On 2010-01-08 15:47 PM, Daniel Fetchinson wrote:
I have a plain text file which I would like to protect in a very
simple minded, yet for my purposes sufficient, way. I'd like to
encrypt/convert it into a binary file in such a way that possession of
a password allows anyone to convert it back into the original text
file while not possessing the password one would only see the
following with the standard linux utility 'file':
[fetchin...@fetch ~]$ file encrypted.data
encrypted.data: data
and the effort required to convert the file back to the original text
file without the password would be equivalent to guessing the
password.
I'm fully aware of the security implications of this loose
specification, but for my purposes this would be a good solution.
What would be the simplest way to achieve this using preferably stock
python without 3rd party modules? If a not too complex 3rd party
module made it really simple that would be acceptable too.
Paul Rubin's p3.py algorithm is probably the most straightforward way to
meet
these requirements. It's not a standard crypto algorithm by any means,
but
Paul
knows his stuff and has devised it with these deployment restrictions in
mind.
http://www.nightsong.com/phr/crypto/p3.py
Thanks a lot, currently I'm having trouble using this code on python
2.6 but probably some small tweaking will fix it.
Actually, it also doesn't work with python 2.5 and currently I don't
have access to anything older. array.array raises a
ValueError: string length not a multiple of item size
Does anyone recall a change to array.array?
The full traceback is
Traceback (most recent call last):
File "p3.py", line 163, in<module>
_test()
File "p3.py", line 143, in _test
c1 = e(plain,key)
File "p3.py", line 69, in p3_encrypt
xkey = _expand_key(k_enc, n+4)
File "p3.py", line 41, in _expand_key
return array ('L', j)
ValueError: string length not a multiple of item size
Are you on a 64-bit platform? Unfortunately, array's integer typecodes are
platform-specific, but p3.py requires a 32-bit integer and was written on a
32-bit platform. It's reasonably straightforward to fix. Put this bit of
(untested) code at the top of the file and replace occurrences of 'L' with uint32:
# Find the typecode of a 32-bit unsigned integer.
for typecode in 'IL':
if len(array(typecode, [0]).tostring()) == 4:
uint32 = typecode
break
else:
raise RuntimeError("Neither 'I' nor 'L' are unsigned 32-bit integers.")
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
--
http://mail.python.org/mailman/listinfo/python-list
