xts128.c

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/* ====================================================================
 * Copyright (c) 2011 The OpenSSL Project.  All rights reserved.
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 * Redistribution and use in source and binary forms, with or without
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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;
}