pprp 0.2.1

A pure-Python Rijndael (AES) and PBKDF2 library. Python2.7- and Python3-compatible.

Overview

This package was a remedy to there being no PyPI-published, pure-Python Rijndael (AES) implementations, and that nothing available, in general, was compatible with both Python2 and Python3. The same is true of the PBKDF2 key-expansion algorithm.

The encryptor takes a source generator (which yields individual blocks). There are source-generators provided for both data from a variable and data from a file. It is trivial if you’d like to write your own. The encryptor and decryptor functions are written as generators. Decrypted data has PKCS7 padding. A utility function is provided to trim this (trim_pkcs7_padding).

The implementation includes Python2 and Python3 implementations of both Rijndael and PBKDF2, and chooses the version when loaded.

The default block-size is 128-bits in order to be compatible with AES.

This project is also referred to as pprp, which stands for “Pure Python Rijndael and PBKDF2”.

Installation

Install via pip:

$ sudo pip install pprp

Example

Encrypt and decrypt the data, and compare the results. This example works in both Python 2 and 3.

Top imports and defines:

import io
import os.path
import hashlib

import pprp
import pprp.config

# Make the strings the right type for the current Python version.
def trans(text):
    return text.encode('ASCII') if sys.version_info[0] >= 3 else text

passphrase = trans('password')
salt = trans('salt')
key_size = 32
data = "this is a test" * 100

Do the key-expansion:

key = pprp.pbkdf2(passphrase, salt, key_size)

Create a source from available data:

sg = pprp.data_source_gen(data)

Feed the source into the encryptor:

eg = pprp.rjindael_encrypt_gen(key, sg)

Feed the encryptor into the decryptor:

dg = pprp.rjindael_decrypt_gen(key, eg)

Sink the output into an IO stream, and trim the padding off the last block:

s = io.BytesIO()
ends_at = 0
for block in dg:
    ends_at += pprp.config.DEFAULT_BLOCK_SIZE
    if ends_at >= len(data):
        block = pprp.trim_pkcs7_padding(block)

    s.write(block)

decrypted = s.getvalue()

Check the result:

assert data == decrypted.decode('ASCII')

The following is a portion of the output of the example script (test/example.py). Notice that, due to this being an efficient, generator-based design, the encryption of each block is followed by a decryption:

2014-07-01 12:24:13,182 - pprp.source - DEBUG - Yielding [data] source block: (0)-(0)
2014-07-01 12:24:13,182 - pprp.adapters - DEBUG - Encrypting and yielding encrypted block: (0)
2014-07-01 12:24:13,183 - pprp.adapters - DEBUG - Decrypting and yielding decrpted block: (0)
2014-07-01 12:24:13,183 - pprp.source - DEBUG - Yielding [data] source block: (1)-(16)
2014-07-01 12:24:13,183 - pprp.adapters - DEBUG - Encrypting and yielding encrypted block: (1)
2014-07-01 12:24:13,183 - pprp.adapters - DEBUG - Decrypting and yielding decrpted block: (1)
2014-07-01 12:24:13,183 - pprp.source - DEBUG - Yielding [data] source block: (2)-(32)
2014-07-01 12:24:13,183 - pprp.adapters - DEBUG - Encrypting and yielding encrypted block: (2)
2014-07-01 12:24:13,183 - pprp.adapters - DEBUG - Decrypting and yielding decrpted block: (2)
2014-07-01 12:24:13,184 - pprp.source - DEBUG - Yielding [data] source block: (3)-(48)
2014-07-01 12:24:13,184 - pprp.adapters - DEBUG - Encrypting and yielding encrypted block: (3)
2014-07-01 12:24:13,184 - pprp.adapters - DEBUG - Decrypting and yielding decrpted block: (3)
...

Notes

A different block-size may be passed in to each of the generators. The default block-size can also be passed via environment variable as PPRP_BLOCK_SIZE.