>>>>> 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.")
Thanks! That was exactly the problem, I'm on a 64 bit machine and your fix seems to work indeed. Cheers, Daniel -- Psss, psss, put it down! - http://www.cafepress.com/putitdown -- http://mail.python.org/mailman/listinfo/python-list
