A fast, pure Python library for parsing and serializing ASN.1 structures.
- Why Another Python ASN.1 Library?
- Related Crypto Libraries
- Current Release
- Continuous Integration
In addition to an ASN.1 BER/DER decoder and DER serializer, the project includes a bunch of ASN.1 structures for use with various common cryptography standards:
||RFC 2986, RFC 2985|
|PKCS#1 v2.1 (RSA keys)||
|Elliptic curve keys||
||SECG SEC1 V2|
|CMS (and PKCS#7)||
||RFC 5652, RFC 2315|
Why Another Python ASN.1 Library?
Python has long had the pyasn1 and pyasn1_modules available for parsing and serializing ASN.1 structures. While the project does include a comprehensive set of tools for parsing and serializing, the performance of the library can be very poor, especially when dealing with bit fields and parsing large structures such as CRLs.
After spending extensive time using pyasn1, the following issues were identified:
- Poor performance
- Verbose, non-pythonic API
- Out-dated and incomplete definitions in pyasn1-modules
- No simple way to map data to native Python data structures
- No mechanism for overridden universal ASN.1 types
The pyasn1 API is largely method driven, and uses extensive configuration objects and lowerCamelCase names. There were no consistent options for converting types of native Python data structures. Since the project supports out-dated versions of Python, many newer language features are unavailable for use.
Time was spent trying to profile issues with the performance, however the
architecture made it hard to pin down the primary source of the poor
performance. Attempts were made to improve performance by utilizing unreleased
patches and delaying parsing using the
Any type. Even with such changes, the
performance was still unacceptably slow.
Finally, a number of structures in the cryptographic space use universal data
types such as
OctetString, but interpret the data as other
types. For instance, signatures are really byte strings, but are encoded as
BitString. Elliptic curve keys use both
represent integers. Parsing these structures as the base universal types and
then re-interpreting them wastes computation.
asn1crypto uses the following techniques to improve performance, especially when extracting one or two fields from large, complex structures:
- Delayed parsing of byte string values
- Persistence of original ASN.1 encoded data until a value is changed
- Lazy loading of child fields
- Utilization of high-level Python stdlib modules
While there is no extensive performance test suite, the
CRLTests.test_parse_crl test case was used to parse a 21MB CRL file on a
late 2013 rMBP. asn1crypto parsed the certificate serial numbers in just
under 8 seconds. With pyasn1, using definitions from pyasn1-modules, the
same parsing took over 4,100 seconds.
For smaller structures the performance difference can range from a few times faster to an order of magnitude of more.
Related Crypto Libraries
asn1crypto is part of the modularcrypto family of Python packages:
0.20.0 - changelog
Python 2.6, 2.7, 3.2, 3.3, 3.4, 3.5, 3.6 or pypy. No third-party packages required.
pip install asn1crypto
asn1crypto is licensed under the terms of the MIT license. See the LICENSE file for the exact license text.
The documentation for asn1crypto is composed of tutorials on basic usage and links to the source for the various pre-defined type classes.
- Universal types,
- Digest, HMAC, signed digest and encryption algorithms,
- Private and public keys,
- X509 certificates,
- Certificate revocation lists (CRLs),
- Online certificate status protocol (OCSP),
- Certificate signing requests (CSRs),
- Private key/certificate containers (PKCS#12),
- Cryptographic message syntax (CMS, PKCS#7),
- Time stamp protocol (TSP),
- PDF signatures,
Tests are written using
unittest and require no third-party packages:
python run.py tests
To run only some tests, pass a regular expression as a parameter to
python run.py tests ocsp
To install required development dependencies, execute:
pip install -r dev-requirements.txt
The following commands will run the linter and test coverage:
python run.py lint python run.py coverage
python run.py release