Network Working Group C. Wallace
Internet-Draft Cygnacom Solutions
Intended status: Informational C. Gardiner
Expires: November 27, 2009 BBN Technologies
May 26, 2009
ASN.1 Translation
draft-ietf-pkix-asn1-translation-00
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on November 27, 2009.
Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Wallace & Gardiner Expires November 27, 2009 [Page 1]
Internet-Draft ASN.1 Translation May 2009
Abstract
Abstract Syntax Notation One (ASN.1) is widely used throughout the
IETF security area and has been for many years. Some specifications
were written using a now deprecated version of ASN.1 and some were
written using the current version of ASN.1. Not all ASN.1 compilers
support both older and current syntax. This document is intended to
provide guidance to specification authors and to implementers
converting ASN.1 modules written using one version of ASN.1 to
another version without causing changes to the "bits on the wire".
This document does not provide a comprehensive tutorial of any
version of ASN.1. Instead, it addresses ASN.1 features that are used
in IETF security area specifications with focus on items that vary
with the ASN.1 version.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. ASN.1 design elements . . . . . . . . . . . . . . . . . . . . 4
2.1. Open types . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.1. ANY DEFINED BY . . . . . . . . . . . . . . . . . . . . 4
2.1.2. OCTET STRINGs and BIT STRINGs . . . . . . . . . . . . 4
2.1.3. Information Object Classes . . . . . . . . . . . . . . 5
2.2. Constraints . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1. Simple table constraints . . . . . . . . . . . . . . . 8
2.2.2. Component relation constraints . . . . . . . . . . . . 8
2.2.3. Content constraints . . . . . . . . . . . . . . . . . 11
2.3. Parameterization . . . . . . . . . . . . . . . . . . . . . 12
2.4. Versioning and Extensibility . . . . . . . . . . . . . . . 14
2.4.1. Extension markers . . . . . . . . . . . . . . . . . . 14
2.4.2. Version brackets . . . . . . . . . . . . . . . . . . . 14
3. Character set differences . . . . . . . . . . . . . . . . . . 16
4. ASN.1 translation . . . . . . . . . . . . . . . . . . . . . . 17
4.1. Downgrading from X.68x to X.208 . . . . . . . . . . . . . 17
4.2. Upgrading from X.208 to X.68x . . . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Normative References . . . . . . . . . . . . . . . . . . . 20
7.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
Wallace & Gardiner Expires November 27, 2009 [Page 2]
Internet-Draft ASN.1 Translation May 2009
1. Introduction
This document is intended to serve as a tutorial for converting ASN.1
modules written using [CCITT.X208.1988] to [CCITT.X680.2002], or vice
versa. Preparation of this document was motivated by
[I-D.ietf-pkix-new-asn1] and [I-D.ietf-smime-new-asn1], which provide
updated ASN.1 modules for a number of RFCs.
The intent of this specification is to assist with translation of
ASN.1 from one version to another without resulting in any changes to
the encoded results when using the Basic Encoding Rules or
Distinguished Encoding Rules [CCITT.X209.1988][CCITT.X690.2002].
Other encoding rules were not considered.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document addresses two different versions of ASN.1. One version
is defined in a single document (X.208) and the other version is
defined in a series of documents (X.680, X.681, X.682 and X.683).
For convenience, the series of documents is henceforth referred to as
X.68x. Specific documents from the series are referenced by name
where appropriate.
Wallace & Gardiner Expires November 27, 2009 [Page 3]
Internet-Draft ASN.1 Translation May 2009
2. ASN.1 design elements
When translating an ASN.1 module from X.208 syntax to X.68x syntax,
or vice versa, many definitions do not require or benefit from
change. Review of the original ASN.1 modules updated by
[I-D.ietf-pkix-new-asn1] and [I-D.ietf-smime-new-asn1] and the
revised modules included in those documents indicates that most
changes can be sorted into one of a few categories. This section
describes these categories.
2.1. Open types
Protocols often feature flexible designs that enable other (later)
specifications to define the syntax and semantics of some features.
For example, [RFC5280] includes the definition of the Extension
structure. There are many instances of extensions defined in other
specifications. Several mechanisms are available in X.208, X.68x or
both to accommodate this practice, as described below.
2.1.1. ANY DEFINED BY
X.208 defines the ANY DEFINED BY production for specifying open
types. This typically appears in a SEQUENCE along with an OBJECT
IDENTIFIER that indicates the type of object that is encoded. The
ContentInfo structure, shown below from [RFC3852], uses ANY DEFINED
BY along with an OBJECT IDENTIFIER field to identify and convey
arbitrary types of data. Each content type to be wrapped in a
ContentInfo is assigned a unique OBJECT IDENTIFIER. However, X.208
does not provide a means for establishing a relationship between a
type and the type identifier.
-- from RFC 3852
ContentInfo ::= SEQUENCE {
contentType ContentType,
content [0] EXPLICIT ANY DEFINED BY contentType }
ContentType ::= OBJECT IDENTIFIER
id-signedData OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) rsadsi(113549) pkcs(1) pkcs7(7) 2 }
2.1.2. OCTET STRINGs and BIT STRINGs
Both X.208 and X.68x allow open types to be implemented using OCTET
STRINGs and BIT STRINGs. The definitions of Extension and
SubjectPublicKeyInfo in [RFC5280] demonstrate the usage of OCTET
Wallace & Gardiner Expires November 27, 2009 [Page 4]
Internet-Draft ASN.1 Translation May 2009
STRING and BIT STRING, respectively, to convey information that is
further defined using ASN.1.
-- from RFC 5280
Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
-- contains the DER encoding of an ASN.1 value
-- corresponding to the extension type identified
-- by extnID
}
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING }
In both cases, the prose of the specification indicates that the
adjacent OBJECT IDENTIFIER value indicates the type of structure
within the value of the primitive OCTET STRING or BIT STRING type.
For example, where an extnID field contains the value id-ce-
basicConstraints, the extnValue field contains an encoded
BasicConstraints as the value of the OCTET STRING, as shown in the
dump of an encoded extension below.
Tag Length Value
30 15: SEQUENCE {
06 3: OBJECT IDENTIFIER basicConstraints (2 5 29 19)
01 1: BOOLEAN TRUE
04 5: OCTET STRING, encapsulates {
30 3: SEQUENCE {
01 1: BOOLEAN TRUE
: }
: }
: }
2.1.3. Information Object Classes
Information object classes are defined in [CCITT.X681.2002]. These
serve to allow protocol designers to express the types of information
associated with a particular data type. The TYPE-IDENTIFIER
information object, defined in Annex A of [CCITT.X681.2002], provides
a basic information object that associates an identifier with a data
Wallace & Gardiner Expires November 27, 2009 [Page 5]
Internet-Draft ASN.1 Translation May 2009
type. [I-D.ietf-smime-new-asn1] uses the TYPE-IDENTIFIER
construction to update the definition of ContentInfo, as shown below.
-- TYPE-IDENTIFIER definition from X.681
TYPE-IDENTIFIER ::= CLASS
{
&id OBJECT IDENTIFIER UNIQUE,
&Type
}
WITH SYNTAX {&Type IDENTIFIED BY &id}
-- from updated RFC 3852 module in [I-D.ietf-smime-new-asn1]
CONTENT-TYPE ::= TYPE-IDENTIFIER
ContentType ::= CONTENT-TYPE.&id
ContentInfo ::= SEQUENCE {
contentType CONTENT-TYPE.
&id({ContentSet}),
content [0] EXPLICIT CONTENT-TYPE.
&Type({ContentSet}{@contentType})}
ContentSet CONTENT-TYPE ::= {
-- Define the set of content types to be recognized.
ct-Data | ct-SignedData | ct-EncryptedData | ct-EnvelopedData |
ct-AuthenticatedData | ct-DigestedData, ... }
-- other CONTENT-TYPE instances not shown for brevity
ct-SignedData CONTENT-TYPE ::=
{ SignedData IDENTIFIED BY id-signedData}
This example illustrates the following:
o Definition of an information object class: TYPE-IDENITIFIER and
CONTENT-TYPE are information object classes.
o Definition of an information object, or an instance of an
information object class: ct-SignedData is an information object.
o Definition of an information object set: ContentSet is an
information object set.
o Usage of an information object: The definition of ContentInfo uses
information from the CONTENT-TYPE information object class.
Wallace & Gardiner Expires November 27, 2009 [Page 6]
Internet-Draft ASN.1 Translation May 2009
o Defining constraints using an object set: Both the contentType and
content fields are constrained by ContentSet.
As noted above, TYPE-IDENTIFIER simply associates an OBJECT
IDENTIFIER with an arbitrary data type. CONTENT-TYPE is a TYPE-
IDENTIFIER. The WITH SYNTAX component allows for a more natural
language expression of information object definitions.
ct-SignedData is the name of an information object that associated
the identifier id-signedData with the data type SignedData. It is an
instance of the CONTENT-TYPE information object class. The &Type
field is assigned the value SignedData and the &id field is assigned
the value id-signedData. The example above uses the syntax provided
by the WITH SYNTAX component of the TYPE-IDENTIFIER definition. An
equivalent definition not using the provided syntax is as follows:
ct-SignedData CONTENT-TYPE ::=
{
&id id-signedData,
&Type SignedData
}
ContentSet is the name of a set of information objects derived from
the CONTENT-TYPE information object class. The set contains six
information objects and is extensible, as indicated by the ellipsis
(see the Versioning and Extensibility section below).
ContentInfo is defined using type information from an information
object, i.e., the type of the contentType field is that of the &id
field from CONTENT-TYPE. An equivalent definition is as follows:
ContentType ::= OBJECT IDENTIFIER
Both fields in ContentInfo are constrained. The contentType field is
constrained using a simple table constraint that restricts the values
to those from the corresponding field of the objects in ContentSet.
The content field is constrained using a component relationship
constraint. Constraints are discussed in the next section.
2.2. Constraints
Wallace & Gardiner Expires November 27, 2009 [Page 7]
Internet-Draft ASN.1 Translation May 2009
2.2.1. Simple table constraints
Simple table constraints are widely used in [I-D.ietf-pkix-new-asn1]
and [I-D.ietf-smime-new-asn1] to limit implementor options (although
the constraints are almost always followed by or include
extensibility markers making the parameters serve an informational
purpose not as a limitation). Table constraints are defined in
[CCITT.X682.2002].
The following example from [I-D.ietf-smime-new-asn1] provides two
examples of using table constraints to clarify the intended usage of
a particular field. The parameters indicate the types of attributes
that are typically found in the signedAttrs and unsignedAttrs fields.
In this example, the object sets are disjoint but this is not
required. For example, in [I-D.ietf-pkix-new-asn1], there is some
overlap between the CertExtensions and CrlExtensions sets.
-- from updated RFC 3852 module in [I-D.ietf-smime-new-asn1]
SignerInfo ::= SEQUENCE {
version CMSVersion,
sid SignerIdentifier,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT Attributes
{{UnsignedAttributes}} OPTIONAL }
SignedAttributes ::= Attributes {{ SignedAttributesSet }}
SignedAttributesSet ATTRIBUTE ::=
{ aa-signingTime | aa-messageDigest | aa-contentType, ... }
UnsignedAttributes ATTRIBUTE ::= { aa-countersignature, ... }
2.2.2. Component relation constraints
Component relation constraints are often used to bind the type field
of an open type to the identifier field. The following example from
[RFC2560] as updated [I-D.ietf-pkix-new-asn1] demonstrates this
usage.
Wallace & Gardiner Expires November 27, 2009 [Page 8]
Internet-Draft ASN.1 Translation May 2009
-- from updated RFC 2560 module in [I-D.ietf-pkix-new-asn1]
RESPONSE ::= TYPE-IDENTIFIER
ResponseSet RESPONSE ::= {basicResponse, ...}
ResponseBytes ::= SEQUENCE {
responseType RESPONSE.
&id ({ResponseSet}),
response OCTET STRING (CONTAINING RESPONSE.
&Type({ResponseSet}{@responseType}))}
In this example, the response field is constrained to contain a type
identified by the responseType field. The field is identified using
atNotation, e.g., "@responseType". atNotation can be defined relative
to the outermost SEQUENCE, SET or CHOICE or relative to the field
with which the atNotation is associated. When there is no '.'
immediately after the '@', the field appears as a member of the
outermost SEQUENCE, SET or CHOICE. When there is a '.' immediately
after the '@', each '.' represents a SEQUENCE, SET or CHOICE starting
with the SEQUENCE, SET or CHOICE that contains the field with which
the atNotation is associated. For example, ResponseBytes could have
been written as shown below. In this case, the syntax is very
similar since the innermost and outermost SEQUENCE, SET or CHOICE are
the same.
ResponseBytes ::= SEQUENCE {
responseType RESPONSE.
&id ({ResponseSet}),
response OCTET STRING (CONTAINING RESPONSE.
&Type({ResponseSet}{@.responseType}))}
The TaggedRequest example from [I-D.ietf-pkix-new-asn1] provides an
example where the outermost and innermost SEQUENCE, SET or CHOICE are
different. Relative to the atNotation included in the definition of
the requestMessageValue field, the outermost SEQUENCE, SET or CHOICE
is TaggedRequest and the innermost is the SEQUENCE used to define the
orm field.
Wallace & Gardiner Expires November 27, 2009 [Page 9]
Internet-Draft ASN.1 Translation May 2009
TaggedRequest ::= CHOICE {
tcr [0] TaggedCertificationRequest,
crm [1] CertReqMsg,
orm [2] SEQUENCE {
bodyPartID BodyPartID,
requestMessageType OTHER-REQUEST.&id({OtherRequests}),
requestMessageValue OTHER-REQUEST.&Type({OtherRequests}
{@.requestMessageType})
}
}
When referencing a field using atNotation, the definition of the
field must be included within the outermost SEQUENCE, SET or CHOICE.
References to fields within structures that are defined separately
are not allowed. For example, the following example includes invalid
atNotation in the defintion of the signed field of ToBeSigned.
AlgorithmIdentifier{ALGORITHM-TYPE, ALGORITHM-TYPE:AlgorithmSet} ::=
SEQUENCE {
algorithm ALGORITHM-TYPE.&id({AlgorithmSet}),
parameters ALGORITHM-TYPE.
&Params({AlgorithmSet}{@algorithm}) OPTIONAL
}
-- example containing invalid atNotation
SIGNED{ToBeSigned} ::= SEQUENCE {
toBeSigned ToBeSigned,
algorithmIdentifier AlgorithmIdentifier
{ SIGNATURE-ALGORITHM, {...}}
},
signature BIT STRING (CONTAINING SIGNATURE-ALGORITHM.&Value(
{SignatureAlgorithms}
{@algorithmIdentifier.algorithm}))
}
The above example could be alternatively written with correct
atNotation as follows, with the definition of the algorithm field
included within ToBeSigned.
Wallace & Gardiner Expires November 27, 2009 [Page 10]
Internet-Draft ASN.1 Translation May 2009
SIGNED{ToBeSigned} ::= SEQUENCE {
toBeSigned ToBeSigned,
algorithmIdentifier SEQUENCE {
algorithm SIGNATURE-ALGORITHM.
&id({SignatureAlgorithms}),
parameters SIGNATURE-ALGORITHM.
&Params({SignatureAlgorithms}
{@algorithmIdentifier.algorithm})
},
signature BIT STRING (CONTAINING SIGNATURE-ALGORITHM.&Value(
{SignatureAlgorithms}
{@algorithmIdentifier.algorithm}))
}
In the above example, the outermost SEQUENCE, SET or CHOICE relative
to the parameters field is the structure named ToBeSigned. The
innermost structure is the SEQUENCE used as the type for the
algorithmIdentifier field. The atNotation for the parameters field
could be expressed using any of the following representations:
@algorithmIdentifier.algorithm
@.algorithm
The atNotation for the signature field has only one representation.
2.2.3. Content constraints
Open types implemented as OCTET STRINGs or BIT STRINGs can be
constrained using contents constraints syntax defined in
[CCITT.X682.2002]. Below are the revised definitions from
[I-D.ietf-pkix-new-asn1] and [I-D.ietf-smime-new-asn1]. These show
usage of OCTET STRING and BIT STRING along with constrained sets of
identifiers. The Extension definition uses a content constraint that
requires the value of the OCTET STRING to be an encoding the type
associated with the information object selected from the ExtensionSet
object set using the value of the extnID field. For reasons
described above in the "Component relation constraints" section, the
SubjectPublicKeyInfo definition relies on prose to bind the BIT
STRING to the type identifier because it is not possible to express a
content constraint that includes a component relationship constraint
to bind the type value within the algorithm field to the
subjectPublicKey field.
Wallace & Gardiner Expires November 27, 2009 [Page 11]
Internet-Draft ASN.1 Translation May 2009
-- from updated RFC 5280 module in [I-D.ietf-pkix-new-asn1]
Extension{EXTENSION:ExtensionSet} ::= SEQUENCE {
extnID EXTENSION.&id({ExtensionSet}),
critical BOOLEAN
-- (EXTENSION.&Critical({ExtensionSet}{@extnID}))
DEFAULT FALSE,
extnValue OCTET STRING (CONTAINING
EXTENSION.&ExtnType({ExtensionSet}{@extnID}))
-- contains the DER encding of the ASN.1 value
-- corresponding to the extension type identified
-- by extnID
}
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier{PUBLIC-KEY,
{PublicKeyAlgorithms}},
subjectPublicKey BIT STRING
}
2.3. Parameterization
Parameterization is defined in [CCITT.X683.2002] and can also be used
to define new types in a way similar to the macro notation described
in Annex A of X.208. The following example from
[I-D.ietf-pkix-new-asn1] shows this usage. The toBeSigned field
takes the type passed as a parameter.
-- from [I-D.ietf-pkix-new-asn1]
SIGNED{ToBeSigned} ::= SEQUENCE {
toBeSigned ToBeSigned,
algorithm AlgorithmIdentifier{SIGNATURE-ALGORITHM,
{SignatureAlgorithms}},
signature BIT STRING
}
-- from updated RFC5280 module in [I-D.ietf-pkix-new-asn1]
Certificate ::= SIGNED{TBSCertificate}
Parameters need not be simple types. The following example
demonstrates the usage of an information object class and an
information object set as parameters. The first parameter in the
definition of AlgorithmIdentifier is an information object class.
Information object classes used for this parameter must have &id and
&Params fields, which determine the type of the algorithm and
parameters fields. Other fields may be present in the information
Wallace & Gardiner Expires November 27, 2009 [Page 12]
Internet-Draft ASN.1 Translation May 2009
object class but they are not used by the definition of
AlgorithmIdentifier, as demonstrated by the the SIGNATURE-ALGORITHM
class shown below. The second parameter is an information object set
that is used to constrain the values that appear in the algorithm and
parameters fields.
-- from [I-D.ietf-pkix-new-asn1]
AlgorithmIdentifier{ALGORITHM-TYPE, ALGORITHM-TYPE:AlgorithmSet}
::= SEQUENCE
{
algorithm ALGORITHM-TYPE.&id({AlgorithmSet}),
parameters ALGORITHM-TYPE.&Params
({AlgorithmSet}{@algorithm}) OPTIONAL
}
SIGNATURE-ALGORITHM ::= CLASS {
&id OBJECT IDENTIFIER,
&Params OPTIONAL,
&Value OPTIONAL,
¶mPresence ParamOptions DEFAULT absent,
&HashSet DIGEST-ALGORITHM OPTIONAL,
&PublicKeySet PUBLIC-KEY OPTIONAL,
&smimeCaps SMIME-CAPS OPTIONAL
} WITH SYNTAX {
IDENTIFIER &id
[VALUE &Value]
[PARAMS [TYPE &Params] ARE ¶mPresence ]
[HASHES &HashSet]
[PUBLIC KEYS &PublicKeySet]
[SMIME CAPS &smimeCaps]
}
-- from updated RFC 2560 module in [I-D.ietf-pkix-new-asn1]
BasicOCSPResponse ::= SEQUENCE {
tbsResponseData ResponseData,
signatureAlgorithm AlgorithmIdentifier{SIGNATURE-ALGORITHM,
{sa-dsaWithSHA1 | sa-rsaWithSHA1 |
sa-rsaWithMD5 | sa-rsaWithMD2, ...}},
signature BIT STRING,
certs [0] EXPLICIT SEQUENCE OF Certificate OPTIONAL
}
Wallace & Gardiner Expires November 27, 2009 [Page 13]
Internet-Draft ASN.1 Translation May 2009
2.4. Versioning and Extensibility
Specifications are often revised and ASN.1 modules updated to include
new components. [CCITT.X681.2002] provides two mechanisms useful in
supporting extensibility: extension markers and version brackets.
2.4.1. Extension markers
An extension marker is represented by an ellipsis (i.e., three
adjacent periods). Extension markers are included in specifications
at points where the protocol designer anticipates future changes.
This can also be achieved by including EXTENSIBILITY IMPLIED in the
ASN.1 module definition. EXTENSIBILITY IMPLIED is the equivalent to
including an extension marker in each type defined in the ASN.1
module. Extensibility markers are used throughout
[I-D.ietf-pkix-new-asn1] and [I-D.ietf-smime-new-asn1] where object
sets are defined. In other instances, the updated modules
retroactively added extension markers where fields were added to an
earlier version by an update, as shown in the CertificateChoices
example below.
Examples:
-- from updated RFC 3370
KeyAgreementAlgs KEY-AGREE ::= { kaa-esdh | kaa-ssdh, ...}
-- from updated RFC 3852
CertificateChoices ::= CHOICE {
certificate Certificate,
extendedCertificate [0] IMPLICIT ExtendedCertificate,
-- Obsolete
...,
[[3: v1AttrCert [1] IMPLICIT AttributeCertificateV1]],
-- Obsolete
[[4: v2AttrCert [2] IMPLICIT AttributeCertificateV2]],
[[5: other [3] IMPLICIT OtherCertificateFormat]]
}
Protocol designers should use extension markers within definitions
that are likely to change. For example, extensibility markers should
be used when enumerating error values.
2.4.2. Version brackets
Version brackets can be used to indicate features that are available
in later versions of an ASN.1 module but not in earlier versions.
Wallace & Gardiner Expires November 27, 2009 [Page 14]
Internet-Draft ASN.1 Translation May 2009
[I-D.ietf-pkix-new-asn1] added version brackets to the definition of
TBSCertificate to illustrate the addition of the issuerUniqueID,
subjectUniqueID and extensions fields, as shown below.
-- from updated RFC 5280 module in [I-D.ietf-pkix-new-asn1]
TBSCertificate ::= SEQUENCE {
version [0] Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature AlgorithmIdentifier{SIGNATURE-ALGORITHM,
{SignatureAlgorithms}},
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
... ,
[[2: -- If present, version MUST be v2
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL,
subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL
]],
[[3: -- If present, version MUST be v3 --
extensions [3] ExtensionSet{{CertExtensions}} OPTIONAL
]], ... }
Wallace & Gardiner Expires November 27, 2009 [Page 15]
Internet-Draft ASN.1 Translation May 2009
3. Character set differences
X.68s uses a character set that is a superset of the character set
defined in X.208. The character set defined in X.208 includes the
following:
A to Z
a to z
0 to 9
:=,{}<.
()[]-'"
The character set in X.68x is additionally includes the following:
!&*/;>@^_|
The > and | characters can also be used in X.208 syntax in macro
defnintions.
Wallace & Gardiner Expires November 27, 2009 [Page 16]
Internet-Draft ASN.1 Translation May 2009
4. ASN.1 translation
4.1. Downgrading from X.68x to X.208
At a minimum, downgrading an ASN.1 module from X.68x syntax to X.208
requires the removal of features not supported by X.208. As
indicated above, the features most commonly used in IETF security
area ASN.1 modules are information object classes (and object sets),
content constraints, parameterization, version brackets and extension
markers. Extension markers and version brackets can simply be
deleted (or commented out). The definitions for information object
classes and object sets can also be deleted or commented out, as
these will not be used.
4.2. Upgrading from X.208 to X.68x
The amount of change associated with upgrading from X.208 syntax to
X.68x syntax is dependent on the reasons for changing and personal
style. A minimalist approach could consist of altering any
deprecated features, most commonly ANY DEFINED BY, and adding any
necessary extensibility markers. A more comprehensive approach may
include of the introduction of constraints, parameterization,
versioning, extensibility, etc.
Wallace & Gardiner Expires November 27, 2009 [Page 17]
Internet-Draft ASN.1 Translation May 2009
5. IANA Considerations
There are no IANA considerations. Please delete this section prior
to RFC publication.
Wallace & Gardiner Expires November 27, 2009 [Page 18]
Internet-Draft ASN.1 Translation May 2009
6. Security Considerations
Where a module is downgraded from X.68x syntax to X.208 there is loss
of potential automated enforcement of constraints expressed by the
author of the module being downgraded. These constraints should be
captured in prose or ASN.1 comments and enforced through other means,
as necessary.
Wallace & Gardiner Expires November 27, 2009 [Page 19]
Internet-Draft ASN.1 Translation May 2009
7. References
7.1. Normative References
[CCITT.X208.1988]
International International Telephone and Telegraph
Consultative Committee, "Specification of Abstract Syntax
Notation One (ASN.1)", CCITT Recommendation X.208,
November 1988.
[CCITT.X680.2002]
International International Telephone and Telegraph
Consultative Committee, "Abstract Syntax Notation One
(ASN.1): Specification of basic notation",
CCITT Recommendation X.680, July 2002.
[CCITT.X681.2002]
International International Telephone and Telegraph
Consultative Committee, "Abstract Syntax Notation One
(ASN.1): Information object specification",
CCITT Recommendation X.681, July 2002.
[CCITT.X682.2002]
International International Telephone and Telegraph
Consultative Committee, "Abstract Syntax Notation One
(ASN.1): Constraint specification", CCITT Recommendation
X.682, July 2002.
[CCITT.X683.2002]
International International Telephone and Telegraph
Consultative Committee, "Abstract Syntax Notation One
(ASN.1): Parameterization of ASN.1 specifications",
CCITT Recommendation X.683, July 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[CCITT.X209.1988]
International Telephone and Telegraph Consultative
Committee, "Specification of Basic Encoding Rules for
Abstract Syntax Notation One (ASN.1)",
CCITT Recommendation X.209, 1988.
[CCITT.X690.2002]
International International Telephone and Telegraph
Consultative Committee, "ASN.1 encoding rules:
Wallace & Gardiner Expires November 27, 2009 [Page 20]
Internet-Draft ASN.1 Translation May 2009
Specification of basic encoding Rules (BER), Canonical
encoding rules (CER) and Distinguished encoding rules
(DER)", CCITT Recommendation X.690, July 2002.
[I-D.ietf-pkix-new-asn1]
Hoffman, P. and J. Schaad, "New ASN.1 Modules for PKIX",
draft-ietf-pkix-new-asn1-05 (work in progress),
April 2009.
[I-D.ietf-smime-new-asn1]
Hoffman, P. and J. Schaad, "New ASN.1 Modules for CMS and
S/MIME", draft-ietf-smime-new-asn1-05 (work in progress),
April 2009.
[RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560, June 1999.
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, May 2008.
Wallace & Gardiner Expires November 27, 2009 [Page 21]
Internet-Draft ASN.1 Translation May 2009
Authors' Addresses
Carl Wallace
Cygnacom Solutions
Suite 5200
7925 Jones Branch Drive
McLean, VA 22102
Email: cwallace@cygnacom.com
Charles Gardiner
BBN Technologies
10 Moulton Street
Cambridge, MA 02138
Email: gardiner@bbn.com
Wallace & Gardiner Expires November 27, 2009 [Page 22]