RC4 algorithm with SBOX extension

rc4_ext.py

def decode_data(data, key, sz): 
    S = list(range(sz)) 
    S = [x&0xff for x in S] 
    j = 0 
    out = []
    for i in range(sz): 
        j = (j + S[i] + ord( key[i % len(key)] )) % sz 
        S[i] , S[j] = S[j] , S[i]
    i = j = 0 
    for char in data: 
        i = ( i + 1 ) % sz 
        j = ( j + S[i] ) % sz 
        S[i] , S[j] = S[j] , S[i] 
        out.append(chr(ord(char) ˆ S[(S[i] + S[j]) % sz])) 
    return ''.join(out)