Hashing an int in Python 3

Question

I would like to show my students that MD5 collides the two integer "messages" given here. This is my original demonstration for Python 2.7:

from hashlib import md5

m1 = "d131dd02c5e6eec4693d9a0698aff95c2fcab58712467eab4004583eb8fb7f8955ad340609f4b30283e488832571415a085125e8f7cdc99fd91dbdf280373c5bd8823e3156348f5bae6dacd436c919c6dd53e2b487da03fd02396306d248cda0e99f33420f577ee8ce54b67080a80d1ec69821bcb6a8839396f9652b6ff72a70"
m2 = "d131dd02c5e6eec4693d9a0698aff95c2fcab50712467eab4004583eb8fb7f8955ad340609f4b30283e4888325f1415a085125e8f7cdc99fd91dbd7280373c5bd8823e3156348f5bae6dacd436c919c6dd53e23487da03fd02396306d248cda0e99f33420f577ee8ce54b67080280d1ec69821bcb6a8839396f965ab6ff72a70"
# differences                               ^                                                   ^                           ^                                               ^                                                   ^                           ^

print md5(m1.decode("hex")).hexdigest()
print md5(m2.decode("hex")).hexdigest()

As expected, it prints twice 79054025255fb1a26e4bc422aef54eb4. Now when I try to translate the last two lines into Python 3.5 as:

print(md5(int(m1, 16)).hexdigest())
print(md5(int(m2, 16)).hexdigest())

All I get is a TypeError: object supporting the buffer API required message. The method decode no longer works in Python 3, but I am not sure it's a good idea to replace it by int(m, base) as above. May be the problem is there, and not with the hash function API?

Martijn Pieters · Accepted Answer · 2017-01-12 16:13:39Z

5

In Python 2, decoding strings as hex gives you a bytestring still, not integers. Don't try to interpret your hex strings as integers.

Use the binascii.unhexlify() function to turn your hex strings into a bytestring:

from binascii import unhexlify

print(md5(unhexlify(m1)).hexdigest())

Note that the same code will work fine in Python 2 as well.

If you want to use decoding anyway, use the codecs.decode() function:

import codecs

print(md5(codecs.decode(m1, 'hex')).hexdigest())

Again, the same code works in Python 2 as well.

edited Jan 12, 2017 at 16:13

answered Jan 12, 2017 at 16:08

Martijn Pieters

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1 Comment

Aristide Over a year ago

This works like a charm, thanks! I didn't know this module.

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