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# ------------------------------------------------------------------------------
#
# SHA-512-BASED FEISTEL CIPHER
# by Toni Mattis
#
# Feistel Function: SHA-512(Block || Key)
# Key Size: Fully Dynamic
# Block Size: 1024 Bits
# Rounds: User-Specified
#
# ------------------------------------------------------------------------------
from hashlib import sha512
BPOS = tuple(range(64))
def enc_block(block, key, rounds = 16):
x = block[:64]
y = block[64:]
for i in xrange(rounds):
h = sha512(x + key).digest()
y = ''.join([chr(ord(y[k]) ^ ord(h[k])) for k in BPOS])
h = sha512(y + key).digest()
x = ''.join([chr(ord(x[k]) ^ ord(h[k])) for k in BPOS])
return x + y
def dec_block(block, key, rounds = 16):
x = block[:64]
y = block[64:]
for i in xrange(rounds):
h = sha512(y + key).digest()
x = ''.join([chr(ord(x[k]) ^ ord(h[k])) for k in BPOS])
h = sha512(x + key).digest()
y = ''.join([chr(ord(y[k]) ^ ord(h[k])) for k in BPOS])
return x + y
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