/* One way encryption based on SHA512 sum.

   Copyright (C) 2007-2017 Free Software Foundation, Inc.

   This library is free software; you can redistribute it and/or

   modify it under the terms of the GNU Lesser General Public License

   as published by the Free Software Foundation; either version 2.1 of

   the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public

   License along with this library; if not, see

   <https://www.gnu.org/licenses/>.  */

#include "crypt-port.h"

#include "crypt-private.h"

#include "alg-sha512.h"

#include <errno.h>

#include <stdio.h>

#include <stdlib.h>

#if INCLUDE_sha512

/* Define our magic string to mark salt for SHA512 "encryption"

   replacement.  */

static const char sha512_salt_prefix[] = "$6$";

/* Prefix for optional rounds specification.  */

static const char sha512_rounds_prefix[] = "rounds=";

/* Maximum salt string length.  */

#define SALT_LEN_MAX 16

/* Default number of rounds if not explicitly specified.  */

#define ROUNDS_DEFAULT 5000

/* Minimum number of rounds.  */

#define ROUNDS_MIN 1000

/* Maximum number of rounds.  */

#define ROUNDS_MAX 999999999

/* The maximum possible length of a SHA512-hashed password string,

   including the terminating NUL character.  Prefix (including its NUL)

   + rounds tag ("rounds=$" = "rounds=\0") + strlen(ROUNDS_MAX)

   + salt (up to SALT_LEN_MAX chars) + '$' + hash (86 chars).  */

#define LENGTH_OF_NUMBER(n) (sizeof #n - 1)

#define SHA512_HASH_LENGTH \

  (sizeof (sha512_salt_prefix) + sizeof (sha512_rounds_prefix) + \

   LENGTH_OF_NUMBER (ROUNDS_MAX) + SALT_LEN_MAX + 1 + 86)

static_assert (SHA512_HASH_LENGTH <= CRYPT_OUTPUT_SIZE,

               "CRYPT_OUTPUT_SIZE is too small for SHA512");

/* A sha512_buffer holds all of the sensitive intermediate data.  */

struct sha512_buffer

{

  struct sha512_ctx ctx;

  uint8_t result[64];

  uint8_t p_bytes[64];

  uint8_t s_bytes[64];

};

static_assert (sizeof (struct sha512_buffer) <= ALG_SPECIFIC_SIZE,

               "ALG_SPECIFIC_SIZE is too small for SHA512");

/* Table with characters for base64 transformation.  */

static const char b64t[] =

  "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

/* Subroutine of _xcrypt_crypt_sha512_rn: Feed CTX with LEN bytes of a

   virtual byte sequence consisting of BLOCK repeated over and over

   indefinitely.  */

static void

sha512_process_recycled_bytes (unsigned char block[64], size_t len,

                               struct sha512_ctx *ctx)

{

  size_t cnt;

  for (cnt = len; cnt >= 64; cnt -= 64)

    sha512_process_bytes (block, 64, ctx);

  sha512_process_bytes (block, cnt, ctx);

}

void

crypt_sha512_rn (const char *phrase, size_t phr_size,

                 const char *setting, size_t ARG_UNUSED (set_size),

                 uint8_t *output, size_t out_size,

                 void *scratch, size_t scr_size)

{

  /* This shouldn't ever happen, but...  */

  if (out_size < SHA512_HASH_LENGTH

      || scr_size < sizeof (struct sha512_buffer))

    {

      errno = ERANGE;

      return;

    }

  struct sha512_buffer *buf = scratch;

  struct sha512_ctx *ctx = &buf->ctx;

  uint8_t *result = buf->result;

  uint8_t *p_bytes = buf->p_bytes;

  uint8_t *s_bytes = buf->s_bytes;

  char *cp = (char *)output;

  const char *salt = setting;

  size_t salt_size;

  size_t cnt;

  /* Default number of rounds.  */

  size_t rounds = ROUNDS_DEFAULT;

  bool rounds_custom = false;

  /* Find beginning of salt string.  The prefix should normally always

     be present.  Just in case it is not.  */

  if (strncmp (sha512_salt_prefix, salt, sizeof (sha512_salt_prefix) - 1) == 0)

    /* Skip salt prefix.  */

    salt += sizeof (sha512_salt_prefix) - 1;

  if (strncmp (salt, sha512_rounds_prefix, sizeof (sha512_rounds_prefix) - 1)

      == 0)

    {

      const char *num = salt + sizeof (sha512_rounds_prefix) - 1;

      /* Do not allow an explicit setting of zero rounds, nor of the

         default number of rounds, nor leading zeroes on the rounds.  */

      if (!(*num >= '1' && *num <= '9'))

        {

          errno = EINVAL;

          return;

        }

      errno = 0;

      char *endp;

      rounds = strtoul (num, &endp, 10);

      if (endp == num || *endp != '$'

          || rounds < ROUNDS_MIN

          || rounds > ROUNDS_MAX

          || errno)

        {

          errno = EINVAL;

          return;

        }

      salt = endp + 1;

      rounds_custom = true;

    }

  salt_size = strspn (salt, b64t);

  if (salt[salt_size] && salt[salt_size] != '$')

    {

      errno = EINVAL;

      return;

    }

  if (salt_size > SALT_LEN_MAX)

    salt_size = SALT_LEN_MAX;

  phr_size = strlen (phrase);

  /* Compute alternate SHA512 sum with input PHRASE, SALT, and PHRASE.  The

     final result will be added to the first context.  */

  sha512_init_ctx (ctx);

  /* Add phrase.  */

  sha512_process_bytes (phrase, phr_size, ctx);

  /* Add salt.  */

  sha512_process_bytes (salt, salt_size, ctx);

  /* Add phrase again.  */

  sha512_process_bytes (phrase, phr_size, ctx);

  /* Now get result of this (64 bytes) and add it to the other

     context.  */

  sha512_finish_ctx (ctx, result);

  /* Prepare for the real work.  */

  sha512_init_ctx (ctx);

  /* Add the phrase string.  */

  sha512_process_bytes (phrase, phr_size, ctx);

  /* The last part is the salt string.  This must be at most 8

     characters and it ends at the first `$' character (for

     compatibility with existing implementations).  */

  sha512_process_bytes (salt, salt_size, ctx);

  /* Add for any character in the phrase one byte of the alternate sum.  */

  for (cnt = phr_size; cnt > 64; cnt -= 64)

    sha512_process_bytes (result, 64, ctx);

  sha512_process_bytes (result, cnt, ctx);

  /* Take the binary representation of the length of the phrase and for every

     1 add the alternate sum, for every 0 the phrase.  */

  for (cnt = phr_size; cnt > 0; cnt >>= 1)

    if ((cnt & 1) != 0)

      sha512_process_bytes (result, 64, ctx);

    else

      sha512_process_bytes (phrase, phr_size, ctx);

  /* Create intermediate result.  */

  sha512_finish_ctx (ctx, result);

  /* Start computation of P byte sequence.  */

  sha512_init_ctx (ctx);

  /* For every character in the password add the entire password.  */

  for (cnt = 0; cnt < phr_size; ++cnt)

    sha512_process_bytes (phrase, phr_size, ctx);

  /* Finish the digest.  */

  sha512_finish_ctx (ctx, p_bytes);

  /* Start computation of S byte sequence.  */

  sha512_init_ctx (ctx);

  /* For every character in the password add the entire password.  */

  for (cnt = 0; cnt < (size_t) 16 + (size_t) result[0]; ++cnt)

    sha512_process_bytes (salt, salt_size, ctx);

  /* Finish the digest.  */

  sha512_finish_ctx (ctx, s_bytes);

  /* Repeatedly run the collected hash value through SHA512 to burn

     CPU cycles.  */

  for (cnt = 0; cnt < rounds; ++cnt)

    {

      /* New context.  */

      sha512_init_ctx (ctx);

      /* Add phrase or last result.  */

      if ((cnt & 1) != 0)

        sha512_process_recycled_bytes (p_bytes, phr_size, ctx);

      else

        sha512_process_bytes (result, 64, ctx);

      /* Add salt for numbers not divisible by 3.  */

      if (cnt % 3 != 0)

        sha512_process_recycled_bytes (s_bytes, salt_size, ctx);

      /* Add phrase for numbers not divisible by 7.  */

      if (cnt % 7 != 0)

        sha512_process_recycled_bytes (p_bytes, phr_size, ctx);

      /* Add phrase or last result.  */

      if ((cnt & 1) != 0)

        sha512_process_bytes (result, 64, ctx);

      else

        sha512_process_recycled_bytes (p_bytes, phr_size, ctx);

      /* Create intermediate result.  */

      sha512_finish_ctx (ctx, result);

    }

  /* Now we can construct the result string.  It consists of four

     parts, one of which is optional.  We already know that buflen is

     at least sha512_hash_length, therefore none of the string bashing

     below can overflow the buffer. */

  memcpy (cp, sha512_salt_prefix, sizeof (sha512_salt_prefix) - 1);

  cp += sizeof (sha512_salt_prefix) - 1;

  if (rounds_custom)

    {

      int n = snprintf (cp,

                        SHA512_HASH_LENGTH - (sizeof (sha512_salt_prefix) - 1),

                        "%s%zu$", sha512_rounds_prefix, rounds);

      cp += n;

    }

  memcpy (cp, salt, salt_size);

  cp += salt_size;

  *cp++ = '$';

#define b64_from_24bit(B2, B1, B0, N)                   \

  do {                                                  \

    unsigned int w = ((((unsigned int)(B2)) << 16) |    \

                      (((unsigned int)(B1)) << 8) |     \

                      ((unsigned int)(B0)));            \

    int n = (N);                                        \

    while (n-- > 0)                                     \

      {                                                 \

        *cp++ = b64t[w & 0x3f];                         \

        w >>= 6;                                        \

      }                                                 \

  } while (0)

  b64_from_24bit (result[0], result[21], result[42], 4);

  b64_from_24bit (result[22], result[43], result[1], 4);

  b64_from_24bit (result[44], result[2], result[23], 4);

  b64_from_24bit (result[3], result[24], result[45], 4);

  b64_from_24bit (result[25], result[46], result[4], 4);

  b64_from_24bit (result[47], result[5], result[26], 4);

  b64_from_24bit (result[6], result[27], result[48], 4);

  b64_from_24bit (result[28], result[49], result[7], 4);

  b64_from_24bit (result[50], result[8], result[29], 4);

  b64_from_24bit (result[9], result[30], result[51], 4);

  b64_from_24bit (result[31], result[52], result[10], 4);

  b64_from_24bit (result[53], result[11], result[32], 4);

  b64_from_24bit (result[12], result[33], result[54], 4);

  b64_from_24bit (result[34], result[55], result[13], 4);

  b64_from_24bit (result[56], result[14], result[35], 4);

  b64_from_24bit (result[15], result[36], result[57], 4);

  b64_from_24bit (result[37], result[58], result[16], 4);

  b64_from_24bit (result[59], result[17], result[38], 4);

  b64_from_24bit (result[18], result[39], result[60], 4);

  b64_from_24bit (result[40], result[61], result[19], 4);

  b64_from_24bit (result[62], result[20], result[41], 4);

  b64_from_24bit (0, 0, result[63], 2);

  *cp = '\0';

}

void

gensalt_sha512_rn (unsigned long count,

                   const uint8_t *rbytes, size_t nrbytes,

                   uint8_t *output, size_t output_size)

{

  gensalt_sha_rn ('6', SALT_LEN_MAX, ROUNDS_DEFAULT, ROUNDS_MIN, ROUNDS_MAX,

                  count, rbytes, nrbytes, output, output_size);

}

#endif