Libtasn1 0.3.2

Libtasn1

This manual is for Libtasn1 (version 0.3.2, 11 February 2006), which is a library for Abstract Syntax Notation One (ASN.1) and Distinguish Encoding Rules (DER) manipulation.

Copyright © 2004, 2006 Free Software Foundation

Copyright © 2001, 2002, 2003 Fabio Fiorina

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”

(a) The FSF's Back-Cover Text is: “You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.”

• ASN.1 structure handling
• Utilities
• Function reference
• Copying This Manual

Indices

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

1 ASN.1 structure handling

This document describes the Libtasn1 library developed for ASN.1 (Abstract Syntax Notation One) structures management.

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.
• 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.

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

1.1 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.

1.2 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.

1.3 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 MAX_ERROR_DESCRIPTION_SIZE bytes (E.g, as in char Description[MAX_ERROR_DESCRIPTION_SIZE];).

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

1.4 Future developments

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

2 Utilities

• Invoking asn1Parser
• Invoking asn1Coding
• Invoking asn1Decoding

2.1 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.

2.2 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.

2.3 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.

3 Function reference

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

3.1 ASN.1 schema functions

3.2 ASN.1 field functions

3.3 DER functions

3.4 Error handling functions

3.5 Auxilliary functions

Appendix A Copying This Manual

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

A.1 GNU Free Documentation License

     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA
     
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

0. PREAMBLE

   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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2. VERBATIM COPYING

   You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

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4. MODIFICATIONS

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   11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
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   If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

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5. COMBINING DOCUMENTS

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   In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”

6. COLLECTIONS OF DOCUMENTS

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   You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

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8. TRANSLATION

   Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

   If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

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10. FUTURE REVISIONS OF THIS LICENSE

    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

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A.1.1 ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       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''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

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         the Front-Cover Texts being list, and with the Back-Cover Texts
         being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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: ASN.1 structure handling
• Supported ASN.1 types, list of: ASN.1 syntax
• threads: ASN.1 structure handling

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_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_print_structure: ASN.1 field functions
• asn1_read_tag: ASN.1 field functions
• asn1_read_value: ASN.1 field functions
• asn1_write_value: ASN.1 field functions
• libtasn1_perror: Error handling functions
• libtasn1_strerror: Error handling functions