Convert::ASN1

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME

Convert::ASN1 - ASN.1 Encode/Decode library

VERSION

version 0.27

SYNOPSYS

  use Convert::ASN1;

  $asn = Convert::ASN1->new;
  $asn->prepare(q<

    [APPLICATION 7] SEQUENCE {
      int INTEGER,
      str OCTET STRING
    }

  >);

  $pdu = $asn->encode( int => 7, str => "string");

  $out = $asn->decode($pdu);
  print $out->{int}," ",$out->{str},"\n";

  use Convert::ASN1 qw(:io);

  $peer   = asn_recv($sock,$buffer,0);
  $nbytes = asn_read($fh, $buffer);
  $nbytes = asn_send($sock, $buffer, $peer);
  $nbytes = asn_send($sock, $buffer);
  $nbytes = asn_write($fh, $buffer);
  $buffer = asn_get($fh);
  $yes    = asn_ready($fh)

DESCRIPTION

Convert::ASN1 encodes and decodes ASN.1 data structures using BER/DER rules.

METHODS

new ( [OPTIONS] )

Contructor, creates a new object.

If given, OPTIONS are the same ones as for ``configure ( OPTIONS )'' below.

error ()

Returns the last error.

configure ( OPTIONS )

Configure options to control how Convert::ASN1 will perform various tasks. Options are passed as name-value pairs.

encode: Reference to a hash which contains various encode options.
decode: Reference to a hash which contains various decode options.
encoding: One of 'BER' or 'DER'. The default is 'BER'
tagdefault: One of 'EXPLICIT' or 'IMPLICIT'. Default tagging conventions are normally given in the ASN.1 module definition (not supported by the parser). The ASN.1 spec states EXPLICIT tagging is the default, but this option has IMPLICIT tagging default for backward compatibility reasons.

Encode options

real

Which encoding to use for real's. One of 'binary', 'nr1', 'nr2', 'nr3'

time

This controls how UTCTime and GeneralizedTime elements are encoded. The default is "withzone".

utctime: The value passed will be encoded without a zone, ie a UTC value.
withzone: The value will be encoded with a zone. By default it will be encoded using the local time offset. The offset may be set using the "timezone" configure option.
raw: The value passed should already be in the correct format and will be copied into the PDU as-is.

timezone

By default UTCTime and GeneralizedTime will be encoded using the local time offset from UTC. This will over-ride that. It is an offset from UTC in seconds. This option can be overridden by passing a reference to a list of two values as the time value. The list should contain the time value and the offset from UTC in seconds.

bigint

If during encoding an value greater than 32 bits is discovered and is not already a big integer object, then the value will first be converted into a big integer object. This option controls the big integer class into which the objects will be blessed. The default is to use Math::BigInt

Decode options

time

This controls how a UTCTime or a GeneralizedTime element will be decoded. The default is "utctime".

utctime: The value returned will be a time value as returned by the "time" function.
withzone: The value returned will be a reference to an array of two values. The first is the same as with "utctime", the second is the timezone offset, in seconds, that was used in the encoding.
raw: The value returned will be the raw encoding as extracted from the PDU.

bigint

If during decoding any big integers are discovered (integers greater than 32 bits), they will be decoded into big integer objects. This option controls the big integer class into which the objects will be blessed. The default is to use Math::BigInt.

null

The value to decode ASN.1 NULL types into. If not set, it defaults to 1.

prepare ( ASN )

Compile the given ASN.1 descripton which can be passed as a string or as a filehandle. The syntax used is very close to ASN.1, but has a few differences. If the ASN decribes only one macro then encode/decode can be called on this object. If ASN describes more than one ASN.1 macro then "find" must be called. The method returns undef on error.

prepare_file ( ASNPATH )

Compile the ASN.1 description to be read from the specified pathname.

find ( MACRO )

Find a macro from a prepared ASN.1 description. Returns an object which can be used for encode/decode.

encode ( VARIABLES )

Encode a PDU. Top-level variable are passed as name-value pairs, or as a reference to a hash containing them. Returns the encoded PDU, or undef on error.

decode ( PDU )

Decode the PDU, returns a reference to a hash containg the values for the PDU. Returns undef if there was an error.

registeroid ( OID, HANDLER )

HANDLER must be a Convert::ASN1 object, e.g. as returned by ``find ( MACRO )''.

registertype ( NAME, OID, HANDLER )

HANDLER must be a Convert::ASN1 object, e.g. as returned by ``find ( MACRO )''.

EXPORTS

As well as providing an object interface for encoding/decoding PDUs Convert::ASN1 also provides the following functions.

IO Functions

asn_recv ( SOCK, BUFFER, FLAGS )

Will read a single element from the socket SOCK into BUFFER. FLAGS may be MSG_PEEK as exported by "Socket". Returns the address of the sender, or undef if there was an error. Some systems do not support the return of the peer address when the socket is a connected socket, in these cases the empty string will be returned. This is the same behaviour as the "recv" function in perl itself.

It is recommended that if the socket is of type SOCK_DGRAM then "recv" be called directly instead of calling "asn_recv".

asn_read ( FH, BUFFER, OFFSET )

asn_read ( FH, BUFFER )

Will read a single element from the filehandle FH into BUFFER. Returns the number of bytes read if a complete element was read, -1 if an incomplete element was read or undef if there was an error. If OFFSET is specified then it is assumed that BUFFER already contains an incomplete element and new data will be appended starting at OFFSET.

If FH is a socket the asn_recv is used to read the element, so the same restiction applies if FH is a socket of type SOCK_DGRAM.

asn_send ( SOCK, BUFFER, FLAGS, TO )

asn_send ( SOCK, BUFFER, FLAGS )

Identical to calling "send", see perlfunc

asn_write ( FH, BUFFER )

Identical to calling "syswrite" with 2 arguments, see perlfunc

asn_get ( FH )

"asn_get" provides buffered IO. Because it needs a buffer FH must be a GLOB or a reference to a GLOB. "asn_get" will use two entries in the hash element of the GLOB to use as its buffer:

  asn_buffer - input buffer
  asn_need   - number of bytes needed for the next element, if known

Returns an element or undef if there was an error.

asn_ready ( FH )

"asn_ready" works with "asn_get". It will return true if "asn_get" has already read enough data into the buffer to return a complete element.

Encode/Decode Functions

asn_tag ( CLASS, VALUE ): Given CLASS and a VALUE, calculate an integer which when encoded will become the tag.
asn_decode_tag ( TAG ): Decode the given ASN.1 encoded "TAG".
asn_encode_tag ( TAG ): Encode TAG value for encoding. We assume that the tag has been correctly generated with ``asn_tag ( CLASS, VALUE )''.
asn_decode_length ( LEN ): Decode the given ASN.1 decoded "LEN".
asn_encode_length ( LEN ): Encode the given "LEN" to its ASN.1 encoding.

Constants

ASN_BIT_STR
ASN_BOOLEAN
ASN_ENUMERATED
ASN_GENERAL_TIME
ASN_IA5_STR
ASN_INTEGER
ASN_NULL
ASN_OBJECT_ID
ASN_OCTET_STR
ASN_PRINT_STR
ASN_REAL
ASN_SEQUENCE
ASN_SET
ASN_UTC_TIME
ASN_APPLICATION
ASN_CONTEXT
ASN_PRIVATE
ASN_UNIVERSAL
ASN_PRIMITIVE
ASN_CONSTRUCTOR
ASN_LONG_LEN
ASN_EXTENSION_ID
ASN_BIT

Debug Functions

asn_dump ( [FH,] BUFFER ): Try to decode the given buffer as ASN.1 structure and dump it to the given file handle, or "STDERR" if the handle is not given.
asn_hexdump ( FH, BUFFER )

EXPORT TAGS

:all: All exported functions
:const: ASN_BOOLEAN, ASN_INTEGER, ASN_BIT_STR, ASN_OCTET_STR, ASN_NULL, ASN_OBJECT_ID, ASN_REAL, ASN_ENUMERATED, ASN_SEQUENCE, ASN_SET, ASN_PRINT_STR, ASN_IA5_STR, ASN_UTC_TIME, ASN_GENERAL_TIME, ASN_UNIVERSAL, ASN_APPLICATION, ASN_CONTEXT, ASN_PRIVATE, ASN_PRIMITIVE, ASN_CONSTRUCTOR, ASN_LONG_LEN, ASN_EXTENSION_ID, ASN_BIT
:debug: asn_dump, asn_hexdump
:io: asn_recv, asn_send, asn_read, asn_write, asn_get, asn_ready
:tag: asn_tag, asn_decode_tag, asn_encode_tag, asn_decode_length, asn_encode_length

MAPPING ASN.1 TO PERL

Every element in the ASN.1 definition has a name, in perl a hash is used with these names as an index and the element value as the hash value.

  # ASN.1
  int INTEGER,
  str OCTET STRING

  # Perl
  { int => 5, str => "text" }

In the case of a SEQUENCE, SET or CHOICE then the value in the namespace will be a hash reference which will be the namespce for the elements with that element.

  # ASN.1
  int INTEGER,
  seq SEQUENCE {
    str OCTET STRING,
    bool BOOLEAN
  }

  # Perl
  { int => 5, seq => { str => "text", bool => 1}}

If the element is a SEQUENCE OF, or SET OF, then the value in the namespace will be an array reference. The elements in the array will be of the type expected by the type following the OF. For example with ``SEQUENCE OF STRING'' the array would contain strings. With ``SEQUENCE OF SEQUENCE { ... }'' the array will contain hash references which will be used as namespaces

  # ASN.1
  int INTEGER,
  str SEQUENCE OF OCTET STRING

  # Perl
  { int => 5, str => [ "text1", "text2"]}

  # ASN.1
  int INTEGER,
  str SEQUENCE OF SEQUENCE {
    type OCTET STRING,
    value INTEGER
  }

  # Perl
  { int => 5, str => [
    { type => "abc", value => 4 },
    { type => "def", value => -1 },
  ]}

Finally, if you wish to pre-parse ASN.1 and hold it to include inline in your PDU, you can coerce it into the ASN.1 spec by defining the value as ANY in the schema, and then pass the pre encoded value inline.

  # ASN.1
  int INTEGER,
  str OCTET STRING,
  pre ANY

  # Perl
  { int => 5, str => "text", pre=>"\x03\x03\x00\x0a\x05" }

passes a pre-encoded BIT STRING instance as hex text. -But it could be a previous run of $obj->encode() from another run held in some variable.

Exceptions

There are some exceptions where Convert::ASN1 does not require an element to be named. These are SEQUENCE {...}, SET {...} and CHOICE. In each case if the element is not given a name then the elements inside the {...} will share the same namespace as the elements outside of the {...}.

TODO

•: XS implementation.
•: More documentation.
•: More tests.

AUTHOR

Graham Barr <gbarr@cpan.org>

SUPPORT

Report issues via github at https://github.com/gbarr/perl-Convert-ASN1/issues

To contribute I encourage you to create a git fork of the repository at https://github.com/gbarr/perl-Convert-ASN1 do you work on a fresh branch created from master and submit a pull request