PyCryptoPlus

From YobiWiki
Jump to navigation Jump to search

Back to SAGE & cryptology

Info

Differences with pycrypto

CryptoPlus PyCrypto
Block Ciphers
Block cipher algorithms
Serpent Py
Blowfish Py C
Twofish Py
Idea C
DES Py C
3DES Py C
AES Py C
Rijndael Py
Present Py
Modes of operation
CMAC Py
XCBC
CBC-MAC
CCM
GCM
ECB Py C
CBC Py C
CTR Py C
LRW
XTS Py
MDC-2
Paddings
bit padding Py
zeros Py
PKCS7 Py
PKCS12 Py
ISO 10126 Py
ANSI X.923 Py


  • ciphers from pycrypto are being used with the python chaining modes and not the original pycrypto ones
    => plaintext can be supplied in arbitrary sizes instead of multiples of the blocksize like in pycrypto: the new chaining modes keep a cache to encrypt/decrypt data once the cachesize holds at least a blocksize of data
  • new possibilities:
    • Rijndael, Serpent, Twofish
      • Rijndael is limited to blocksizes of 128, 192 and 256 bits
    • CMAC, XTS, CTR
      • XTS is usable for ciphers with blocksizes of 16 bytes => XTS-AES, Serpent, Twofish
      • XTS encrypts the given input at once while all other chain modes encrypt only when a block plaintext is available in the cache
      • CMAC is usable for blocksizes of 8 and 16 bytes
    • OFB,CFB and CTR can be accessed as a stream cipher (you get the encrypted message immediately, you don't have to wait until a complete block of plaintext has been provided to the cipher)
  • test functions are available via doctests and extensive tests that loop through dictionary of test vectors
    • new pycrypto version will have it's own test bench for ciphers, this is not implemented yet

source structure

root of CryptoPlus package
src/Hash.py make all Crypto.Hash modules available under CryptoPlus.Hash
src/Protocol.py make all Crypto.Protocol modules available under CryptoPlus.Protocol
src/PublicKey.py make all Crypto.PublicKey modules available under CryptoPlus.PublicKey
src/__init__.py make the following modules available under the CryptoPlus package: "Cipher","PublicKey","Util","Protocol","Hash","testvectors"
src/testvectors.py
  • contains dictionaries with testvectors for: CBC, CFB, OFB and CTR with AES, DES,TDES2/3, Serpent128/192/256, CMAC-AES128/192/256, CMAC-TDES2/3, XTS-AES
  • used by test/test.py
CryptoPlus.Cipher subpackage
src/Cipher/__init__.py specify all the ciphers in the CryptoPlus.Cipher package + import of the streamcipher ARC4 and XOR
src/Cipher/blockcipher.py
  • class BlockCipher: parent class for every cipher you constructs. Holds some variabeles (key, blocksize) and objects (blockcipher, chain mode).
  • classes for every chain mode: the BlockCipher uses one of these as the chaining mode object. They are all own python code but sometimes based on non-complete code that was available.
Wrappers for pycrypto
src/Cipher/AES.py
  • wraps Crypto.Cipher.AES
  • doctests for: ECB, CBC, CFB, OFB, CTR, XTS, CMAC (verified)
src/Cipher/ARC2.py
  • wraps Crypto.Cipher.ARC2
  • doctests for: 1 ECB example
src/Cipher/Blowfish.py
  • wraps Crypto.Cipher.Blowfish
  • doctests for: ECB, CBC, CFB, OFB
src/Cipher/CAST.py
  • wraps Crypto.Cipher.CAST
  • doctests for: 2 ECB examples (128 bit and 40 bit key size)
src/Cipher/DES.py
  • wraps Crypto.Cipher.DES
  • doctests for: ECB (verified)
src/Cipher/DES3.py
  • wraps Crypto.Cipher.DES3
  • doctests for: CBC, CMAC TDES-EDE3, CMAC TDES-EDE2 (verified)
src/Cipher/IDEA.py
  • wraps Crypto.Cipher.IDEA
  • doctests for: 1 ECB example
src/Cipher/RC5.py
  • wraps Crypto.Cipher.RC5
  • doctests for: 1 ECB example
Wrappers for pure python implementations
src/Cipher/python_AES.py
  • wraps rijndael.py (only for the AES blocksize of 128bits)
  • doctests same as in the pycrypto wrapper
src/Cipher/python_Blowfish.py
  • wraps pyblowfish.py
  • doctests same as in the pycrypto wrapper
src/Cipher/python_DES.py
  • wraps pyDes.py (only using "des" class)
  • doctests same as in the pycrypto wrapper
src/Cipher/python_DES3.py
  • wraps pyDes.py (only using "triple_des" class)
  • doctests same as in the pycrypto wrapper
src/Cipher/python_Rijndael.py
  • wraps pyrijndael.py
  • doctests for ECB, CBC, XTS (CBC and XTS are AES test vectors)
src/Cipher/python_Serpent.py
  • wraps pyserpent.py
  • doctests for ECB, CBC (?verified?)
src/Cipher/python_Twofish.py
  • wraps pytwofish.py
  • doctests for ECB (?unverified?)
src/Cipher/python_PRESENT.py
  • wraps pypresent.py
  • doctests for ECB and with varying amount of rounds (verified with reference C implementation)
Pure python implementations for blockciphers
src/Cipher/pyDes.py
src/Cipher/pyblowfish.py
src/Cipher/pyserpent.py
  • originally found here: http://www.cl.cam.ac.uk/~fms27/serpent/
  • added class to wrap all the functions needed in one class so that the serpent cipher can be accessed like all other pure python ciphers
src/Cipher/pytwofish.py
src/Cipher/rijndael.py
src/Cipher/pypresent.py
Util subpackage
src/Util/__init__.py
  • import modules from original Crypto.Util: number, randpool, RFC1751
  • make new modules available: padding, util
src/Util/padding.py
  • own code for (un)padding raw strings
  • testbench that will pad/unpad a string with all available methods and check for errors between original and unpadded string
src/Util/util.py
  • provides: number2string, roundUp, string2number, xorstring
Test scripts
test/test.py runs extensive test with verified test vectors for: CBC, CFB, OFB and CTR with AES, DES,TDES2/3, Serpent128/192/256, CMAC-AES128/192/256, CMAC-TDES2/3, XTS-AES, PRESENT (80 and 128 bit key)
test/test_doctests.py script to run all doctest available in every cipher wrapper (pure python and pycrypto wrapper)
  • verified = test vectors are support by an online source. A link is available in the doctest.

TODO

  • add chaining modes: CMAC, CTR mod?
  • further importing of pycrypto
  • make test vectors available as variables
  • add tests:
    • CBC for serpent, twofish, blowfish
    • XTS is only tested by comparing deciphered ciphertext, not by checking ciphertext: XTS-AES doctest done
  • check other implementation of Blowfish
  • final() method of chains
    • add a cipher.final() method? pycrypto doesn't have it, but it doesn't really conflict with the pycrypto API. It will just extend it
    • final() method should use padding. Choose padding function at initialization of the cipher => again: extending the API
  • XTS
    • make other blocksizes available besides 16 bytes?
  • CMAC
    • make other blocksizes available besides 8 and 16 bytes?
    • supply XTS keys by splitting 1 big key or by supplying two keys?
  • add rijndael instead of only AES
  • add docstring to every "new" function of every module, explaining what should be passed as arguments (probably the same for every function)
    Move doctests there so they are easily viewable
  • check GF2 in XTS + can it be replaced by Sage's implementation of GF2 ( -> [1]? ) ?
    • decision: stays the way it is. When Sage's GF2 would be used, then CryptoPlus wouldn't work without sage.
    • GF2 not necessary anymore in XTS
  • use unittest for test functions
  • check development of pycrypto:
    • Util.Counter & Util._counter
    • SelfTest: usable to perform the test for python algo's in CryptoPlus if testvectors are in right format?

Tests available

  • Doctests
    • Blowfish: ECB, CBC, CFB, OFB
    • all chain modes in AES
  • Extensive external test (via tester.py)
    • DES,TDES2,TDES3: ECB
    • Serpent 128/192/256: ECB
    • CMAC: AES128/192/256
    • XTS: AES128/256 and plaintext multiples and non-multiples of 16 bytes

Licenses

  • used from python truecrypt implementation
    all original code is under MIT license (much freedom according to [2])
    • pyTwofish (untouched)
      python truecrypt author isn't the original author = > extra copyright notice that should be left in place
    • pyserpent (untouched)
      python truecrypt author isn't the original author = > extra copyright notice that should be left in place
    • XTS (modified)
      python truecrypt author is the original author => only MIT License
    • GF2n.py(untouched)
      python truecrypt author is the original author => only MIT License
  • pyblowfish (untouched)
    gpl or artistic license
    To not affect the rest of the distribution we've to redistribute it only under Artistic license terms
  • rijndael.py (untouched)
    using tls lite (public domain) implementation which uses code from Bram Cohen (public domain)
  • pyDes (untouched)
    public domain according to its homepage
  • blockciphers CBC, ECB, CTR from [3] (modified)
    keep copyright notice in place?
  • CMAC: omac.py
    GPL but not really used it, just used as a starting point

Various info

Python

Setup Script

distutils vs setuptools

Dependencies checking on install: some info here.

It seems that the 'requires' keyword in distutils has only a purpose of documentation, but 'install_requires' in setuptools really takes care of dependencies: availability of dependencies will be checked. If a package is not available, it will be checked for on pypi and installed automatically.
distutils
  • setup.py
    • creating a distribution tar.gz: "python setup.py sdist"
    • installing the source distribution (sdist):
      - untar .tar.gz: "cd dist && tar zxfv CryptoPlus-1.0.tar.gz -C ~/"
      - "cd ~/CryptoPlus-1.0 && python setup.py install"
    • "egg way":
      $ python setup.py bdist_egg
      $ sudo easy_install dist/CryptoPlus-1.0-py2.5.egg
setuptools

Test Vectors

Chaining Modes

many blocks, successive T values can and should be computed from prior ones via multiplication by alpha (providing that i remains fixed). This optimization, which is one of the best features of XEX, should be explicitly recommended in the standard."

Ciphers

Retrieved from "https://wiki.yobi.be/index.php?title=PyCryptoPlus&oldid=5113"