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

 *                                  _   _ ____  _

 *  Project                     ___| | | |  _ \| |

 *                             / __| | | | |_) | |

 *                            | (__| |_| |  _ <| |___

 *                             \___|\___/|_| \_\_____|

 *

 * Copyright (C) Evgeny Grin (Karlson2k), <k2k@narod.ru>.

 *

 * This software is licensed as described in the file COPYING, which

 * you should have received as part of this distribution. The terms

 * are also available at https://curl.se/docs/copyright.html.

 *

 * You may opt to use, copy, modify, merge, publish, distribute and/or sell

 * copies of the Software, and permit persons to whom the Software is

 * furnished to do so, under the terms of the COPYING file.

 *

 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY

 * KIND, either express or implied.

 *

 * SPDX-License-Identifier: curl

 *

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

#include "curl_setup.h"

#if !defined(CURL_DISABLE_DIGEST_AUTH) && !defined(CURL_DISABLE_SHA512_256)

#include "curl_sha512_256.h"

/* The recommended order of the TLS backends:

 * 1. USE_OPENSSL

 * 2. USE_WOLFSSL

 * 3. USE_GNUTLS

 * 4. USE_MBEDTLS (TBD)

 * 5. USE_RUSTLS (TBD)

 * 6. USE_WIN32_CRYPTO (TBD)

 * Skip the backend if it does not support the required algorithm */

#ifdef USE_OPENSSL

#  include <openssl/opensslv.h>

#  if !defined(LIBRESSL_VERSION_NUMBER) || \

  (defined(LIBRESSL_VERSION_NUMBER) && LIBRESSL_VERSION_NUMBER >= 0x3080000fL)

#    include <openssl/evp.h>

#    define USE_OPENSSL_SHA512_256          1

#    define HAS_SHA512_256_IMPLEMENTATION   1

#    ifdef __NetBSD__

/* Some NetBSD versions has a bug in SHA-512/256.

 * See https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=58039

 * The problematic versions:

 * - NetBSD before 9.4

 * - NetBSD 9 all development versions (9.99.x)

 * - NetBSD 10 development versions (10.99.x) before 10.99.11

 * The bug was fixed in NetBSD 9.4 release, NetBSD 10.0 release,

 * NetBSD 10.99.11 development.

 * It is safe to apply the workaround even if the bug is not present, as

 * the workaround reduces performance slightly. */

#      include <sys/param.h>

#      if  __NetBSD_Version__ <   904000000 ||  \

          (__NetBSD_Version__ >=  999000000 &&  \

           __NetBSD_Version__ <  1000000000) || \

          (__NetBSD_Version__ >= 1099000000 &&  \

           __NetBSD_Version__ <  1099001100)

#        define NEED_NETBSD_SHA512_256_WORKAROUND 1

#      endif

#    endif

#  endif

#endif /* USE_OPENSSL */

#if !defined(HAS_SHA512_256_IMPLEMENTATION) && defined(USE_WOLFSSL)

#  include <wolfssl/options.h>

#  ifndef WOLFSSL_NOSHA512_256

#    define USE_WOLFSSL_SHA512_256          1

#    define HAS_SHA512_256_IMPLEMENTATION   1

#  endif

#endif

#if !defined(HAS_SHA512_256_IMPLEMENTATION) && defined(USE_GNUTLS)

#  include <nettle/sha.h>

#  ifdef SHA512_256_DIGEST_SIZE

#    define USE_GNUTLS_SHA512_256           1

#  endif

#endif /* !HAS_SHA512_256_IMPLEMENTATION && USE_GNUTLS */

#ifdef USE_OPENSSL_SHA512_256

/* OpenSSL does not provide macros for SHA-512/256 sizes */

/**

 * Size of the SHA-512/256 single processing block in bytes.

 */

#define CURL_SHA512_256_BLOCK_SIZE 128

/**

 * Size of the SHA-512/256 resulting digest in bytes.

 * This is the final digest size, not intermediate hash.

 */

#define CURL_SHA512_256_DIGEST_SIZE CURL_SHA512_256_DIGEST_LENGTH

/**

 * Context type used for SHA-512/256 calculations

 */

typedef EVP_MD_CTX *Curl_sha512_256_ctx;

/**

 * Initialise structure for SHA-512/256 calculation.

 *

 * @param context the calculation context

 * @return CURLE_OK if succeed,

 *         error code otherwise

 */

static CURLcode Curl_sha512_256_init(void *context)

{

  Curl_sha512_256_ctx * const ctx = (Curl_sha512_256_ctx *)context;

  *ctx = EVP_MD_CTX_create();

  if(!*ctx)

    return CURLE_OUT_OF_MEMORY;

  if(EVP_DigestInit_ex(*ctx, EVP_sha512_256(), NULL)) {

    /* Check whether the header and this file use the same numbers */

    DEBUGASSERT(EVP_MD_CTX_size(*ctx) == CURL_SHA512_256_DIGEST_SIZE);

    /* Check whether the block size is correct */

    DEBUGASSERT(EVP_MD_CTX_block_size(*ctx) == CURL_SHA512_256_BLOCK_SIZE);

    return CURLE_OK; /* Success */

  }

  /* Cleanup */

  EVP_MD_CTX_destroy(*ctx);

  return CURLE_FAILED_INIT;

}

/**

 * Process portion of bytes.

 *

 * @param context the calculation context

 * @param data bytes to add to hash

 * @return CURLE_OK if succeed,

 *         error code otherwise

 */

static CURLcode Curl_sha512_256_update(void *context,

                                       const unsigned char *data,

                                       size_t length)

{

  Curl_sha512_256_ctx * const ctx = (Curl_sha512_256_ctx *)context;

  if(!EVP_DigestUpdate(*ctx, data, length))

    return CURLE_SSL_CIPHER;

  return CURLE_OK;

}

/**

 * Finalise SHA-512/256 calculation, return digest.

 *

 * @param context the calculation context

 * @param[out] digest set to the hash, must be #CURL_SHA512_256_DIGEST_SIZE

 *             bytes

 * @return CURLE_OK if succeed,

 *         error code otherwise

 */

static CURLcode Curl_sha512_256_finish(unsigned char *digest, void *context)

{

  CURLcode ret;

  Curl_sha512_256_ctx * const ctx = (Curl_sha512_256_ctx *)context;

#ifdef NEED_NETBSD_SHA512_256_WORKAROUND

  /* Use a larger buffer to work around a bug in NetBSD:

     https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=58039 */

  unsigned char tmp_digest[CURL_SHA512_256_DIGEST_SIZE * 2];

  ret = EVP_DigestFinal_ex(*ctx,

                           tmp_digest, NULL) ? CURLE_OK : CURLE_SSL_CIPHER;

  if(ret == CURLE_OK)

    memcpy(digest, tmp_digest, CURL_SHA512_256_DIGEST_SIZE);

  explicit_memset(tmp_digest, 0, sizeof(tmp_digest));

#else /* !NEED_NETBSD_SHA512_256_WORKAROUND */

  ret = EVP_DigestFinal_ex(*ctx, digest, NULL) ? CURLE_OK : CURLE_SSL_CIPHER;

#endif /* NEED_NETBSD_SHA512_256_WORKAROUND */

  EVP_MD_CTX_destroy(*ctx);

  *ctx = NULL;

  return ret;

}

#elif defined(USE_WOLFSSL_SHA512_256)

#include <wolfssl/wolfcrypt/sha512.h>

#define CURL_SHA512_256_DIGEST_SIZE WC_SHA512_256_DIGEST_SIZE

#define CURL_SHA512_256_BLOCK_SIZE  WC_SHA512_256_BLOCK_SIZE

typedef struct wc_Sha512 Curl_sha512_256_ctx;

static CURLcode Curl_sha512_256_init(void *ctx)

{

  if(wc_InitSha512_256(ctx))

    return CURLE_FAILED_INIT;

  return CURLE_OK;

}

static CURLcode Curl_sha512_256_update(void *ctx,

                                       const unsigned char *data,

                                       size_t length)

{

  do {

    word32 ilen = (word32) CURLMIN(length, UINT_MAX);

    if(wc_Sha512_256Update(ctx, data, ilen))

      return CURLE_SSL_CIPHER;

    length -= ilen;

    data += ilen;

  } while(length);

  return CURLE_OK;

}

static CURLcode Curl_sha512_256_finish(unsigned char *digest, void *ctx)

{

  if(wc_Sha512_256Final(ctx, digest))

    return CURLE_SSL_CIPHER;

  return CURLE_OK;

}

#elif defined(USE_GNUTLS_SHA512_256)

#define CURL_SHA512_256_BLOCK_SIZE  SHA512_256_BLOCK_SIZE

#define CURL_SHA512_256_DIGEST_SIZE SHA512_256_DIGEST_SIZE

/**

 * Context type used for SHA-512/256 calculations

 */

typedef struct sha512_256_ctx Curl_sha512_256_ctx;

/**

 * Initialise structure for SHA-512/256 calculation.

 *

 * @param context the calculation context

 * @return always CURLE_OK

 */

static CURLcode Curl_sha512_256_init(void *context)

{

  Curl_sha512_256_ctx * const ctx = (Curl_sha512_256_ctx *)context;

  /* Check whether the header and this file use the same numbers */

  DEBUGASSERT(CURL_SHA512_256_DIGEST_LENGTH == CURL_SHA512_256_DIGEST_SIZE);

  sha512_256_init(ctx);

  return CURLE_OK;

}

/**

 * Process portion of bytes.

 *

 * @param context the calculation context

 * @param data bytes to add to hash

 * @param length number of bytes in @a data

 * @return always CURLE_OK

 */

static CURLcode Curl_sha512_256_update(void *context,

                                       const unsigned char *data,

                                       size_t length)

{

  Curl_sha512_256_ctx * const ctx = (Curl_sha512_256_ctx *)context;

  DEBUGASSERT((data != NULL) || (length == 0));

  sha512_256_update(ctx, length, (const uint8_t *)data);

  return CURLE_OK;

}

/**

 * Finalise SHA-512/256 calculation, return digest.

 *

 * @param context the calculation context

 * @param[out] digest set to the hash, must be #CURL_SHA512_256_DIGEST_SIZE

 *             bytes

 * @return always CURLE_OK

 */

static CURLcode Curl_sha512_256_finish(unsigned char *digest, void *context)

{

  Curl_sha512_256_ctx * const ctx = (Curl_sha512_256_ctx *)context;

  sha512_256_digest(ctx,

                    (size_t)CURL_SHA512_256_DIGEST_SIZE, (uint8_t *)digest);

  return CURLE_OK;

}

#else /* No system or TLS backend SHA-512/256 implementation available */

/* ** This implementation of SHA-512/256 hash calculation was originally ** *

 * ** written by Evgeny Grin (Karlson2k) for GNU libmicrohttpd.          ** *

 * ** The author ported the code to libcurl. The ported code is provided ** *

 * ** under curl license.                                                ** *

 * ** This is a minimal version with minimal optimizations. Performance  ** *

 * ** can be significantly improved. Big-endian store and load macros    ** *

 * ** are obvious targets for optimization.                              ** */

#ifdef __GNUC__

#  if defined(__has_attribute) && defined(__STDC_VERSION__)

#    if __has_attribute(always_inline) && __STDC_VERSION__ >= 199901

#      define CURL_FORCEINLINE CURL_INLINE __attribute__((always_inline))

#    endif

#  endif

#endif

#if !defined(CURL_FORCEINLINE) && \

  defined(_MSC_VER) && !defined(__GNUC__) && !defined(__clang__)

#define CURL_FORCEINLINE __forceinline

#endif

/* Assume that 'CURL_INLINE' keyword works or the

 * macro was already defined correctly. */

#ifndef CURL_FORCEINLINE

#define CURL_FORCEINLINE CURL_INLINE

#endif

/* Bits manipulation macros and functions.

   Can be moved to other headers to reuse. */

#define CURL_GET_64BIT_BE(ptr)                       \

  (((uint64_t)(((const uint8_t *)(ptr))[0]) << 56) | \

   ((uint64_t)(((const uint8_t *)(ptr))[1]) << 48) | \

   ((uint64_t)(((const uint8_t *)(ptr))[2]) << 40) | \

   ((uint64_t)(((const uint8_t *)(ptr))[3]) << 32) | \

   ((uint64_t)(((const uint8_t *)(ptr))[4]) << 24) | \

   ((uint64_t)(((const uint8_t *)(ptr))[5]) << 16) | \

   ((uint64_t)(((const uint8_t *)(ptr))[6]) << 8)  | \

    (uint64_t)(((const uint8_t *)(ptr))[7]))

#define CURL_PUT_64BIT_BE(ptr, val)                             \

  do {                                                          \

    ((uint8_t *)(ptr))[7] = (uint8_t)((uint64_t)(val));         \

    ((uint8_t *)(ptr))[6] = (uint8_t)(((uint64_t)(val)) >> 8);  \

    ((uint8_t *)(ptr))[5] = (uint8_t)(((uint64_t)(val)) >> 16); \

    ((uint8_t *)(ptr))[4] = (uint8_t)(((uint64_t)(val)) >> 24); \

    ((uint8_t *)(ptr))[3] = (uint8_t)(((uint64_t)(val)) >> 32); \

    ((uint8_t *)(ptr))[2] = (uint8_t)(((uint64_t)(val)) >> 40); \

    ((uint8_t *)(ptr))[1] = (uint8_t)(((uint64_t)(val)) >> 48); \

    ((uint8_t *)(ptr))[0] = (uint8_t)(((uint64_t)(val)) >> 56); \

  } while(0)

/* Defined as a function. The macro version may duplicate the binary code

 * size as each argument is used twice, so if any calculation is used

 * as an argument, the calculation could be done twice. */

static CURL_FORCEINLINE uint64_t Curl_rotr64(uint64_t value, unsigned int bits)

{

  bits %= 64;

  if(bits == 0)

    return value;

  /* Defined in a form which modern compiler could optimize. */

  return (value >> bits) | (value << (64 - bits));

}

/* SHA-512/256 specific data */

/**

 * Number of bits in a single SHA-512/256 word.

 */

#define SHA512_256_WORD_SIZE_BITS 64

/**

 * Number of bytes in a single SHA-512/256 word.

 */

#define SHA512_256_BYTES_IN_WORD (SHA512_256_WORD_SIZE_BITS / 8)

/**

 * Hash is kept internally as 8 64-bit words.

 * This is the intermediate hash size, used during computing the final digest.

 */

#define SHA512_256_HASH_SIZE_WORDS 8

/**

 * Size of the SHA-512/256 resulting digest in words.

 * This is the final digest size, not intermediate hash.

 */

#define SHA512_256_DIGEST_SIZE_WORDS (SHA512_256_HASH_SIZE_WORDS / 2)

/**

 * Size of the SHA-512/256 resulting digest in bytes

 * This is the final digest size, not intermediate hash.

 */

#define CURL_SHA512_256_DIGEST_SIZE \

  (SHA512_256_DIGEST_SIZE_WORDS * SHA512_256_BYTES_IN_WORD)

/**

 * Size of the SHA-512/256 single processing block in bits.

 */

#define SHA512_256_BLOCK_SIZE_BITS 1024

/**

 * Size of the SHA-512/256 single processing block in bytes.

 */

#define CURL_SHA512_256_BLOCK_SIZE (SHA512_256_BLOCK_SIZE_BITS / 8)

/**

 * Size of the SHA-512/256 single processing block in words.

 */

#define SHA512_256_BLOCK_SIZE_WORDS \

  (SHA512_256_BLOCK_SIZE_BITS / SHA512_256_WORD_SIZE_BITS)

/**

 * SHA-512/256 calculation context

 */

struct Curl_sha512_256ctx {

  /**

   * Intermediate hash value. The variable is properly aligned. Smart

   * compilers may automatically use fast load/store instruction for big

   * endian data on little endian machine.

   */

  uint64_t H[SHA512_256_HASH_SIZE_WORDS];

  /**

   * SHA-512/256 input data buffer. The buffer is properly aligned. Smart

   * compilers may automatically use fast load/store instruction for big

   * endian data on little endian machine.

   */

  uint64_t buffer[SHA512_256_BLOCK_SIZE_WORDS];

  /**

   * The number of bytes, lower part

   */

  uint64_t count;

  /**

   * The number of bits, high part. Unlike lower part, this counts the number

   * of bits, not bytes.

   */

  uint64_t count_bits_hi;

};

/**

 * Context type used for SHA-512/256 calculations

 */

typedef struct Curl_sha512_256ctx Curl_sha512_256_ctx;

/**

 * Initialise structure for SHA-512/256 calculation.

 *

 * @param context the calculation context

 * @return always CURLE_OK

 */

static CURLcode Curl_sha512_256_init(void *context)

{

  struct Curl_sha512_256ctx * const ctx = (struct Curl_sha512_256ctx *)context;

  /* Check whether the header and this file use the same numbers */

  DEBUGASSERT(CURL_SHA512_256_DIGEST_LENGTH == CURL_SHA512_256_DIGEST_SIZE);

  DEBUGASSERT(sizeof(uint64_t) == 8);

  /* Initial hash values, see FIPS PUB 180-4 section 5.3.6.2 */

  /* Values generated by "IV Generation Function" as described in

   * section 5.3.6 */

  ctx->H[0] = UINT64_C(0x22312194FC2BF72C);

  ctx->H[1] = UINT64_C(0x9F555FA3C84C64C2);

  ctx->H[2] = UINT64_C(0x2393B86B6F53B151);

  ctx->H[3] = UINT64_C(0x963877195940EABD);

  ctx->H[4] = UINT64_C(0x96283EE2A88EFFE3);

  ctx->H[5] = UINT64_C(0xBE5E1E2553863992);

  ctx->H[6] = UINT64_C(0x2B0199FC2C85B8AA);

  ctx->H[7] = UINT64_C(0x0EB72DDC81C52CA2);

  /* Initialise number of bytes and high part of number of bits. */

  ctx->count = UINT64_C(0);

  ctx->count_bits_hi = UINT64_C(0);

  return CURLE_OK;

}

/**

 * Base of the SHA-512/256 transformation.

 * Gets a full 128 bytes block of data and updates hash values;

 * @param H     hash values

 * @param data  the data buffer with #CURL_SHA512_256_BLOCK_SIZE bytes block

 */

static void Curl_sha512_256_transform(uint64_t H[SHA512_256_HASH_SIZE_WORDS],

                                      const void *data)

{

  /* Working variables,

     see FIPS PUB 180-4 section 6.7, 6.4. */

  uint64_t a = H[0];

  uint64_t b = H[1];

  uint64_t c = H[2];

  uint64_t d = H[3];

  uint64_t e = H[4];

  uint64_t f = H[5];

  uint64_t g = H[6];

  uint64_t h = H[7];

  /* Data buffer, used as a cyclic buffer.

     See FIPS PUB 180-4 section 5.2.2, 6.7, 6.4. */

  uint64_t W[16];

  /* 'Ch' and 'Maj' macro functions are defined with widely-used optimization.

     See FIPS PUB 180-4 formulae 4.8, 4.9. */

#define Sha512_Ch(x, y, z)    ((z) ^ ((x) & ((y) ^ (z))))

#define Sha512_Maj(x, y, z)   (((x) & (y)) ^ ((z) & ((x) ^ (y))))

  /* Four 'Sigma' macro functions.

     See FIPS PUB 180-4 formulae 4.10, 4.11, 4.12, 4.13. */

#define SIG0(x)                                                  \

  (Curl_rotr64(x, 28) ^ Curl_rotr64(x, 34) ^ Curl_rotr64(x, 39))

#define SIG1(x)                                                  \

  (Curl_rotr64(x, 14) ^ Curl_rotr64(x, 18) ^ Curl_rotr64(x, 41))

#define sig0(x)                                                  \

  (Curl_rotr64(x,  1) ^ Curl_rotr64(x,  8) ^ ((x) >> 7))

#define sig1(x)                                                  \

  (Curl_rotr64(x, 19) ^ Curl_rotr64(x, 61) ^ ((x) >> 6))

  if(1) {

    unsigned int t;

    /* K constants array.

       See FIPS PUB 180-4 section 4.2.3 for K values. */

    static const uint64_t K[80] = {

      UINT64_C(0x428a2f98d728ae22), UINT64_C(0x7137449123ef65cd),

      UINT64_C(0xb5c0fbcfec4d3b2f), UINT64_C(0xe9b5dba58189dbbc),

      UINT64_C(0x3956c25bf348b538), UINT64_C(0x59f111f1b605d019),

      UINT64_C(0x923f82a4af194f9b), UINT64_C(0xab1c5ed5da6d8118),

      UINT64_C(0xd807aa98a3030242), UINT64_C(0x12835b0145706fbe),

      UINT64_C(0x243185be4ee4b28c), UINT64_C(0x550c7dc3d5ffb4e2),

      UINT64_C(0x72be5d74f27b896f), UINT64_C(0x80deb1fe3b1696b1),

      UINT64_C(0x9bdc06a725c71235), UINT64_C(0xc19bf174cf692694),

      UINT64_C(0xe49b69c19ef14ad2), UINT64_C(0xefbe4786384f25e3),

      UINT64_C(0x0fc19dc68b8cd5b5), UINT64_C(0x240ca1cc77ac9c65),

      UINT64_C(0x2de92c6f592b0275), UINT64_C(0x4a7484aa6ea6e483),

      UINT64_C(0x5cb0a9dcbd41fbd4), UINT64_C(0x76f988da831153b5),

      UINT64_C(0x983e5152ee66dfab), UINT64_C(0xa831c66d2db43210),

      UINT64_C(0xb00327c898fb213f), UINT64_C(0xbf597fc7beef0ee4),

      UINT64_C(0xc6e00bf33da88fc2), UINT64_C(0xd5a79147930aa725),

      UINT64_C(0x06ca6351e003826f), UINT64_C(0x142929670a0e6e70),

      UINT64_C(0x27b70a8546d22ffc), UINT64_C(0x2e1b21385c26c926),

      UINT64_C(0x4d2c6dfc5ac42aed), UINT64_C(0x53380d139d95b3df),

      UINT64_C(0x650a73548baf63de), UINT64_C(0x766a0abb3c77b2a8),

      UINT64_C(0x81c2c92e47edaee6), UINT64_C(0x92722c851482353b),

      UINT64_C(0xa2bfe8a14cf10364), UINT64_C(0xa81a664bbc423001),

      UINT64_C(0xc24b8b70d0f89791), UINT64_C(0xc76c51a30654be30),

      UINT64_C(0xd192e819d6ef5218), UINT64_C(0xd69906245565a910),

      UINT64_C(0xf40e35855771202a), UINT64_C(0x106aa07032bbd1b8),

      UINT64_C(0x19a4c116b8d2d0c8), UINT64_C(0x1e376c085141ab53),

      UINT64_C(0x2748774cdf8eeb99), UINT64_C(0x34b0bcb5e19b48a8),

      UINT64_C(0x391c0cb3c5c95a63), UINT64_C(0x4ed8aa4ae3418acb),

      UINT64_C(0x5b9cca4f7763e373), UINT64_C(0x682e6ff3d6b2b8a3),

      UINT64_C(0x748f82ee5defb2fc), UINT64_C(0x78a5636f43172f60),

      UINT64_C(0x84c87814a1f0ab72), UINT64_C(0x8cc702081a6439ec),

      UINT64_C(0x90befffa23631e28), UINT64_C(0xa4506cebde82bde9),

      UINT64_C(0xbef9a3f7b2c67915), UINT64_C(0xc67178f2e372532b),

      UINT64_C(0xca273eceea26619c), UINT64_C(0xd186b8c721c0c207),

      UINT64_C(0xeada7dd6cde0eb1e), UINT64_C(0xf57d4f7fee6ed178),

      UINT64_C(0x06f067aa72176fba), UINT64_C(0x0a637dc5a2c898a6),

      UINT64_C(0x113f9804bef90dae), UINT64_C(0x1b710b35131c471b),

      UINT64_C(0x28db77f523047d84), UINT64_C(0x32caab7b40c72493),

      UINT64_C(0x3c9ebe0a15c9bebc), UINT64_C(0x431d67c49c100d4c),

      UINT64_C(0x4cc5d4becb3e42b6), UINT64_C(0x597f299cfc657e2a),

      UINT64_C(0x5fcb6fab3ad6faec), UINT64_C(0x6c44198c4a475817)

    };

    /* One step of SHA-512/256 computation,

       see FIPS PUB 180-4 section 6.4.2 step 3.

       * Note: this macro updates working variables in-place, without rotation.

       * Note: the first (vH += SIG1(vE) + Ch(vE,vF,vG) + kt + wt) equals T1 in

       FIPS PUB 180-4 section 6.4.2 step 3.

       the second (vH += SIG0(vA) + Maj(vE,vF,vC) equals T1 + T2 in

       FIPS PUB 180-4 section 6.4.2 step 3.

       * Note: 'wt' must be used exactly one time in this macro as macro for

       'wt' calculation may change other data as well every time when

       used. */

#define SHA2STEP64(vA, vB, vC, vD, vE, vF, vG, vH, kt, wt)                    \

  do {                                                                        \

    (vD) += ((vH) += SIG1(vE) + Sha512_Ch(vE, vF, vG) + (kt) + (wt));         \

    (vH) += SIG0(vA) + Sha512_Maj(vA, vB, vC);                                \

  } while(0)

    /* One step of SHA-512/256 computation with working variables rotation,

       see FIPS PUB 180-4 section 6.4.2 step 3. This macro version reassigns

       all working variables on each step. */

#define SHA2STEP64RV(vA, vB, vC, vD, vE, vF, vG, vH, kt, wt)                  \

  do {                                                                        \

    uint64_t tmp_h_ = (vH);                                                   \

    SHA2STEP64(vA, vB, vC, vD, vE, vF, vG, tmp_h_, kt, wt);                   \

    (vH) = (vG);                                                              \

    (vG) = (vF);                                                              \

    (vF) = (vE);                                                              \

    (vE) = (vD);                                                              \

    (vD) = (vC);                                                              \

    (vC) = (vB);                                                              \

    (vB) = (vA);                                                              \

    (vA) = tmp_h_;                                                            \

  } while(0)

    /* Get value of W(t) from input data buffer for 0 <= t <= 15,

       See FIPS PUB 180-4 section 6.2.

       Input data must be read in big-endian bytes order,

       see FIPS PUB 180-4 section 3.1.2. */

#define SHA512_GET_W_FROM_DATA(buf, t) \

  CURL_GET_64BIT_BE((const uint8_t *)(buf) + ((t) * SHA512_256_BYTES_IN_WORD))

    /* During first 16 steps, before making any calculation on each step, the

       W element is read from the input data buffer as a big-endian value and

       stored in the array of W elements. */

    for(t = 0; t < 16; ++t) {

      SHA2STEP64RV(a, b, c, d, e, f, g, h, K[t],

                   W[t] = SHA512_GET_W_FROM_DATA(data, t));

    }

    /* 'W' generation and assignment for 16 <= t <= 79.

       See FIPS PUB 180-4 section 6.4.2.

       As only the last 16 'W' are used in calculations, it is possible to

       use 16 elements array of W as a cyclic buffer.

       Note: ((t-16) & 15) have same value as (t & 15) */

#define Wgen(w, t)                                               \

  (uint64_t)((w)[((t) - 16) & 15] + sig1((w)[((t) -  2) & 15]) + \

             (w)[((t) -  7) & 15] + sig0((w)[((t) - 15) & 15]))

    /* During the last 64 steps, before making any calculation on each step,

       current W element is generated from other W elements of the cyclic

       buffer and the generated value is stored back in the cyclic buffer. */

    for(t = 16; t < 80; ++t) {

      SHA2STEP64RV(a, b, c, d, e, f, g, h, K[t],

                   W[t & 15] = Wgen(W, t));

    }

  }

  /* Compute and store the intermediate hash.

     See FIPS PUB 180-4 section 6.4.2 step 4. */

  H[0] += a;

  H[1] += b;

  H[2] += c;

  H[3] += d;

  H[4] += e;

  H[5] += f;

  H[6] += g;

  H[7] += h;

}

/**

 * Process portion of bytes.

 *

 * @param context the calculation context

 * @param data bytes to add to hash

 * @param length number of bytes in @a data

 * @return always CURLE_OK

 */

static CURLcode Curl_sha512_256_update(void *context,

                                       const unsigned char *data,

                                       size_t length)

{

  unsigned int bytes_have; /* Number of bytes in the context buffer */

  struct Curl_sha512_256ctx * const ctx = (struct Curl_sha512_256ctx *)context;

  /* the void pointer here is required to mute Intel compiler warning */

  void * const ctx_buf = ctx->buffer;

  DEBUGASSERT((data != NULL) || (length == 0));

  if(length == 0)

    return CURLE_OK; /* Shortcut, do nothing */

  /* Note: (count & (CURL_SHA512_256_BLOCK_SIZE-1))

     equals (count % CURL_SHA512_256_BLOCK_SIZE) for this block size. */

  bytes_have = (unsigned int)(ctx->count & (CURL_SHA512_256_BLOCK_SIZE - 1));

  ctx->count += length;

  if(length > ctx->count)

    ctx->count_bits_hi += 1U << 3; /* Value wrap */

  ctx->count_bits_hi += ctx->count >> 61;

  ctx->count &= UINT64_C(0x1FFFFFFFFFFFFFFF);

  if(bytes_have) {

    unsigned int bytes_left = CURL_SHA512_256_BLOCK_SIZE - bytes_have;

    if(length >= bytes_left) {

      /* Combine new data with data in the buffer and process the full

         block. */

      memcpy((unsigned char *)ctx_buf + bytes_have, data, bytes_left);

      data += bytes_left;

      length -= bytes_left;

      Curl_sha512_256_transform(ctx->H, ctx->buffer);

      bytes_have = 0;

    }

  }

  while(CURL_SHA512_256_BLOCK_SIZE <= length) {

    /* Process any full blocks of new data directly,

       without copying to the buffer. */

    Curl_sha512_256_transform(ctx->H, data);

    data += CURL_SHA512_256_BLOCK_SIZE;

    length -= CURL_SHA512_256_BLOCK_SIZE;

  }

  if(length) {

    /* Copy incomplete block of new data (if any)

       to the buffer. */

    memcpy((unsigned char *)ctx_buf + bytes_have, data, length);

  }

  return CURLE_OK;

}

/**

 * Size of "length" insertion in bits.

 * See FIPS PUB 180-4 section 5.1.2.

 */

#define SHA512_256_SIZE_OF_LEN_ADD_BITS 128

/**

 * Size of "length" insertion in bytes.

 */

#define SHA512_256_SIZE_OF_LEN_ADD (SHA512_256_SIZE_OF_LEN_ADD_BITS / 8)

/**

 * Finalise SHA-512/256 calculation, return digest.

 *

 * @param context the calculation context

 * @param[out] digest set to the hash, must be #CURL_SHA512_256_DIGEST_SIZE

 *             bytes

 * @return always CURLE_OK

 */

static CURLcode Curl_sha512_256_finish(unsigned char *digest, void *context)

{

  struct Curl_sha512_256ctx * const ctx = (struct Curl_sha512_256ctx *)context;

  uint64_t num_bits;   /* Number of processed bits */

  unsigned int bytes_have; /* Number of bytes in the context buffer */

  /* the void pointer here is required to mute Intel compiler warning */

  void * const ctx_buf = ctx->buffer;

  /* Memorise the number of processed bits.

     The padding and other data added here during the postprocessing must

     not change the amount of hashed data. */

  num_bits = ctx->count << 3;

  /* Note: (count & (CURL_SHA512_256_BLOCK_SIZE-1))

           equals (count % CURL_SHA512_256_BLOCK_SIZE) for this block size. */

  bytes_have = (unsigned int)(ctx->count & (CURL_SHA512_256_BLOCK_SIZE - 1));

  /* Input data must be padded with a single bit "1", then with zeros and

     the finally the length of data in bits must be added as the final bytes

     of the last block.

     See FIPS PUB 180-4 section 5.1.2. */

  /* Data is always processed in form of bytes (not by individual bits),

     therefore position of the first padding bit in byte is always

     predefined (0x80). */

  /* Buffer always have space at least for one byte (as full buffers are

     processed when formed). */

  ((unsigned char *)ctx_buf)[bytes_have++] = 0x80U;

  if(CURL_SHA512_256_BLOCK_SIZE - bytes_have < SHA512_256_SIZE_OF_LEN_ADD) {

    /* No space in the current block to put the total length of message.

       Pad the current block with zeros and process it. */

    if(bytes_have < CURL_SHA512_256_BLOCK_SIZE)

      memset((unsigned char *)ctx_buf + bytes_have, 0,

             CURL_SHA512_256_BLOCK_SIZE - bytes_have);

    /* Process the full block. */

    Curl_sha512_256_transform(ctx->H, ctx->buffer);

    /* Start the new block. */

    bytes_have = 0;

  }

  /* Pad the rest of the buffer with zeros. */

  memset((unsigned char *)ctx_buf + bytes_have, 0,

         CURL_SHA512_256_BLOCK_SIZE - SHA512_256_SIZE_OF_LEN_ADD - bytes_have);

  /* Put high part of number of bits in processed message and then lower

     part of number of bits as big-endian values.

     See FIPS PUB 180-4 section 5.1.2. */

  /* Note: the target location is predefined and buffer is always aligned */

  CURL_PUT_64BIT_BE((unsigned char *)ctx_buf +

                    CURL_SHA512_256_BLOCK_SIZE - SHA512_256_SIZE_OF_LEN_ADD,

                    ctx->count_bits_hi);

  CURL_PUT_64BIT_BE((unsigned char *)ctx_buf +

                    CURL_SHA512_256_BLOCK_SIZE - SHA512_256_SIZE_OF_LEN_ADD +

                    SHA512_256_BYTES_IN_WORD,

                    num_bits);

  /* Process the full final block. */

  Curl_sha512_256_transform(ctx->H, ctx->buffer);

  /* Put in BE mode the leftmost part of the hash as the final digest.

     See FIPS PUB 180-4 section 6.7. */

  CURL_PUT_64BIT_BE(digest + (0 * SHA512_256_BYTES_IN_WORD), ctx->H[0]);

  CURL_PUT_64BIT_BE(digest + (1 * SHA512_256_BYTES_IN_WORD), ctx->H[1]);

  CURL_PUT_64BIT_BE(digest + (2 * SHA512_256_BYTES_IN_WORD), ctx->H[2]);

  CURL_PUT_64BIT_BE(digest + (3 * SHA512_256_BYTES_IN_WORD), ctx->H[3]);

  /* Erase potentially sensitive data. */

  memset(ctx, 0, sizeof(struct Curl_sha512_256ctx));

  return CURLE_OK;

}

#endif /* Local SHA-512/256 code */

/**

 * Compute SHA-512/256 hash for the given data in one function call

 * @param[out] output the pointer to put the hash

 * @param[in] input the pointer to the data to process

 * @param input_size the size of the data pointed by @a input

 * @return always #CURLE_OK

 */

CURLcode Curl_sha512_256it(unsigned char *output, const unsigned char *input,

                           size_t input_size)

{

  Curl_sha512_256_ctx ctx;

  CURLcode res;

  res = Curl_sha512_256_init(&ctx);

  if(res != CURLE_OK)

    return res;

  res = Curl_sha512_256_update(&ctx, (const void *)input, input_size);

  if(res != CURLE_OK) {

    (void)Curl_sha512_256_finish(output, &ctx);

    return res;

  }

  return Curl_sha512_256_finish(output, &ctx);

}

/* Wrapper function, takes 'unsigned int' as length type, returns void */

static void Curl_sha512_256_update_i(void *context,

                                     const unsigned char *data,

                                     unsigned int length)

{

  /* Hypothetically the function may fail, but assume it does not */

  (void)Curl_sha512_256_update(context, data, length);

}

/* Wrapper function, returns void */

static void Curl_sha512_256_finish_v(unsigned char *result, void *context)

{

  /* Hypothetically the function may fail, but assume it does not */

  (void)Curl_sha512_256_finish(result, context);

}

/* Wrapper function, takes 'unsigned int' as length type, returns void */

const struct HMAC_params Curl_HMAC_SHA512_256[] = {

  {

    /* Initialize context procedure. */

    Curl_sha512_256_init,

    /* Update context with data. */

    Curl_sha512_256_update_i,

    /* Get final result procedure. */

    Curl_sha512_256_finish_v,

    /* Context structure size. */

    sizeof(Curl_sha512_256_ctx),

    /* Maximum key length (bytes). */

    CURL_SHA512_256_BLOCK_SIZE,

    /* Result length (bytes). */

    CURL_SHA512_256_DIGEST_SIZE

  }

};

#endif /* !CURL_DISABLE_DIGEST_AUTH && !CURL_DISABLE_SHA512_256 */