/*
 * public domain sha512 crypt implementation
 *
 * original sha crypt design: http://people.redhat.com/drepper/SHA-crypt.txt
 * in this implementation at least 32bit int is assumed,
 * key length is limited, the $6$ prefix is mandatory, '\n' and ':' is rejected
 * in the salt and rounds= setting must contain a valid iteration count,
 * on error "*" is returned.
 */
#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>

/* public domain sha512 implementation based on fips180-3 */
/* >=2^64 bits messages are not supported (about 2000 peta bytes) */

struct sha512 {
  uint64_t len;     /* processed message length */
  uint64_t h[8];    /* hash state */
  uint8_t buf[128]; /* message block buffer */
};

static uint64_t ror(uint64_t n, int k) {
  return (n >> k) | (n << (64 - k));
}
#define Ch(x, y, z) (z ^ (x & (y ^ z)))
#define Maj(x, y, z) ((x & y) | (z & (x | y)))
#define S0(x) (ror(x, 28) ^ ror(x, 34) ^ ror(x, 39))
#define S1(x) (ror(x, 14) ^ ror(x, 18) ^ ror(x, 41))
#define R0(x) (ror(x, 1) ^ ror(x, 8) ^ (x >> 7))
#define R1(x) (ror(x, 19) ^ ror(x, 61) ^ (x >> 6))

static const uint64_t K[80] = {
    0x428a2f98d728ae22ULL, 0x7137449123ef65cdULL, 0xb5c0fbcfec4d3b2fULL,
    0xe9b5dba58189dbbcULL, 0x3956c25bf348b538ULL, 0x59f111f1b605d019ULL,
    0x923f82a4af194f9bULL, 0xab1c5ed5da6d8118ULL, 0xd807aa98a3030242ULL,
    0x12835b0145706fbeULL, 0x243185be4ee4b28cULL, 0x550c7dc3d5ffb4e2ULL,
    0x72be5d74f27b896fULL, 0x80deb1fe3b1696b1ULL, 0x9bdc06a725c71235ULL,
    0xc19bf174cf692694ULL, 0xe49b69c19ef14ad2ULL, 0xefbe4786384f25e3ULL,
    0x0fc19dc68b8cd5b5ULL, 0x240ca1cc77ac9c65ULL, 0x2de92c6f592b0275ULL,
    0x4a7484aa6ea6e483ULL, 0x5cb0a9dcbd41fbd4ULL, 0x76f988da831153b5ULL,
    0x983e5152ee66dfabULL, 0xa831c66d2db43210ULL, 0xb00327c898fb213fULL,
    0xbf597fc7beef0ee4ULL, 0xc6e00bf33da88fc2ULL, 0xd5a79147930aa725ULL,
    0x06ca6351e003826fULL, 0x142929670a0e6e70ULL, 0x27b70a8546d22ffcULL,
    0x2e1b21385c26c926ULL, 0x4d2c6dfc5ac42aedULL, 0x53380d139d95b3dfULL,
    0x650a73548baf63deULL, 0x766a0abb3c77b2a8ULL, 0x81c2c92e47edaee6ULL,
    0x92722c851482353bULL, 0xa2bfe8a14cf10364ULL, 0xa81a664bbc423001ULL,
    0xc24b8b70d0f89791ULL, 0xc76c51a30654be30ULL, 0xd192e819d6ef5218ULL,
    0xd69906245565a910ULL, 0xf40e35855771202aULL, 0x106aa07032bbd1b8ULL,
    0x19a4c116b8d2d0c8ULL, 0x1e376c085141ab53ULL, 0x2748774cdf8eeb99ULL,
    0x34b0bcb5e19b48a8ULL, 0x391c0cb3c5c95a63ULL, 0x4ed8aa4ae3418acbULL,
    0x5b9cca4f7763e373ULL, 0x682e6ff3d6b2b8a3ULL, 0x748f82ee5defb2fcULL,
    0x78a5636f43172f60ULL, 0x84c87814a1f0ab72ULL, 0x8cc702081a6439ecULL,
    0x90befffa23631e28ULL, 0xa4506cebde82bde9ULL, 0xbef9a3f7b2c67915ULL,
    0xc67178f2e372532bULL, 0xca273eceea26619cULL, 0xd186b8c721c0c207ULL,
    0xeada7dd6cde0eb1eULL, 0xf57d4f7fee6ed178ULL, 0x06f067aa72176fbaULL,
    0x0a637dc5a2c898a6ULL, 0x113f9804bef90daeULL, 0x1b710b35131c471bULL,
    0x28db77f523047d84ULL, 0x32caab7b40c72493ULL, 0x3c9ebe0a15c9bebcULL,
    0x431d67c49c100d4cULL, 0x4cc5d4becb3e42b6ULL, 0x597f299cfc657e2aULL,
    0x5fcb6fab3ad6faecULL, 0x6c44198c4a475817ULL};

static void processblock(struct sha512* s, const uint8_t* buf) {
  uint64_t W[80], t1, t2, a, b, c, d, e, f, g, h;
  int i;

  for (i = 0; i < 16; i++) {
    W[i] = (uint64_t)buf[8 * i] << 56;
    W[i] |= (uint64_t)buf[8 * i + 1] << 48;
    W[i] |= (uint64_t)buf[8 * i + 2] << 40;
    W[i] |= (uint64_t)buf[8 * i + 3] << 32;
    W[i] |= (uint64_t)buf[8 * i + 4] << 24;
    W[i] |= (uint64_t)buf[8 * i + 5] << 16;
    W[i] |= (uint64_t)buf[8 * i + 6] << 8;
    W[i] |= buf[8 * i + 7];
  }
  for (; i < 80; i++)
    W[i] = R1(W[i - 2]) + W[i - 7] + R0(W[i - 15]) + W[i - 16];
  a = s->h[0];
  b = s->h[1];
  c = s->h[2];
  d = s->h[3];
  e = s->h[4];
  f = s->h[5];
  g = s->h[6];
  h = s->h[7];
  for (i = 0; i < 80; i++) {
    t1 = h + S1(e) + Ch(e, f, g) + K[i] + W[i];
    t2 = S0(a) + Maj(a, b, c);
    h = g;
    g = f;
    f = e;
    e = d + t1;
    d = c;
    c = b;
    b = a;
    a = t1 + t2;
  }
  s->h[0] += a;
  s->h[1] += b;
  s->h[2] += c;
  s->h[3] += d;
  s->h[4] += e;
  s->h[5] += f;
  s->h[6] += g;
  s->h[7] += h;
}

static void pad(struct sha512* s) {
  unsigned r = s->len % 128;

  s->buf[r++] = 0x80;
  if (r > 112) {
    memset(s->buf + r, 0, 128 - r);
    r = 0;
    processblock(s, s->buf);
  }
  memset(s->buf + r, 0, 120 - r);
  s->len *= 8;
  s->buf[120] = s->len >> 56;
  s->buf[121] = s->len >> 48;
  s->buf[122] = s->len >> 40;
  s->buf[123] = s->len >> 32;
  s->buf[124] = s->len >> 24;
  s->buf[125] = s->len >> 16;
  s->buf[126] = s->len >> 8;
  s->buf[127] = s->len;
  processblock(s, s->buf);
}

static void sha512_init(struct sha512* s) {
  s->len = 0;
  s->h[0] = 0x6a09e667f3bcc908ULL;
  s->h[1] = 0xbb67ae8584caa73bULL;
  s->h[2] = 0x3c6ef372fe94f82bULL;
  s->h[3] = 0xa54ff53a5f1d36f1ULL;
  s->h[4] = 0x510e527fade682d1ULL;
  s->h[5] = 0x9b05688c2b3e6c1fULL;
  s->h[6] = 0x1f83d9abfb41bd6bULL;
  s->h[7] = 0x5be0cd19137e2179ULL;
}

static void sha512_sum(struct sha512* s, uint8_t* md) {
  int i;

  pad(s);
  for (i = 0; i < 8; i++) {
    md[8 * i] = s->h[i] >> 56;
    md[8 * i + 1] = s->h[i] >> 48;
    md[8 * i + 2] = s->h[i] >> 40;
    md[8 * i + 3] = s->h[i] >> 32;
    md[8 * i + 4] = s->h[i] >> 24;
    md[8 * i + 5] = s->h[i] >> 16;
    md[8 * i + 6] = s->h[i] >> 8;
    md[8 * i + 7] = s->h[i];
  }
}

static void sha512_update(struct sha512* s, const void* m, unsigned long len) {
  const uint8_t* p = m;
  unsigned r = s->len % 128;

  s->len += len;
  if (r) {
    if (len < 128 - r) {
      memcpy(s->buf + r, p, len);
      return;
    }
    memcpy(s->buf + r, p, 128 - r);
    len -= 128 - r;
    p += 128 - r;
    processblock(s, s->buf);
  }
  for (; len >= 128; len -= 128, p += 128)
    processblock(s, p);
  memcpy(s->buf, p, len);
}

static const unsigned char b64[] =
    "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

static char* to64(char* s, unsigned int u, int n) {
  while (--n >= 0) {
    *s++ = b64[u % 64];
    u /= 64;
  }
  return s;
}

/* key limit is not part of the original design, added for DoS protection.
 * rounds limit has been lowered (versus the reference/spec), also for DoS
 * protection. runtime is O(klen^2 + klen*rounds) */
#define KEY_MAX 256
#define SALT_MAX 16
#define ROUNDS_DEFAULT 5000
#define ROUNDS_MIN 1000
#define ROUNDS_MAX 9999999

/* hash n bytes of the repeated md message digest */
static void hashmd(struct sha512* s, unsigned int n, const void* md) {
  unsigned int i;

  for (i = n; i > 64; i -= 64)
    sha512_update(s, md, 64);
  sha512_update(s, md, i);
}

static char* sha512crypt(const char* key, const char* setting, char* output) {
  struct sha512 ctx;
  unsigned char md[64], kmd[64], smd[64];
  unsigned int i, r, klen, slen;
  char rounds[20] = "";
  const char* salt;
  char* p;

  /* reject large keys */
  for (i = 0; i <= KEY_MAX && key[i]; i++)
    ;
  if (i > KEY_MAX)
    return 0;
  klen = i;

  /* setting: $6$rounds=n$salt$ (rounds=n$ and closing $ are optional) */
  if (strncmp(setting, "$6$", 3) != 0)
    return 0;
  salt = setting + 3;

  r = ROUNDS_DEFAULT;
  if (strncmp(salt, "rounds=", sizeof "rounds=" - 1) == 0) {
    unsigned long u;
    char* end;

    /*
     * this is a deviation from the reference:
     * bad rounds setting is rejected if it is
     * - empty
     * - unterminated (missing '$')
     * - begins with anything but a decimal digit
     * the reference implementation treats these bad
     * rounds as part of the salt or parse them with
     * strtoul semantics which may cause problems
     * including non-portable hashes that depend on
     * the host's value of ULONG_MAX.
     */
    salt += sizeof "rounds=" - 1;
    if (!isdigit(*salt))
      return 0;
    u = strtoul(salt, &end, 10);
    if (*end != '$')
      return 0;
    salt = end + 1;
    if (u < ROUNDS_MIN)
      r = ROUNDS_MIN;
    else if (u > ROUNDS_MAX)
      r = ROUNDS_MAX;
    else
      r = u;
    /* needed when rounds is zero prefixed or out of bounds */
    sprintf(rounds, "rounds=%u$", r);
  }

  for (i = 0; i < SALT_MAX && salt[i] && salt[i] != '$'; i++)
    /* reject characters that interfere with /etc/shadow parsing */
    if (salt[i] == '\n' || salt[i] == ':')
      return 0;
  slen = i;

  /* B = sha(key salt key) */
  sha512_init(&ctx);
  sha512_update(&ctx, key, klen);
  sha512_update(&ctx, salt, slen);
  sha512_update(&ctx, key, klen);
  sha512_sum(&ctx, md);

  /* A = sha(key salt repeat-B alternate-B-key) */
  sha512_init(&ctx);
  sha512_update(&ctx, key, klen);
  sha512_update(&ctx, salt, slen);
  hashmd(&ctx, klen, md);
  for (i = klen; i > 0; i >>= 1)
    if (i & 1)
      sha512_update(&ctx, md, sizeof md);
    else
      sha512_update(&ctx, key, klen);
  sha512_sum(&ctx, md);

  /* DP = sha(repeat-key), this step takes O(klen^2) time */
  sha512_init(&ctx);
  for (i = 0; i < klen; i++)
    sha512_update(&ctx, key, klen);
  sha512_sum(&ctx, kmd);

  /* DS = sha(repeat-salt) */
  sha512_init(&ctx);
  for (i = 0; i < 16 + md[0]; i++)
    sha512_update(&ctx, salt, slen);
  sha512_sum(&ctx, smd);

  /* iterate A = f(A,DP,DS), this step takes O(rounds*klen) time */
  for (i = 0; i < r; i++) {
    sha512_init(&ctx);
    if (i % 2)
      hashmd(&ctx, klen, kmd);
    else
      sha512_update(&ctx, md, sizeof md);
    if (i % 3)
      sha512_update(&ctx, smd, slen);
    if (i % 7)
      hashmd(&ctx, klen, kmd);
    if (i % 2)
      sha512_update(&ctx, md, sizeof md);
    else
      hashmd(&ctx, klen, kmd);
    sha512_sum(&ctx, md);
  }

  /* output is $6$rounds=n$salt$hash */
  p = output;
  p += sprintf(p, "$6$%s%.*s$", rounds, slen, salt);
  static const unsigned char perm[][3] = {
      0,  21, 42, 22, 43, 1,  44, 2,  23, 3,  24, 45, 25, 46, 4,  47,
      5,  26, 6,  27, 48, 28, 49, 7,  50, 8,  29, 9,  30, 51, 31, 52,
      10, 53, 11, 32, 12, 33, 54, 34, 55, 13, 56, 14, 35, 15, 36, 57,
      37, 58, 16, 59, 17, 38, 18, 39, 60, 40, 61, 19, 62, 20, 41};
  for (i = 0; i < 21; i++)
    p = to64(p, (md[perm[i][0]] << 16) | (md[perm[i][1]] << 8) | md[perm[i][2]],
             4);
  p = to64(p, md[63], 2);
  *p = 0;
  return output;
}

char* __crypt_sha512(const char* key, const char* setting, char* output) {
  static const char testkey[] = "Xy01@#\x01\x02\x80\x7f\xff\r\n\x81\t !";
  static const char testsetting[] = "$6$rounds=1234$abc0123456789$";
  static const char testhash[] =
      "$6$rounds=1234$abc0123456789$BCpt8zLrc/"
      "RcyuXmCDOE1ALqMXB2MH6n1g891HhFj8.w7LxGv.FTkqq6Vxc/km3Y0jE0j24jY5PIv/"
      "oOu6reg1";
  char testbuf[128];
  char *p, *q;

  p = sha512crypt(key, setting, output);
  /* self test and stack cleanup */
  q = sha512crypt(testkey, testsetting, testbuf);
  if (!p || q != testbuf || memcmp(testbuf, testhash, sizeof testhash))
    return "*";
  return p;
}