TEA encryption with 128bit key

源：TEA encryption with 128bit key

If anyone needs some basic encryption in software, here's one solution. This TEA implementation fits within less than 700 bytes. It's based on original TEA. P89LPC901 needs 300ms for 32 iterations. Compiled with "OPTIMIZE (9,SIZE)".

#define _DELTA    0x9E3779B9
#define _ITER     32    
                                /* _ITER = the number of iterations.*/
                                /* 32 is ample, 16 is sufficient,   */
                                /* as few as eight should be OK.    */
#define _SUM      0xC6EF3720
/********************************************************************/
/* Global variables for encryption                                  */
/********************************************************************/
unsigned long int v0,v1;          /* encrypted/decrypted data    */

volatile unsigned long int code
    k0=0x1234aaaa,                /* 128 bit key                */
    k1=0x5678bbbb,                /* hard coded in internal     */
    k2=0x9abc4321,                /* flash memory               */
    k3=0xdef0ffff;                /* Same key used by host      */

/********************************************************************/
/*                                                                  */
/* TEA : The Tiny Encryption Algorithm (TEA)                        */
/*       ba David Wheeler and Roger Needham at the Computer         */
/*         Laboratory of Cambridge University                       */
/*       More info: http://www.simonshepherd.supanet.com/tea.htm    */
/*                                                                  */
/* TEA_decipher - decryption procedure                              */
/*                uses global variables                             */
/*                                                                  */
/* Source ported to Keil C51 by Marko Pavlin                        */
/********************************************************************/
void TEA_decipher(void)
{
    unsigned long int sum=_SUM, delta=_DELTA;
    unsigned char n = _ITER;

　　while(n-->0)
   {
      v1 -= (v0 << 4)+k2 ^ v0+sum ^ (v0 >> 5)+k3;
      v0 -= (v1 << 4)+k0 ^ v1+sum ^ (v1 >> 5)+k1;
      sum -= delta;
   }
}

/********************************************************************/
/*                                                                  */
/* TEA : The Tiny Encryption Algorithm (TEA)                        */
/*                                                                  */
/* TEA_encipher - encryption procedure                              */
/*                uses global variables                             */
/*                                                                  */
/********************************************************************/
void TEA_encipher(void)
{
   unsigned long int sum=0,delta=_DELTA;
   unsigned char n=_ITER;

   while(n-->0)
   {
      sum += delta;
      v0 += (v1 << 4)+k0 ^ v1+sum ^ (v1 >> 5)+k1;
      v1 += (v0 << 4)+k2 ^ v0+sum ^ (v0 >> 5)+k3;
   }
}

Variables are global. If there's enough memory available, use pointer parameters for key and data (adds about 400 bytes for pointer opertions).

Works with 16 bit (unsigned int), too. In this case replace constants with:

#define _DELTA    0x9E37
#define _SUM      0xC6EF

But key in this case is only 64bit.