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ASN.1 library for Python
------------------------
[](https://pypi.python.org/pypi/pyasn1)
[](https://pypi.python.org/pypi/pyasn1/)
[](https://secure.travis-ci.org/etingof/pyasn1)
[](https://codecov.io/github/etingof/pyasn1)
[](https://raw.githubusercontent.com/etingof/pyasn1/master/LICENSE.txt)
This is a free and open source implementation of ASN.1 types and codecs
as a Python package. It has been first written to support particular
protocol (SNMP) but then generalized to be suitable for a wide range
of protocols based on
[ASN.1 specification](https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-X.208-198811-W!!PDF-E&type=items).
Features
--------
* Generic implementation of ASN.1 types (X.208)
* Fully standard compliant BER/CER/DER codecs
* 100% Python, works with Python 2.4 up to Python 3.6
* MT-safe
* Contributed ASN.1 compiler [Asn1ate](https://github.com/kimgr/asn1ate)
Why using pyasn1
----------------
ASN.1 solves the data serialization problem. This solution was
designed long ago by the wise Ancients. Back then, they did not
have the luxury of wasting bits. That is why ASN.1 is designed
to serialize data structures of unbounded complexity into
something compact and efficient when it comes to processing
the data.
That probably explains why many network protocols and file formats
still rely on the 30+ years old technology. Including a number of
high-profile Internet protocols and file formats.
Quite a number of books cover the topic of ASN.1.
[Communication between heterogeneous systems](http://www.oss.com/asn1/dubuisson.html)
by Olivier Dubuisson is one of those high quality books freely
available on the Internet.
The pyasn1 package is designed to help Python programmers tackling
network protocols and file formats at the comfort of their Python
prompt. The tool struggles to capture all aspects of a rather
complicated ASN.1 system and to represent it on the Python terms.
How to use pyasn1
-----------------
With pyasn1 you can build Python objects from ASN.1 data structures.
For example, the following ASN.1 data structure:
```bash
Record ::= SEQUENCE {
id INTEGER,
room [0] INTEGER OPTIONAL,
house [1] INTEGER DEFAULT 0
}
```
Could be expressed in pyasn1 like this:
```python
class Record(Sequence):
componentType = NamedTypes(
NamedType('id', Integer()),
OptionalNamedType(
'room',
Integer().subtype(
implicitTag=Tag(tagClassContext, tagFormatSimple, 0)
)
),
DefaultedNamedType(
'house',
Integer(0).subtype(
implicitTag=Tag(tagClassContext, tagFormatSimple, 1)
)
)
)
```
It is in the spirit of ASN.1 to take abstract data description
and turn it into a programming language specific form.
Once you have your ASN.1 data structure expressed in Python, you
can use it along the lines of similar Python type (e.g. ASN.1
`SET` is similar to Python `dict`, `SET OF` to `list`):
```python
>>> record = Record()
>>> record['id'] = 123
>>> record['room'] = 321
>>> print(record.prettyPrint())
Record:
id=123
room=321
>>>
```
Part of the power of ASN.1 comes from its serialization features. You
can serialize your data structure and send it over the network.
```python
>>> substrate = encode(record)
>>> hexdump(substrate)
00000: 30 07 02 01 7B 80 02 01 41
```
Conversely, you can turn serialized ASN.1 content, as received from
network or read from a file, into a Python object which you can
introspect, modify, encode and send back.
```python
>>> received_record, rest_of_substrate = decode(substrate, asn1Spec=Record())
>>>
>>> print(received_record.prettyPrint())
Record:
id=123
room=321
house=0
>>>
>>> record == received_record
True
>>> received_record['room'] = 123
>>> substrate = encode(received_record)
>>> hexdump(substrate)
00000: 30 06 02 01 7B 80 01 7B
```
With ASN.1 design, serialization codecs are decoupled from data objects,
so you could turn every single ASN.1 object into many different
serialized forms. As of this moment, pyasn1 supports BER, DER and CER
formats. The extremely compact PER encoding is expected to be introduced
in the upcoming pyasn1 release.
More information on pyasn1 APIs can be found in the
[documentation](http://pyasn1.sourceforge.net),
compiled ASN.1 modules for different protocols and file formats
could be found in the pyasn1-modules
[repo](https://github.com/etingof/pyasn1-modules).
Download
--------
The pyasn1 package is distributed under terms and conditions of 2-clause
BSD [license](http://pyasn1.sourceforge.net/license.html). Source code is freely
available as a Github [repo](https://github.com/etingof/pyasn1).
Installation
------------
Download pyasn1 from [PyPI](https://pypi.python.org/pypi/pyasn1) or just run:
```bash
$ pip install pyasn1
```
Getting help
------------
If something does not work as expected,
[open an issue](https://github.com/etingof/pyasn1/issues) at Github or
post your question [to Stack Overflow](http://stackoverflow.com/questions/ask)
or try browsing pyasn1
[mailing list archives](https://sourceforge.net/p/pyasn1/mailman/pyasn1-users/).
Copyright (c) 2005-2017, [Ilya Etingof](http://etingof@gmail.com).
All rights reserved.
|
