MUST be a certs-only CMC Simple PKI Response,
as defined in , containing the certificates described in the
following paragraph. The HTTP content-type of
"application/pkcs7-mime" is used. The CMC Simple PKI Response is
encoded in base64 .
Section 4.3.1
Replace:
If the HTTP POST to /fullcmc is not a valid Full PKI Request, the
server MUST reject the message. The HTTP content-type used is
"application/pkcs7-mime" with an smime-type parameter "CMC-request",
as specified in . The body of the message is the binary
value of the encoding of the PKI Request with a
Content-Transfer-Encoding of "base64" .
with:
If the HTTP POST to /fullcmc is not a valid Full PKI Request, the
server MUST reject the message. The HTTP content-type used is
"application/pkcs7-mime" with an smime-type parameter "CMC-request",
as specified in . The body of the message is encoded
in base64 .
Section 4.3.2
Replace:
The body of the message is the binary value of the encoding of the
PKI Response with a Content-Transfer-Encoding of "base64" .
with:
The body of the message is the base64 encoding of the
PKI Response.
Section 4.4.2
Replace:
An "application/pkcs8"
part consists of the base64-encoded DER-encoded
PrivateKeyInfo with a Content-Transfer-Encoding of "base64"
.
with:
An "application/pkcs8" part consists of the base64-encoded,
DER-encoded PrivateKeyInfo.
Replace:
In all three additional encryption cases, the EnvelopedData is
returned in the response as an "application/pkcs7-mime" part with an
smime-type parameter of "server-generated-key" and a Content-
Transfer-Encoding of "base64".
with:
In all three additional encryption cases, the EnvelopedData is
returned in the response as an "application/pkcs7-mime" part
with an smime-type parameter of "server-generated-key". It is
base64 encoded .
Section 4.5.2
This section is updated in its entirety in .
Clarification of ASN.1 for Certificate Attribute Set
is to be
replaced with the following text:
4.5.2 CSR Attributes Response
If locally configured policy for an authenticated EST client indicates
a CSR Attributes Response is to be provided, the server response MUST
include an HTTP 200 response code. An HTTP response code of 204 or 404
indicates that a CSR Attributes Response is not available. Regardless
of the response code, the EST server and CA MAY reject any subsequent
enrollment requests for any reason, e.g., incomplete CSR attributes in
the request.
Responses to attribute request messages MUST be encoded as the
content-type of "application/csrattrs" and are to be "base64"
encoded. The syntax for application/csrattrs body is as follows:
An EST server includes zero or more OIDs or attributes that it requests the client to use
in the certification request. The client MUST ignore any
OID or attribute it does not recognize. When the server encodes CSR
attributes as an empty SEQUENCE, it means that the server has no
specific additional information it desires in a client certification
request (this is functionally equivalent to an HTTP response code of 204
or 404).
If the CA requires a particular cryptographic algorithm or use of a particular
signature scheme (e.g., certification of a public key based on a
certain elliptic curve or signing using a certain hash algorithm), it
MUST provide that information in the CSR Attribute Response. If an
EST server requires the linking of identity and POP information (see
Section 3.5), it MUST include the challengePassword OID in the CSR
Attributes Response.
The structure of the CSR Attributes Response SHOULD, to the greatest
extent possible, reflect the structure of the CSR it is requesting.
Requests to use a particular signature scheme (e.g., using a
particular hash function) are represented as an OID to be reflected
in the SignatureAlgorithm of the CSR. Requests to use a particular
cryptographic algorithm (e.g., certification of a public key based on a certain
elliptic curve) are represented as an attribute, to be reflected as
the AlgorithmIdentifier of the SubjectPublicKeyInfo, with a type
indicating the algorithm and the values indicating the particular
parameters specific to the algorithm. Requests for descriptive
information from the client are made by an attribute, to be
represented as Attributes of the CSR, with a type indicating the
extensionRequest and the values indicating the particular
attributes desired to be included in the resulting certificate's
extensions.
The sequence is Distinguished Encoding Rules (DER) encoded and then base64 encoded (). The resulting text
forms the application/csrattr body, without headers.
For example, if a CA requests that a client a) submit a certification
request containing the challengePassword (indicating that linking of
identity and POP information is requested; see Section ), b) submit an
extensionRequest with the Media Access Control (MAC) address
of the client, and c) use the secp384r1 elliptic curve
to sign using the SHA384 hash function, then it takes the
following:
OID: challengePassword (1.2.840.113549.1.9.7)
Attribute: type = extensionRequest (1.2.840.113549.1.9.14)
value = macAddress (1.3.6.1.1.1.1.22)
Attribute: type = id-ecPublicKey (1.2.840.10045.2.1)
value = secp384r1 (1.3.132.0.34)
OID: ecdsaWithSHA384 (1.2.840.10045.4.3.3)
and encodes them into an ASN.1 SEQUENCE to produce:
30 41 06 09 2a 86 48 86 f7 0d 01 09 07 30 12 06 07 2a 86 48 ce 3d
02 01 31 07 06 05 2b 81 04 00 22 30 16 06 09 2a 86 48 86 f7 0d 01
09 0e 31 09 06 07 2b 06 01 01 01 01 16 06 08 2a 86 48 ce 3d 04 03
03
and then base64 encodes the resulting ASN.1 SEQUENCE to produce:
MEEGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiMBYGCSqGSIb3DQEJDjEJ
BgcrBgEBAQEWBggqhkjOPQQDAw==
Clarification of Error Messages for Certificate Enrollment Operations
clarifies what format
the error messages are to be in. Previously, a client might be confused
into believing that an error returned with type text/plain was not
intended to be an error.
Updating Section 4.2.3: Simple Enroll and Re-enroll Response
Replace:
If the content-type is not set, the response data MUST be a
plaintext human-readable error message containing explanatory
information describing why the request was rejected (for
example, indicating that CSR attributes are incomplete).
with:
If the content-type is not set, the response data MUST be a
plaintext human-readable error message containing explanatory
information describing why the request was rejected (for
example, indicating that CSR attributes are incomplete).
Servers MAY use the "text/plain" content-type
for human-readable errors.
Updating Section 4.4.2: Server-Side Key Generation Response
Replace:
If the content-type is not set, the response data MUST be a
plaintext human-readable error message.
with:
If the content-type is not set, the response data MUST be a
plaintext human-readable error message.
Servers MAY use the "text/plain" content-type
for human-readable errors.
Privacy Considerations
This document does not disclose any additional identities that either
an active or passive observer would see with .
Security Considerations
This document clarifies an existing security mechanism.
It does not create any new protocol mechanisms.
All security considerations from also apply to the clarifications described in this document.
IANA Considerations
The ASN.1 module in of
this document makes use of object identifiers (OIDs).
IANA has registered an OID for id-mod-est-2019 (1.3.6.1.5.5.7.0.98)
in the "SMI Security for PKIX Module Identifier" registry for the ASN.1 module.
The OID for the Asymmetric Decryption Key Identifier (1.2.840.113549.1.9.16.2.54)
was previously defined in .
IANA has updated the Reference column for the Asymmetric
Decryption Key Identifier attribute to also include a reference to this document.
References
Normative References
Information technology -- Abstract Syntax Notation One
(ASN.1): Specification of basic notation
ITU-T
Information Technology - Abstract Syntax Notation One (ASN.1): Information object specification
ITU-T
Information Technology - Abstract Syntax Notation One (ASN.1): Constraint specification
ITU-T
Information Technology - Abstract Syntax Notation One (ASN.1): Parameterization of ASN.1 specifications
ITU-T
Information Technology - ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)
ITU-T
Power systems management and associated information exchange - Data and communications security - Part 9: Cyber security key management for power system equipment
International Electrotechnical Commission
Erratum ID 4384
RFC Errata
RFC 7030
Erratum ID 5107
RFC Errata
RFC 7030
Erratum ID 5108
RFC Errata
RFC 7030
Erratum ID 5904
RFC Errata
RFC 7030
Informative References
ASN.1 Module
This annex provides the normative ASN.1 definitions for the
structures described in this specification using ASN.1 as defined in
, , , and .
The ASN.1 modules makes imports from the ASN.1 modules in and .
There is no ASN.1 Module in . This module has been created by combining the lines
that are contained in the document body.
Acknowledgements
Huawei Technologies supported the efforts of and .
The ASN.1 Module was assembled by
and formatted by . provided editorial review.