6 * BER/CER/DER decoding, DER encoding
7 * Basic ASN.1 data types (X.208): BOOLEAN, INTEGER, BIT STRING, OCTET
8 STRING, NULL, OBJECT IDENTIFIER, ENUMERATED, all strings, UTCTime,
9 GeneralizedTime, CHOICE, ANY, SEQUENCE (OF), SET (OF)
10 * Size :ref:`constraints <bounds>` checking
11 * Working with sequences as high level data objects with ability to
13 * Python 2.7/3.5/3.6 compatibility
14 * Aimed to be complaint with `X.690-201508 <https://www.itu.int/rec/T-REC-X.690-201508-I/en>`__
16 Why yet another library? `pyasn1 <http://snmplabs.com/pyasn1/>`__
17 had all of this a long time ago. PyDERASN resembles it in many ways. In
18 practice it should be relatively easy to convert ``pyasn1``'s code to
20 Also there is `asn1crypto <https://github.com/wbond/asn1crypto>`__.
22 * Small, simple and trying to be reviewable code. Just a single file
23 with `six <https://pypi.org/project/six/>`__ dependency
24 * Ability to know :ref:`exact decoded <decoding>` objects offsets and
25 lengths inside the binary
26 * Automatic decoding of :ref:`DEFINED BY <definedby>` fields
27 * Ability to know exact decoded field presence, emptiness: for example
28 ``SEQUENCE`` can lack ``OPTIONAL SEQUENCE OF`` field, but also can
29 have it with no elements inside
30 * **Strict** DER-encoding checks. If whole input binary is parsed, then
31 it must be completely valid DER-encoded structure
32 * Ability to allow BER-encoded data with knowing if any of specified
33 field has either DER or BER encoding (or possibly indefinite-length
34 encoding). For example
35 `CMS <https://en.wikipedia.org/wiki/Cryptographic_Message_Syntax>`__
36 structures allow BER encoding for the whole message, except for
37 ``SignedAttributes`` -- you can easily verify your CMS satisfies that
39 * Extensive and comprehensive
40 `hypothesis <https://hypothesis.readthedocs.io/en/master/>`__
41 driven tests coverage. It also has been fuzzed with
42 `python-afl <http://jwilk.net/software/python-afl>`__
43 * Some kind of strong typing: SEQUENCEs require the exact **type** of
44 settable values, even when they are inherited (assigning ``Integer``
45 to the field with the type ``CMSVersion(Integer)`` is not allowed)
46 * However they do not require exact tags matching: IMPLICIT/EXPLICIT
47 tags will be set automatically in the given sequence (assigning of
48 ``CMSVersion()`` object to the field ``CMSVersion(expl=...)`` will
49 automatically set required tags)
50 * Descriptive errors, like ``pyderasn.DecodeError: UTCTime
51 (tbsCertificate:validity:notAfter:utcTime) (at 328) invalid UTCTime format``
52 * ``__slots__``, ``copy.copy()`` friendliness
53 * Workability with ``pickle``
54 * `Cython <https://cython.org/>`__ compatibility
55 * Could be significantly :ref:`faster <performance>` and have lower memory usage
56 * :ref:`Pretty printer <pprinting>` and
57 :ref:`command-line decoder <cmdline>`, that could
58 conveniently replace utilities like either ``dumpasn1`` or
61 .. figure:: pprinting.png
62 :alt: Pretty printing example output
64 An example of pretty printed X.509 certificate with automatically
65 parsed DEFINED BY fields.