# GNU Libtasn1 4.2

## Table of Contents

- 1 Introduction
- 2 ASN.1 structure handling
  - 2.1 ASN.1 syntax
  - 2.2 Naming
  - 2.3 Simple parsing
  - 2.4 Library Notes
  - 2.5 Future developments
- 3 Utilities
  - 3.1 Invoking asn1Parser
  - 3.2 Invoking asn1Coding
  - 3.3 Invoking asn1Decoding
- 4 Function reference
  - 4.1 ASN.1 schema functions
  - 4.2 ASN.1 field functions
  - 4.3 DER functions
  - 4.4 Error handling functions
  - 4.5 Auxilliary functions
- Appendix A Copying Information
  - A.1 GNU Free Documentation License
- Concept Index
- Function and Data Index

Next: Introduction, Up: (dir) [Contents][Index]

# Libtasn1

This manual is for GNU Libtasn1 (version 4.2, 27 April 2014), which is a library for Abstract Syntax Notation One (ASN.1) and Distinguished Encoding Rules (DER) manipulation.

Copyright © 2001-2014 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”.

Next: ASN.1 structure handling, Previous: Top, Up: Top [Contents][Index]

## 1 Introduction

This document describes the Libtasn1 library that provides Abstract Syntax Notation One (ASN.1, as specified by the X.680 ITU-T recommendation) parsing and structures management, and Distinguished Encoding Rules (DER, as per X.690) encoding and decoding functions.

The main features of this library are:

- On-line ASN.1 structure management that doesn’t require any C code file generation.
- Off-line ASN.1 structure management with C code file generation containing an array.
- Distinguished Encoding Rules (DER) encoding support.
- 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.
- Thread-safety. No global variables are used and multiple library handles and session handles may be used in parallel.
- Portability. The code should work on all Unix like operating systems, and Windows. The library itself should be portable to any C89 system, not even POSIX is required.

Next: Utilities, Previous: Introduction, Up: Top [Contents][Index]

## 2 ASN.1 structure handling

Next: Naming, Up: ASN.1 structure handling [Contents][Index]

### 2.1 ASN.1 syntax

The parser is case sensitive. The comments begin with `--` and end either with another `--`, or at the end of the respective line, whichever comes first. The C-style `/*`, `*/` comments are not supported.

For an example of the syntax, check the `pkix.asn` file distributed with the library.

ASN.1 definitions must follow the syntax below:

          definitions_name {<object definition>}

          DEFINITIONS <EXPLICIT or IMPLICIT> TAGS ::=

          BEGIN

          <type and constants definitions>

          END

The `::=` token must be separate from other elements, so the following declaration is invalid:

       -- 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`;
- `NumericString`;
- `IA5String`;
- `TeletexString`;
- `PrintableString`;
- `UniversalString`;
- `BMPString`;
- `UTF8String`;
- `VisibleString`;
- `SEQUENCE`;
- `SEQUENCE OF`;
- `SET`;
- `SET OF`;
- `CHOICE`;
- `ANY`;
- `ANY DEFINED BY`.

This version doesn’t handle the `REAL` type. It doesn’t support the `AUTOMATIC TAGS` option, and the `EXPORT` and `IMPORT` sections, either.

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

Next: Simple parsing, Previous: ASN.1 syntax, Up: ASN.1 structure handling [Contents][Index]

### 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

The notation to access the ‘`Group`’ type of the ‘`Example`’ definition above is ‘`Example.Group`’ (as a NUL-terminated string.) Such strings are used in the functions described below.

Others examples:

- field ‘`id`’ of the ‘`Group`’ type: ‘`Example.Group.id`’;
- field ‘`value1`’ of the ‘`value`’ field of the ‘`Group`’ type: ‘`Example.Group.value.value1`’.

Elements of structured types unnamed by the respective definition receive the names `?1`, `?2`, and so on.

The `?LAST` name indicates the last element of a `SET OF` or `SEQUENCE OF`.

Next: Library Notes, Previous: Naming, Up: ASN.1 structure handling [Contents][Index]

### 2.3 Simple parsing

For simple types like `OCTET STRING` the simple parsing functions listed below may be used instead.

- asn1_decode_simple_der
- asn1_encode_simple_der

Next: Future developments, Previous: Simple parsing, Up: ASN.1 structure handling [Contents][Index]

### 2.4 Library Notes

The header file of this library is `libtasn1.h`.

The main type used in it is `asn1_node`, and it’s used to store the ASN.1 definitions and structures (instances).

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

     asn1_node definitions = NULL;

Some functions require an `errorDescription` argument of type `char *`, pointing to a pre-allocated buffer of at least `ASN1_MAX_ERROR_DESCRIPTION_SIZE` bytes size (e.g., as in ‘`char description[ASN1_MAX_ERROR_DESCRIPTION_SIZE];`’).

`ASN1_MAX_NAME_SIZE` is the maximum number of characters allowed for an ASN.1 identifier.

Previous: Library Notes, Up: ASN.1 structure handling [Contents][Index]

### 2.5 Future developments

- Add functions for a C code file generation containing equivalent data structures (not a single array like now).
- The `REAL` type.

Next: Function reference, Previous: ASN.1 structure handling, Up: Top [Contents][Index]

## 3 Utilities

Next: Invoking asn1Coding, Up: Utilities [Contents][Index]

### 3.1 Invoking asn1Parser

`asn1Parser` reads a single file with ASN.1 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.

Next: Invoking asn1Decoding, Previous: Invoking asn1Parser, Up: Utilities [Contents][Index]

### 3.2 Invoking asn1Coding

`asn1Coding` generates a DER encoding from a file with ASN.1 definitions and another one with assignments.

The file with assignments must have this syntax:

    InstanceName  Asn1Definition

    nameString  value

    nameString  value
    ...

To specify the field of a `CHOICE` to be used, specify its name as a value to the `CHOICE` element itself. Use `''` to denote the root element itself. (as in the example below.)

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.

For example, consider an ASN.1 definitions file as follows:

    PKIX1 { }

    DEFINITIONS IMPLICIT TAGS ::=

    BEGIN

    Dss-Sig-Value ::= SEQUENCE {
         r       INTEGER,
         s       INTEGER
    }

    END

And a assignments file as follows:

    dp PKIX1.Dss-Sig-Value

    r 42
    s 47

Running the command below will generate a `assign.out` file, containing the DER encoding of `PKIX1.Dss-Sig-Value`.

    $ asn1Coding pkix.asn assign.asn1

If the root element is of the `CHOICE` type, the assignment file may be like (using the types defined in `pkix.asn`):

    elt PKIX1Implicit88.GeneralName

    ''      dNSName
    dNSName example.org

Previous: Invoking asn1Coding, Up: Utilities [Contents][Index]

### 3.3 Invoking asn1Decoding

`asn1Decoding` generates an ASN.1 structure from a file with ASN.1 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.
     -o file : output file.

For example, after generating the `assign.out` file from the example section of the `asn1Coding` command above, the following invocation will decode the DER data.

    $ asn1Decoding pkix.asn assign.out PKIX1.Dss-Sig-Value

Next: Copying Information, Previous: Utilities, Up: Top [Contents][Index]

## 4 Function reference

Next: ASN.1 field functions, Up: Function reference [Contents][Index]

### 4.1 ASN.1 schema functions

#### asn1_parser2tree

Function: int asn1_parser2tree (const char * file, asn1_node * definitions, char * error_desc)

  file: specify the path and the name of file that contains ASN.1 declarations.

  definitions: return the pointer to the structure created from "file" ASN.1 declarations.

  error_desc: return the error description or an empty string if success.

  Function used to start the parse algorithm. Creates the structures needed to manage the definitions included in `file` file.

  Returns: `ASN1_SUCCESS` if the file has a correct syntax and every identifier is known, `ASN1_ELEMENT_NOT_EMPTY` if `definitions` not `NULL` , `ASN1_FILE_NOT_FOUND` if an error occured while opening `file` , `ASN1_SYNTAX_ERROR` if the syntax is not correct, `ASN1_IDENTIFIER_NOT_FOUND` if in the file there is an identifier that is not defined, `ASN1_NAME_TOO_LONG` if in the file there is an identifier whith more than `ASN1_MAX_NAME_SIZE` characters.

#### asn1_parser2array

Function: int asn1_parser2array (const char * inputFileName, const char * outputFileName, const char * vectorName, char * error_desc)

  inputFileName: specify the path and the name of file that contains ASN.1 declarations.

  outputFileName: specify the path and the name of file that will contain the C vector definition.

  vectorName: specify the name of the C vector.

  error_desc: return the error description or an empty string if success.

  Function that generates a C structure from an ASN1 file. 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` if the file has a correct syntax and every identifier is known, `ASN1_FILE_NOT_FOUND` if an error occured while opening `inputFileName` , `ASN1_SYNTAX_ERROR` if the syntax is not correct, `ASN1_IDENTIFIER_NOT_FOUND` if in the file there is an identifier that is not defined, `ASN1_NAME_TOO_LONG` if in the file there is an identifier whith more than `ASN1_MAX_NAME_SIZE` characters.

Next: DER functions, Previous: ASN.1 schema functions, Up: Function reference [Contents][Index]

### 4.2 ASN.1 field functions

#### asn1_array2tree

Function: int asn1_array2tree (const asn1_static_node * array, asn1_node * definitions, char * errorDescription)

  array: specify the array that contains ASN.1 declarations

  definitions: return the pointer to the structure created by *ARRAY ASN.1 declarations

  errorDescription: return the error description.

  Creates the structures needed to manage the ASN.1 definitions. `array` is a vector created by `asn1_parser2array()` .

  Returns: `ASN1_SUCCESS` if structure was created correctly, `ASN1_ELEMENT_NOT_EMPTY` if * `definitions` not NULL, `ASN1_IDENTIFIER_NOT_FOUND` if in the file there is an identifier that is not defined (see `errorDescription` for more information), `ASN1_ARRAY_ERROR` if the array pointed by `array` is wrong.

#### asn1_delete_structure

Function: int asn1_delete_structure (asn1_node * structure)

  structure: pointer to the structure that you want to delete.

  Deletes the structure * `structure` . At the end, * `structure` is set to NULL.

  Returns: `ASN1_SUCCESS` if successful, `ASN1_ELEMENT_NOT_FOUND` if * `structure` was NULL.

#### asn1_delete_structure2

Function: int asn1_delete_structure2 (asn1_node * structure, unsigned int flags)

  structure: pointer to the structure that you want to delete.

  flags: additional flags (see `ASN1_DELETE_FLAG` )

  Deletes the structure * `structure` . At the end, * `structure` is set to NULL.

  Returns: `ASN1_SUCCESS` if successful, `ASN1_ELEMENT_NOT_FOUND` if * `structure` was NULL.

#### asn1_delete_element

Function: int asn1_delete_element (asn1_node structure, const char * element_name)

  structure: pointer to the structure that contains the element you want to delete.

  element_name: element’s name you want to delete.

  Deletes the element named * `element_name` inside * `structure` .

  Returns: `ASN1_SUCCESS` if successful, `ASN1_ELEMENT_NOT_FOUND` if the `element_name` was not found.

#### asn1_create_element

Function: int asn1_create_element (asn1_node definitions, const char * source_name, asn1_node * element)

  definitions: pointer to the structure returned by "parser_asn1" function

  source_name: the name of the type of the new structure (must be inside p_structure).

  element: pointer to the structure created.

  Creates a structure of type `source_name` . Example using "pkix.asn":

  rc = asn1_create_element(cert_def, "PKIX1.Certificate", certptr);

  Returns: `ASN1_SUCCESS` if creation OK, `ASN1_ELEMENT_NOT_FOUND` if `source_name` is not known.

#### asn1_print_structure

Function: void asn1_print_structure (FILE * out, asn1_node structure, const char * name, int mode)

  out: pointer to the output file (e.g. stdout).

  structure: pointer to the structure that you want to visit.

  name: an element of the structure

  mode: specify how much of the structure to print, can be `ASN1_PRINT_NAME` , `ASN1_PRINT_NAME_TYPE` , `ASN1_PRINT_NAME_TYPE_VALUE` , or `ASN1_PRINT_ALL` .

  Prints on the `out` file descriptor the structure’s tree starting from the `name` element inside the structure `structure` .

#### asn1_number_of_elements

Function: int asn1_number_of_elements (asn1_node element, const char * name, int * num)

  element: pointer to the root of an ASN1 structure.

  name: the name of a sub-structure of ROOT.

  num: pointer to an integer where the result will be stored

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

  Returns: `ASN1_SUCCESS` if successful, `ASN1_ELEMENT_NOT_FOUND` if `name` is not known, `ASN1_GENERIC_ERROR` if pointer `num` is `NULL` .

#### asn1_find_structure_from_oid

Function: const char * asn1_find_structure_from_oid (asn1_node definitions, const char * oidValue)

  definitions: ASN1 definitions

  oidValue: value of the OID to search (e.g. "1.2.3.4").

  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_copy_node

Function: int asn1_copy_node (asn1_node dst, const char * dst_name, asn1_node src, const char * src_name)

  dst: Destination asn1 node.

  dst_name: Field name in destination node.

  src: Source asn1 node.

  src_name: Field name in source node.

  Create a deep copy of a asn1_node variable. That function requires `dst` to be expanded using `asn1_create_element()` .

  Returns: Return `ASN1_SUCCESS` on success.

#### asn1_dup_node

Function: asn1_node asn1_dup_node (asn1_node src, const char * src_name)

  src: Source asn1 node.

  src_name: Field name in source node.

  Create a deep copy of a asn1_node variable. This function will return an exact copy of the provided structure.

  Returns: Return `NULL` on failure.

#### asn1_write_value

Function: int asn1_write_value (asn1_node node_root, const char * name, const void * ivalue, int len)

  node_root: pointer to a structure

  name: the name of the element inside the structure that you want to set.

  ivalue: vector used to specify the value to set. If len is >0, VALUE must be a two’s complement form integer. if len=0 *VALUE must be a null terminated string with an integer value.

  len: number of bytes of *value to use to set the value: value[0]..value[len-1] or 0 if value is a null terminated string

  Set the value of one element inside a structure.

  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);

  Description for each type:

  INTEGER: VALUE must contain a two’s complement form integer.

  value[0]=0xFF , len=1 -> integer=-1. value[0]=0xFF value[1]=0xFF , len=2 -> integer=-1. value[0]=0x01 , len=1 -> integer= 1. value[0]=0x00 value[1]=0x01 , len=2 -> integer= 1. value="123" , len=0 -> integer= 123.

  ENUMERATED: As INTEGER (but only with not negative numbers).

  BOOLEAN: VALUE must be the null terminated string "TRUE" or "FALSE" and LEN != 0.

  value="TRUE" , len=1 -> boolean=TRUE. value="FALSE" , len=1 -> boolean=FALSE.

  OBJECT IDENTIFIER: VALUE must be a null terminated string with each number separated by a dot (e.g. "1.2.3.543.1"). LEN != 0.

  value="1 2 840 10040 4 3" , len=1 -> OID=dsa-with-sha.

  UTCTime: VALUE must be a null terminated string in one of these formats: "YYMMDDhhmmssZ", "YYMMDDhhmmssZ", "YYMMDDhhmmss+hh’mm’", "YYMMDDhhmmss-hh’mm’", "YYMMDDhhmm+hh’mm’", or "YYMMDDhhmm-hh’mm’". LEN != 0.

  value="9801011200Z" , len=1 -> time=Jannuary 1st, 1998 at 12h 00m Greenwich Mean Time

  GeneralizedTime: VALUE must be in one of this format: "YYYYMMDDhhmmss.sZ", "YYYYMMDDhhmmss.sZ", "YYYYMMDDhhmmss.s+hh’mm’", "YYYYMMDDhhmmss.s-hh’mm’", "YYYYMMDDhhmm+hh’mm’", or "YYYYMMDDhhmm-hh’mm’" where ss.s indicates the seconds with any precision like "10.1" or "01.02". LEN != 0

  value="2001010112001.12-0700" , len=1 -> time=Jannuary 1st, 2001 at 12h 00m 01.12s Pacific Daylight Time

  OCTET STRING: VALUE contains the octet string and LEN is the number of octets.

  value="$\backslash$x01$\backslash$x02$\backslash$x03" , len=3 -> three bytes octet string

  GeneralString: VALUE contains the generalstring and LEN is the number of octets.

  value="$\backslash$x01$\backslash$x02$\backslash$x03" , len=3 -> three bytes generalstring

  BIT STRING: VALUE contains the bit string organized by bytes and LEN is the number of bits.

  value="$\backslash$xCF" , len=6 -> bit string="110011" (six bits)

  CHOICE: if NAME indicates a choice type, VALUE must specify one of the alternatives with a null terminated string. LEN != 0. Using "pkix.asn"\:

  result=asn1_write_value(cert, "certificate1.tbsCertificate.subject", "rdnSequence", 1);

  ANY: VALUE indicates the der encoding of a structure. LEN != 0.

  SEQUENCE OF: VALUE must be the null terminated string "NEW" and LEN != 0. With this instruction another element is appended in the sequence. The name of this element will be "?1" if it’s the first one, "?2" for the second and so on.

  Using "pkix.asn"\:

  result=asn1_write_value(cert, "certificate1.tbsCertificate.subject.rdnSequence", "NEW", 1);

  SET OF: the same as SEQUENCE OF. Using "pkix.asn":

  result=asn1_write_value(cert, "tbsCertificate.subject.rdnSequence.?LAST", "NEW", 1);

  Returns: `ASN1_SUCCESS` if the value was set, `ASN1_ELEMENT_NOT_FOUND` if `name` is not a valid element, and `ASN1_VALUE_NOT_VALID` if `ivalue` has a wrong format.

#### asn1_read_value

Function: int asn1_read_value (asn1_node root, const char * name, void * ivalue, int * len)

  root: pointer to a structure.

  name: the name of the element inside a structure that you want to read.

  ivalue: vector that will contain the element’s content, must be a pointer to memory cells already allocated (may be `NULL` ).

  len: number of bytes of *value: value[0]..value[len-1]. Initialy holds the sizeof value.

  Returns the value of one element inside a structure. If an element is OPTIONAL and this 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. If the `root` provided is a node to specific sequence element, then the keyword "?CURRENT" is also acceptable and indicates the current sequence element of this node.

  Note that there can be valid values with length zero. In these case this function will succeed and `len` will be zero.

  INTEGER: VALUE will contain a two’s complement form integer.

  integer=-1 -> value[0]=0xFF , len=1. integer=1 -> value[0]=0x01 , len=1.

  ENUMERATED: As INTEGER (but only with not negative numbers).

  BOOLEAN: VALUE will be the null terminated string "TRUE" or "FALSE" and LEN=5 or LEN=6.

  OBJECT IDENTIFIER: VALUE will be a null terminated string with each number separated by a dot (i.e. "1.2.3.543.1").

  LEN = strlen(VALUE)+1

  UTCTime: VALUE will be a null terminated string in one of these formats: "YYMMDDhhmmss+hh’mm’" or "YYMMDDhhmmss-hh’mm’". LEN=strlen(VALUE)+1.

  GeneralizedTime: VALUE will be a null terminated string in the same format used to set the value.

  OCTET STRING: VALUE will contain the octet string and LEN will be the number of octets.

  GeneralString: VALUE will contain the generalstring and LEN will be the number of octets.

  BIT STRING: VALUE will contain the bit string organized by bytes and LEN will be the number of bits.

  CHOICE: If NAME indicates a choice type, VALUE will specify the alternative selected.

  ANY: If NAME indicates an any type, VALUE will indicate the DER encoding of the structure actually used.

  Returns: `ASN1_SUCCESS` if value is returned, `ASN1_ELEMENT_NOT_FOUND` if `name` is not a valid element, `ASN1_VALUE_NOT_FOUND` if there isn’t any value for the element selected, and `ASN1_MEM_ERROR` if The value vector isn’t big enough to store the result, and in this case `len` will contain the number of bytes needed.

#### asn1_read_value_type

Function: int asn1_read_value_type (asn1_node root, const char * name, void * ivalue, int * len, unsigned int * etype)

  root: pointer to a structure.

  name: the name of the element inside a structure that you want to read.

  ivalue: vector that will contain the element’s content, must be a pointer to memory cells already allocated (may be `NULL` ).

  len: number of bytes of *value: value[0]..value[len-1]. Initialy holds the sizeof value.

  etype: The type of the value read (ASN1_ETYPE)

  Returns the type and value of one element inside a structure. If an element is OPTIONAL and this 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. If the `root` provided is a node to specific sequence element, then the keyword "?CURRENT" is also acceptable and indicates the current sequence element of this node.

  Note that there can be valid values with length zero. In these case this function will succeed and `len` will be zero.

  INTEGER: VALUE will contain a two’s complement form integer.

  integer=-1 -> value[0]=0xFF , len=1. integer=1 -> value[0]=0x01 , len=1.

  ENUMERATED: As INTEGER (but only with not negative numbers).

  BOOLEAN: VALUE will be the null terminated string "TRUE" or "FALSE" and LEN=5 or LEN=6.

  OBJECT IDENTIFIER: VALUE will be a null terminated string with each number separated by a dot (i.e. "1.2.3.543.1").

  LEN = strlen(VALUE)+1

  UTCTime: VALUE will be a null terminated string in one of these formats: "YYMMDDhhmmss+hh’mm’" or "YYMMDDhhmmss-hh’mm’". LEN=strlen(VALUE)+1.

  GeneralizedTime: VALUE will be a null terminated string in the same format used to set the value.

  OCTET STRING: VALUE will contain the octet string and LEN will be the number of octets.

  GeneralString: VALUE will contain the generalstring and LEN will be the number of octets.

  BIT STRING: VALUE will contain the bit string organized by bytes and LEN will be the number of bits.

  CHOICE: If NAME indicates a choice type, VALUE will specify the alternative selected.

  ANY: If NAME indicates an any type, VALUE will indicate the DER encoding of the structure actually used.

  Returns: `ASN1_SUCCESS` if value is returned, `ASN1_ELEMENT_NOT_FOUND` if `name` is not a valid element, `ASN1_VALUE_NOT_FOUND` if there isn’t any value for the element selected, and `ASN1_MEM_ERROR` if The value vector isn’t big enough to store the result, and in this case `len` will contain the number of bytes needed.

#### asn1_read_tag

Function: int asn1_read_tag (asn1_node root, const char * name, int * tagValue, int * classValue)

  root: pointer to a structure

  name: the name of the element inside a structure.

  tagValue: variable that will contain the TAG value.

  classValue: variable that will specify the TAG type.

  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` if successful, `ASN1_ELEMENT_NOT_FOUND` if `name` is not a valid element.

#### asn1_read_node_value

Function: int asn1_read_node_value (asn1_node node, asn1_data_node_st * data)

  node: pointer to a node.

  data: a point to a asn1_data_node_st

  Returns the value a data node inside a asn1_node structure. The data returned should be handled as constant values.

  Returns: `ASN1_SUCCESS` if the node exists.

Next: Error handling functions, Previous: ASN.1 field functions, Up: Function reference [Contents][Index]

### 4.3 DER functions

#### asn1_length_der

Function: void asn1_length_der (unsigned long int len, unsigned char * der, int * der_len)

  len: value to convert.

  der: buffer to hold the returned encoding (may be `NULL` ).

  der_len: number of meaningful bytes of ANS (der[0]..der[der_len-1]).

  Creates the DER encoding of the provided length value. The `der` buffer must have enough room for the output. The maximum length this function will encode is `ASN1_MAX_LENGTH_SIZE` .

  To know the size of the DER encoding use a `NULL` value for `der` .

#### asn1_octet_der

Function: void asn1_octet_der (const unsigned char * str, int str_len, unsigned char * der, int * der_len)

  str: the input data.

  str_len: STR length (str[0]..str[*str_len-1]).

  der: encoded string returned.

  der_len: number of meaningful bytes of DER (der[0]..der[der_len-1]).

  Creates a length-value DER encoding for the input data. The DER encoding of the input data will be placed in the `der` variable.

  Note that the OCTET STRING tag is not included in the output.

  This function does not return any value because it is expected that `der_len` will contain enough bytes to store the string plus the DER encoding. The DER encoding size can be obtained using `asn1_length_der()` .

#### asn1_encode_simple_der

Function: int asn1_encode_simple_der (unsigned int etype, const unsigned char * str, unsigned int str_len, unsigned char * tl, unsigned int * tl_len)

  etype: The type of the string to be encoded (ASN1_ETYPE_)

  str: the string data.

  str_len: the string length

  tl: the encoded tag and length

  tl_len: the bytes of the `tl` field

  Creates the DER encoding for various simple ASN.1 types like strings etc. It stores the tag and length in `tl` , which should have space for at least `ASN1_MAX_TL_SIZE` bytes. Initially `tl_len` should contain the size of `tl` .

  The complete DER encoding should consist of the value in `tl` appended with the provided `str` .

  Returns: `ASN1_SUCCESS` if successful or an error value.

#### asn1_bit_der

Function: void asn1_bit_der (const unsigned char * str, int bit_len, unsigned char * der, int * der_len)

  str: BIT string.

  bit_len: number of meaningful bits in STR.

  der: string returned.

  der_len: number of meaningful bytes of DER (der[0]..der[ans_len-1]).

  Creates a length-value DER encoding for the input data as it would have been for a BIT STRING. The DER encoded data will be copied in `der` .

  Note that the BIT STRING tag is not included in the output.

  This function does not return any value because it is expected that `der_len` will contain enough bytes to store the string plus the DER encoding. The DER encoding size can be obtained using `asn1_length_der()` .

#### asn1_der_coding

Function: int asn1_der_coding (asn1_node element, const char * name, void * ider, int * len, char * ErrorDescription)

  element: pointer to an ASN1 element

  name: the name of the structure you want to encode (it must be inside *POINTER).

  ider: vector that will contain the DER encoding. DER must be a pointer to memory cells already allocated.

  len: number of bytes of * `ider` : `ider` [0].. `ider` [len-1], Initialy holds the sizeof of der vector.

  ErrorDescription: return the error description or an empty string if success.

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

  Returns: `ASN1_SUCCESS` if DER encoding OK, `ASN1_ELEMENT_NOT_FOUND` if `name` is not a valid element, `ASN1_VALUE_NOT_FOUND` if there is an element without a value, `ASN1_MEM_ERROR` if the `ider` vector isn’t big enough and in this case `len` will contain the length needed.

#### asn1_get_length_der

Function: long asn1_get_length_der (const unsigned char * der, int der_len, int * len)

  der: DER data to decode.

  der_len: Length of DER data to decode.

  len: Output variable containing the length of the DER length field.

  Extract a length field from DER data.

  Returns: Return the decoded length value, or -1 on indefinite length, or -2 when the value was too big to fit in a int, or -4 when the decoded length value plus `len` would exceed `der_len` .

#### asn1_get_tag_der

Function: int asn1_get_tag_der (const unsigned char * der, int der_len, unsigned char * cls, int * len, unsigned long * tag)

  der: DER data to decode.

  der_len: Length of DER data to decode.

  cls: Output variable containing decoded class.

  len: Output variable containing the length of the DER TAG data.

  tag: Output variable containing the decoded tag.

  Decode the class and TAG from DER code.

  Returns: Returns `ASN1_SUCCESS` on success, or an error.

#### asn1_get_length_ber

Function: long asn1_get_length_ber (const unsigned char * ber, int ber_len, int * len)

  ber: BER data to decode.

  ber_len: Length of BER data to decode.

  len: Output variable containing the length of the BER length field.

  Extract a length field from BER data. The difference to `asn1_get_length_der()` is that this function will return a length even if the value has indefinite encoding.

  Returns: Return the decoded length value, or negative value when the value was too big.

  Since: 2.0

#### asn1_get_octet_der

Function: int asn1_get_octet_der (const unsigned char * der, int der_len, int * ret_len, unsigned char * str, int str_size, int * str_len)

  der: DER data to decode containing the OCTET SEQUENCE.

  der_len: Length of DER data to decode.

  ret_len: Output variable containing the length of the DER data.

  str: Pre-allocated output buffer to put decoded OCTET SEQUENCE in.

  str_size: Length of pre-allocated output buffer.

  str_len: Output variable containing the length of the OCTET SEQUENCE.

  Extract an OCTET SEQUENCE from DER data.

  Returns: Returns `ASN1_SUCCESS` on success, or an error.

#### asn1_get_bit_der

Function: int asn1_get_bit_der (const unsigned char * der, int der_len, int * ret_len, unsigned char * str, int str_size, int * bit_len)

  der: DER data to decode containing the BIT SEQUENCE.

  der_len: Length of DER data to decode.

  ret_len: Output variable containing the length of the DER data.

  str: Pre-allocated output buffer to put decoded BIT SEQUENCE in.

  str_size: Length of pre-allocated output buffer.

  bit_len: Output variable containing the size of the BIT SEQUENCE.

  Extract a BIT SEQUENCE from DER data.

  Returns: Return `ASN1_SUCCESS` on success, or an error.

#### asn1_der_decoding2

Function: int asn1_der_decoding2 (asn1_node * element, const void * ider, int * max_ider_len, unsigned int flags, char * errorDescription)

  element: pointer to an ASN1 structure.

  ider: vector that contains the DER encoding.

  max_ider_len: pointer to an integer giving the information about the maximal number of bytes occupied by * `ider` . The real size of the DER encoding is returned through this pointer.

  flags: flags controlling the behaviour of the function.

  errorDescription: null-terminated string contains details when an error occurred.

  Fill the structure * `element` with values of a DER encoding string. The structure must just be created with function `asn1_create_element()` .

  If `ASN1_DECODE_FLAG_ALLOW_PADDING` flag is set then the function will ignore padding after the decoded DER data. Upon a successful return the value of * `max_ider_len` will be set to the number of bytes decoded.

  Returns: `ASN1_SUCCESS` if DER encoding OK, `ASN1_ELEMENT_NOT_FOUND` if `ELEMENT` is `NULL` , and `ASN1_TAG_ERROR` or `ASN1_DER_ERROR` if the der encoding doesn’t match the structure name (* `ELEMENT` deleted).

#### asn1_der_decoding

Function: int asn1_der_decoding (asn1_node * element, const void * ider, int ider_len, char * errorDescription)

  element: pointer to an ASN1 structure.

  ider: vector that contains the DER encoding.

  ider_len: number of bytes of * `ider` : `ider` [0].. `ider` [len-1].

  errorDescription: null-terminated string contains details when an error occurred.

  Fill the structure * `element` with values of a DER encoding string. The structure must just be created with function `asn1_create_element()` .

  Note that the * `element` variable is provided as a pointer for historical reasons.

  Returns: `ASN1_SUCCESS` if DER encoding OK, `ASN1_ELEMENT_NOT_FOUND` if `ELEMENT` is `NULL` , and `ASN1_TAG_ERROR` or `ASN1_DER_ERROR` if the der encoding doesn’t match the structure name (* `ELEMENT` deleted).

#### asn1_der_decoding_element

Function: int asn1_der_decoding_element (asn1_node * structure, const char * elementName, const void * ider, int len, char * errorDescription)

  structure: pointer to an ASN1 structure

  elementName: name of the element to fill

  ider: vector that contains the DER encoding of the whole structure.

  len: number of bytes of *der: der[0]..der[len-1]

  errorDescription: null-terminated string contains details when an error occurred.

  Fill the element named `ELEMENTNAME` with values of a DER encoding string. The structure must just be created with function `asn1_create_element()` . The DER vector must contain the encoding string of the whole `STRUCTURE` . If an error occurs during the decoding procedure, the * `STRUCTURE` is deleted and set equal to `NULL` .

  This function is deprecated and may just be an alias to asn1_der_decoding in future versions. Use `asn1_der_decoding()` instead.

  Returns: `ASN1_SUCCESS` if DER encoding OK, `ASN1_ELEMENT_NOT_FOUND` if ELEMENT is `NULL` or `elementName` == NULL, and `ASN1_TAG_ERROR` or `ASN1_DER_ERROR` if the der encoding doesn’t match the structure `structure` (*ELEMENT deleted).

#### asn1_der_decoding_startEnd

Function: int asn1_der_decoding_startEnd (asn1_node element, const void * ider, int ider_len, const char * name_element, int * start, int * end)

  element: pointer to an ASN1 element

  ider: vector that contains the DER encoding.

  ider_len: number of bytes of * `ider` : `ider` [0].. `ider` [len-1]

  name_element: an element of NAME structure.

  start: the position of the first byte of NAME_ELEMENT decoding ( `ider` [*start])

  end: the position of the last byte of NAME_ELEMENT decoding ( `ider` [*end])

  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.

  One example is the sequence "tbsCertificate" inside an X509 certificate.

  Note that since libtasn1 3.7 the `ider` and `ider_len` parameters can be omitted, if the element is already decoded using `asn1_der_decoding()` .

  Returns: `ASN1_SUCCESS` if DER encoding OK, `ASN1_ELEMENT_NOT_FOUND` if ELEMENT is `asn1_node` EMPTY or `name_element` is not a valid element, `ASN1_TAG_ERROR` or `ASN1_DER_ERROR` if the der encoding doesn’t match the structure ELEMENT.

#### asn1_expand_any_defined_by

Function: int asn1_expand_any_defined_by (asn1_node definitions, asn1_node * element)

  definitions: ASN1 definitions

  element: pointer to an ASN1 structure

  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` if Substitution OK, `ASN1_ERROR_TYPE_ANY` if some "ANY DEFINED BY" element couldn’t be expanded due to a problem in OBJECT_ID -> TYPE association, or other error codes depending on DER decoding.

#### asn1_expand_octet_string

Function: int asn1_expand_octet_string (asn1_node definitions, asn1_node * element, const char * octetName, const char * objectName)

  definitions: ASN1 definitions

  element: pointer to an ASN1 structure

  octetName: name of the OCTECT STRING field to expand.

  objectName: name of the OBJECT IDENTIFIER field to use to define the type for expansion.

  Expands an "OCTET STRING" element of a structure created from a DER decoding process (the `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` if substitution OK, `ASN1_ELEMENT_NOT_FOUND` if `objectName` or `octetName` are not correct, `ASN1_VALUE_NOT_VALID` if it wasn’t possible to find the type to use for expansion, or other errors depending on DER decoding.

#### asn1_decode_simple_der

Function: int asn1_decode_simple_der (unsigned int etype, const unsigned char * der, unsigned int der_len, const unsigned char ** str, unsigned int * str_len)

  etype: The type of the string to be encoded (ASN1_ETYPE_)

  der: the encoded string

  der_len: the bytes of the encoded string

  str: a pointer to the data

  str_len: the length of the data

  Decodes a simple DER encoded type (e.g. a string, which is not constructed). The output is a pointer inside the `der` .

  Returns: `ASN1_SUCCESS` if successful or an error value.

Next: Auxilliary functions, Previous: DER functions, Up: Function reference [Contents][Index]

### 4.4 Error handling functions

#### asn1_perror

Function: void asn1_perror (int error)

  error: is an error returned by a libtasn1 function.

  Prints a string to stderr with a description of an error. This function is like `perror()` . The only difference is that it accepts an error returned by a libtasn1 function.

  Since: 1.6

#### asn1_strerror

Function: const char * asn1_strerror (int error)

  error: is an error returned by a libtasn1 function.

  Returns a string with a description of an error. This function is similar to strerror. The only difference is that it accepts an error (number) returned by a libtasn1 function.

  Returns: Pointer to static zero-terminated string describing error code.

  Since: 1.6

Previous: Error handling functions, Up: Function reference [Contents][Index]

### 4.5 Auxilliary functions

#### asn1_find_node

Function: asn1_node asn1_find_node (asn1_node pointer, const char * name)

  pointer: NODE_ASN element pointer.

  name: null terminated string with the element’s name to find.

  Searches for an element called `name` starting from `pointer` . The name is composed by differents identifiers separated by dots. When * `pointer` has a name, the first identifier must be the name of * `pointer` , otherwise it must be the name of one child of * `pointer` .

  Returns: the search result, or `NULL` if not found.

#### asn1_check_version

Function: const char * asn1_check_version (const char * req_version)

  req_version: Required version number, or `NULL` .

  Check that 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.

  See `ASN1_VERSION` for a suitable `req_version` string.

  Returns: Version string of run-time library, or `NULL` if the run-time library does not meet the required version number.

Next: Concept Index, Previous: Function reference, Up: Top [Contents][Index]

## Appendix A Copying Information

Up: Copying Information [Contents][Index]

### A.1 GNU Free Documentation License

Version 1.3, 3 November 2008

    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.

1. 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.

2. APPLICABILITY AND DEFINITIONS

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   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.

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3. VERBATIM COPYING

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5. MODIFICATIONS

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   1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
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6. 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, and that you preserve all their Warranty Disclaimers.

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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.”

7. COLLECTIONS OF DOCUMENTS

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### ADDENDUM: How to use this License for your documents

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Next: Function and Data Index, Previous: Copying Information, Up: Top [Contents][Index]

## Concept Index

Jump to: | A F H M P S T

| Index Entry |  | Section
A |  |
| ASN.1 schema: |  | ASN.1 syntax
| asn1Coding program: |  | Invoking asn1Coding
| asn1Decoding program: |  | Invoking asn1Decoding
| asn1Parser program: |  | Invoking asn1Parser
F |  |
| FDL, GNU Free Documentation License: |  | GNU Free Documentation License
| Future developments: |  | Future developments
H |  |
| Header file libtasn1.h: |  | Library Notes
M |  |
| Main type asn1_node: |  | Library Notes
P |  |
| Porting: |  | Introduction
S |  |
| Supported ASN.1 types, list of: |  | ASN.1 syntax
T |  |
| threads: |  | Introduction

Jump to: | A F H M P S T

Previous: Concept Index, Up: Top [Contents][Index]

## Function and Data Index

Jump to: | A

| Index Entry |  | Section
A |  |
| `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_decode_simple_der`: |  | DER functions
| `asn1_delete_element`: |  | ASN.1 field functions
| `asn1_delete_structure`: |  | ASN.1 field functions
| `asn1_delete_structure2`: |  | ASN.1 field functions
| `asn1_der_coding`: |  | DER functions
| `asn1_der_decoding`: |  | DER functions
| `asn1_der_decoding2`: |  | DER functions
| `asn1_der_decoding_element`: |  | DER functions
| `asn1_der_decoding_startEnd`: |  | DER functions
| `asn1_dup_node`: |  | ASN.1 field functions
| `asn1_encode_simple_der`: |  | 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_node_value`: |  | ASN.1 field functions
| `asn1_read_tag`: |  | ASN.1 field functions
| `asn1_read_value`: |  | ASN.1 field functions
| `asn1_read_value_type`: |  | ASN.1 field functions
| `asn1_strerror`: |  | Error handling functions
| `asn1_write_value`: |  | ASN.1 field functions

Jump to: | A