Features¶
- BER/CER/DER decoding, DER encoding
- Basic ASN.1 data types (X.208): BOOLEAN, INTEGER, BIT STRING, OCTET STRING, NULL, OBJECT IDENTIFIER, ENUMERATED, all strings, UTCTime, GeneralizedTime, CHOICE, ANY, SEQUENCE (OF), SET (OF)
- Size constraints checking
- Working with sequences as high level data objects with ability to (un)marshall them
- Python 2.7/3.5/3.6 compatibility
- Aimed to be complaint with X.690-201508
Why yet another library? pyasn1
had all of this a long time ago. PyDERASN resembles it in many ways. In
practice it should be relatively easy to convert pyasn1
’s code to
pyderasn
’s one. But additionally it offers:
Small, simple and trying to be reviewable code. Just a single file
Automatic decoding of DEFINED BY fields
Ability to know exact decoded objects offsets and lengths inside the binary
Pretty printer and command-line decoder, that could conveniently replace utilities like either
dumpasn1
oropenssl asn1parse
Some kind of strong typing: SEQUENCEs require the exact type of settable values, even when they are inherited
However they do not require tags matching: IMPLICIT/EXPLICIT tags will be set automatically in the given sequence
Descriptive errors, like
pyderasn.DecodeError: UTCTime (tbsCertificate:validity:notAfter:utcTime) (at 328) invalid UTCTime format
__slots__
friendlinessCould be significantly faster. For example parsing of CACert.org’s CRL under Python 3.5.2:
python -m pyderasn revoke.crl
:~2 min ( pyderasn == 1.0
)python -m pyderasn --schema path.to.CertificateList revoke.crl
:~38 sec ( pyderasn == 1.0
)pyasn1.decode(asn1Spec=pyasn1.CertificateList())
:~22 min ( pyasn1 == 0.2.3
)
There are drawbacks:
- No old Python versions support
- Strings are not validated in any way, except just trying to be decoded
in
ascii
,iso-8859-1
,utf-8/16/32
correspondingly - No REAL, RELATIVE OID, EXTERNAL, INSTANCE OF, EMBEDDED PDV, CHARACTER STRING