ASN.1 structures parser



This is part of the GnuTLS project


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, no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the chapter entitled "GNU Free Documentation License".


Contents

ASN.1 structures handling

Introduction

This document describes the version 0.2.4 of library 'libtasn1' developed for ASN1 (Abstract Syntax Notation One) structures management. The main features of this library are:

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: Version ::=INTEGER the correct one is : Version ::= INTEGER Here is the list of types that the parser can manage:

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.

Naming

With this definitions:

      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". Others examples: Field 'id' in 'Group' type : "Example.Group.id" Field 'value1' in field 'value' in type 'Group': "Example.Group.value.value1" These strings are used in functions that are described below. 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.

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 ASN1 definitions and structures (instances). The constant ASN1_TYPE_EMPTY can be used for the variable initialization.

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: char Description[MAX_ERROR_DESCRIPTION_SIZE];).

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

Future developments

  1. add functions for a C code file generation containing equivalent data structures (not a single array like now).
  2. type REAL

Utilities

asn1Parser

asn1Parser reads one file with ASN1 definitions and generates a file with an array to use with libasn1 functions.

Usage: asn1Parser [options] file

Options:

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

Options:

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

Options:

Function reference


asn1_parser2tree

asn1_retCode asn1_parser2tree ( const char * file_name , ASN1_TYPE * definitions , char * errorDescription )

Arguments

Description

Creates the structures needed to manage the definitions included in *FILE_NAME file.

Returns

ASN1_SUCCESS: the file has a correct syntax and every identifier is known.

ASN1_ELEMENT_NOT_EMPTY: *POINTER not ASN1_TYPE_EMPTY.

ASN1_FILE_NOT_FOUND: an error occured while opening FILE_NAME.

ASN1_SYNTAX_ERROR: the syntax is not correct.

ASN1_IDENTIFIER_NOT_FOUND: in the file there is an identifier that is not defined. ASN1_NAME_TOO_LONG: in the file there is an identifier whith more than MAX_NAME_SIZE characters.


asn1_parser2array

int asn1_parser2array ( const char * inputFileName , const char * outputFileName , const char * vectorName , char * errorDescription )

Arguments

Description

Creates a file containing a C vector to use to manage the definitions included in *INPUTFILENAME file. If *INPUTFILENAME is "/aa/bb/xx.yy" and OUTPUTFILENAME is NULL, the file created is "/aa/bb/xx_asn1_tab.c". If VECTORNAME is NULL the vector name will be "xx_asn1_tab".

Returns

ASN1_SUCCESS: the file has a correct syntax and every identifier is known.

ASN1_FILE_NOT_FOUND: an error occured while opening FILE_NAME.

ASN1_SYNTAX_ERROR: the syntax is not correct.

ASN1_IDENTIFIER_NOT_FOUND: in the file there is an identifier that is not defined. ASN1_NAME_TOO_LONG: in the file there is an identifier whith more than MAX_NAME_SIZE characters.


asn1_der_decoding

asn1_retCode asn1_der_decoding ( ASN1_TYPE * element , const unsigned char * der , int len , char * errorDescription )

Arguments

Description

Fill the structure *ELEMENT with values of a DER encoding string. The sructure must just be created with function 'create_stucture'. If an error accurs during de decoding procedure, the *ELEMENT is deleted and set equal to ASN1_TYPE_EMPTY.

Returns

ASN1_SUCCESS: DER encoding OK

ASN1_ELEMENT_NOT_FOUND: ELEMENT is ASN1_TYPE_EMPTY.

ASN1_TAG_ERROR,ASN1_DER_ERROR: the der encoding doesn't match the structure NAME. *ELEMENT deleted.


asn1_der_decoding_element

asn1_retCode asn1_der_decoding_element ( ASN1_TYPE * structure , const char * elementName , const unsigned char * der , int len , char * errorDescription )

Arguments

Description

Fill the element named ELEMENTNAME with values of a DER encoding string. The sructure must just be created with function 'create_stucture'. The DER vector must contain the encoding string of the whole STRUCTURE. If an error accurs during the decoding procedure, the *STRUCTURE is deleted and set equal to ASN1_TYPE_EMPTY.

Returns

ASN1_SUCCESS: DER encoding OK

ASN1_ELEMENT_NOT_FOUND: ELEMENT is ASN1_TYPE_EMPTY or elementName == NULL.

ASN1_TAG_ERROR,ASN1_DER_ERROR: the der encoding doesn't match the structure STRUCTURE. *ELEMENT deleted.


asn1_der_decoding_startEnd

asn1_retCode asn1_der_decoding_startEnd ( ASN1_TYPE element , const unsigned char * der , int len , const char * name_element , int * start , int * end )

Arguments

Description

Find the start and end point of an element in a DER encoding string. I mean that if you have a der encoding and you have already used the function "asn1_der_decoding" to fill a structure, it may happen that you want to find the piece of string concerning an element of the structure.

Example

the sequence "tbsCertificate" inside an X509 certificate.

Returns

ASN1_SUCCESS: DER encoding OK

ASN1_ELEMENT_NOT_FOUND: ELEMENT is ASN1_TYPE EMPTY or NAME_ELEMENT is not a valid element.

ASN1_TAG_ERROR,ASN1_DER_ERROR: the der encoding doesn't match the structure ELEMENT.


asn1_expand_any_defined_by

asn1_retCode asn1_expand_any_defined_by ( ASN1_TYPE definitions , ASN1_TYPE * element )

Arguments

Description

Expands every "ANY DEFINED BY" element of a structure created from a DER decoding process (asn1_der_decoding function). The element ANY must be defined by an OBJECT IDENTIFIER. The type used to expand the element ANY is the first one following the definition of the actual value of the OBJECT IDENTIFIER.

Description

Expands every "ANY DEFINED BY" element of a structure created from a DER decoding process (asn1_der_decoding function). The element ANY must be defined by an OBJECT IDENTIFIER. The type used to expand the element ANY is the first one following the definition of the actual value of the OBJECT IDENTIFIER.

Returns

ASN1_SUCCESS: substitution OK

ASN1_ERROR_TYPE_ANY: some "ANY DEFINED BY" element couldn't be expanded due to a problem in OBJECT_ID $ \rightarrow$ TYPE association. other errors: result of der decoding process.


asn1_expand_octet_string

asn1_retCode asn1_expand_octet_string ( ASN1_TYPE definitions , ASN1_TYPE * element , const char * octetName , const char * objectName )

Arguments

Description

Expands an "OCTET STRING" element of a structure created from a DER decoding process (asn1_der_decoding function). The type used for expansion is the first one following the definition of the actual value of the OBJECT IDENTIFIER indicated by OBJECTNAME.

Description

Expands an "OCTET STRING" element of a structure created from a DER decoding process (asn1_der_decoding function). The type used for expansion is the first one following the definition of the actual value of the OBJECT IDENTIFIER indicated by OBJECTNAME.

Returns

ASN1_SUCCESS: substitution OK

ASN1_ELEMENT_NOT_FOUND: OBJECTNAME or OCTETNAME are not correct.

ASN1_VALUE_NOT_VALID: wasn't possible to find the type to use for expansion.

other errors: result of der decoding process.


libtasn1_perror

void libtasn1_perror ( asn1_retCode error )

Arguments

Description

This function is like perror(). The only difference is that it accepts an error returned by a libasn1 function.


libtasn1_strerror

const char* libtasn1_strerror ( asn1_retCode error )

Arguments

Description

This function is similar to strerror(). The only difference is that it accepts an error (number) returned by a libasn1 function.


asn1_check_version

const char * asn1_check_version ( const char * req_version )

Arguments

Description

Check that the the version of the library is at minimum the requested one and return the version string; return NULL if the condition is not satisfied. If a NULL is passed to this function, no check is done, but the version string is simply returned.


asn1_array2tree

asn1_retCode asn1_array2tree ( const ASN1_ARRAY_TYPE * array , ASN1_TYPE * definitions , char * errorDescription )

Arguments

Description

Creates the structures needed to manage the ASN1 definitions. ARRAY is a vector created by 'asn1_parser_asn1_file_c' function.

Returns

ASN1_SUCCESS: structure created correctly.

ASN1_ELEMENT_NOT_EMPTY: *DEFINITIONS not ASN1_TYPE_EMPTY

ASN1_IDENTIFIER_NOT_FOUND: in the file there is an identifier that is not defined (see ERRORDESCRIPTION for more information).

ASN1_ARRAY_ERROR: the array pointed by ARRAY is wrong.


asn1_delete_structure

asn1_retCode asn1_delete_structure ( ASN1_TYPE * structure )

Arguments

Description

Deletes the structure *ROOT. At the end *ROOT is setted to ASN1_TYPE_EMPTY.

Returns

ASN1_SUCCESS: everything OK

ASN1_ELEMENT_NOT_FOUND: *root==ASN1_TYPE_EMPTY.


asn1_create_element

asn1_retCode asn1_create_element ( ASN1_TYPE definitions , const char * source_name , ASN1_TYPE * element )

Arguments

Description

Creates a structure called DEST_NAME of type SOURCE_NAME.

Returns

ASN1_SUCCESS: creation OK

ASN1_ELEMENT_NOT_FOUND: SOURCE_NAME isn't known

Example

using "pkix.asn" result=asn1_create_structure(cert_def,"PKIX1.Certificate",cert);


asn1_print_structure

void asn1_print_structure ( FILE * out , ASN1_TYPE structure , const char * name , int mode )

Arguments

Description

Prints on the standard output the structure's tree starting from the NAME element inside the structure *POINTER.


asn1_number_of_elements

asn1_retCode asn1_number_of_elements ( ASN1_TYPE element , const char * name , int * num )

Arguments

Description

Counts the number of elements of a sub-structure called NAME with names equal to "?1","?2", ...

Returns

ASN1_SUCCESS: creation OK ASN1_ELEMENT_NOT_FOUND: NAME isn't known ASN1_GENERIC_ERROR: pointer num equal to NULL


asn1_find_structure_from_oid

const char* asn1_find_structure_from_oid ( ASN1_TYPE definitions , const char * oidValue )

Arguments

Description

Search the structure that is defined just after an OID definition.

Description

Search the structure that is defined just after an OID definition.

Returns

NULL when OIDVALUE not found,

otherwise the pointer to a constant string that contains the element name defined just after the OID.


asn1_write_value

asn1_retCode asn1_write_value ( node_asn * node_root , const char * name , const unsigned char * value , int len )

Arguments

Description

Set the value of one element inside a structure.

Returns

ASN1_SUCCESS: set value OK

ASN1_ELEMENT_NOT_FOUND: NAME is not a valid element.

ASN1_VALUE_NOT_VALID: VALUE has a wrong format.

Examples

description for each type

If an element is OPTIONAL and you want to delete it, you must use the value=NULL and len=0.

Using "pkix.asn":

result=asn1_write_value(cert,"tbsCertificate.issuerUniqueID",NULL,0);


asn1_read_value

asn1_retCode asn1_read_value ( node_asn * root , const char * name , unsigned char * value , int * len )

Arguments

Description

Returns the value of one element inside a structure.

Returns

ASN1_SUCCESS: set value OK

ASN1_ELEMENT_NOT_FOUND: NAME is not a valid element.

ASN1_VALUE_NOT_FOUND: there isn't any value for the element selected.

ASN1_MEM_ERROR: the value vector isn't big enough to store the result. In this case LEN will contain the number of bytes needed.

Examples

a description for each type

If an element is OPTIONAL and the function "read_value" returns ASN1_ELEMENT_NOT_FOUND, it means that this element wasn't present in the der encoding that created the structure. The first element of a SEQUENCE_OF or SET_OF is named "?1". The second one "?2" and so on.


asn1_read_tag

asn1_retCode asn1_read_tag ( node_asn * root , const char * name , int * tagValue , int * classValue )

Arguments

Description

Returns the TAG and the CLASS of one element inside a structure.

CLASS can have one of these constants

ASN1_CLASS_APPLICATION, ASN1_CLASS_UNIVERSAL, ASN1_CLASS_PRIVATE or ASN1_CLASS_CONTEXT_SPECIFIC.

Returns

ASN1_SUCCESS: set value OK

ASN1_ELEMENT_NOT_FOUND: NAME is not a valid element.


asn1_der_coding

asn1_retCode asn1_der_coding ( ASN1_TYPE element , const char * name , unsigned char * der , int * len , char * ErrorDescription )

Arguments

Description

Creates the DER encoding for the NAME structure (inside *POINTER structure).

Returns

ASN1_SUCCESS: DER encoding OK

ASN1_ELEMENT_NOT_FOUND: NAME is not a valid element.

ASN1_VALUE_NOT_FOUND: there is an element without a value.

ASN1_MEM_ERROR: der vector isn't big enough. Also in this case LEN will contain the length needed.

GNU Free Documentation License

Version 1.1, March 2000

Copyright © 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

Preamble

The purpose of this License is to make a manual, textbook, or other written 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.

Applicability and Definitions

This License applies to any manual or other work that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. The ``Document'', below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as ``you''.

A ``Modified Version'' of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

A ``Secondary Section'' is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

The ``Invariant Sections'' are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License.

The ``Cover Texts'' are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License.

A ``Transparent'' copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, whose contents can be viewed and edited directly and straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup has been designed to thwart or discourage subsequent modification by readers is not Transparent. A copy that is not ``Transparent'' is called ``Opaque''.

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LATEX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML designed for human modification. Opaque formats include PostScript, PDF, proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML produced by some word processors for output purposes only.

The ``Title Page'' means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, ``Title Page'' means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

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.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

Copying in Quantity

If you publish printed copies of the Document numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a publicly-accessible computer-network location containing a complete Transparent copy of the Document, free of added material, which the general network-using public has access to download anonymously at no charge using public-standard network protocols. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

Modifications

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

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.

You may add a section entitled ``Endorsements'', provided it contains nothing but endorsements of your Modified Version by various parties - for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

Combining Documents

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

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.''

Collections of Documents

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

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.

Aggregation With Independent Works

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, does not as a whole count as a Modified Version of the Document, provided no compilation copyright is claimed for the compilation. Such a compilation is called an ``aggregate'', and this License does not apply to the other self-contained works thus compiled with the Document, on account of their being thus compiled, if they are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one quarter of the entire aggregate, the Document's Cover Texts may be placed on covers that surround only the Document within the aggregate. Otherwise they must appear on covers around the whole aggregate.

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 provided that you also include the original English version of this License. In case of a disagreement between the translation and the original English version of this License, the original English version will prevail.

Termination

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

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/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

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 © YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. A copy of the license is included in the section entitled ``GNU Free Documentation License''.

If you have no Invariant Sections, write ``with no Invariant Sections'' instead of saying which ones are invariant. If you have no Front-Cover Texts, write ``no Front-Cover Texts'' instead of ``Front-Cover Texts being LIST''; likewise for Back-Cover Texts.

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.



Nikos Mavroyanopoulos 2003-08-25