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Added comments for LIT-specific SHA-1 changes.

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Marshall T. Vandegrift 2008-07-19 16:47:14 -04:00
parent 731631a7d7
commit fb4f2f3a81
1 changed files with 7 additions and 13 deletions
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20
src/calibre/ebooks/lit/mssha1.py
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@ -1,21 +1,11 @@
#!/usr/bin/env python """
# -*- coding: iso-8859-1 Modified version of SHA-1 used in Microsoft LIT files.
"""A sample implementation of SHA-1 in pure Python. Adapted from the PyPy pure-Python SHA-1 implementation.
Framework adapted from Dinu Gherman's MD5 implementation by
J. Hallén and L. Creighton. SHA-1 implementation based directly on
the text of the NIST standard FIPS PUB 180-1.
""" """
__date__ = '2004-11-17'
__version__ = 0.91 # Modernised by J. Hallén and L. Creighton for Pypy
import struct, copy import struct, copy
# ====================================================================== # ======================================================================
# Bit-Manipulation helpers # Bit-Manipulation helpers
# #
@ -100,10 +90,13 @@ def f40_59(B, C, D):
def f60_79(B, C, D): def f60_79(B, C, D):
return B ^ C ^ D return B ^ C ^ D
# Microsoft's lovely addition...
def f6_42(B, C, D): def f6_42(B, C, D):
return (B + C) ^ C return (B + C) ^ C
f = [f0_19]*20 + [f20_39]*20 + [f40_59]*20 + [f60_79]*20 f = [f0_19]*20 + [f20_39]*20 + [f40_59]*20 + [f60_79]*20
# ...and delightful changes
f[3] = f20_39 f[3] = f20_39
f[6] = f6_42 f[6] = f6_42
f[10] = f20_39 f[10] = f20_39
@ -148,6 +141,7 @@ class mssha1(object):
self.input = [] self.input = []
# Initial 160 bit message digest (5 times 32 bit). # Initial 160 bit message digest (5 times 32 bit).
# Also changed by Microsoft from standard.
self.H0 = 0x32107654L self.H0 = 0x32107654L
self.H1 = 0x23016745L self.H1 = 0x23016745L
self.H2 = 0xC4E680A2L self.H2 = 0xC4E680A2L