#-----------------------------------------
# 
# Swap Values 
#
# (primitive Way for some Kind of ANSI-C
#  Compatibility when comparing the Listing)
#
def swap(X,Y):
  return Y, X


# -----------------------------------------
# 
#  Global Varaiable Definition
#  
KeyWord  = bytearray(256)
Nonce    = bytearray(256)
KeyLen   = int(0)
NonceLen = int(0)

# Secret State Arrays
z = bytearray(256)
x = bytearray(256)

# Global Carry on Array Indices
a = int(0)
b = int(0)


#-----------------------------------------
# 
# RC4 Reference Implemantation
#
def KSA():
    global KeyWord, KeyLen
    global z, x, a, b
    
    i = int(0)
    
    # Prefill the Arrays
    for i in range(256):
        x[i] = i;
    
    k = j = int(0)
    
    for i in range(256):
        k = (i % KeyLen)
        j = (j + x[i] + KeyWord[k]) % 256
        x[i], x[j] = swap(x[i], x[j])
        
    a = b = int(0)


def PRGA():
    global a, b
    t = int(0) 

    # Update the global Carry on Array Indices
    a = (a + 1) % 256
    b = (b + x[a]) % 256
    
    x[a], x[b] = swap(x[a], x[b])
    
    # XOR Plaintext/Ciphertext
    t = (x[a] + x[b]) % 256
    
    return x[t]



# 
# /*------------------------------------------------------------------
# # RC4 Test vectors
# #------------------------------------------------------------------
# Key			Keystream 				Plaintext 			Ciphertext
# --------------------------------------------------------------------
# Key 		EB9F7781B734CA72A719... 	Plaintext 			BBF316E8D940AF0AD3
# 
# Wiki		6044DB6D41B7...						pedia						1021BF0420
# 
# Secret	04D46B053CA87B59...				Attack at dawn	45A01F645FC35B383552544B9BF5
# -------------------------------------------------------------------*/
#