yawPyCrypto : encrypt file in blocks

[John Hunter]

>>>>> "John" == John Hunter <jdhunter at ace.bsd.uchicago.edu> writes:

    John> Apparently, I am not handling the final bytes correctly.
    John> The file size are listed below the code.

    John> Any advice?  Also, is this the best way to encrypt large
    John> files?  Is there a preferred block size?

Hmmm, I thought I had posted a follow up to this yesterday but it
didn't appear to come through.  Apologies if you get a duplicate.

I discovered the source of this problem.  I needed to write the
encrypted/decrypted stream one more time after the call to finish.
The following works

from yawPyCrypto.Cipher import DecryptCipher, EncryptCipher
from yawPyCrypto.Cipher import ZipDecryptCipher, ZipEncryptCipher
from yawPyCrypto.Constants import CIPHER_BLOWFISH, MODE_CBC

def encrypt(passwd, infile, outfile, blocksize=1024, enc=None):
    """
    Encrypt the data in the file handle infile to the file handle
    outfile in blocks of length blocksize

    enc is a EncryptCipher instace.  If None, default to
    EncryptCipher(passwd, CIPHER_BLOWFISH, MODE_CBC)
    """

    if enc is None:
        enc = EncryptCipher(passwd, CIPHER_BLOWFISH, MODE_CBC)
    while 1:
        data = infile.read(blocksize)
        if len(data)==0: break
        enc.feed(data)
        outfile.write(enc.data)
    enc.finish()
    outfile.write(enc.data)
    infile.close()
    outfile.close()


def decrypt(passwd, infile, outfile, blocksize=1024, dec=None):
    """
    Decrypt the data in the file handle infile to the file handle
    outfile in blocks of length blocksize

    dec is a DecryptCipher instace.  If None, default to
    DecryptCipher(passwd)
    """
    if dec is None:
        dec = DecryptCipher(passwd)

    while 1:
        data = infile.read(blocksize)
        if len(data)==0: break
        dec.feed(data)
        outfile.write(dec.data)
    dec.finish()
    outfile.write(dec.data)
    infile.close()
    outfile.close()


passwd = 'a really bad passwd'
infile = file('source.mp3', 'rb')
outfile = file('crypted.mp3.cr', 'wb')
encrypt(passwd, infile, outfile)

infile = file('crypted.mp3.cr', 'rb')
outfile = file('decrypted.mp3', 'wb')
decrypt(passwd, infile, outfile)