/* $OpenBSD: xts128.c,v 1.15 2025/05/18 09:05:59 jsing Exp $ */
/* ====================================================================
 * Copyright (c) 2011 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 * 2. Redistributions in binary form must reproduce the above copyright
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 *    distribution.
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 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
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 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
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 *    openssl-core@openssl.org.
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 * 5. Products derived from this software may not be called "OpenSSL"
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 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
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 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
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 * ====================================================================
 */

#include <endian.h>
#include <string.h>

#include <openssl/crypto.h>

#include "modes_local.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)
{
        union {
                uint64_t u[2];
                uint32_t d[4];
                uint8_t 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) {
#ifdef __STRICT_ALIGNMENT
                memcpy(scratch.c, inp, 16);
                scratch.u[0] ^= tweak.u[0];
                scratch.u[1] ^= tweak.u[1];
#else
                scratch.u[0] = ((uint64_t *)inp)[0] ^ tweak.u[0];
                scratch.u[1] = ((uint64_t *)inp)[1] ^ tweak.u[1];
#endif
                (*ctx->block1)(scratch.c, scratch.c, ctx->key1);
#ifdef __STRICT_ALIGNMENT
                scratch.u[0] ^= tweak.u[0];
                scratch.u[1] ^= tweak.u[1];
                memcpy(out, scratch.c, 16);
#else
                ((uint64_t *)out)[0] = scratch.u[0] ^= tweak.u[0];
                ((uint64_t *)out)[1] = scratch.u[1] ^= tweak.u[1];
#endif
                inp += 16;
                out += 16;
                len -= 16;

                if (len == 0)
                        return 0;

#if BYTE_ORDER == LITTLE_ENDIAN
                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 /* BIG_ENDIAN */
                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] = (uint8_t)c;
                        c = c >> 8;
                }
                tweak.c[0] ^= (uint8_t)(0x87 & (0 - c));
#endif
        }
        if (enc) {
                for (i = 0; i < len; ++i) {
                        uint8_t ch = inp[i];
                        out[i] = scratch.c[i];
                        scratch.c[i] = ch;
                }
                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 {
                        uint64_t u[2];
                        uint8_t c[16];
                } tweak1;

#if BYTE_ORDER == LITTLE_ENDIAN
                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] = (uint8_t)c;
                        c = c >> 8;
                }
                tweak1.c[0] ^= (uint8_t)(0x87 & (0 - c));
#endif
#ifdef __STRICT_ALIGNMENT
                memcpy(scratch.c, inp, 16);
                scratch.u[0] ^= tweak1.u[0];
                scratch.u[1] ^= tweak1.u[1];
#else
                scratch.u[0] = ((uint64_t *)inp)[0] ^ tweak1.u[0];
                scratch.u[1] = ((uint64_t *)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) {
                        uint8_t ch = inp[16 + i];
                        out[16 + i] = scratch.c[i];
                        scratch.c[i] = ch;
                }
                scratch.u[0] ^= tweak.u[0];
                scratch.u[1] ^= tweak.u[1];
                (*ctx->block1)(scratch.c, scratch.c, ctx->key1);
#ifdef __STRICT_ALIGNMENT
                scratch.u[0] ^= tweak.u[0];
                scratch.u[1] ^= tweak.u[1];
                memcpy(out, scratch.c, 16);
#else
                ((uint64_t *)out)[0] = scratch.u[0] ^ tweak.u[0];
                ((uint64_t *)out)[1] = scratch.u[1] ^ tweak.u[1];
#endif
        }

        return 0;
}
LCRYPTO_ALIAS(CRYPTO_xts128_encrypt);