blowfish 0.4.0

Fast, efficient Blowfish cipher implementation in pure Python (3.4+).

Fast, efficient Blowfish cipher implementation in pure Python (3.4+).

• Dependencies

• Features

• Installation

  • distutils

  • pip

• Development

• Bugs

• Usage

  • Block

  • Electronic Codebook Mode (ECB)

  • Cipher-Block Chaining Mode (CBC)

  • Propagating Cipher-Block Chaining Mode (PCBC)

  • Cipher Feedback Mode (CFB)

  • Output Feedback Mode (OFB)

  • Counter Mode (CTR)

Dependencies

• Python 3.4+

Features

• Fast (well, as fast you can possibly go using only Python 3.4+)

• Efficient; generators/iterators are used liberally to reduce memory usage

• Electronic Codebook (ECB) mode

• Cipher-Block Chaining (CBC) mode

• Propagating Cipher-Block Chaining (PCBC) mode

• Cipher Feedback (CFB) mode

• Output Feedback (OFB) mode

• Counter (CTR) mode

Installation

If you just need a Blowfish cipher in your Python project, feel free to manually copy blowfish.py to your package directory (license permitting).

distutils

To install the module to your Python distribution, use the included distutils script:

$ python setup.py install

pip

Stable versions can be installed from pypi using pip:

$ pip install blowfish

pip can also install the latest development version directly from git:

$ pip install 'git+https://github.com/jashandeep-sohi/python-blowfish.git'

Development

Want to add a mode of operation? Speed up encryption?

Make your changes to a clone of the repository at https://github.com/jashandeep-sohi/python-blowfish and send me a pull request.

Bugs

Are you having problems? Please let me know at https://github.com/jashandeep-sohi/python-blowfish/issues

Usage

Warning

Cryptography is complex, so please don’t use this module in anything critical without understanding what you are doing and checking the source code to make sure it is doing what you want it to.

Note

This is just a quick overview on how to use the module. For detailed documentation please see the docstrings in the module.

First create a Cipher object with a key.

import blowfish

cipher = blowfish.Cipher(b"Key must be between 8 and 56 bytes long.")

By default this initializes a Blowfish cipher that will interpret bytes using big-endian byte order. This should not be a problem since most implementations use big-endian byte order as well. However, should the need arrive to use little-endian byte order, provide "little" as the second argument.

Block

To encrypt or decrypt a block of data (8 bytes), use the encrypt_block or decrypt_block methods of the Cipher object.

from os import urandom

block = urandom(8)

ciphertext = cipher.encrypt_block(block)
plaintext = cipher.decrypt_block(ciphertext)

assert block == plaintext

As these methods can only operate on 8 bytes of data, they’re of little practical use. Instead, use one of the implemented modes of operation.

Electronic Codebook Mode (ECB)

To encrypt or decrypt data in ECB mode, use encrypt_ecb or decrypt_ecb methods of the Cipher object.

block_multiple_data = urandom(10 * 8) # data to encrypt

ecb_ciphertext_iter = cipher.encrypt_ecb(block_multiple_data)
ecb_plaintext_iter = cipher.decrypt_ecb(b"".join(ecb_ciphertext_iter))

assert block_multiple_data == b"".join(ecb_plaintext_iter)

Cipher-Block Chaining Mode (CBC)

To encrypt or decrypt data in CBC mode, use encrypt_cbc or decrypt_cbc methods of the Cipher object.

iv = urandom(8) # initialization vector
cbc_ciphertext_iter = cipher.encrypt_cbc(block_multiple_data, iv)
cbc_plaintext_iter = cipher.decrypt_cbc(b"".join(cbc_ciphertext_iter), iv)

assert block_multiple_data == b"".join(cbc_plaintext_iter)

Propagating Cipher-Block Chaining Mode (PCBC)

To encrypt or decrypt data in PCBC mode, use encrypt_pcbc or decrypt_pcbc methods of the Cipher object.

pcbc_ciphertext_iter = cipher.encrypt_pcbc(block_multiple_data, iv)
pcbc_plaintext_iter = cipher.decrypt_pcbc(
  b"".join(pcbc_ciphertext_iter),
  iv
)

assert block_multiple_data == b"".join(pcbc_plaintext_iter)

Cipher Feedback Mode (CFB)

To encrypt or decrypt data in CFB mode, use encrypt_cfb or decrypt_cfb methods of the Cipher object. Although CFB mode can be implemented to allow input data of any length, the current implementation does not. So, the input data has to be a block multiple in length.

cfb_ciphertext_iter = cipher.encrypt_cfb(block_multiple_data, iv)
cfb_plaintext_iter = cipher.decrypt_cfb(b"".join(cfb_ciphertext_iter), iv)

assert block_multiple_data == b"".join(cfb_plaintext_iter)

Output Feedback Mode (OFB)

To encrypt or decrypt data in OFB mode, use encrypt_ofb or decrypt_ofb methods of the Cipher object. Like CFB mode, OFB mode can also be implemented to allow input data of any length. As the current implementation does not, input data has to be a block multiple in length.

ofb_ciphertext_iter = cipher.encrypt_ofb(block_multiple_data, iv)
ofb_plaintext_iter = cipher.decrypt_ofb(b"".join(ofb_ciphertext_iter), iv)

assert block_multiple_data == b"".join(ofb_plaintext_iter)

Counter Mode (CTR)

To encrypt or decrypt data in CTR mode, use encrypt_ctr or decrypt_ctr methods of the Cipher object. Although you can use any counter you want, a simple increment by one counter is secure and the most popular. So for convenience sake, a simple increment by one counter is implemented by the blowfish.ctr_counter function.

from operator import xor

non_block_multiple_data = urandom(10 * 8 + 5) # data to encrypt

encrypt_counter = blowfish.ctr_counter(nonce = 0xfaff1fffffffffff, f = xor)
decrypt_counter = blowfish.ctr_counter(nonce = 0xfaff1fffffffffff, f = xor)

ctr_ciphertext_iter = cipher.encrypt_ctr(
  non_block_multiple_data,
  encrypt_counter
)
ctr_plaintext_iter = cipher.decrypt_ctr(
  b"".join(ctr_ciphertext_iter),
  decrypt_counter
)

assert block_multiple_data == b"".join(ctr_plaintext_iter)