add sha256/sha512 crypt

based on versions sent to the list by nsz, with some simplification
and debloating. i'd still like to get them a bit smaller, or ideally
merge them into a single file with most of the code being shared, but
that can be done later.

src/misc/crypt.c

@@ -6,6 +6,6 @@ char *__crypt_r(const char *, const char *, struct crypt_data *);
 char *crypt(const char *key, const char *salt)
 {
 	/* Note: update this size when we add more hash types */
-	static char buf[64];
+	static char buf[128];
 	return __crypt_r(key, salt, (struct crypt_data *)buf);
 }

src/misc/crypt_r.c

@@ -6,6 +6,8 @@ struct crypt_data;
 char *__crypt_des(const char *, const char *, char *);
 char *__crypt_md5(const char *, const char *, char *);
 char *__crypt_blowfish(const char *, const char *, char *);
+char *__crypt_sha256(const char *, const char *, char *);
+char *__crypt_sha512(const char *, const char *, char *);
 
 char *__crypt_r(const char *key, const char *salt, struct crypt_data *data)
 {
@@ -17,6 +19,10 @@ char *__crypt_r(const char *key, const char *salt, struct crypt_data *data)
 #endif
 		if (salt[1] == '2' && salt[3] == '$')
 			return __crypt_blowfish(key, salt, output);
+		if (salt[1] == '5' && salt[2] == '$')
+			return __crypt_sha256(key, salt, output);
+		if (salt[1] == '6' && salt[2] == '$')
+			return __crypt_sha512(key, salt, output);
 	}
 	return __crypt_des(key, salt, output);
 }

src/misc/crypt_sha256.c

+/*
+ * public domain sha256 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 $5$ 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 sha256 implementation based on fips180-3 */
+
+struct sha256 {
+	uint64_t len;    /* processed message length */
+	uint32_t h[8];   /* hash state */
+	uint8_t buf[64]; /* message block buffer */
+};
+
+static uint32_t ror(uint32_t n, int k) { return (n >> k) | (n << (32-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,2) ^ ror(x,13) ^ ror(x,22))
+#define S1(x)      (ror(x,6) ^ ror(x,11) ^ ror(x,25))
+#define R0(x)      (ror(x,7) ^ ror(x,18) ^ (x>>3))
+#define R1(x)      (ror(x,17) ^ ror(x,19) ^ (x>>10))
+
+static const uint32_t K[64] = {
+0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
+0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
+0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
+0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
+0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
+0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
+};
+
+static void processblock(struct sha256 *s, const uint8_t *buf)
+{
+	uint32_t W[64], t1, t2, a, b, c, d, e, f, g, h;
+	int i;
+
+	for (i = 0; i < 16; i++) {
+		W[i] = (uint32_t)buf[4*i]<<24;
+		W[i] |= (uint32_t)buf[4*i+1]<<16;
+		W[i] |= (uint32_t)buf[4*i+2]<<8;
+		W[i] |= buf[4*i+3];
+	}
+	for (; i < 64; 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 < 64; 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 sha256 *s)
+{
+	unsigned r = s->len % 64;
+
+	s->buf[r++] = 0x80;
+	if (r > 56) {
+		memset(s->buf + r, 0, 64 - r);
+		r = 0;
+		processblock(s, s->buf);
+	}
+	memset(s->buf + r, 0, 56 - r);
+	s->len *= 8;
+	s->buf[56] = s->len >> 56;
+	s->buf[57] = s->len >> 48;
+	s->buf[58] = s->len >> 40;
+	s->buf[59] = s->len >> 32;
+	s->buf[60] = s->len >> 24;
+	s->buf[61] = s->len >> 16;
+	s->buf[62] = s->len >> 8;
+	s->buf[63] = s->len;
+	processblock(s, s->buf);
+}
+
+void sha256_init(struct sha256 *s)
+{
+	s->len = 0;
+	s->h[0] = 0x6a09e667;
+	s->h[1] = 0xbb67ae85;
+	s->h[2] = 0x3c6ef372;
+	s->h[3] = 0xa54ff53a;
+	s->h[4] = 0x510e527f;
+	s->h[5] = 0x9b05688c;
+	s->h[6] = 0x1f83d9ab;
+	s->h[7] = 0x5be0cd19;
+}
+
+void sha256_sum(struct sha256 *s, uint8_t md[20])
+{
+	int i;
+
+	pad(s);
+	for (i = 0; i < 8; i++) {
+		md[4*i] = s->h[i] >> 24;
+		md[4*i+1] = s->h[i] >> 16;
+		md[4*i+2] = s->h[i] >> 8;
+		md[4*i+3] = s->h[i];
+	}
+}
+
+void sha256_update(struct sha256 *s, const void *m, unsigned long len)
+{
+	const uint8_t *p = m;
+	unsigned r = s->len % 64;
+
+	s->len += len;
+	if (r) {
+		if (len < 64 - r) {
+			memcpy(s->buf + r, p, len);
+			return;
+		}
+		memcpy(s->buf + r, p, 64 - r);
+		len -= 64 - r;
+		p += 64 - r;
+		processblock(s, s->buf);
+	}
+	for (; len >= 64; len -= 64, p += 64)
+		processblock(s, p);
+	memcpy(s->buf, p, len);
+}
+
+static 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 50000
+
+/* hash n bytes of the repeated md message digest */
+static void hashmd(struct sha256 *s, unsigned int n, const void *md)
+{
+	unsigned int i;
+
+	for (i = n; i > 32; i -= 32)
+		sha256_update(s, md, 32);
+	sha256_update(s, md, i);
+}
+
+static char *sha256crypt(const char *key, const char *setting, char *output)
+{
+	struct sha256 ctx;
+	unsigned char md[32], kmd[32], smd[32];
+	unsigned int i, r, klen, slen;
+	char rounds[20] = "";
+	const char *salt;
+	char *p;
+
+	/* reject large keys */
+	klen = strnlen(key, KEY_MAX+1);
+	if (klen > KEY_MAX)
+		return 0;
+
+	/* setting: $5$rounds=n$salt$ (rounds=n$ and closing $ are optional) */
+	if (strncmp(setting, "$5$", 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) */
+	sha256_init(&ctx);
+	sha256_update(&ctx, key, klen);
+	sha256_update(&ctx, salt, slen);
+	sha256_update(&ctx, key, klen);
+	sha256_sum(&ctx, md);
+
+	/* A = sha(key salt repeat-B alternate-B-key) */
+	sha256_init(&ctx);
+	sha256_update(&ctx, key, klen);
+	sha256_update(&ctx, salt, slen);
+	hashmd(&ctx, klen, md);
+	for (i = klen; i > 0; i >>= 1)
+		if (i & 1)
+			sha256_update(&ctx, md, sizeof md);
+		else
+			sha256_update(&ctx, key, klen);
+	sha256_sum(&ctx, md);
+
+	/* DP = sha(repeat-key), this step takes O(klen^2) time */
+	sha256_init(&ctx);
+	for (i = 0; i < klen; i++)
+		sha256_update(&ctx, key, klen);
+	sha256_sum(&ctx, kmd);
+
+	/* DS = sha(repeat-salt) */
+	sha256_init(&ctx);
+	for (i = 0; i < 16 + md[0]; i++)
+		sha256_update(&ctx, salt, slen);
+	sha256_sum(&ctx, smd);
+
+	/* iterate A = f(A,DP,DS), this step takes O(rounds*klen) time */
+	for (i = 0; i < r; i++) {
+		sha256_init(&ctx);
+		if (i % 2)
+			hashmd(&ctx, klen, kmd);
+		else
+			sha256_update(&ctx, md, sizeof md);
+		if (i % 3)
+			sha256_update(&ctx, smd, slen);
+		if (i % 7)
+			hashmd(&ctx, klen, kmd);
+		if (i % 2)
+			sha256_update(&ctx, md, sizeof md);
+		else
+			hashmd(&ctx, klen, kmd);
+		sha256_sum(&ctx, md);
+	}
+
+	/* output is $5$rounds=n$salt$hash */
+	p = output;
+	p += sprintf(p, "$5$%s%.*s$", rounds, slen, salt);
+	static const unsigned char perm[][3] = {
+		0,10,20,21,1,11,12,22,2,3,13,23,24,4,14,
+		15,25,5,6,16,26,27,7,17,18,28,8,9,19,29 };
+	for (i=0; i<10; i++) p = to64(p,
+		(md[perm[i][0]]<<16)|(md[perm[i][1]]<<8)|md[perm[i][2]], 4);
+	p = to64(p, (md[31]<<8)|md[30], 3);
+	*p = 0;
+	return output;
+}
+
+char *__crypt_sha256(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[] = "$5$rounds=1234$abc0123456789$";
+	static const char testhash[] = "$5$rounds=1234$abc0123456789$3VfDjPt05VHFn47C/ojFZ6KRPYrOjj1lLbH.dkF3bZ6";
+	char testbuf[128];
+	char *p, *q;
+
+	p = sha256crypt(key, setting, output);
+	/* self test and stack cleanup */
+	q = sha256crypt(testkey, testsetting, testbuf);
+	if (!p || q != testbuf || memcmp(testbuf, testhash, sizeof testhash))
+		return "*";
+	return p;
+}

src/misc/crypt_sha512.c

+/*
+ * 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[20])
+{
+	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 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 50000
+
+/* 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);
+#if 1
+	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);
+#else
+	p = to64(p, (md[0]<<16)|(md[21]<<8)|md[42], 4);
+	p = to64(p, (md[22]<<16)|(md[43]<<8)|md[1], 4);
+	p = to64(p, (md[44]<<16)|(md[2]<<8)|md[23], 4);
+	p = to64(p, (md[3]<<16)|(md[24]<<8)|md[45], 4);
+	p = to64(p, (md[25]<<16)|(md[46]<<8)|md[4], 4);
+	p = to64(p, (md[47]<<16)|(md[5]<<8)|md[26], 4);
+	p = to64(p, (md[6]<<16)|(md[27]<<8)|md[48], 4);
+	p = to64(p, (md[28]<<16)|(md[49]<<8)|md[7], 4);
+	p = to64(p, (md[50]<<16)|(md[8]<<8)|md[29], 4);
+	p = to64(p, (md[9]<<16)|(md[30]<<8)|md[51], 4);
+	p = to64(p, (md[31]<<16)|(md[52]<<8)|md[10], 4);
+	p = to64(p, (md[53]<<16)|(md[11]<<8)|md[32], 4);
+	p = to64(p, (md[12]<<16)|(md[33]<<8)|md[54], 4);
+	p = to64(p, (md[34]<<16)|(md[55]<<8)|md[13], 4);
+	p = to64(p, (md[56]<<16)|(md[14]<<8)|md[35], 4);
+	p = to64(p, (md[15]<<16)|(md[36]<<8)|md[57], 4);
+	p = to64(p, (md[37]<<16)|(md[58]<<8)|md[16], 4);
+	p = to64(p, (md[59]<<16)|(md[17]<<8)|md[38], 4);
+	p = to64(p, (md[18]<<16)|(md[39]<<8)|md[60], 4);
+	p = to64(p, (md[40]<<16)|(md[61]<<8)|md[19], 4);
+	p = to64(p, (md[62]<<16)|(md[20]<<8)|md[41], 4);
+#endif
+	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;
+}