GNU Libtasn1 2.8

Libtasn1

This manual is for GNU Libtasn1 (version 2.8, 20 April 2010), which is a library for Abstract Syntax Notation One (ASN.1) and Distinguish Encoding Rules (DER) manipulation.

Copyright © 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.

• Introduction
• ASN.1 structure handling
• Utilities
• Function reference
• Copying Information

Indices

• Concept Index: Index of concepts and programs.
• Function and Data Index: Index of functions, variables and data types.

1 Introduction

This document describes the Libtasn1 library developed for ASN.1 (Abstract Syntax Notation One) structures management and DER (Distinguished Encoding Rules) encoding functions.

The main features of this library are:

• On line ASN1 structure management that doesn't require any C code file generation.
• Off line ASN1 structure management with C code file generation containing an array.
• DER (Distinguish Encoding Rules) encoding.
• No limits for INTEGER and ENUMERATED values.
• It's Free Software. Anybody can use, modify, and redistribute the library under the terms of the GNU Lesser General Public License version 2.1 or later. The command line tools, self-tests and build infrastructure are licensed under the GNU General Public License version 3.0 or later.
• It's thread-safe. No global variables are used and multiple library handles and session handles may be used in parallel.
• It's portable. It should work on all Unix like operating systems, including Windows. The library itself should be portable to any C89 system, not even POSIX is required.

2 ASN.1 structure handling

• ASN.1 syntax
• Naming
• Library Notes
• Future developments

2.1 ASN.1 syntax

The parser is case sensitive. The comments begin with "– " and end at the end of lines. An example is in "pkix.asn" file. ASN.1 definitions must have this syntax:

      definitions_name {<object definition>}

      DEFINITIONS <EXPLICIT or IMPLICIT> TAGS ::=

      BEGIN

      <type and constants definitions>

      END

The token "::=" must be separate from others elements, so this is a wrong declaration:

           ;; INCORRECT
           Version ::=INTEGER

the correct form is:

        Version ::= INTEGER

Here is the list of types that the parser can manage:

• INTEGER
• ENUMERATED
• BOOLEAN
• OBJECT IDENTIFIER
• NULL
• BIT STRING
• OCTET STRING
• UTCTime
• GeneralizedTime
• GeneralString
• SEQUENCE
• SEQUENCE OF
• SET
• SET OF
• CHOICE
• ANY
• ANY DEFINED BY

This version doesn't manage REAL type. It doesn't allow the "EXPORT" and "IMPORT" sections too.

The SIZE constraints are allowed, but no check is done on them.

2.2 Naming

Consider this definition:

      Example { 1 2 3 4 }

      DEFINITIONS EXPLICIT TAGS ::=

      BEGIN

      Group ::= SEQUENCE {
         id   OBJECT IDENTIFIER,
         value  Value
      }

      Value ::= SEQUENCE {
         value1  INTEGER,
         value2  BOOLEAN
      }

      END

To identify the type 'Group' you have to use the null terminated string "Example.Group". These strings are used in functions that are described below.

Others examples:

Field 'id' in 'Group' type : "Example.Group.id".

Field 'value1' in field 'value' in type 'Group': "Example.Group.value.value1".

Elements of structured types that don't have a name, receive the name "?1","?2", and so on.

The name "?LAST" indicates the last element of a SET_OF or SEQUENCE_OF.

2.3 Library Notes

The header file of this library is libtasn1.h.

The main type used in it is ASN1_TYPE, and it's used to store the ASN.1 definitions and structures (instances).

The constant ASN1_TYPE_EMPTY can be used for the variable initialization. For example:

      ASN1_TYPE definitions=ASN1_TYPE_EMPTY;

Some functions require a parameter named errorDescription of char* type. The array must be already allocated and must have at least ASN1_MAX_ERROR_DESCRIPTION_SIZE bytes (E.g, as in char Description[ASN1_MAX_ERROR_DESCRIPTION_SIZE];).

ASN1_MAX_NAME_SIZE indicates the maximum number of characters of a name inside a file with ASN1 definitions.

2.4 Future developments

• Add functions for a C code file generation containing equivalent data structures (not a single array like now).
• Type REAL.

3 Utilities

• Invoking asn1Parser
• Invoking asn1Coding
• Invoking asn1Decoding

3.1 Invoking asn1Parser

asn1Parser reads one file with ASN1 definitions and generates a file with an array to use with libtasn1 functions.

Usage:  asn1Parser [options] file

Options:
 -h : shows the help message.
 -v : shows version information and exit.
 -c : checks the syntax only.
 -o file : output file.
 -n name : array name.

3.2 Invoking asn1Coding

asn1Coding generates a DER encoding from a file with ASN1 definitions and another one with assignments.

The file with assignments must have this syntax:

InstanceName  Asn1Definition

nameString  value

nameString  value
...

The output file is a binary file with the DER encoding.

Usage:  asn1Coding [options] file1 file2
 file1 : file with ASN1 definitions.
 file2 : file with assignments.
Options:
 -h : shows the help message.
 -v : shows version information and exit.
 -c : checks the syntax only.
 -o file : output file.

3.3 Invoking asn1Decoding

asn1Decoding generates an ASN1 structure from a file with ASN1 definitions and a binary file with a DER encoding.

Usage:  asn1Decoding [options] file1 file2 type
 file1 : file with ASN1 definitions.
 file2 : binary file with a DER encoding.
 type : ASN1 definition name.
Options:
 -h : shows the help message.
 -v : shows version information and exit.
 -c : checks the syntax only.
 -o file : output file.

4 Function reference

• ASN.1 schema functions
• ASN.1 field functions
• DER functions
• Error handling functions
• Auxilliary functions

4.1 ASN.1 schema functions

asn1_parser2tree

asn1_parser2array

4.2 ASN.1 field functions

asn1_array2tree

asn1_delete_structure

asn1_delete_element

asn1_create_element

asn1_print_structure

asn1_number_of_elements

asn1_find_structure_from_oid

asn1_copy_node

asn1_write_value

asn1_read_value

asn1_read_tag

4.3 DER functions

asn1_length_der

asn1_octet_der

asn1_bit_der

asn1_der_coding

asn1_get_length_der

asn1_get_tag_der

asn1_get_length_ber

asn1_get_octet_der

asn1_get_bit_der

asn1_der_decoding

asn1_der_decoding_element

asn1_der_decoding_startEnd

asn1_expand_any_defined_by

asn1_expand_octet_string

4.4 Error handling functions

asn1_perror

asn1_strerror

libtasn1_perror

libtasn1_strerror

4.5 Auxilliary functions

asn1_find_node

asn1_check_version

Appendix A Copying Information

• GNU Free Documentation License: License for copying this manual.

A.1 GNU Free Documentation License

     Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     http://fsf.org/
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

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   The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

   This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

   We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

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ADDENDUM: How to use this License for your documents

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Concept Index

• ASN.1 schema: ASN.1 syntax
• asn1Coding program: Invoking asn1Coding
• asn1Decoding program: Invoking asn1Decoding
• asn1Parser program: Invoking asn1Parser
• FDL, GNU Free Documentation License: GNU Free Documentation License
• Future developments: Future developments
• Header file libtasn1.h: Library Notes
• Main type ASN1_TYPE: Library Notes
• Porting: Introduction
• Supported ASN.1 types, list of: ASN.1 syntax
• threads: Introduction

Function and Data Index

• asn1_array2tree: ASN.1 field functions
• asn1_bit_der: DER functions
• asn1_check_version: Auxilliary functions
• asn1_copy_node: ASN.1 field functions
• asn1_create_element: ASN.1 field functions
• asn1_delete_element: ASN.1 field functions
• asn1_delete_structure: ASN.1 field functions
• asn1_der_coding: DER functions
• asn1_der_decoding: DER functions
• asn1_der_decoding_element: DER functions
• asn1_der_decoding_startEnd: DER functions
• asn1_expand_any_defined_by: DER functions
• asn1_expand_octet_string: DER functions
• asn1_find_node: Auxilliary functions
• asn1_find_structure_from_oid: ASN.1 field functions
• asn1_get_bit_der: DER functions
• asn1_get_length_ber: DER functions
• asn1_get_length_der: DER functions
• asn1_get_octet_der: DER functions
• asn1_get_tag_der: DER functions
• asn1_length_der: DER functions
• asn1_number_of_elements: ASN.1 field functions
• asn1_octet_der: DER functions
• asn1_parser2array: ASN.1 schema functions
• asn1_parser2tree: ASN.1 schema functions
• asn1_perror: Error handling functions
• asn1_print_structure: ASN.1 field functions
• asn1_read_tag: ASN.1 field functions
• asn1_read_value: ASN.1 field functions
• asn1_strerror: Error handling functions
• asn1_write_value: ASN.1 field functions
• libtasn1_perror: Error handling functions
• libtasn1_strerror: Error handling functions