fusl/src/crypt/crypt_sha512.c - mojo-tools - Git at Google

 /*
  * 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;
 }
	/*
	* 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 + klenrounds) /
	#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(roundsklen) 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;
	}