Documentation

XTEA documentation

This is the documentation for xtea in python.

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|Content |

|1. Functions | |2. The XTEACipher object| |3. Helper functions | |4. Constants |

Functions

New in 0.3.0: Added CFB-mode

function new(key, **kwargs):

Constructor for an "XTEACipher" object

• key - a string, must have a length of 8 (128-bits)

• Optional parameters:

• MODE - int or long, must be one of the following (default 1):

  • 1 (ECB)
  • 2 (CBC)
  • 3 (CFB)
  • 5 (OFB)
  • 6 (CTR) - Buggy (you may loose data)

  Number 4 is the OpenPGP format, it is not used (see more at PEP 272. If 4 is given to the function, a NotImplementedError will be raised.

• IV - string, must have a length of one block (8), needed with CBC and CFB, optional with OFB, if not given in CBC/CFB, raises a value error

• counter - callable function/object, the counter function for CTR, must return a number (int or long

  Warning: In future versions, the counter can return a string or a number

• endian - on of the strings "@", "=", "<", ">" or "!", look in the struct documentation for details, (default is "!", its the same as ">" (network/big endian)).

• rounds - int or long, rounds for the cipher; more rounds = more security = more slowness; 2 rounds = 1 cycle

The XTEACipher object

class XTEACipher(object):

The cipher object

• block_size = 8

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function init(self, key, **kwargs):

Alternative constructor, same as new

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function encrypt(self, data):

Encrpyts data. Modes with initialisation vector will reset, if you recall the function!

• text - string, the text to encrypt. It must have a fixed size (e.g. a multiple of 8 in length)

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function decrypt(self, data):

Decrypts data. Modes with initialisation vector will reset, if you recall the function!

• text - string, the text to decrypt. It must have a fixed size (e.g. a multiple of 8 in length)

Helper functions

function xor_strings(s, t):

Xor to strings together.

• s, t - strings with same length

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function stringToLong(s):

Convert a string(with more then an char) into a long.

• s - strings

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function longToString(n):

Convert a long into a string.

• n - int or long, not every number works

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function _test():

xtea-module self-test. Example result (CTR will fail):

ECB	CBC	OFB	CTR
00	00	00	08

Constants

New in 0.3.0: Added PGP-constant

MODE_ECB = 1
MODE_CBC = 2
MODE_CFB = 3
MODE_PGP = 4
MODE_OFB = 5
MODE_CTR = 6

block_size = 64
key_size = 128