[pycrypto] DES3 problem

Dave Pawson dave.pawson at gmail.com
Sun Nov 24 06:50:27 PST 2013

https://www.dlitz.net/software/pycrypto/api/current/ states DES3 requires an iv.

in the api docs the example uses DES not DES3?

As an example, encryption can be done as follows:

>>> from Crypto.Cipher import DES
>>> from Crypto import Random
>>> from Crypto.Util import Counter
>>> key = b'-8B key-'
>>> nonce = Random.new().read(DES.block_size/2)
>>> ctr = Counter.new(DES.block_size*8/2, prefix=nonce)
>>> cipher = DES.new(key, DES.MODE_CTR, counter=ctr)
>>> plaintext = b'We are no longer the knights who say ni!'
>>> msg = nonce + cipher.encrypt(plaintext)

        ciphere = DES3.new(key,mode,IV=iv)

I'm getting
Traceback (most recent call last):
  File "./tester.py", line 405, in testBlock5
    ciphere = DES3.new(key,mode,IV=iv)
  File "/usr/lib64/python3.3/site-packages/Crypto/Cipher/DES3.py",
line 114, in new
    return DES3Cipher(key, *args, **kwargs)
  File "/usr/lib64/python3.3/site-packages/Crypto/Cipher/DES3.py",
line 76, in __init__
    blockalgo.BlockAlgo.__init__(self, _DES3, key, *args, **kwargs)
  File "/usr/lib64/python3.3/site-packages/Crypto/Cipher/blockalgo.py",
line 155, in __init__
    raise ValueError("MODE_OPENPGP requires an IV")
ValueError: MODE_OPENPGP requires an IV

Am I wrong in my usage or is the code incorrect please
wrt iv parameter?


Dave Pawson
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