RFC 4913 EXPERIMENTAL DATA · XML
ASN.X for GSER: Abstract Syntax Notation X (ASN.X) Representation of Encoding Instructions for the Generic String Encoding Rules (GSER)
How to write encoding hints for text-based data in a structured XML notation.
RFC EDITOR
Legg, S., "Abstract Syntax Notation X (ASN.X) Representation of Encoding Instructions for the Generic String Encoding Rules (GSER)", RFC 4913, DOI 10.17487/RFC4913, July 2007, <https://www.rfc-editor.org/info/rfc4913>.
BIBTEX
@misc{rfc4913,
series = {Request for Comments},
number = 4913,
howpublished = {RFC 4913},
publisher = {RFC Editor},
doi = {10.17487/RFC4913},
url = {https://www.rfc-editor.org/info/rfc4913},
author = {S. Legg},
title = {{Abstract Syntax Notation X (ASN.X) Representation of Encoding Instructions for the Generic String Encoding Rules (GSER)}},
pagetotal = 9,
year = 2007,
month = jul,
} RFC text
Contents
Network Working Group S. Legg
Request for Comments: 4913 eB2Bcom
Category: Experimental July 2007
Abstract Syntax Notation X (ASN.X) Representation
of Encoding Instructions for
the Generic String Encoding Rules (GSER)
Status of This Memo
This memo defines an Experimental Protocol for the Internet
community. It does not specify an Internet standard of any kind.
Discussion and suggestions for improvement are requested.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Abstract Syntax Notation X (ASN.X) is an Extensible Markup Language
(XML) representation for Abstract Syntax Notation One (ASN.1)
specifications. This document specifies the ASN.X representation of
encoding instructions for the Generic String Encoding Rules (GSER).
Table of Contents
1. Introduction ....................................................2
2. Conventions .....................................................2
3. EncodingInstructionAssignmentList Translation ...................3
4. EncodingInstruction Translation .................................3
4.1. ChoiceOfStringsInstruction Translation .....................3
5. Security Considerations .........................................4
6. Normative References ............................................4
Appendix A. ASN.1 for GSER Encoding Instruction Notation ...........6
Appendix B. ASN.X for GSER Encoding Instruction Notation ...........7
1. Introduction
Abstract Syntax Notation X (ASN.X) [ASN.X] is an Extensible Markup
Language (XML) [XML10][XML11] representation for Abstract Syntax
Notation One (ASN.1) [X.680] specifications. The ASN.X
representation for the ASN.1 basic notation [X.680] [X.680-1] is
described elsewhere [ASN.X].
The grammar of ASN.1 permits the application of encoding instructions
[X.680-1], through type prefixes and encoding control sections, that
modify how abstract values are encoded by nominated encoding rules.
The generic notation for type prefixes and encoding control sections
is defined by the ASN.1 basic notation; however, the notation for
specific encoding instructions, i.e., the EncodingInstruction and
EncodingInstructionAssignmentList productions of the notation, are
defined separately for each set of encoding rules using encoding
instructions. This document specifies the ASN.X representation for
EncodingInstructionAssignmentList and EncodingInstruction as they are
defined for the Generic String Encoding Rules (GSER) [GSER][GSEREI].
ASN.X is defined in terms of rules for translating from an ASN.1
specification. This does not preclude an ASN.X module being written
directly without a pre-existing ASN.1 module; however, such an ASN.X
module is considered valid if and only if there exists, in principle,
an ASN.1 module that when translated would yield the ASN.X module.
By design, an ASN.X module is also the Robust XML Encoding Rules
(RXER) [RXER] encoding of an ASN.1 value. The ASN.1 type definitions
for such values, insofar as they pertain to the ASN.1 basic notation,
are provided elsewhere [ASN.X]; however, this document provides the
ASN.1 type definitions for representing GSER encoding instructions as
abstract values. These definitions appear in Appendix A.
The ASN.X translation of the ASN.1 module in Appendix A is presented
in Appendix B.
The General Considerations of the specification for ASN.X [ASN.X]
also apply here.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", and "MAY" in this document are
to be interpreted as described in BCP 14, RFC 2119 [BCP14]. The key
word "OPTIONAL" is exclusively used with its ASN.1 meaning.
A reference to an ASN.1 production [X.680] (e.g., Type, NamedType) is
a reference to the text in an ASN.1 specification corresponding to
that production.
The description of the translation of GSER encoding instructions into
ASN.X makes use of definitions from the XML Information Set (Infoset)
[INFOSET]. In particular, information item property names follow the
Infoset convention of being shown in square brackets, e.g.,
[local name]. Literal values of Infoset properties are enclosed in
double quotes; however, the double quotes are not part of the
property values. In the sections that follow, "information item"
will be abbreviated to "item", e.g., "element information item" is
abbreviated to "element item". Element items will be referred to by
their [local name] in angle brackets, e.g., "the <type> element item"
means the element item with the [local name] "type".
3. EncodingInstructionAssignmentList Translation
As described in the specification for ASN.X [ASN.X], the translation
of an EncodingControlSection for GSER is an element item with the
[local name] "GSER". The translation of the
EncodingInstructionAssignmentList in such an EncodingControlSection
determines the content of the <GSER> element item.
The EncodingInstructionAssignmentList for GSER is currently defined
to be empty [GSEREI]; therefore, the [attributes] and [children] of
the <GSER> element item are both empty.
4. EncodingInstruction Translation
The translation of an EncodingInstruction for GSER can appear in the
translation of an EncodingPrefix. The translation for an
EncodingPrefix is described by the specification for ASN.X.
The translation of an EncodingInstruction for GSER is the translation
of the ChoiceOfStringsInstruction in the EncodingInstruction
(currently the only defined encoding instruction for GSER).
4.1. ChoiceOfStringsInstruction Translation
The translation of a ChoiceOfStringsInstruction is an element item
with the [local name] "choiceOfStrings".
If the ChoiceOfStringsInstruction has an AlternativesPrecedence, then
an attribute item with the [local name] "precedence" SHALL be added
to the [attributes] of the <choiceOfStrings> element item. The
[normalized value] of this attribute item is the white space
separated list of qualified names for the expanded names [XMLNS10] of
the NamedType instances (see [RXEREI]) corresponding to the
identifiers nested in the PrecedenceList in the
AlternativesPrecedence.
Example
[GSER:CHOICE-OF-STRINGS PRECEDENCE utf8 visible] CHOICE {
visible [RXER:NAME "ascii"] VisibleString,
utf8 UTF8String
}
<type xmlns:asnx="urn:ietf:params:xml:ns:asnx">
<prefixed>
<GSER><choiceOfStrings precedence="utf8 ascii"/></GSER>
<type>
<choice>
<element name="ascii" identifier="visible"
type="asnx:VisibleString"/>
<element name="utf8" type="asnx:UTF8String"/>
</choice>
</type>
</prefixed>
</type>
5. Security Considerations
The ASN.X translation of a GSER encoding instruction is semantically
equivalent to the original GSER encoding instruction. The security
considerations that apply to an application built from an original
ASN.1 specification with GSER encoding instructions apply equally to
an application built from the ASN.X translation of the ASN.1
specification.
See the main specification for ASN.X [ASN.X] for security
considerations related to ASN.X modules.
6. Normative References
[BCP14] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[GSER] Legg, S., "Generic String Encoding Rules (GSER) for ASN.1
Types", RFC 3641, October 2003.
[GSEREI] Legg, S., "Encoding Instructions for the Generic String
Encoding Rules (GSER)", RFC 4792, January 2007.
[RXER] Legg, S. and D. Prager, "Robust XML Encoding Rules (RXER)
for Abstract Syntax Notation One (ASN.1)", RFC 4910, July
2007.
[RXEREI] Legg, S., "Encoding Instructions for the Robust XML
Encoding Rules (RXER)", RFC 4911, July 2007.
[ASN.X] Legg, S., "Abstract Syntax Notation X (ASN.X)", RFC 4912,
July 2007.
[X.680] ITU-T Recommendation X.680 (07/02) | ISO/IEC 8824-1,
Information technology - Abstract Syntax Notation One
(ASN.1): Specification of basic notation.
[X.680-1] ITU-T Recommendation X.680 (2002) Amendment 1 (10/03) |
ISO/IEC 8824-1:2002/Amd 1:2004, Support for EXTENDED-XER.
[XML10] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E. and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth
Edition)", W3C Recommendation,
http://www.w3.org/TR/2006/REC-xml-20060816, August 2006.
[XML11] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E.,
Yergeau, F., and J. Cowan, "Extensible Markup Language
(XML) 1.1 (Second Edition)", W3C Recommendation,
http://www.w3.org/TR/2006/REC-xml11-20060816, August 2006.
[XMLNS10] Bray, T., Hollander, D., Layman, A., and R. Tobin,
"Namespaces in XML 1.0 (Second Edition)", W3C
Recommendation,
http://www.w3.org/TR/2006/REC-xml-names-20060816, August
2006.
[INFOSET] Cowan, J. and R. Tobin, "XML Information Set (Second
Edition)", W3C Recommendation,
http://www.w3.org/TR/2004/REC-xml-infoset-20040204,
February 2004.
Appendix A. ASN.1 for GSER Encoding Instruction Notation
This appendix is normative.
GSER-EncodingInstructionNotation
{ iso(1) identified-organization(3) dod(6)
internet(1) private(4) enterprise(1)
xmled(21472) asnx(1) module(0) gser-ei-notation(2) }
-- Copyright (C) The IETF Trust (2007). This version of
-- this ASN.1 module is part of RFC 4913; see the RFC itself
-- for full legal notices.
--
-- Regarding this ASN.1 module or any portion of it, the author
-- makes no guarantees and is not responsible for any damage
-- resulting from its use. The author grants irrevocable permission
-- to anyone to use, modify, and distribute it in any way that does
-- not diminish the rights of anyone else to use, modify, and
-- distribute it, provided that redistributed derivative works do
-- not contain misleading author or version information.
-- Derivative works need not be licensed under similar terms.
DEFINITIONS
RXER INSTRUCTIONS
AUTOMATIC TAGS
EXTENSIBILITY IMPLIED ::= BEGIN
IMPORTS
PrecedenceList
FROM AbstractSyntaxNotation-X
{ iso(1) identified-organization(3) dod(6)
internet(1) private(4) enterprise(1)
xmled(21472) asnx(1) module(0) notation(1) }
;
GSER-EncodingInstruction ::= [SINGULAR-INSERTIONS] CHOICE {
choiceOfStrings GSER-ChoiceOfStringsInstruction
}
GSER-EncodingInstructionAssignmentList ::= SEQUENCE { }
GSER-ChoiceOfStringsInstruction ::= SEQUENCE {
precedence [ATTRIBUTE] PrecedenceList OPTIONAL
}
ENCODING-CONTROL RXER
SCHEMA-IDENTITY "urn:oid:1.3.6.1.4.1.21472.1.0.2"
TARGET-NAMESPACE "urn:ietf:params:xml:ns:asnx" PREFIX "asnx"
END
Appendix B. ASN.X for GSER Encoding Instruction Notation
This appendix is non-normative.
<?xml version="1.0"?>
<asnx:module xmlns:asnx="urn:ietf:params:xml:ns:asnx"
name="GSER-EncodingInstructionNotation"
identifier="1.3.6.1.4.1.21472.1.0.2"
schemaIdentity="urn:oid:1.3.6.1.4.1.21472.1.0.2"
targetNamespace="urn:ietf:params:xml:ns:asnx"
targetPrefix="asnx"
extensibilityImplied="true">
<annotation>
Copyright (C) The IETF Trust (2007). This version of
this ASN.X module is part of RFC 4913; see the RFC itself
for full legal notices.
Regarding this ASN.X module or any portion of it, the author
makes no guarantees and is not responsible for any damage
resulting from its use. The author grants irrevocable permission
to anyone to use, modify, and distribute it in any way that does
not diminish the rights of anyone else to use, modify, and
distribute it, provided that redistributed derivative works do
not contain misleading author or version information.
Derivative works need not be licensed under similar terms.
</annotation>
<import name="AbstractSyntaxNotation-X"
identifier="1.3.6.1.4.1.21472.1.0.1"
schemaIdentity="urn:oid:1.3.6.1.4.1.21472.1.0.1"
namespace="urn:ietf:params:xml:ns:asnx"/>
<namedType name="GSER-EncodingInstruction">
<type>
<choice insertions="singular">
<element name="choiceOfStrings"
type="asnx:GSER-ChoiceOfStringsInstruction"/>
</choice>
</type>
</namedType>
<namedType name="GSER-EncodingInstructionAssignmentList">
<type>
<sequence/>
</type>
</namedType>
<namedType name="GSER-ChoiceOfStringsInstruction">
<type>
<sequence>
<optional>
<attribute name="precedence" type="asnx:PrecedenceList"/>
</optional>
</sequence>
</type>
</namedType>
</asnx:module>
Author's Address
Dr. Steven Legg
eB2Bcom
Suite 3, Woodhouse Corporate Centre
935 Station Street
Box Hill North, Victoria 3129
AUSTRALIA
Phone: +61 3 9896 7830
Fax: +61 3 9896 7801
EMail: steven.legg@eb2bcom.com
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AI ELI5
On this page
PROBLEMEncoding instructions allow ASN.1 specifications to control how data gets serialized, but they are defined differently for each encoding standard. GSER (Generic String Encoding Rules) needed its own XML representation.
MECHANISMRFC 4913 specifies how to express GSER encoding instructions using ASN.X, an XML representation of ASN.1. It defines translation rules for the single GSER instruction (ChoiceOfStrings) and the control section that holds such instructions.
STATUS TODAYDevelopers can now write GSER encoding instructions directly in ASN.X form, which is valid XML and can be round-tripped with ASN.1 source.
§1Introduction
ASN.X is an XML-based way to write ASN.1 specifications. Instead of the traditional text syntax, you write your data structure definitions in XML elements and attributes. This RFC specifies how encoding instructions (optional notes that change how data is serialized) are represented in ASN.X form, specifically for the Generic String Encoding Rules (GSER).
ASN.1 allows type prefixes and encoding control sections to specify how values should be encoded by various encoding rules. However, each set of encoding rules (XER, GSER, RXER, etc.) defines its own notation for these instructions. This document bridges that gap for GSER.
ASN.X is like rewriting a form from pen-and-paper to a web form. This RFC shows how to move the special instructions from the ASN.1 form to the web form.
§2Encoding Instructions and Translation
An encoding instruction is a directive placed in an ASN.1 specification that changes how abstract values are encoded. GSER is a text-based encoding standard, and its encoding instructions tell the encoder how to handle certain data structures.
The main concept is translation: when you convert an ASN.1 specification to ASN.X (XML form), you must also convert the encoding instructions. The GSER instructions in ASN.1 become corresponding XML elements in ASN.X. The RFC defines the exact mapping: an encoding control section with GSER instructions becomes a <GSER> element item, and within it, specific instruction types (like choiceOfStrings) become child elements with specific attributes.
When you move from the text form to the XML form, the special instructions move too. A note that says 'write field X first' becomes an XML tag that says the same thing.
§3The ChoiceOfStrings Instruction
GSER currently defines only one encoding instruction: ChoiceOfStrings. This instruction tells the encoder the order in which to try alternatives when encoding a CHOICE type (a data type that holds one of several possible values).
In ASN.X, a ChoiceOfStrings instruction becomes a <choiceOfStrings> element. If the instruction specifies a precedence (an order for trying alternatives), that precedence becomes a precedence attribute. The attribute value is a whitespace-separated list of qualified names corresponding to the choices, telling the encoder which alternative to try first.
Example in ASN.1: [GSER:CHOICE-OF-STRINGS PRECEDENCE utf8 visible] becomes in ASN.X: <GSER><choiceOfStrings precedence='utf8 ascii'/></GSER>.
ChoiceOfStrings is like saying 'when you have to pick one of several options, prefer this one first.' In XML form, you write that preference as an attribute on a tag.
§4Security and Status
An ASN.X translation of a GSER encoding instruction is semantically equivalent to the original ASN.1 form. The security properties of the two forms are identical: an application built from ASN.1 with GSER instructions has the same security profile as one built from the ASN.X translation.
RFC 4913 is an Experimental protocol from 2007. It remains experimental and has not been updated or superseded. The translation rules it defines are stable and unchanged.
Whether you write the instruction in ASN.1 or in ASN.X, the instruction means the same thing and works the same way.
§5References
[GSER]RFC 3641Legg, S., "Generic String Encoding Rules (GSER) for ASN.1 Types", RFC 3641, October 2003.October 2003[GSEREI]RFC 4792Legg, S., "Encoding Instructions for the Generic String Encoding Rules (GSER)", RFC 4792, January 2007.January 2007[ASN.X]RFC 4912Legg, S., "Abstract Syntax Notation X (ASN.X)", RFC 4912, July 2007.July 2007[RXER]RFC 4910Legg, S. and D. Prager, "Robust XML Encoding Rules (RXER) for Abstract Syntax Notation One (ASN.1)", RFC 4910, July 2007.July 2007