135 lines
2.8 KiB
C
135 lines
2.8 KiB
C
/* serpent.c
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* a bitsliced implementation of the serpent cipher for avr microcontrollers
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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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#include <stdint.h>
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#include <string.h> /* memset() */
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#include <avr/pgmspace.h>
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#include "serpent.h"
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#include "serpent-sboxes.h"
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/******************************************************************************/
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void memxor(void * dest, void * src, uint8_t size){
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while(size--){
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*((uint8_t*)dest) ^= *((uint8_t*)src);
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dest = (uint8_t*)dest +1;
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src = (uint8_t*)src +1;
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}
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}
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/******************************************************************************/
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uint32_t rotl32(uint32_t a, uint8_t n){
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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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return ((a>>n) | (a<<(32-n)));
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}
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#define X0 (((uint32_t*)b)[0])
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#define X1 (((uint32_t*)b)[1])
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#define X2 (((uint32_t*)b)[2])
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#define X3 (((uint32_t*)b)[3])
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static void lt(uint8_t *b){
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X0 = rotl32(X0, 13);
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X2 = rotl32(X2, 3);
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X1 ^= X0 ^ X2;
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X3 ^= X2 ^ (X0 << 3);
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X1 = rotl32(X1, 1);
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X3 = rotl32(X3, 7);
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X0 ^= X1 ^ X3;
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X2 ^= X3 ^ (X1 << 7);
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X0 = rotl32(X0, 5);
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X2 = rotr32(X2, 10);
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}
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static void inv_lt(uint8_t *b){
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X2 = rotl32(X2, 10);
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X0 = rotr32(X0, 5);
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X2 ^= X3 ^ (X1 << 7);
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X0 ^= X1 ^ X3;
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X3 = rotr32(X3, 7);
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X1 = rotr32(X1, 1);
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X3 ^= X2 ^ (X0 << 3);
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X1 ^= X0 ^ X2;
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X2 = rotr32(X2, 3);
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X0 = rotr32(X0, 13);
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}
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#define GOLDEN_RATIO 0x9e3779b9l
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static uint32_t gen_w(uint32_t * b, uint8_t i){
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uint32_t ret;
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ret = b[0] ^ b[3] ^ b[5] ^ b[7] ^ GOLDEN_RATIO ^ (uint32_t)i;
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ret = rotl32(ret, 11);
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return ret;
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}
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/* key must be 256bit (32 byte) large! */
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void serpent_genctx(void * key, uint8_t keysize, serpent_ctx_t * ctx){
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uint32_t buffer[8];
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uint8_t i,j;
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if(keysize){
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/* keysize is less than 256 bit, padding needed */
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memset(buffer, 0, 32);
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memcpy(buffer, key, (keysize+7)/8);
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((uint8_t*)buffer)[keysize/8] |= 1<<(keysize%8);
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} else {
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/* keysize is 256 bit */
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memcpy(buffer, key, 32);
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}
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for(i=0; i<33; ++i){
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for(j=0; j<4; ++j){
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ctx->k[i][j] = gen_w(buffer, i*4+j);
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memmove(buffer, &(buffer[1]), 7*4); /* shift buffer one to the "left" */
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buffer[7] = ctx->k[i][j];
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}
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}
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for(i=0; i<33; ++i){
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sbox128(ctx->k[i],3-i);
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}
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}
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void serpent_enc(void* buffer, serpent_ctx_t * ctx){
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uint8_t i;
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for(i=0; i<31; ++i){
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memxor((uint8_t*)buffer, ctx->k[i], 16);
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sbox128(buffer, i);
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lt((uint8_t*)buffer);
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}
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memxor((uint8_t*)buffer, ctx->k[i], 16);
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sbox128(buffer, i);
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++i;
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memxor((uint8_t*)buffer, ctx->k[i], 16);
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}
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void serpent_dec(void* buffer, serpent_ctx_t * ctx){
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int8_t i=32;
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memxor((uint8_t*)buffer, ctx->k[i], 16);
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--i;
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inv_sbox128(buffer, i);
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memxor((uint8_t*)buffer, ctx->k[i], 16);
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--i;
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for(; i>=0; --i){
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inv_lt((uint8_t*)buffer);
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inv_sbox128(buffer, i);
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memxor((uint8_t*)buffer, ctx->k[i], 16);
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}
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}
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