Question

I’m looking for a small easy program to scramble and descramble a file’s contents. The file is a zip file so it might contain any characters. Was thinking something like two’s complement or something, but not sure how to do it in Python.

The reason for this is that my current employer has draconian internet and file installation laws and I would like to mail myself files without the mailer detecting the attachment as a zip file (which it does even if you rename it to .jpg).

I already have Python installed on my work machine.

Answer 1

You could try xor‘ing the contents of the file with a specific value, creating an XOR-cipher, just be sure to read/write the file in binary mode. You’d have to test this out to see if this works for your purposes (it does fine with text files, and I don’t see why it wouldn’t work for binaries.)

Of course you have to use the same (key) value (for instance a character) to encode and decode – though you can use the same code for both of these operations.

Here’s some code I recently put together which does just that:

import sys

def processData(filename, key):
    with open(filename, 'rb') as inf, open(filename+'.xor', 'wb') as outf:
        for line in inf:
            line = ''.join([chr(ord(c)^ord(key)) for c in line])
            outf.write(line)

if __name__ == '__main__':
    if len(sys.argv) != 3:
        print 'Usage: xor_it filename key'
        print '       key = a single character'
    else:
        processData(sys.argv[1], sys.argv[2])