PySecretHandshake/secret_handshake/util.py

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2017-06-04 19:50:49 +00:00
import struct
# Stolen from PyCypto (Public Domain)
def b(s):
return s.encode("latin-1") # utf-8 would cause some side-effects we don't want
def long_to_bytes(n, blocksize=0):
"""long_to_bytes(n:long, blocksize:int) : string
Convert a long integer to a byte string.
If optional blocksize is given and greater than zero, pad the front of the
byte string with binary zeros so that the length is a multiple of
blocksize.
"""
# after much testing, this algorithm was deemed to be the fastest
s = b('')
pack = struct.pack
while n > 0:
s = pack('>I', n & 0xffffffff) + s
n = n >> 32
# strip off leading zeros
for i in range(len(s)):
if s[i] != b('\000')[0]:
break
else:
# only happens when n == 0
s = b('\000')
i = 0
s = s[i:]
# add back some pad bytes. this could be done more efficiently w.r.t. the
# de-padding being done above, but sigh...
if blocksize > 0 and len(s) % blocksize:
s = (blocksize - len(s) % blocksize) * b('\000') + s
return s
def bytes_to_long(s):
"""bytes_to_long(string) : long
Convert a byte string to a long integer.
This is (essentially) the inverse of long_to_bytes().
"""
acc = 0
unpack = struct.unpack
length = len(s)
if length % 4:
extra = (4 - length % 4)
s = b('\000') * extra + s
length = length + extra
for i in range(0, length, 4):
acc = (acc << 32) + unpack('>I', s[i:i+4])[0]
return acc