4 * BER/CER/DER decoding, DER encoding
5 * Basic ASN.1 data types (X.208): BOOLEAN, INTEGER, BIT STRING, OCTET
6 STRING, NULL, OBJECT IDENTIFIER, ENUMERATED, all strings, UTCTime,
7 GeneralizedTime, CHOICE, ANY, SEQUENCE (OF), SET (OF)
8 * Size :ref:`constraints <bounds>` checking
9 * Working with sequences as high level data objects with ability to
11 * Python 2.7/3.5/3.6 compatibility
12 * Aimed to be complaint with `X.690-201508 <https://www.itu.int/rec/T-REC-X.690-201508-I/en>`__
14 Why yet another library? `pyasn1 <http://snmplabs.com/pyasn1/>`__
15 had all of this a long time ago. PyDERASN resembles it in many ways. In
16 practice it should be relatively easy to convert ``pyasn1``'s code to
18 Also there is `asn1crypto <https://github.com/wbond/asn1crypto>`__.
20 * Small, simple and trying to be reviewable code. Just a single file
21 with `six <https://pypi.org/project/six/>`__ dependency
22 * Ability to know :ref:`exact decoded <decoding>` objects offsets and
23 lengths inside the binary
24 * Automatic decoding of :ref:`DEFINED BY <definedby>` fields
25 * Ability to know exact decoded field presence, emptiness: for example
26 ``SEQUENCE`` can lack ``OPTIONAL SEQUENCE OF`` field, but also can
27 have it with no elements inside
28 * **Strict** DER-encoding checks. If whole input binary is parsed, then
29 it must be completely valid DER-encoded structure
30 * Ability to allow BER-encoded data with knowing if any of specified
31 field has either DER or BER encoding (or possibly indefinite-length
32 encoding). For example
33 `CMS <https://en.wikipedia.org/wiki/Cryptographic_Message_Syntax>`__
34 structures allow BER encoding for the whole message, except for
35 ``SignedAttributes`` -- you can easily verify your CMS satisfies that
37 * Extensive and comprehensive
38 `hypothesis <https://hypothesis.readthedocs.io/en/master/>`__
39 driven tests coverage. It also has been fuzzed with
40 `python-afl <http://jwilk.net/software/python-afl>`__
41 * Some kind of strong typing: SEQUENCEs require the exact **type** of
42 settable values, even when they are inherited (assigning ``Integer``
43 to the field with the type ``CMSVersion(Integer)`` is not allowed)
44 * However they do not require exact tags matching: IMPLICIT/EXPLICIT
45 tags will be set automatically in the given sequence (assigning of
46 ``CMSVersion()`` object to the field ``CMSVersion(expl=...)`` will
47 automatically set required tags)
48 * Descriptive errors, like ``pyderasn.DecodeError: UTCTime
49 (tbsCertificate:validity:notAfter:utcTime) (at 328) invalid UTCTime format``
50 * ``__slots__``, ``copy.copy()``, ``pickle``, `Cython <https://cython.org/>`__
52 * Could be significantly faster and have lower memory usage
53 For example parsing of CACert.org's CRL (8.48 MiB) on FreeBSD 12.0
54 amd64, Intel Core i5-6200U 2.3 GHz machine, Python 3.5.5/2.7.15:
63 - Memory used, MiB (Py3/Py2)
65 - ``der_decode(data, asn1Spec=rfc5280.CertificateList())``
69 - ``asn1crypto.crl.CertificateList.load(data).native``
73 - ``CertificateList().decode(data)`` (CertificateList is
74 converted ``pyasn1`` scheme definition)
77 * :ref:`Pretty printer <pprinting>` and
78 :ref:`command-line decoder <cmdline>`, that could
79 conveniently replace utilities like either ``dumpasn1`` or
82 .. figure:: pprinting.png
83 :alt: Pretty printing example output
85 An example of pretty printed X.509 certificate with automatically
86 parsed DEFINED BY fields.