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}