Help with script error

[mason28]

Hi everyone,

I found the following code at (devnote.stokemaster.com/2009/07/simple-way-to-encrpt-and-decrypt-short.html).

When I put print statements to debug, the script dies in the function "p3_encrypt" at the line "stream = array('L', plain+'0000'[n&3:])". I am using Python 2.7.

How do fix it to make it work?

from string import join
from array import array
#import sha
import hashlib
from time import time

class CryptError(Exception): pass
def _hash(str): return hashlib.sha224(str).digest()


_ivlen = 16
_maclen = 8
_state = _hash(`time()`)

try:
   import os
   _pid = `os.getpid()`
except ImportError, AttributeError:
   _pid = ''

def _expand_key(key, clen):
   blocks = (clen+19)/20
   xkey=[]
   seed=key
   for i in xrange(blocks):
       seed=hashlib.sha224(key+seed).digest()
       xkey.append(seed)
   j = join(xkey,'')
   return array ('L', j)

def p3_encrypt(plain,key):
   global _state
   H = _hash

   # change _state BEFORE using it to compute nonce, in case there's
   # a thread switch between computing the nonce and folding it into
   # the state. This way if two threads compute a nonce from the
   # same data, they won't both get the same nonce. (There's still
   # a small danger of a duplicate nonce--see below).
   _state = 'X'+_state

   # Attempt to make nlist unique for each call, so we can get a
   # unique nonce. It might be good to include a process ID or
   # something, but I don't know if that's portable between OS's.
   # Since is based partly on both the key and plaintext, in the
   # worst case (encrypting the same plaintext with the same key in
   # two separate Python instances at the same time), you might get
   # identical ciphertexts for the identical plaintexts, which would
   # be a security failure in some applications. Be careful.
   nlist = [`time()`, _pid, _state, `len(plain)`,plain, key]
   nonce = H(join(nlist,','))[:_ivlen]
   _state = H('update2'+_state+nonce)
   k_enc, k_auth = H('enc'+key+nonce), H('auth'+key+nonce)
   n=len(plain) # cipher size not counting IV

   ####### Script dies here! ###########
   stream = array('L', plain+'0000'[n&3:]) # pad to fill 32-bit words
   xkey = _expand_key(k_enc, n+4)
   for i in xrange(len(stream)):
       stream[i] = stream[i] ^ xkey[i]
   ct = nonce + stream.tostring()[:n]
   auth = _hmac(ct, k_auth)
   return ct + auth[:_maclen]

def p3_decrypt(cipher,key):
   H = _hash
   n=len(cipher)-_ivlen-_maclen # length of ciphertext
   if n < 0:
       raise CryptError, "invalid ciphertext"
   nonce,stream,auth = \
     cipher[:_ivlen], cipher[_ivlen:-_maclen]+'0000'[n&3:],cipher[-_maclen:]
   k_enc, k_auth = H('enc'+key+nonce), H('auth'+key+nonce)
   vauth = _hmac (cipher[:-_maclen], k_auth)[:_maclen]
   if auth != vauth:
       raise CryptError, "invalid key or ciphertext"

   stream = array('L', stream)
   xkey = _expand_key (k_enc, n+4)
   for i in xrange (len(stream)):
       stream[i] = stream[i] ^ xkey[i]
   plain = stream.tostring()[:n]
   return plain

# RFC 2104 HMAC message authentication code
# This implementation is faster than Python 2.2's hmac.py, and also works in
# old Python versions (at least as old as 1.5.2).
from string import translate
def _hmac_setup():
   global _ipad, _opad, _itrans, _otrans
   _itrans = array('B',[0]*256)
   _otrans = array('B',[0]*256)
   for i in xrange(256):
       _itrans[i] = i ^ 0x36
       _otrans[i] = i ^ 0x5c
   _itrans = _itrans.tostring()
   _otrans = _otrans.tostring()

   _ipad = '\x36'*64
   _opad = '\x5c'*64

def _hmac(msg, key):
   if len(key)>64:
       key=sha.new(key).digest()
   ki = (translate(key,_itrans)+_ipad)[:64] # inner
   ko = (translate(key,_otrans)+_opad)[:64] # outer
   return hashlib.sha224(ko+hashlib.sha224(ki+msg).digest()).digest()

_hmac_setup()
#_test()
#_speed() # uncomment to run speed test