des_dec.py

It is an experimental testing for python M2Crypto module. M2Crypto is not well document. User may no

from M2Crypto import EVP
import cStringIO

def cipher_filter(cipher,inf,outf):
    while 1:
        buf = inf.read()
        if not buf:
            break
        outf.write(cipher.update(buf))
    outf.write(cipher.final())
    return outf.getvalue()


def decript(keyfn,ctxtfn,outfn):

    fk = open(keyfn, 'rb')
    key = fk.read()
    fk.close()
    enc=1
    dec =0
    fc = open(ctxtfn, 'rb')
    ctxt = fc.read()
    fc.close()
    print 'ctxt:', `ctxt`
    j = EVP.Cipher('des_ede_cbc',key,'\x00\x00\x00\x00\x00\x00\x00\x00',dec) #,1,'sha1','saltsalt',5)
    pbuf =cStringIO.StringIO()
    cbuf =cStringIO.StringIO(ctxt)
    ptxt = cipher_filter(j, cbuf, pbuf)
    pbuf.close()
    cbuf.close()
    print `ptxt`
    fo = open(outfn,'wb')
    fo.write(ptxt)
    fo.close()


if __name__=='__main__':
    from optparse import OptionParser
    parser = OptionParser(usage='enc [-k] [-o] msg', version='enc 1.0')
    parser.add_option('-k','--key',dest='keyfile', help='key file',default='des_data/EFsk.4.bin')
    parser.add_option('-o','--out',dest='output',help='output file',default='des_txt.dat')

    (options,args) = parser.parse_args()
    keyfn = options.keyfile
    outfn = options.output
    msgfn = args[0]    

    decript(keyfn,msgfn,outfn)