/* 
 * File:	rc6.c
 * Author:	Daniel Otte
 * Date: 	06.08.2006
 * License: GPL
 * Description: Implementation of the RC6 cipher algorithm.
 * 	This implementation is restricted to 32-bit words and to keys up to 65535 bit in length (but this is
 *  quite easy to expand), but free in the choice of number of rounds (0 to 125).
 * 	so it is RC6-32/r/b
 * THIS ONLY WORKS FOR LITTEL ENDIAN!!!
 */
 
 #include <stdint.h>
 #include <stdlib.h>
 #include "rc6.h"
 #include "config.h"
 
 #define P32 0xB7E15163		/* e -2 */
 #define Q32 0x9E3779B9		/* Golden Ratio -1 */
 
uint32_t rotl32(uint32_t a, uint8_t n){
 	n &= 0x1f; /* higher rotates would not bring anything */
 	return ( (a<<n)| (a>>(32-n)) );
 }

uint32_t rotr32(uint32_t a, uint8_t n){
 	n &= 0x1f; /* higher rotates would not bring anything */
 	return ( (a>>n)| (a<<(32-n)) );
 }
 
 uint8_t rc6_init(rc6_ctx_t *s,void* key, uint16_t keylength){
 	return rc6_initl(s, key, keylength, 20);
 }
 
 
 uint8_t rc6_initl(rc6_ctx_t *s,void* key, uint16_t keylength, uint8_t rounds){
 	uint8_t i,j;
 	uint16_t v,p,c;
 	uint32_t a,b, l=0;
 	if (rounds>125)
 		return 2;
 	if(!(s->S=malloc((2*rounds+4)*sizeof(uint32_t))))
 		return 1;
 	
 	s->rounds=rounds;
 	
 	c = keylength/32;
 	if (keylength%32){ 
 		++c;
 		j=(keylength%32)/8;
 		if(keylength%8)
 			++j;
 		for (i=0; i<j; ++i) 
 			((uint8_t*)&l)[i] = ((uint8_t*)key)[(c-1)*4 + i];
 	} else {
 		l = ((uint32_t*)key)[c-1];
 	}
 	
 	s->S[0] = P32;
 	for(i=1; i<2*rounds+4; ++i){
		s->S[i] = s->S[i-1] + Q32;
	}
	
	a=b=j=i=0;
	v = 3 * ((c > 2*rounds+4)?c:(2*rounds+4));
	for(p=1; p<=v; ++p){
		a = s->S[i] = rotl32(s->S[i] + a + b, 3);
		if (j==c-1){
			b = l = rotl32(l+a+b, a+b);
		} else {
			b = ((uint32_t*)key)[j] = rotl32(((uint32_t*)key)[j]+a+b, a+b);
		}
		i = (i+1) % (2*rounds+4);
		j = (j+1) % c;
	}
	return 0;
 }
 
 void rc6_free(rc6_ctx_t *s){
 	free(s->S);
 } 
 
 #define LG_W 5
 #define A (((uint32_t*)block)[0])
 #define B (((uint32_t*)block)[1])
 #define C (((uint32_t*)block)[2])
 #define D (((uint32_t*)block)[3])
 
 void rc6_enc(rc6_ctx_t *s, void* block){
 	uint8_t i;
 	uint32_t t,u,x; /* greetings to Linux? */
 	B += s->S[0];
 	D += s->S[1];
 	for (i=1; i<=s->rounds; ++i){
 		t = rotl32(B * (2*B+1), LG_W);
 		u = rotl32(D * (2*D+1), LG_W);
 		A = rotl32((A ^ t), u) + s->S[2*i];
 		C = rotl32((C ^ u), t) + s->S[2*i+1];
 		x = A;
 		A = B;
 		B = C;
 		C = D;
 		D = x;
 	}
 	A += s->S[2*s->rounds+2];
 	C += s->S[2*s->rounds+3];
 }
 
 void rc6_dec(rc6_ctx_t *s, void* block)
 {
 	uint8_t i;
 	uint32_t t,u,x; /* greetings to Linux? */
 
 	C -= s->S[2*s->rounds+3];
 	A -= s->S[2*s->rounds+2];
 	
 	for (i=s->rounds; i>0; --i){
 		x=D;
 		D=C;
 		C=B;
 		B=A;
 		A=x;
 		u = rotl32(D * (2*D+1), LG_W);
 		t = rotl32(B * (2*B+1), LG_W);
 		C = rotr32(C - s->S[2*i+1], t) ^ u;
 		A = rotr32(A - s->S[2*i+0], u) ^ t;
 	}
 	D -= s->S[1];
 	B -= s->S[0];
 }