Binary conversion and XOR in python

Question

I am doing an assignment to decipher a one-time-pad code (7 sentences, repeated keys for each character position among all 7 sentences). I'm solving it by guess work and I need to XOR the binary value of my guess letter with the binary value of the cypher character in order to get a key.

However, I cannot XOR the binary values returned by Python as they are in string format. I cannot convert them to integers since I need the '0b' part, but I also cannot XOR it because it's a string.

Any suggestions as to how to work around this?

Martijn Pieters · Accepted Answer · 2015-03-11 10:16:18Z

4

Integers in Python support binary bitwise operations; the binary bitwise operators take integer operands and produce new integers with the bits altered, just like they would in C code.

Convert your string (presumably you have something like 0b1001101) to integer, use the ^ XOR operator on that. If you need string output at the end, you can always use bin() again on the integer:

>>> bin(102)
'0b1100110'
>>> 102 ^ 255
153
>>> bin(102 ^ 255)
'0b10011001'

If you have ASCII bytes (characters in Python 2 strings are bytes), use ord() to get an integer representation, chr() to go back to a byte (character) again.

answered Mar 11, 2015 at 10:16

Martijn Pieters

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