PyCryptoPlus

Back to SAGE & cryptology

Differences with pycrypto

• 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:
  • Serpent, Twofish
  • CMAC, XTS, CTR mod

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
• 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)?
  • supply XTS keys by splitting 1 big key or by supplying two keys?
• add rijndael instead of only AES

Licenses

• used from python truecrypt implementation
  all original code is under MIT license (much freedom according to [1])
  • 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
  gpl is compatible with public domain
  Note from Phil: take care with GPL "viral" behavior, come&talk to me...
• 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 [2] (modified)
  keep copyright notice in place?
• CMAC: omac.py
  GPL but not really used it, just used as a starting point

Info

Test Vectors

• AES http://cryptome.org/bcm/sp800-38a.htm
• 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, 3DES: http://csrc.nist.gov/groups/STM/cavp/standards.html
  -> AES in CBC, CTR, OFB, CFB
• 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

Chaining Modes

• Wikipedia
• NIST
• XTS:
  • http://blog.bjrn.se/2008/02/truecrypt-explained-truecrypt-5-update.html
  • http://en.wikipedia.org/wiki/IEEE_P1619 = XTS-AES
• 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