asn

asn1tools

ASN.1 parsing, encoding and decoding.

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About

A Python package for ASN.1_ parsing, encoding and decoding.

This project is under development and does only support a subset of the ASN.1 specification syntax.

Supported codecs:

  • Basic Encoding Rules (BER)
  • Distinguished Encoding Rules (DER)
  • Generic String Encoding Rules (GSER)
  • JSON Encoding Rules (JER)
  • Basic Octet Encoding Rules (OER)
  • Aligned Packed Encoding Rules (PER)
  • Unaligned Packed Encoding Rules (UPER)
  • XML Encoding Rules (XER)

Miscellaneous features:

  • C source code generator for OER and UPER (with some limitations).

Project homepage: https://github.com/eerimoq/asn1tools

Documentation: http://asn1tools.readthedocs.org/en/latest

Known limitations

  • The CLASS keyword (X.681) and its friends are not yet supported.

  • Parametrization (X.683) is not yet supported.

  • The EMBEDDED PDV type is not yet supported.

  • The ANY and ANY DEFINED BY types are not supported. They were removed from the ASN.1 standard 1994.

  • WITH COMPONENT and WITH COMPONENTS constraints are ignored, except for OER REAL.

  • The DURATION type is not yet supported.

Installation

.. code-block:: python

pip install asn1tools

Example Usage

This is an example ASN.1 specification defining the messages of a fictitious Foo protocol (based on the FooProtocol on Wikipedia).

.. code-block:: text

Foo DEFINITIONS ::= BEGIN

   Question ::= SEQUENCE {
       id        INTEGER,
       question  IA5String
   }

   Answer ::= SEQUENCE {
       id        INTEGER,
       answer    BOOLEAN
   }

END

Scripting

Compile the ASN.1 specification, and encode and decode_ a question using the default codec (BER).

.. code-block:: python

import asn1tools foo = asn1tools.compile_files('tests/files/foo.asn') encoded = foo.encode('Question', {'id': 1, 'question': 'Is 1+1=3?'}) encoded bytearray(b'0\x0e\x02\x01\x01\x16\x09Is 1+1=3?') foo.decode('Question', encoded) {'id': 1, 'question': 'Is 1+1=3?'}

The same ASN.1 specification, but using the PER codec.

.. code-block:: python

import asn1tools foo = asn1tools.compile_files('tests/files/foo.asn', 'per') encoded = foo.encode('Question', {'id': 1, 'question': 'Is 1+1=3?'}) encoded bytearray(b'\x01\x01\tIs 1+1=3?') foo.decode('Question', encoded) {'id': 1, 'question': 'Is 1+1=3?'}

See the examples_ folder for additional examples.

Command line tool

The shell subcommand ^^^^^^^^^^^^^^^^^^^^

Use the command line shell to convert data between given formats. The default input codec is BER and output codec is GSER (produces human readable text).

.. code-block:: text

asn1tools shell

Welcome to the asn1tools shell!

$ help Commands: compile convert exit help $ compile tests/files/foo.asn $ convert Question 300e0201011609497320312b313d333f question Question ::= { id 1, question "Is 1+1=3?" } $ compile --output-codec xer tests/files/foo.asn $ convert Question 300e0201011609497320312b313d333f 1 Is 1+1=3? $ compile -o uper tests/files/foo.asn $ convert Question 300e0201011609497320312b313d333f 01010993cd03156c5eb37e $ exit

The convert subcommand ^^^^^^^^^^^^^^^^^^^^^^

Convert given encoded Question from BER to GSER (produces human readable text).

.. code-block:: text

asn1tools convert tests/files/foo.asn Question 300e0201011609497320312b313d333f question Question ::= { id 1, question "Is 1+1=3?" }

Convert given encoded Question from UPER to XER (xml).

.. code-block:: text

asn1tools convert -i uper -o xer tests/files/foo.asn Question 01010993cd03156c5eb37e 1 Is 1+1=3?

Convert given encoded Question from UPER to JER (json).

.. code-block:: text

asn1tools convert -i uper -o jer tests/files/foo.asn Question 01010993cd03156c5eb37e { "id": 1, "question": "Is 1+1=3?" }

Continuously convert encoded Questions read from standard input. Any line that cannot be converted is printed as is, in this example the dates.

.. code-block:: text

cat encoded.txt 2018-02-24 11:22:09 300e0201011609497320312b313d333f 2018-02-24 11:24:15 300e0201021609497320322b323d353f cat encoded.txt | asn1tools convert tests/files/foo.asn Question - 2018-02-24 11:22:09 question Question ::= { id 1, question "Is 1+1=3?" } 2018-02-24 11:24:15 question Question ::= { id 2, question "Is 2+2=5?" }

The convert subcommand with a cache ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Convert given encoded PCCH-Message from UPER to GSER with the --cache-dir option set to my_cache. Using a cache significantly reduces the command execution time after the first call.

.. code-block:: text

time asn1tools convert --cache-dir my_cache -i uper tests/files/3gpp/rrc_8_6_0.asn PCCH-Message 28 pcch-message PCCH-Message ::= { message c1 : paging : { systemInfoModification true, nonCriticalExtension { } } }

real 0m2.090s user 0m1.977s sys 0m0.032s

time asn1tools convert --cache-dir my_cache -i uper tests/files/3gpp/rrc_8_6_0.asn PCCH-Message 28 pcch-message PCCH-Message ::= { message c1 : paging : { systemInfoModification true, nonCriticalExtension { } } }

real 0m0.276s user 0m0.197s sys 0m0.026s

The parse subcommand ^^^^^^^^^^^^^^^^^^^^

Parse given ASN.1 specification and write it as a Python dictionary to given file. Use the created file to convert given encoded Question from BER to GSER (produces human readable text). The conversion is significantly faster than passing .asn-file(s) to the convert subcommand, especially for larger ASN.1 specifications.

.. code-block:: text

asn1tools parse tests/files/foo.asn foo.py asn1tools convert foo.py Question 300e0201011609497320312b313d333f question Question ::= { id 1, question "Is 1+1=3?" }

The generate C source subcommand ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Generate OER or UPER C source code from an ASN.1 specification.

No dynamic memory is used in the generated code. To achieve this all types in the ASN.1 specification must have a known maximum size, i.e. INTEGER (0..7), OCTET STRING (SIZE(12)), etc.

Below is an example generating OER C source code from tests/files/c_source/c_source.asn_.

.. code-block:: text

asn1tools generate_c_source --namespace oer tests/files/c_source/c_source.asn Successfully generated oer.h and oer.c.

The same as above, but generate UPER C source code instead of OER.

.. code-block:: text

asn1tools generate_c_source --codec uper --namespace uper tests/files/c_source/c_source.asn Successfully generated uper.h and uper.c.

The same as the first example, but also generate fuzz testing C source code for libFuzzer_.

.. code-block:: text

asn1tools generate_c_source --namespace oer --generate-fuzzer tests/files/c_source/c_source.asn Successfully generated oer.h and oer.c. Successfully generated oer_fuzzer.c and oer_fuzzer.mk.

Run "make -f oer_fuzzer.mk" to build and run the fuzzer. Requires a recent version of clang.

See oer.h, oer.c, uper.h, uper.c, oer_fuzzer.c and oer_fuzzer.mk for the contents of the generated files.

Limitations by design:

  • Only the types BOOLEAN, INTEGER, NULL, OCTET STRING, BIT STRING, ENUMERATED, SEQUENCE, SEQUENCE OF, and CHOICE are supported. The OER generator also supports REAL.

  • All types must have a known maximum size, i.e. INTEGER (0..7), OCTET STRING (SIZE(12)).

  • INTEGER must be 64 bits or less.

  • REAL must be IEEE 754 binary32 or binary64. binary32 is generated as float and binary64 as double.

  • Recursive types are not supported.

Known limitations:

  • Extension additions (...) are only supported in the OER generator. See compact_extensions_uper_ for how to make UPER CHOICE and SEQUENCE extendable without using ....

  • Named numbers in ENUMERATED are not yet supported.

Other OER and/or UPER C code generators:

See the benchmark example_ for a comparison of asn1c, asn1scc and asn1tools.

Contributing

#. Fork the repository.

#. Install prerequisites.

.. code-block:: text

  pip install -r requirements.txt

#. Implement the new feature or bug fix.

#. Implement test case(s) to ensure that future changes do not break legacy.

#. Run the tests.

.. code-block:: text

  make test

#. Create a pull request.

Specifications

ASN.1 specifications released by ITU and IETF.

General

  • X.680: Specification of basic notation <https://www.itu.int/ITU-T/studygroups/com17/languages/X.680-0207.pdf>_

  • X.681: Information object specification <https://www.itu.int/ITU-T/studygroups/com17/languages/X.681-0207.pdf>_

  • X.682: Constraint specification <https://www.itu.int/ITU-T/studygroups/com17/languages/X.682-0207.pdf>_

  • X.683: Parameterization of ASN.1 specifications <https://www.itu.int/ITU-T/studygroups/com17/languages/X.683-0207.pdf>_

Encodings

  • X.690: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER) <https://www.itu.int/ITU-T/studygroups/com17/languages/X.690-0207.pdf>_

  • X.691: Specification of Packed Encoding Rules (PER) <https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-X.691-201508-I!!PDF-E&type=items>_

  • X.693: XML Encoding Rules (XER) <https://www.itu.int/ITU-T/studygroups/com17/languages/X.693-0112.pdf>_

  • X.696: Specification of Octet Encoding Rules (OER) <https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-X.696-201508-I!!PDF-E&type=items>_

  • RFC 3641: Generic String Encoding Rules (GSER) for ASN.1 <https://tools.ietf.org/html/rfc3641>_

  • Overview of the JSON Encoding Rules (JER) <http://www.oss.com/asn1/resources/asn1-papers/Overview_of_JER.pdf>_

.. |coverage| image:: https://coveralls.io/repos/github/eerimoq/asn1tools/badge.svg?branch=master .. _coverage: https://coveralls.io/github/eerimoq/asn1tools

.. |codecov| image:: https://codecov.io/gh/eerimoq/asn1tools/branch/master/graph/badge.svg .. _codecov: https://codecov.io/gh/eerimoq/asn1tools

.. |nala| image:: https://img.shields.io/badge/nala-test-blue.svg .. _nala: https://github.com/eerimoq/nala

.. _ASN.1: https://en.wikipedia.org/wiki/Abstract_Syntax_Notation_One

.. _Compile: http://asn1tools.readthedocs.io/en/latest/#asn1tools.compile_files .. _encode: http://asn1tools.readthedocs.io/en/latest/#asn1tools.compiler.Specification.encode .. _decode: http://asn1tools.readthedocs.io/en/latest/#asn1tools.compiler.Specification.decode .. _examples: https://github.com/eerimoq/asn1tools/tree/master/examples

.. _tests/files/c_source/c_source.asn: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/c_source.asn

.. _oer.h: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/oer.h

.. _oer.c: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/oer.c

.. _uper.h: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/uper.h

.. _uper.c: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/uper.c

.. _oer_fuzzer.c: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/oer_fuzzer.c

.. _oer_fuzzer.mk: https://github.com/eerimoq/asn1tools/blob/master/tests/files/c_source/oer_fuzzer.mk

.. _libFuzzer: https://llvm.org/docs/LibFuzzer.html

.. _benchmark example: https://github.com/eerimoq/asn1tools/blob/master/examples/benchmarks/c_source

.. _compact_extensions_uper: https://github.com/eerimoq/asn1tools/blob/master/examples/compact_extensions_uper

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