81 lines
1.7 KiB
C
81 lines
1.7 KiB
C
/* rc5.c a C implementation of RC5 for AVR microcontrollers
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*
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* author: Daniel Otte
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* email: daniel.otte@rub.de
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* license: GPLv3
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*
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* this implementation is limited to 64bit blocks and a maximum of 255 rounds
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*
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*/
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#include <stdint.h>
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#include <stdlib.h> /* malloc() & free() */
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#include <string.h> /* memset() & memcpy() */
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#include "rc5.h"
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#define A (((uint32_t*)buffer)[0])
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#define B (((uint32_t*)buffer)[1])
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#define ROTL32(v,n) (((v)<<(n))|((v)>>(32-(n))))
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#define ROTR32(v,n) (((v)>>(n))|((v)<<(32-(n))))
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void rc5_enc(void* buffer, const rc5_ctx_t* ctx){
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uint8_t i;
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A += ctx->s[0];
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B += ctx->s[1];
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for(i=0; i<ctx->rounds; ++i){
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A = ROTL32(A^B, B&31) + ctx->s[(i+1)*2+0];
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B = ROTL32(A^B, A&31) + ctx->s[(i+1)*2+1];
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}
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}
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void rc5_dec(void* buffer, const rc5_ctx_t* ctx){
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uint8_t i;
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for(i=ctx->rounds; i>0; --i){
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B = ROTR32(B - ctx->s[i*2+1], A&31) ^ A;
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A = ROTR32(A - ctx->s[i*2+0], B&31) ^ B;
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}
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B -= ctx->s[1];
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A -= ctx->s[0];
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}
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/*
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P32 = 10110111111000010101000101100011 = b7e15163
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Q32 = 10011110001101110111100110111001 = 9e3779b9
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*/
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#define P32 0xb7e15163
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#define Q32 0x9e3779b9
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void rc5_init(void* key, uint16_t keysize_b, uint8_t rounds, rc5_ctx_t* ctx){
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uint16_t c,n,m,j,i,t;
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uint32_t a,b,l[(keysize_b+31)/32];
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ctx->rounds = rounds;
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t=2*(rounds+1);
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c=(keysize_b+31)/32;
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ctx->s = malloc(t*sizeof(uint32_t));
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memset(l, 0, sizeof(uint32_t)*c);
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memcpy(l, key, (keysize_b+7)/8);
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ctx->s[0] = P32;
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for(i=1; i<t; ++i){
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ctx->s[i] = ctx->s[i-1] + Q32;
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}
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m = ((t>c)?t:c)*3;
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i=j=0;
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a=b=0;
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for(n=0; n<m; ++n){
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a=ctx->s[i]=ROTL32(ctx->s[i]+a+b, 3);
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b=l[j]=ROTL32(l[j]+a+b, (a+b)&31);
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i=(i+1)%t;
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j=(j+1)%c;
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}
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}
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void rc5_free(rc5_ctx_t* ctx){
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if(ctx->s)
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free(ctx->s);
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}
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