/* zx8 (ps) - Stream Cipher Algorithm/Source Code */

/*
Copyright (c) 2012, Karl-Uwe Frank
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

  1. Redistributions of source code must retain the above copyright
  notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#** zx8 (ps) algorithm developed by Karl-Uwe Frank
*/



/*
------------------------------------------------------------------
 zx8 (ps) Test vectors
------------------------------------------------------------------
 Key:        Password 
 Keystream:  8A1A89B3221AC4AB9AAB   
 Plaintext:  Plaintext
 Ciphertext: DA76E8DA4C6EA1D3EEA1
--------------------------------------------------------------------
 Key:        SecretKey  
 Keystream:  983283BFE117A0B211E5B433FD0799DCBB43           
 Plaintext:  Secure my Secrets   
 Ciphertext: CB57E0CA937280DF68C5E7569E75FCA8C849
--------------------------------------------------------------------
 Key:        HQQMG005
 Keystream:  9094D05D6D1F67EAE75C6A6FD59D35
 Plaintext:  Attack at dawn
 Ciphertext: D1E0A43C0E74478B937C0E0EA2F33F
-------------------------------------------------------------------
 Key:        HQQMG007
 Keystream:  295C7428FC2C329C627ADD05043F76AC
 Plaintext:  Victory is near
 Ciphertext: 7F35175C935E4BBC0B09FD6B615E04A6
-------------------------------------------------------------------
*/



//-----------------------------------------
//
// zx8_ps  ***** #1 * 23.01.2012 *****
//


//-----------------------------------------
// 
// Swap Values
//
// http://rosettacode.org/wiki/Generic_swap#Works_with:_gcc
//
#define swap(X,Y)  do { __typeof__ (X) _T = X; X = Y; Y = _T; } while(0)


//-----------------------------------------
//
// Global Varaiable Definition
// 
static unsigned char KeyWord[256]; int KeyLen=0;  


// Secret State Arrays
//
static unsigned char z[256], x[256];

// Global Carry on Array Indices
//
static unsigned char a, b;

// function
unsigned char PRGA();


//-----------------------------------------
// 
// Key Schedule Algorithm (ps)
//
void KSA() 
{
  // Key must be at least 12 Characters long
  // and should have >= 60-Bit of Entropy.
  int i;
  unsigned char j, k, n, t; 

  // Prefill the Arrays
  for (i=0; i<256; i++) {
    z[i] = i;
    x[i] = i;
  }
   
  a=0; b=0; j=0; k=0; n=0;
  
  for (i=0; i<256; i++) {
    k = (i % KeyLen);

    for (n=0; n<128; n++) t = PRGA();
    j = (t + j + z[i] + KeyWord[k]);
    swap(z[i], z[j]);
    
    for (n=0; n<128; n++) t = PRGA();
    j = (t + j + x[i] + z[x[j]]);
    swap(x[i], x[j]);
  } 

  // Reset the Array Indices Start Point
  a=0; b=0;
}


//-----------------------------------------
//
// Pseudo Random Generation Algorithm (ps)
//
unsigned char PRGA()
{
  unsigned char n1, n2, y, m;
  
  // Calculate distant Array Element Indices
  n1 = z[a] + x[a];
  n2 = z[b] + x[b];

  // First Swap randomly selected Array Element
  swap(z[a], z[n1]);
  swap(x[a], x[n2]);

  // Update the global Carry on Array Indices
  a = a + b + (n1^n2);
  b = b + 1;

  // Second Swap sequentially cycle over every Array Element
  swap(z[b], z[n1]);
  swap(x[b], x[n2]);

  // Calculate the internal State Selector Value
  y = (z[n1] ^ x[n2]);

  // Calculate the internal State Protection Value
  m = (n1 + n2);

  // Never reveal internal State Values directly
  return (z[x[y]] ^ m);
}