[utils] Add bytes_to_long() and long_to_bytes()

Used in daisuki.net (#4738)

Both are adapted from public domain PyCrypto:
https://github.com/dlitz/pycrypto/blob/master/lib/Crypto/Util/number.py
This commit is contained in:
Yen Chi Hsuan 2017-02-28 19:16:55 +08:00
parent f48409c7ac
commit 0a5445ddbe

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@ -3319,6 +3319,57 @@ class PerRequestProxyHandler(compat_urllib_request.ProxyHandler):
self, req, proxy, type)
# Both long_to_bytes and bytes_to_long are adapted from PyCrypto, which is
# released into Public Domain
# https://github.com/dlitz/pycrypto/blob/master/lib/Crypto/Util/number.py#L387
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''
n = int(n)
while n > 0:
s = compat_struct_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
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) + compat_struct_unpack('>I', s[i:i + 4])[0]
return acc
def ohdave_rsa_encrypt(data, exponent, modulus):
'''
Implement OHDave's RSA algorithm. See http://www.ohdave.com/rsa/