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ASN.1 parsing, encoding and decoding.

Project description

buildstatus coverage

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.

Codecs under development:

  • Basic Encoding Rules (BER)
  • Distinguished Encoding Rules (DER)
  • JSON Encoding Rules (JER)
  • Aligned Packed Encoding Rules (PER)
  • Unaligned Packed Encoding Rules (UPER)
  • XML Encoding Rules (XER)
  • Basic ASN.1 value notation

Planned codecs:

  • Octet Encoding Rules (OER)

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

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

Installation

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).

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).

>>> 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.

>>> 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 decode encoded data.

> asn1tools shell

Welcome to the asn1tools shell.

$ help
Commands:
  compile <codec> <specification> [<specification> ...]
  decode <type> <hexstring>
$ compile ber tests/files/foo.asn
$ decode Question 300e0201011609497320312b313d333f
question Question ::= {
    id 1,
    question "Is 1+1=3?"
}
$ exit
>

The decode subcommand

Decode given encoded Question using the default codec (BER).

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

Decode given encoded Question using the UPER codec.

> asn1tools decode --codec uper tests/files/foo.asn Question 01010993cd03156c5eb37e
question Question ::= {
    id 1,
    question "Is 1+1=3?"
}
>

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

> cat encoded.txt
2018-02-24 11:22:09
300e0201011609497320312b313d333f
2018-02-24 11:24:15
300e0201021609497320322b323d353f
> cat encoded.txt | asn1tools decode 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?"
}
>

Contributing

  1. Fork the repository.

  2. Install prerequisites.

    pip install -r requirements.txt
    
  3. Implement the new feature or bug fix.

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

  5. Run the tests.

    make test
    
  6. Create a pull request.

Project details


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