xts128.c

/* ====================================================================
 * Copyright (c) 2011 The OpenSSL Project.  All rights reserved.
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 *    "This product includes software developed by the OpenSSL Project
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 */

#include <openssl/crypto.h>
#include "modes_lcl.h"
#include <string.h>

#ifndef MODES_DEBUG
# ifndef NDEBUG
#  define NDEBUG
# endif
#endif
#include <assert.h>

int CRYPTO_xts128_encrypt(const XTS128_CONTEXT *ctx, const unsigned char iv[16],
	const unsigned char *inp, unsigned char *out,
	size_t len, int enc)
{
	const union { long one; char little; } is_endian = {1};
	union { u64 u[2]; u32 d[4]; u8 c[16]; } tweak, scratch;
	unsigned int i;

	if (len<16) return -1;

	memcpy(tweak.c, iv, 16);

	(*ctx->block2)(tweak.c,tweak.c,ctx->key2);

	if (!enc && (len%16)) len-=16;

	while (len>=16) {
#if defined(STRICT_ALIGNMENT)
		memcpy(scratch.c,inp,16);
		scratch.u[0] ^= tweak.u[0];
		scratch.u[1] ^= tweak.u[1];
#else
		scratch.u[0] = ((u64*)inp)[0]^tweak.u[0];
		scratch.u[1] = ((u64*)inp)[1]^tweak.u[1];
#endif
		(*ctx->block1)(scratch.c,scratch.c,ctx->key1);
#if defined(STRICT_ALIGNMENT)
		scratch.u[0] ^= tweak.u[0];
		scratch.u[1] ^= tweak.u[1];
		memcpy(out,scratch.c,16);
#else
		((u64*)out)[0] = scratch.u[0]^=tweak.u[0];
		((u64*)out)[1] = scratch.u[1]^=tweak.u[1];
#endif
		inp += 16;
		out += 16;
		len -= 16;

		if (len==0)	return 0;

		if (is_endian.little) {
			unsigned int carry,res;
			
			res = 0x87&(((int)tweak.d[3])>>31);
			carry = (unsigned int)(tweak.u[0]>>63);
			tweak.u[0] = (tweak.u[0]<<1)^res;
			tweak.u[1] = (tweak.u[1]<<1)|carry;
		}
		else {
			size_t c;

			for (c=0,i=0;i<16;++i) {
				/*+ substitutes for |, because c is 1 bit */ 
				c += ((size_t)tweak.c[i])<<1;
				tweak.c[i] = (u8)c;
				c = c>>8;
			}
			tweak.c[0] ^= (u8)(0x87&(0-c));
		}
	}
	if (enc) {
		for (i=0;i<len;++i) {
			u8 c = inp[i];
			out[i] = scratch.c[i];
			scratch.c[i] = c;
		}
		scratch.u[0] ^= tweak.u[0];
		scratch.u[1] ^= tweak.u[1];
		(*ctx->block1)(scratch.c,scratch.c,ctx->key1);
		scratch.u[0] ^= tweak.u[0];
		scratch.u[1] ^= tweak.u[1];
		memcpy(out-16,scratch.c,16);
	}
	else {
		union { u64 u[2]; u8 c[16]; } tweak1;

		if (is_endian.little) {
			unsigned int carry,res;

			res = 0x87&(((int)tweak.d[3])>>31);
			carry = (unsigned int)(tweak.u[0]>>63);
			tweak1.u[0] = (tweak.u[0]<<1)^res;
			tweak1.u[1] = (tweak.u[1]<<1)|carry;
		}
		else {
			size_t c;

			for (c=0,i=0;i<16;++i) {
				/*+ substitutes for |, because c is 1 bit */ 
				c += ((size_t)tweak.c[i])<<1;
				tweak1.c[i] = (u8)c;
				c = c>>8;
			}
			tweak1.c[0] ^= (u8)(0x87&(0-c));
		}
#if defined(STRICT_ALIGNMENT)
		memcpy(scratch.c,inp,16);
		scratch.u[0] ^= tweak1.u[0];
		scratch.u[1] ^= tweak1.u[1];
#else
		scratch.u[0] = ((u64*)inp)[0]^tweak1.u[0];
		scratch.u[1] = ((u64*)inp)[1]^tweak1.u[1];
#endif
		(*ctx->block1)(scratch.c,scratch.c,ctx->key1);
		scratch.u[0] ^= tweak1.u[0];
		scratch.u[1] ^= tweak1.u[1];

		for (i=0;i<len;++i) {
			u8 c = inp[16+i];
			out[16+i] = scratch.c[i];
			scratch.c[i] = c;
		}
		scratch.u[0] ^= tweak.u[0];
		scratch.u[1] ^= tweak.u[1];
		(*ctx->block1)(scratch.c,scratch.c,ctx->key1);
#if defined(STRICT_ALIGNMENT)
		scratch.u[0] ^= tweak.u[0];
		scratch.u[1] ^= tweak.u[1];
		memcpy (out,scratch.c,16);
#else
		((u64*)out)[0] = scratch.u[0]^tweak.u[0];
		((u64*)out)[1] = scratch.u[1]^tweak.u[1];
#endif
	}

	return 0;
}