asn1crypto

A fast, pure Python library for parsing and serializing ASN.1 structures.

Features
Why Another Python ASN.1 Library?
Related Crypto Libraries
Current Release
Dependencies
Installation
License
Security Policy
Documentation
Continuous Integration
Testing
Development
CI Tasks

Features

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:

Standard	Module	Source
X.509	`asn1crypto.x509`	RFC 5280
CRL	`asn1crypto.crl`	RFC 5280
CSR	`asn1crypto.csr`	RFC 2986, RFC 2985
OCSP	`asn1crypto.ocsp`	RFC 6960
PKCS#12	`asn1crypto.pkcs12`	RFC 7292
PKCS#8	`asn1crypto.keys`	RFC 5208
PKCS#1 v2.1 (RSA keys)	`asn1crypto.keys`	RFC 3447
DSA keys	`asn1crypto.keys`	RFC 3279
Elliptic curve keys	`asn1crypto.keys`	SECG SEC1 V2
PKCS#3 v1.4	`asn1crypto.algos`	PKCS#3 v1.4
PKCS#5 v2.1	`asn1crypto.algos`	PKCS#5 v2.1
CMS (and PKCS#7)	`asn1crypto.cms`	RFC 5652, RFC 2315
TSP	`asn1crypto.tsp`	RFC 3161
PDF signatures	`asn1crypto.pdf`	PDF 1.7

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 BitString and 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 BitString and OctetString to
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 or more.

Related Crypto Libraries

asn1crypto is part of the modularcrypto family of Python packages:

Current Release

1.5.0 - changelog

Dependencies

Python 2.6, 2.7, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 3.10 or pypy. No third-party
packages required.

Installation

pip install asn1crypto

License

asn1crypto is licensed under the terms of the MIT license. See the
LICENSE file for the exact license text.

Security Policy

The security policies for this project are covered in
SECURITY.md.

Documentation

The documentation for asn1crypto is composed of tutorials on basic usage and
links to the source for the various pre-defined type classes.

Tutorials

Reference

Universal types, asn1crypto.core
Digest, HMAC, signed digest and encryption algorithms, asn1crypto.algos
Private and public keys, asn1crypto.keys
X509 certificates, asn1crypto.x509
Certificate revocation lists (CRLs), asn1crypto.crl
Online certificate status protocol (OCSP), asn1crypto.ocsp
Certificate signing requests (CSRs), asn1crypto.csr
Private key/certificate containers (PKCS#12), asn1crypto.pkcs12
Cryptographic message syntax (CMS, PKCS#7), asn1crypto.cms
Time stamp protocol (TSP), asn1crypto.tsp
PDF signatures, asn1crypto.pdf

Continuous Integration

Various combinations of platforms and versions of Python are tested via:

macOS, Linux, Windows via GitHub Actions
arm64 via CircleCI

Testing

Tests are written using unittest and require no third-party packages.

Depending on what type of source is available for the package, the following
commands can be used to run the test suite.

Git Repository

When working within a Git working copy, or an archive of the Git repository,
the full test suite is run via:

python run.py tests

To run only some tests, pass a regular expression as a parameter to tests.

python run.py tests ocsp

PyPi Source Distribution

When working within an extracted source distribution (aka .tar.gz) from
PyPi, the full test suite is run via:

python setup.py test

Package

When the package has been installed via pip (or another method), the package
asn1crypto_tests may be installed and invoked to run the full test suite:

pip install asn1crypto_tests
python -m asn1crypto_tests

Development

To install the package used for linting, execute:

pip install --user -r requires/lint

The following command will run the linter:

python run.py lint

Support for code coverage can be installed via:

pip install --user -r requires/coverage

Coverage is measured by running:

python run.py coverage

To change the version number of the package, run:

python run.py version {pep440_version}

To install the necessary packages for releasing a new version on PyPI, run:

pip install --user -r requires/release

Releases are created by:

Making a git tag in PEP 440 format
Running the command:
```
python run.py release
```

Existing releases can be found at https://pypi.org/project/asn1crypto/.

CI Tasks

A task named deps exists to download and stage all necessary testing
dependencies. On posix platforms, curl is used for downloads and on Windows
PowerShell with Net.WebClient is used. This configuration sidesteps issues
related to getting pip to work properly and messing with site-packages for
the version of Python being used.

The ci task runs lint (if flake8 is available for the version of Python) and
coverage (or tests if coverage is not available for the version of Python).
If the current directory is a clean git working copy, the coverage data is
submitted to codecov.io.

python run.py deps
python run.py ci

Package profile

asn1crypto

Releases

Release table

PyPI Downloads

Dependencies

Details

Project URLs

Dependencies

Package description