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test_crypto.doctest - test various internal crypto helper functions
Copyright (C) 2016 Arthur de Jong
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA
>>> import random
>>> from binascii import a2b_hex, b2a_hex
>>> def tostr(x):
... return str(x.decode())
>>> def decode(f):
... return lambda x: tostr(f(x))
>>> b2a_hex = decode(b2a_hex)
>>> from pskc.crypto import pad, unpad
Tests for padding and unpadding. This should follow PKCS#7 as defined in RFC
5652 section 6.3.
>>> b2a_hex(pad(a2b_hex('1234'), 16))
'12340e0e0e0e0e0e0e0e0e0e0e0e0e0e'
>>> b2a_hex(pad(a2b_hex('abcdefabcdefabcdefabcdefabcdef'), 16))
'abcdefabcdefabcdefabcdefabcdef01'
>>> b2a_hex(pad(bytearray(16 * [65]), 16))
'4141414141414141414141414141414110101010101010101010101010101010'
>>> b2a_hex(unpad(a2b_hex('12340e0e0e0e0e0e0e0e0e0e0e0e0e0e'), 16))
'1234'
>>> b2a_hex(unpad(a2b_hex('abcdefabcdefabcdefabcdefabcdef01'), 16))
'abcdefabcdefabcdefabcdefabcdef'
Padding should always work but there are some conditions where unpadding does
not work. Specifically, the to be removed padding should all have the same
bytes:
>>> b2a_hex(unpad(a2b_hex('ffff0606060f0606'), 8)) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
DecryptionError: Invalid padding
The unpadding should also refuse to remove more than a block size worth of
data:
>>> b2a_hex(unpad(a2b_hex('ffff0e0e0e0e0e0e0e0e0e0e0e0e0e0e'), 8)) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
DecryptionError: Invalid padding
We generate a number of (non-cryptographically strong) random strings and
ensure that padding and unpadding works for them.
>>> for i in range(100):
... l = random.randrange(1, 255)
... r = bytearray(random.getrandbits(8) for x in range(l))
... b = random.randrange(10, 100)
... p = pad(r, b)
... u = unpad(p, b)
... if u != r:
... raise ValueError('%s -> %s -> %s (%d)' % (
... b2a_hex(r), b2a_hex(p), b2a_hex(u), b))
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