[PYTHON-CRYPTO] amkCrypto: Cipher decrypt(string) output

[Jason R. Mastaler]

"Jason R. Mastaler" <jason-list-python-crypto at MASTALER.COM> writes:

> I'm experimenting with amkCrypto, and I'm confused about the output
> I'm getting back from a decrypted string.
>
>         #!/usr/bin/env python
>         import time
>         from Crypto.Cipher import Blowfish
>         key = '146bfea4ab7274e6f0ccff25351c2f39'
>         cipherobj=Blowfish.new(key, Blowfish.CBC)
>         input =  '%16d' % (time.time() +1)
>         dated_cookie = cipherobj.encrypt(input)
>         plaintext = cipherobj.decrypt(dated_cookie)
>
>         print input
>         print plaintext
>
> This code produces the following output where `*' is really a binary
> character:
>
>        985728133
> ********85728133
>
> Why aren't input and plaintext identical?  The strings end the same,
> but plaintext has some binary characters at its beginning.

Strangely, if I create a new cipher object using ECB mode instead of
CBC mode, I no longer have this problem, but I'm unsure as to why this
makes a difference.  Here is the above piece of code with only line 5
changed:

         #!/usr/bin/env python
         import time
         from Crypto.Cipher import Blowfish
         key = '146bfea4ab7274e6f0ccff25351c2f39'
         cipherobj=Blowfish.new(key, Blowfish.ECB)
         input =  '%16d' % (time.time() +1)
         dated_cookie = cipherobj.encrypt(input)
         plaintext = cipherobj.decrypt(dated_cookie)

         print input
         print plaintext

Output:

       985740024
       985740024