// Copyright 2024 The Centipede Authors.

//

// Licensed under the Apache License, Version 2.0 (the "License");

// you may not use this file except in compliance with the License.

// You may obtain a copy of the License at

//

//      https://www.apache.org/licenses/LICENSE-2.0

//

// Unless required by applicable law or agreed to in writing, software

// distributed under the License is distributed on an "AS IS" BASIS,

// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

// See the License for the specific language governing permissions and

// limitations under the License.

#include "./common/sha1.h"

#include <cstdint>

#include <cstring>

#include "absl/base/nullability.h"

namespace centipede {

namespace {

// We vendor our own implementation of SHA1 (taken from public domain) to avoid

// availability and linkage issues with implementations from OpenSSL/BoringSSL.

#ifdef __BIG_ENDIAN__

#define SHA_BIG_ENDIAN

#elif defined __LITTLE_ENDIAN__

/* override */

#elif defined __BYTE_ORDER

#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__

#define SHA_BIG_ENDIAN

#endif

#else                // ! defined __LITTLE_ENDIAN__

#include <endian.h>  // machine/endian.h

#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__

#define SHA_BIG_ENDIAN

#endif

#endif

/* header */

#define HASH_LENGTH 20

#define BLOCK_LENGTH 64

typedef struct sha1nfo {

  uint32_t buffer[BLOCK_LENGTH / 4];

  uint32_t state[HASH_LENGTH / 4];

  uint32_t byteCount;

  uint8_t bufferOffset;

  uint8_t keyBuffer[BLOCK_LENGTH];

  uint8_t innerHash[HASH_LENGTH];

} sha1nfo;

/* public API - prototypes - TODO: doxygen*/

/**

 */

void sha1_init(sha1nfo *s);

/**

 */

void sha1_writebyte(sha1nfo *s, uint8_t data);

/**

 */

void sha1_write(sha1nfo *s, const char *data, size_t len);

/**

 */

uint8_t *sha1_result(sha1nfo *s);

/* code */

#define SHA1_K0 0x5a827999

#define SHA1_K20 0x6ed9eba1

#define SHA1_K40 0x8f1bbcdc

#define SHA1_K60 0xca62c1d6

void sha1_init(sha1nfo *s) {

  s->state[0] = 0x67452301;

  s->state[1] = 0xefcdab89;

  s->state[2] = 0x98badcfe;

  s->state[3] = 0x10325476;

  s->state[4] = 0xc3d2e1f0;

  s->byteCount = 0;

  s->bufferOffset = 0;

}

uint32_t sha1_rol32(uint32_t number, uint8_t bits) {

  return ((number << bits) | (number >> (32 - bits)));

}

void sha1_hashBlock(sha1nfo *s) {

  uint8_t i;

  uint32_t a, b, c, d, e, t;

  a = s->state[0];

  b = s->state[1];

  c = s->state[2];

  d = s->state[3];

  e = s->state[4];

  for (i = 0; i < 80; i++) {

    if (i >= 16) {

      t = s->buffer[(i + 13) & 15] ^ s->buffer[(i + 8) & 15] ^

          s->buffer[(i + 2) & 15] ^ s->buffer[i & 15];

      s->buffer[i & 15] = sha1_rol32(t, 1);

    }

    if (i < 20) {

      t = (d ^ (b & (c ^ d))) + SHA1_K0;

    } else if (i < 40) {

      t = (b ^ c ^ d) + SHA1_K20;

    } else if (i < 60) {

      t = ((b & c) | (d & (b | c))) + SHA1_K40;

    } else {

      t = (b ^ c ^ d) + SHA1_K60;

    }

    t += sha1_rol32(a, 5) + e + s->buffer[i & 15];

    e = d;

    d = c;

    c = sha1_rol32(b, 30);

    b = a;

    a = t;

  }

  s->state[0] += a;

  s->state[1] += b;

  s->state[2] += c;

  s->state[3] += d;

  s->state[4] += e;

}

void sha1_addUncounted(sha1nfo *s, uint8_t data) {

  uint8_t *const b = (uint8_t *)s->buffer;

#ifdef SHA_BIG_ENDIAN

  b[s->bufferOffset] = data;

#else

  b[s->bufferOffset ^ 3] = data;

#endif

  s->bufferOffset++;

  if (s->bufferOffset == BLOCK_LENGTH) {

    sha1_hashBlock(s);

    s->bufferOffset = 0;

  }

}

void sha1_writebyte(sha1nfo *s, uint8_t data) {

  ++s->byteCount;

  sha1_addUncounted(s, data);

}

void sha1_write(sha1nfo *s, const char *data, size_t len) {

  for (; len--;) sha1_writebyte(s, (uint8_t)*data++);

}

void sha1_pad(sha1nfo *s) {

  // Implement SHA-1 padding (fips180-2 §5.1.1)

  // Pad with 0x80 followed by 0x00 until the end of the block

  sha1_addUncounted(s, 0x80);

  while (s->bufferOffset != 56) sha1_addUncounted(s, 0x00);

  // Append length in the last 8 bytes

  sha1_addUncounted(s, 0);  // We're only using 32 bit lengths

  sha1_addUncounted(s, 0);  // But SHA-1 supports 64 bit lengths

  sha1_addUncounted(s, 0);  // So zero pad the top bits

  sha1_addUncounted(s, s->byteCount >> 29);  // Shifting to multiply by 8

  sha1_addUncounted(

      s, s->byteCount >> 21);  // as SHA-1 supports bitstreams as well as

  sha1_addUncounted(s, s->byteCount >> 13);  // byte.

  sha1_addUncounted(s, s->byteCount >> 5);

  sha1_addUncounted(s, s->byteCount << 3);

}

uint8_t *sha1_result(sha1nfo *s) {

  // Pad to complete the last block

  sha1_pad(s);

#ifndef SHA_BIG_ENDIAN

  // Swap byte order back

  int i;

  for (i = 0; i < 5; i++) {

    s->state[i] = (((s->state[i]) << 24) & 0xff000000) |

                  (((s->state[i]) << 8) & 0x00ff0000) |

                  (((s->state[i]) >> 8) & 0x0000ff00) |

                  (((s->state[i]) >> 24) & 0x000000ff);

  }

#endif

  // Return pointer to hash (20 characters)

  return (uint8_t *)s->state;

}

static_assert(kShaDigestLength == HASH_LENGTH);

}  // namespace

void SHA1(absl::Nonnull<const uint8_t *> data, size_t len,

          absl::Nonnull<uint8_t *> out) {

  sha1nfo s;

  sha1_init(&s);

  sha1_write(&s, reinterpret_cast<const char *>(data), len);

  memcpy(out, sha1_result(&s), kShaDigestLength);

}

}  // namespace centipede