xor function in python

Question

I'll be happy if someone can help with XOR function in python.

for example, I have two quite big messages (about 300 symbols) that is writteb by hex code how can I XOR them properly? I tried use general functions and converted to another types, but I wasn't able to do that(

I don't know which type of data I need to convert for?

Can you please clarify, the "symbols" in the messages are in hex in text, i.e. strings like "46 6f 6f"? — Some programmer dude
– Some programmer dude, Commented Nov 10, 2012 at 18:01
right, there it is -->> e877a5e68bea88d61b93ac5ee0d562e8e9... — Leo
– Leo, Commented Nov 10, 2012 at 18:04
1. It looks like you're trying to do crypto. Use an existing crypto library instead of rolling your own. 2. What are your inputs and desired outputs? What have you tried? — Russell Borogove
– Russell Borogove, Commented Nov 10, 2012 at 18:08

kaspersky · Accepted Answer · 2012-11-10 19:22:24Z

6

If I get your question correctly, if you have 2 hex numbers represented as string:

a = "e877a5e68bea88d61b93ac5ee0d562e8e9"
b = "23fe3231699ade23482"

you can xor any of them with some mask, by converting to int, and applying bitwise xor operator:

xor_result = int(a, 16) ^ int(b, 16)

print '%x' % xor_result

and, if you want to keep the original format

string_xor_result = hex(xor_result)[2:]

edited Nov 10, 2012 at 19:22

answered Nov 10, 2012 at 18:16

kaspersky

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5 Comments

Xavier Over a year ago

The best way to find out is to try, but python has arbitrary precision ints, so it should be ok.

kaspersky Over a year ago

As Xavier said, python can handle very, very large integers (the only limit comes from the machine available memory), so a 300 digits hex number (~16 ** 300) isn't a problem.

martineau Over a year ago

I'd up-vote this if it included converting the result back to a string of hex digits...

Leo Over a year ago

by the way, does it appropriate to strings with differents lengths? –

kaspersky Over a year ago

@user1813163, yes, technically the shorter string (smaller number) will be prepending with leading zeroes.

Xavier · Accepted Answer · 2012-11-10 19:26:04Z

1

Iterate over the string chars, then convert each char to int (int(a,16)), then apply xor, reconvert to hex with hex, strip the leading '0x' with [2:], and finally join everything

stra = 'abc'
strb = 'abd'
''.join(hex( int(a,16) ^ int(b,16) )[2:] for a,b in zip(stra, strb))

Note that, as pointed in the comments, it will work only if the two strings have the same length. Otherwise some chars of the longer string will be ignored.

edited Nov 10, 2012 at 19:26

answered Nov 10, 2012 at 18:13

Xavier

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3 Comments

yati sagade Over a year ago

Won't this break if the two strings have unequal lengths?

Xavier Over a year ago

It depends on what you call break :). zip will return tuples only for the minimum length of its parameters. zip('abc','ab') is [('a', 'a'), ('b', 'b')]

martineau Over a year ago

I'd call ignoring part of one of the values "broken".

ozpeke · Accepted Answer · 2014-04-08 08:37:51Z

1

If two strings do not have the same length you can add one line, cycle()

stra = raw_input("msg: ")
strb = raw_input("key: ")
strb = cycle(strb)

print ''.join(hex( int(a,16) ^ int(b,16) )[2:] for a,b in zip(stra, strb))

answered Apr 8, 2014 at 8:37

ozpeke

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