[pycrypto] checksum problem.

Dave Pawson dave.pawson at gmail.com
Thu Sep 1 03:46:58 CST 2011

I've been ignoring a checksum error for some time now,  and decided to
ask for help.

def decrypt(ciphertext, secret, lazy=True, checksum=True):
    """decrypt ciphertext with secret
    ciphertext  - encrypted content to decrypt
    secret      - secret to decrypt ciphertext
    lazy        - pad secret if less than legal blocksize (default: True)
    checksum    - verify crc32 byte encoded checksum (default: True)
    returns plaintext
    secret = _lazysecret(secret) if lazy else secret
    encobj = AES.new(secret, AES.MODE_CFB)
    plaintext = encobj.decrypt(ciphertext)
    if checksum:
        crc, plaintext = (plaintext[-4:], plaintext[:-4])
        if not crc == struct.pack("i", zlib.crc32(plaintext)):
            print "Checksum error"
            #raise CheckSumError("checksum mismatch")
    return plaintext

1. I'm not sure how its happening or what I can do to resolve it?

Currently working on windows.
Reading the file using binary mode
Ditto writing.

I'm creating a plain text file,
then writing back to disk

Access then reads the file, decrypts and returns the sought string.
The checksum error is showing in the decrypt fn above.

Any help appreciated.

Dave Pawson
Docbook FAQ.

More information about the pycrypto mailing list