1/*
2 * public domain sha256 crypt implementation
3 *
4 * original sha crypt design: http://people.redhat.com/drepper/SHA-crypt.txt
5 * in this implementation at least 32bit int is assumed,
6 * key length is limited, the $5$ prefix is mandatory, '\n' and ':' is rejected
7 * in the salt and rounds= setting must contain a valid iteration count,
8 * on error "*" is returned.
9 */
10#include <ctype.h>
11#include <stdlib.h>
12#include <stdio.h>
13#include <string.h>
14#include <stdint.h>
15
16/* public domain sha256 implementation based on fips180-3 */
17
18struct sha256 {
19	uint64_t len;    /* processed message length */
20	uint32_t h[8];   /* hash state */
21	uint8_t buf[64]; /* message block buffer */
22};
23
24static uint32_t ror(uint32_t n, int k) { return (n >> k) | (n << (32-k)); }
25#define Ch(x,y,z)  (z ^ (x & (y ^ z)))
26#define Maj(x,y,z) ((x & y) | (z & (x | y)))
27#define S0(x)      (ror(x,2) ^ ror(x,13) ^ ror(x,22))
28#define S1(x)      (ror(x,6) ^ ror(x,11) ^ ror(x,25))
29#define R0(x)      (ror(x,7) ^ ror(x,18) ^ (x>>3))
30#define R1(x)      (ror(x,17) ^ ror(x,19) ^ (x>>10))
31
32static const uint32_t K[64] = {
330x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
340xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
350xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
360x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
370x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
380xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
390x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
400x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
41};
42
43static void processblock(struct sha256 *s, const uint8_t *buf)
44{
45	uint32_t W[64], t1, t2, a, b, c, d, e, f, g, h;
46	int i;
47
48	for (i = 0; i < 16; i++) {
49		W[i] = (uint32_t)buf[4*i]<<24;
50		W[i] |= (uint32_t)buf[4*i+1]<<16;
51		W[i] |= (uint32_t)buf[4*i+2]<<8;
52		W[i] |= buf[4*i+3];
53	}
54	for (; i < 64; i++)
55		W[i] = R1(W[i-2]) + W[i-7] + R0(W[i-15]) + W[i-16];
56	a = s->h[0];
57	b = s->h[1];
58	c = s->h[2];
59	d = s->h[3];
60	e = s->h[4];
61	f = s->h[5];
62	g = s->h[6];
63	h = s->h[7];
64	for (i = 0; i < 64; i++) {
65		t1 = h + S1(e) + Ch(e,f,g) + K[i] + W[i];
66		t2 = S0(a) + Maj(a,b,c);
67		h = g;
68		g = f;
69		f = e;
70		e = d + t1;
71		d = c;
72		c = b;
73		b = a;
74		a = t1 + t2;
75	}
76	s->h[0] += a;
77	s->h[1] += b;
78	s->h[2] += c;
79	s->h[3] += d;
80	s->h[4] += e;
81	s->h[5] += f;
82	s->h[6] += g;
83	s->h[7] += h;
84}
85
86static void pad(struct sha256 *s)
87{
88	unsigned r = s->len % 64;
89
90	s->buf[r++] = 0x80;
91	if (r > 56) {
92		memset(s->buf + r, 0, 64 - r);
93		r = 0;
94		processblock(s, s->buf);
95	}
96	memset(s->buf + r, 0, 56 - r);
97	s->len *= 8;
98	s->buf[56] = s->len >> 56;
99	s->buf[57] = s->len >> 48;
100	s->buf[58] = s->len >> 40;
101	s->buf[59] = s->len >> 32;
102	s->buf[60] = s->len >> 24;
103	s->buf[61] = s->len >> 16;
104	s->buf[62] = s->len >> 8;
105	s->buf[63] = s->len;
106	processblock(s, s->buf);
107}
108
109static void sha256_init(struct sha256 *s)
110{
111	s->len = 0;
112	s->h[0] = 0x6a09e667;
113	s->h[1] = 0xbb67ae85;
114	s->h[2] = 0x3c6ef372;
115	s->h[3] = 0xa54ff53a;
116	s->h[4] = 0x510e527f;
117	s->h[5] = 0x9b05688c;
118	s->h[6] = 0x1f83d9ab;
119	s->h[7] = 0x5be0cd19;
120}
121
122static void sha256_sum(struct sha256 *s, uint8_t *md)
123{
124	int i;
125
126	pad(s);
127	for (i = 0; i < 8; i++) {
128		md[4*i] = s->h[i] >> 24;
129		md[4*i+1] = s->h[i] >> 16;
130		md[4*i+2] = s->h[i] >> 8;
131		md[4*i+3] = s->h[i];
132	}
133}
134
135static void sha256_update(struct sha256 *s, const void *m, unsigned long len)
136{
137	const uint8_t *p = m;
138	unsigned r = s->len % 64;
139
140	s->len += len;
141	if (r) {
142		if (len < 64 - r) {
143			memcpy(s->buf + r, p, len);
144			return;
145		}
146		memcpy(s->buf + r, p, 64 - r);
147		len -= 64 - r;
148		p += 64 - r;
149		processblock(s, s->buf);
150	}
151	for (; len >= 64; len -= 64, p += 64)
152		processblock(s, p);
153	memcpy(s->buf, p, len);
154}
155
156static const unsigned char b64[] =
157"./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
158
159static char *to64(char *s, unsigned int u, int n)
160{
161	while (--n >= 0) {
162		*s++ = b64[u % 64];
163		u /= 64;
164	}
165	return s;
166}
167
168/* key limit is not part of the original design, added for DoS protection.
169 * rounds limit has been lowered (versus the reference/spec), also for DoS
170 * protection. runtime is O(klen^2 + klen*rounds) */
171#define KEY_MAX 256
172#define SALT_MAX 16
173#define ROUNDS_DEFAULT 5000
174#define ROUNDS_MIN 1000
175#define ROUNDS_MAX 9999999
176
177/* hash n bytes of the repeated md message digest */
178static void hashmd(struct sha256 *s, unsigned int n, const void *md)
179{
180	unsigned int i;
181
182	for (i = n; i > 32; i -= 32)
183		sha256_update(s, md, 32);
184	sha256_update(s, md, i);
185}
186
187static char *sha256crypt(const char *key, const char *setting, char *output)
188{
189	struct sha256 ctx;
190	unsigned char md[32], kmd[32], smd[32];
191	unsigned int i, r, klen, slen;
192	char rounds[20] = "";
193	const char *salt;
194	char *p;
195
196	/* reject large keys */
197	klen = strnlen(key, KEY_MAX+1);
198	if (klen > KEY_MAX)
199		return 0;
200
201	/* setting: $5$rounds=n$salt$ (rounds=n$ and closing $ are optional) */
202	if (strncmp(setting, "$5$", 3) != 0)
203		return 0;
204	salt = setting + 3;
205
206	r = ROUNDS_DEFAULT;
207	if (strncmp(salt, "rounds=", sizeof "rounds=" - 1) == 0) {
208		unsigned long u;
209		char *end;
210
211		/*
212		 * this is a deviation from the reference:
213		 * bad rounds setting is rejected if it is
214		 * - empty
215		 * - unterminated (missing '$')
216		 * - begins with anything but a decimal digit
217		 * the reference implementation treats these bad
218		 * rounds as part of the salt or parse them with
219		 * strtoul semantics which may cause problems
220		 * including non-portable hashes that depend on
221		 * the host's value of ULONG_MAX.
222		 */
223		salt += sizeof "rounds=" - 1;
224		if (!isdigit(*salt))
225			return 0;
226		u = strtoul(salt, &end, 10);
227		if (*end != '$')
228			return 0;
229		salt = end+1;
230		if (u < ROUNDS_MIN)
231			r = ROUNDS_MIN;
232		else if (u > ROUNDS_MAX)
233			return 0;
234		else
235			r = u;
236		/* needed when rounds is zero prefixed or out of bounds */
237		sprintf(rounds, "rounds=%u$", r);
238	}
239
240	for (i = 0; i < SALT_MAX && salt[i] && salt[i] != '$'; i++)
241		/* reject characters that interfere with /etc/shadow parsing */
242		if (salt[i] == '\n' || salt[i] == ':')
243			return 0;
244	slen = i;
245
246	/* B = sha(key salt key) */
247	sha256_init(&ctx);
248	sha256_update(&ctx, key, klen);
249	sha256_update(&ctx, salt, slen);
250	sha256_update(&ctx, key, klen);
251	sha256_sum(&ctx, md);
252
253	/* A = sha(key salt repeat-B alternate-B-key) */
254	sha256_init(&ctx);
255	sha256_update(&ctx, key, klen);
256	sha256_update(&ctx, salt, slen);
257	hashmd(&ctx, klen, md);
258	for (i = klen; i > 0; i >>= 1)
259		if (i & 1)
260			sha256_update(&ctx, md, sizeof md);
261		else
262			sha256_update(&ctx, key, klen);
263	sha256_sum(&ctx, md);
264
265	/* DP = sha(repeat-key), this step takes O(klen^2) time */
266	sha256_init(&ctx);
267	for (i = 0; i < klen; i++)
268		sha256_update(&ctx, key, klen);
269	sha256_sum(&ctx, kmd);
270
271	/* DS = sha(repeat-salt) */
272	sha256_init(&ctx);
273	for (i = 0; i < 16 + md[0]; i++)
274		sha256_update(&ctx, salt, slen);
275	sha256_sum(&ctx, smd);
276
277	/* iterate A = f(A,DP,DS), this step takes O(rounds*klen) time */
278	for (i = 0; i < r; i++) {
279		sha256_init(&ctx);
280		if (i % 2)
281			hashmd(&ctx, klen, kmd);
282		else
283			sha256_update(&ctx, md, sizeof md);
284		if (i % 3)
285			sha256_update(&ctx, smd, slen);
286		if (i % 7)
287			hashmd(&ctx, klen, kmd);
288		if (i % 2)
289			sha256_update(&ctx, md, sizeof md);
290		else
291			hashmd(&ctx, klen, kmd);
292		sha256_sum(&ctx, md);
293	}
294
295	/* output is $5$rounds=n$salt$hash */
296	p = output;
297	p += sprintf(p, "$5$%s%.*s$", rounds, slen, salt);
298	static const unsigned char perm[][3] = {
299		0,10,20,21,1,11,12,22,2,3,13,23,24,4,14,
300		15,25,5,6,16,26,27,7,17,18,28,8,9,19,29 };
301	for (i=0; i<10; i++) p = to64(p,
302		(md[perm[i][0]]<<16)|(md[perm[i][1]]<<8)|md[perm[i][2]], 4);
303	p = to64(p, (md[31]<<8)|md[30], 3);
304	*p = 0;
305	return output;
306}
307
308char *__crypt_sha256(const char *key, const char *setting, char *output)
309{
310	static const char testkey[] = "Xy01@#\x01\x02\x80\x7f\xff\r\n\x81\t !";
311	static const char testsetting[] = "$5$rounds=1234$abc0123456789$";
312	static const char testhash[] = "$5$rounds=1234$abc0123456789$3VfDjPt05VHFn47C/ojFZ6KRPYrOjj1lLbH.dkF3bZ6";
313	char testbuf[128];
314	char *p, *q;
315
316	p = sha256crypt(key, setting, output);
317	/* self test and stack cleanup */
318	q = sha256crypt(testkey, testsetting, testbuf);
319	if (!p || q != testbuf || memcmp(testbuf, testhash, sizeof testhash))
320		return "*";
321	return p;
322}
323