PyCryptoPlus

Back to SAGE & cryptology

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
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
  • CMAC, XTS, CTR
    • XTS is usable for blocksizes of 8 and 16bytes (check the source code for more explanation)
  • 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)

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
  • XTS-AES? XTS-AES just denotes XTS using AES cipher? Make only that one available (which is the case for the moment)?
  • XTS-DES? des bs = 8, xts bs = 16 ??
  • 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]? ) ?
• 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

Info

Python

• absolute relative imports: links with some info
  • http://bugs.python.org/issue1510172
  • http://www.python.org/dev/peps/pep-0366/
  • http://www.python.org/dev/peps/pep-0328/
  • http://groups.google.com/group/comp.lang.python/msg/e35b1746b425b4c1
• collect all doctests
  • http://docs.python.org/lib/doctest-unittest-api.html
• making a package
  • http://docs.python.org/dist/

Setup Script

• 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"

Test Vectors

• AES, DES, 3DES: http://csrc.nist.gov/groups/STM/cavp/standards.html
  • AES in CBC, CTR, OFB, CFB: html version of pdf
  • CMAC test vectors in Special Publication 800-38B are faulty, use the corrected ones from here
• Rijndael: http://fp.gladman.plus.com/cryptography_technology/rijndael/
  • zip file contains a full set of round values for each of the 25 block and key length combinations from 128, 160, 192, 224 and 256 bits for one input block and one key value
• DES (enkel ECB): http://www.skepticfiles.org/faq/testdes.htm
• Blowfish: http://www.schneier.com/code/vectors.txt
• Serpent: http://www.cs.technion.ac.il/~biham/Reports/Serpent/
• Twofish: http://www.schneier.com/code/ecb_ival.txt
• AES, DES: http://svn.python.org/projects/external/openssl-0.9.8a/test/evptests.txt
• https://www.cosic.esat.kuleuven.be/nessie/testvectors/
• CMAC
  • AES & TDES: http://www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html
  • AES, TDES2 & TDES3: http://csrc.nist.gov/groups/STM/cavp/documents/mac/cmactestvectors.zip
    • fax folder contains usefull stuff: generation and verification tests with results
      generation test: generate a correct mac
      verification test: verify if provided mac for plaintext is correct
• XTS-AES: IEEE P1619TM/D16: Standard for Cryptographic Protection of Data on Block-Oriented Storage Devices

Chaining Modes

• Wikipedia
• NIST
• XTS:
  • https://siswg.net/index.php?option=com_content&task=view&id=38&Itemid=73
  • http://blog.bjrn.se/2008/02/truecrypt-explained-truecrypt-5-update.html
  • http://en.wikipedia.org/wiki/IEEE_P1619 = XTS-AES
  • XTS-AES: IEEE P1619TM/D16: Standard for Cryptographic Protection of Data on Block-Oriented Storage Devices
• CMAC = OMAC1:
  • AES-CMAC: http://tools.ietf.org/html/rfc4493#page-2
  • NIST:
    Recommendation for Block Cipher Modes of Operation: The CMAC Mode for Authentication:SP 800-38B.pdf
    Updated CMAC Examples
  • OMAC.py: http://github.com/jlhutch/jac/tree/master/omac.py
  • OMAC page: http://www.nuee.nagoya-u.ac.jp/labs/tiwata/omac/omac.html

Ciphers

• Present
  • Article: PRESENT: An Ultra-Lightweight Block Cipher
  • Test Vector generator + ANSI-C implementation of present: [4]