avr-crypto-lib/serpent.c

/* serpent.c
 * a bitsliced implementation of the serpent cipher for avr microcontrollers
 * author: Daniel Otte 
 * email:  daniel.otte@rub.de
 * license: GPLv3
 */

#include <stdint.h>
#include <string.h> /* memset() */
#include <avr/pgmspace.h>
#include "serpent.h"

uint8_t sbox[] PROGMEM = {
 0x38, 0xF1, 0xA6, 0x5B, 0xED, 0x42, 0x70, 0x9C,
 0xFC, 0x27, 0x90, 0x5A, 0x1B, 0xE8, 0x6D, 0x34, 
 0x86, 0x79, 0x3C, 0xAF, 0xD1, 0xE4, 0x0B, 0x52,
 0x0F, 0xB8, 0xC9, 0x63, 0xD1, 0x24, 0xA7, 0x5E,
 0x1F, 0x83, 0xC0, 0xB6, 0x25, 0x4A, 0x9E, 0x7D,
 0xF5, 0x2B, 0x4A, 0x9C, 0x03, 0xE8, 0xD6, 0x71,
 0x72, 0xC5, 0x84, 0x6B, 0xE9, 0x1F, 0xD3, 0xA0,
 0x1D, 0xF0, 0xE8, 0x2B, 0x74, 0xCA, 0x93, 0x56,
/* now the inverted sboxes */
 0xD3, 0xB0, 0xA6, 0x5C, 0x1E, 0x47, 0xF9, 0x82,
 0x58, 0x2E, 0xF6, 0xC3, 0xB4, 0x79, 0x1D, 0xA0,
 0xC9, 0xF4, 0xBE, 0x12, 0x03, 0x6D, 0x58, 0xA7,
 0x09, 0xA7, 0xBE, 0x6D, 0x35, 0xC2, 0x48, 0xF1,
 0x50, 0x83, 0xA9, 0x7E, 0x2C, 0xB6, 0x4F, 0xD1,
 0x8F, 0x29, 0x41, 0xDE, 0xB6, 0x53, 0x7C, 0xA0,
 0xFA, 0x1D, 0x53, 0x60, 0x49, 0xE7, 0x2C, 0x8B,
 0x30, 0x6D, 0x9E, 0xF8, 0x5C, 0xB7, 0xA1, 0x42
};        
         

#define SHR_O(a) c=(a)&1; ((a) = (a)>>1)
#define SHR_I(a) ((a) = (c?0x80:0x00)| ((a)>>1))

static void ip(uint8_t *o, uint32_t *i){
	uint8_t c; // carry 
	uint8_t n,m;
	memset(o, 0, 16);
	for(n=0; n<16; ++n){
		for(m=0; m<2; ++m){
		SHR_O(i[0]);
		SHR_I(o[n]);
		SHR_O(i[1]);
		SHR_I(o[n]);
		SHR_O(i[2]);
		SHR_I(o[n]);
		SHR_O(i[3]);
		SHR_I(o[n]);
		}
	}
}

#undef SHR_I
#define SHR_I(a) ((a) = (c?0x80000000L:0x00L)| ((a)>>1)) /* we use 32-bit words here */


static void fp(uint32_t *o, uint32_t *i){
	uint8_t c; // carry 
	uint8_t n,m;
	memset(o, 0, 16);
	for(n=0; n<4; ++n){
		for(m=0; m<8; ++m){
		SHR_O(i[n]);
		SHR_I(o[0]);
		SHR_O(i[n]);
		SHR_I(o[1]);
		SHR_O(i[n]);
		SHR_I(o[2]);
		SHR_O(i[n]);
		SHR_I(o[3]);
		}
	}
}

/******************************************************************************/

static void sbox128x(uint8_t box, void* w){
	uint8_t sb[16];
	uint8_t i,t,x;
	box &= 0x0f;
	/* load sbox */
	for(i=0; i<8; ++i){
		t = pgm_read_byte(sbox + box*8 + i);
		sb[2*i+0]=t>>4;
		sb[2*i+1]=t&0xf;
	}
	uint8_t o[16];
	ip(o, w);
	
	for(i=0; i<16; ++i){
		t = ((uint8_t*)o)[i];
		x = sb[t>>4];
		x <<= 4;
		x |= sb[t&0xf];
		((uint8_t*)o)[i] = x;
	}
	fp(w, (uint32_t*)o);
}

static void sbox128(void * w, uint8_t box){
	sbox128x(box&0x7, w);
}

static void inv_sbox128(void * w, uint8_t box){
	sbox128x(((box&0x7)|0x8), w);
}

/******************************************************************************/

void memxor(void * dest, void * src, uint8_t size){
	while(size--){
		*((uint8_t*)dest) ^= *((uint8_t*)src);
		dest = (uint8_t*)dest +1;
		src  = (uint8_t*)src  +1;
	}
}

/******************************************************************************/

uint32_t rotl32(uint32_t a, uint8_t n){
	return ((a<<n) | (a>>(32-n)));
}


uint32_t rotr32(uint32_t a, uint8_t n){
	return ((a>>n) | (a<<(32-n)));
}


#define X0 (((uint32_t*)b)[0])
#define X1 (((uint32_t*)b)[1])
#define X2 (((uint32_t*)b)[2])
#define X3 (((uint32_t*)b)[3])

static void lt(uint8_t *b){
	X0 = rotl32(X0, 13);
	X2 = rotl32(X2,  3);
	X1 ^= X0 ^ X2;
	X3 ^= X2 ^ (X0 << 3);
	X1 = rotl32(X1, 1);
	X3 = rotl32(X3, 7);
	X0 ^= X1 ^ X3;
	X2 ^= X3 ^ (X1 << 7);
	X0 = rotl32(X0, 5);
	X2 = rotr32(X2, 10);
}

static void inv_lt(uint8_t *b){
	X2 = rotl32(X2, 10);
	X0 = rotr32(X0, 5);
	X2 ^= X3 ^ (X1 << 7);
	X0 ^= X1 ^ X3;
	X3 = rotr32(X3, 7);
	X1 = rotr32(X1, 1);
	X3 ^= X2 ^ (X0 << 3);
	X1 ^= X0 ^ X2;
	X2 = rotr32(X2,  3);
	X0 = rotr32(X0, 13);
}

#define GOLDEN_RATIO 0x9e3779b9l

static uint32_t gen_w(uint32_t * b, uint8_t i){
	uint32_t ret;
	ret = b[0] ^ b[3] ^ b[5] ^ b[7] ^ GOLDEN_RATIO ^ (uint32_t)i;
	ret = rotl32(ret, 11);
	return ret;
} 

/* key must be 256bit (32 byte) large! */
void serpent_genctx(void * key, uint8_t keysize, serpent_ctx_t * ctx){
	uint32_t buffer[8];
	uint8_t i,j;
	if(keysize){
		/* keysize is less than 256 bit, padding needed */
		memset(buffer, 0, 32);
		memcpy(buffer, key, (keysize+7)/8);
		((uint8_t*)buffer)[keysize/8] |= 1<<(keysize%8);
	} else {
		/* keysize is 256 bit */
		memcpy(buffer, key, 32); 
	}
	for(i=0; i<33; ++i){
		for(j=0; j<4; ++j){
			ctx->k[i][j] = gen_w(buffer, i*4+j);
			memmove(buffer, &(buffer[1]), 7*4); /* shift buffer one to the "left" */
			buffer[7] = ctx->k[i][j];
		}
	}
	for(i=0; i<33; ++i){
		sbox128(ctx->k[i],3-i);
	}
}


void serpent_enc(void* buffer, serpent_ctx_t * ctx){
	uint8_t i;
	for(i=0; i<31; ++i){
		memxor((uint8_t*)buffer, ctx->k[i], 16);
		sbox128(buffer, i);
		lt((uint8_t*)buffer);
	}
	memxor((uint8_t*)buffer, ctx->k[i], 16);
	sbox128(buffer, i);
	++i;
	memxor((uint8_t*)buffer, ctx->k[i], 16);
}

void serpent_dec(void* buffer, serpent_ctx_t * ctx){
	int8_t i=32;
	
	memxor((uint8_t*)buffer, ctx->k[i], 16);
	--i;
	inv_sbox128(buffer, i);
	memxor((uint8_t*)buffer, ctx->k[i], 16);
	--i;
	for(; i>=0; --i){
		inv_lt((uint8_t*)buffer);
		inv_sbox128(buffer, i);
		memxor((uint8_t*)buffer, ctx->k[i], 16);
	}
}