132 lines
2.8 KiB
C
132 lines
2.8 KiB
C
/*
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* File: rc6.c
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* Author: Daniel Otte
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* Date: 06.08.2006
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* License: GPL
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* Description: Implementation of the RC6 cipher algorithm.
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* This implementation is restricted to 32-bit words and to keys up to 65535 bit in length (but this is
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* quite easy to expand), but free in the choice of number of rounds (0 to 125).
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* so it is RC6-32/r/b
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* THIS ONLY WORKS FOR LITTEL ENDIAN!!!
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*/
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#include <stdint.h>
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#include <stdlib.h>
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#include "rc6.h"
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#include "config.h"
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#define P32 0xB7E15163 /* e -2 */
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#define Q32 0x9E3779B9 /* Golden Ratio -1 */
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uint32_t rotl32(uint32_t a, uint8_t n){
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n &= 0x1f; /* higher rotates would not bring anything */
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return ( (a<<n)| (a>>(32-n)) );
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}
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uint32_t rotr32(uint32_t a, uint8_t n){
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n &= 0x1f; /* higher rotates would not bring anything */
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return ( (a>>n)| (a<<(32-n)) );
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}
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uint8_t rc6_init(rc6_ctx_t *s,void* key, uint16_t keylength){
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return rc6_initl(s, key, keylength, 20);
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}
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uint8_t rc6_initl(rc6_ctx_t *s,void* key, uint16_t keylength, uint8_t rounds){
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uint8_t i,j;
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uint16_t v,p,c;
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uint32_t a,b, l=0;
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if (rounds>125)
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return 2;
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if(!(s->S=malloc((2*rounds+4)*sizeof(uint32_t))))
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return 1;
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s->rounds=rounds;
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c = keylength/32;
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if (keylength%32){
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++c;
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j=(keylength%32)/8;
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if(keylength%8)
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++j;
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for (i=0; i<j; ++i)
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((uint8_t*)&l)[i] = ((uint8_t*)key)[(c-1)*4 + i];
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} else {
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l = ((uint32_t*)key)[c-1];
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}
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s->S[0] = P32;
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for(i=1; i<2*rounds+4; ++i){
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s->S[i] = s->S[i-1] + Q32;
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}
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a=b=j=i=0;
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v = 3 * ((c > 2*rounds+4)?c:(2*rounds+4));
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for(p=1; p<=v; ++p){
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a = s->S[i] = rotl32(s->S[i] + a + b, 3);
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if (j==c-1){
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b = l = rotl32(l+a+b, a+b);
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} else {
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b = ((uint32_t*)key)[j] = rotl32(((uint32_t*)key)[j]+a+b, a+b);
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}
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i = (i+1) % (2*rounds+4);
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j = (j+1) % c;
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}
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return 0;
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}
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void rc6_free(rc6_ctx_t *s){
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free(s->S);
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}
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#define LG_W 5
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#define A (((uint32_t*)block)[0])
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#define B (((uint32_t*)block)[1])
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#define C (((uint32_t*)block)[2])
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#define D (((uint32_t*)block)[3])
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void rc6_enc(rc6_ctx_t *s, void* block){
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uint8_t i;
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uint32_t t,u,x; /* greetings to Linux? */
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B += s->S[0];
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D += s->S[1];
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for (i=1; i<=s->rounds; ++i){
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t = rotl32(B * (2*B+1), LG_W);
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u = rotl32(D * (2*D+1), LG_W);
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A = rotl32((A ^ t), u) + s->S[2*i];
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C = rotl32((C ^ u), t) + s->S[2*i+1];
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x = A;
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A = B;
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B = C;
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C = D;
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D = x;
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}
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A += s->S[2*s->rounds+2];
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C += s->S[2*s->rounds+3];
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}
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void rc6_dec(rc6_ctx_t *s, void* block)
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{
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uint8_t i;
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uint32_t t,u,x; /* greetings to Linux? */
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C -= s->S[2*s->rounds+3];
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A -= s->S[2*s->rounds+2];
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for (i=s->rounds; i>0; --i){
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x=D;
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D=C;
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C=B;
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B=A;
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A=x;
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u = rotl32(D * (2*D+1), LG_W);
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t = rotl32(B * (2*B+1), LG_W);
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C = rotr32(C - s->S[2*i+1], t) ^ u;
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A = rotr32(A - s->S[2*i+0], u) ^ t;
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}
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D -= s->S[1];
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B -= s->S[0];
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}
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