FIX: @Aczid suggested this to fix a Coverity scan warning.

[proxmark3-svn] / common / tea.c

//-----------------------------------------------------------------------------
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Generic TEA crypto code.
// ref: http://143.53.36.235:8080/source.htm#ansi
//-----------------------------------------------------------------------------
#include "tea.h"
#define ROUNDS 32
#define DELTA  0x9E3779B9
#define SUM    0xC6EF3720

void tea_encrypt(uint8_t *v, uint8_t *key) {

	uint32_t a=0,b=0,c=0,d=0,y=0,z=0;
	uint32_t sum = 0;
	uint8_t n = ROUNDS;
		
	//key
	a = bytes_to_num(key, 4);
	b = bytes_to_num(key+4, 4);
	c = bytes_to_num(key+8, 4);
	d = bytes_to_num(key+12, 4);
	
	//input
	y = bytes_to_num(v, 4);
	z = bytes_to_num(v+4, 4);
		
	while ( n-- > 0 ) {
		sum += DELTA;
		y += ((z << 4) + a) ^ (z + sum) ^ ((z >> 5) + b);
		z += ((y << 4) + c) ^ (y + sum) ^ ((y >> 5) + d);
	}

	num_to_bytes(y, 4, v);
	num_to_bytes(z, 4, v+4);
}

void tea_decrypt(uint8_t *v, uint8_t *key) {

	uint32_t a=0,b=0,c=0,d=0,y=0,z=0;
	uint32_t sum = SUM;
	uint8_t n = ROUNDS;

	//key
	a = bytes_to_num(key, 4);
	b = bytes_to_num(key+4, 4);
	c = bytes_to_num(key+8, 4);
	d = bytes_to_num(key+12, 4);
	
	//input
	y = bytes_to_num(v, 4);
	z = bytes_to_num(v+4, 4);

	/* sum = delta<<5, in general sum = delta * n */
	while ( n-- > 0 ) {
		z -= ((y << 4) + c) ^ (y + sum) ^ ((y >> 5) + d);
		y -= ((z << 4) + a) ^ (z + sum) ^ ((z >> 5) + b);
		sum -= DELTA;
	}
	num_to_bytes(y, 4, v);
	num_to_bytes(z, 4, v+4);
}