2 * a bitsliced implementation of the serpent cipher for avr microcontrollers
4 * email: daniel.otte@rub.de
9 #include <string.h> /* memset() */
10 #include <avr/pgmspace.h>
12 #include "serpent-sboxes.h"
14 /******************************************************************************/
16 void memxor(void * dest, void * src, uint8_t size){
18 *((uint8_t*)dest) ^= *((uint8_t*)src);
19 dest = (uint8_t*)dest +1;
20 src = (uint8_t*)src +1;
24 /******************************************************************************/
26 uint32_t rotl32(uint32_t a, uint8_t n){
27 return ((a<<n) | (a>>(32-n)));
31 uint32_t rotr32(uint32_t a, uint8_t n){
32 return ((a>>n) | (a<<(32-n)));
36 #define X0 (((uint32_t*)b)[0])
37 #define X1 (((uint32_t*)b)[1])
38 #define X2 (((uint32_t*)b)[2])
39 #define X3 (((uint32_t*)b)[3])
41 static void lt(uint8_t *b){
54 static void inv_lt(uint8_t *b){
67 #define GOLDEN_RATIO 0x9e3779b9l
69 static uint32_t gen_w(uint32_t * b, uint8_t i){
71 ret = b[0] ^ b[3] ^ b[5] ^ b[7] ^ GOLDEN_RATIO ^ (uint32_t)i;
72 ret = rotl32(ret, 11);
76 /* key must be 256bit (32 byte) large! */
77 void serpent_genctx(void * key, uint8_t keysize, serpent_ctx_t * ctx){
81 /* keysize is less than 256 bit, padding needed */
82 memset(buffer, 0, 32);
83 memcpy(buffer, key, (keysize+7)/8);
84 ((uint8_t*)buffer)[keysize/8] |= 1<<(keysize%8);
86 /* keysize is 256 bit */
87 memcpy(buffer, key, 32);
91 ctx->k[i][j] = gen_w(buffer, i*4+j);
92 memmove(buffer, &(buffer[1]), 7*4); /* shift buffer one to the "left" */
93 buffer[7] = ctx->k[i][j];
97 sbox128(ctx->k[i],3-i);
102 void serpent_enc(void* buffer, serpent_ctx_t * ctx){
105 memxor((uint8_t*)buffer, ctx->k[i], 16);
107 lt((uint8_t*)buffer);
109 memxor((uint8_t*)buffer, ctx->k[i], 16);
112 memxor((uint8_t*)buffer, ctx->k[i], 16);
115 void serpent_dec(void* buffer, serpent_ctx_t * ctx){
118 memxor((uint8_t*)buffer, ctx->k[i], 16);
120 inv_sbox128(buffer, i);
121 memxor((uint8_t*)buffer, ctx->k[i], 16);
124 inv_lt((uint8_t*)buffer);
125 inv_sbox128(buffer, i);
126 memxor((uint8_t*)buffer, ctx->k[i], 16);