Python Standard Library

The md5 Module

The md5 module is used to calculate message signatures (message digests).

The md5 algorithm calculates a strong 128-bit signature. This means that if two strings are different, it’s highly likely that their md5 signatures are different as well. To put it another way, given an md5 digest, it’s supposed to be nearly impossible to come up with a string that generates that digest. Example 2-35 demonstrates the md5 module.

Example 2-35. Using the md5 Module

File: md5-example-1.py

import md5

hash = md5.new()
hash.update("spam, spam, and eggs")

print repr(hash.digest())

 'L\005J\243\266\355\243u`\305r\203\267\020F\303'

Note that the checksum is returned as a binary string. Getting a hexadecimal or base64-encoded string is quite easy, though, as Example 2-36 shows.

Example 2-36. Using the md5 Module to Get a Hexadecimal or Base64-Encoded md5 Value

File: md5-example-2.py

import md5
import string
import base64

hash = md5.new()
hash.update("spam, spam, and eggs")

value = hash.digest()
print string.join(map(lambda v: "%02x" % ord(v), value), "")
# in 2.0, the above can be written as
# print hash.hexdigest()

print base64.encodestring(value)

4c054aa3b6eda37560c57283b71046c3
TAVKo7bto3VgxXKDtxBGww==

Example 2-37 shows how, among other things, the md5 checksum can be used for challenge-response authentication (but see the note on random numbers later).

Example 2-37. Using the md5 Module for Challenge-Response Authentication

File: md5-example-3.py import md5 import string, random def getchallenge(): ...