1/* One way encryption based on SHA256 sum.
2 Copyright (C) 2007-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <errno.h>
21#include <stdbool.h>
22#include <stdlib.h>
23#include <string.h>
24#include <stdint.h>
25#include <sys/param.h>
26
27#include "sha256.h"
28#include "crypt-private.h"
29
30
31#ifdef USE_NSS
32typedef int PRBool;
33# include <hasht.h>
34# include <nsslowhash.h>
35
36# define sha256_init_ctx(ctxp, nss_ctxp) \
37 do \
38 { \
39 if (((nss_ctxp = NSSLOWHASH_NewContext (nss_ictx, HASH_AlgSHA256)) \
40 == NULL)) \
41 { \
42 if (nss_ctx != NULL) \
43 NSSLOWHASH_Destroy (nss_ctx); \
44 if (nss_alt_ctx != NULL) \
45 NSSLOWHASH_Destroy (nss_alt_ctx); \
46 return NULL; \
47 } \
48 NSSLOWHASH_Begin (nss_ctxp); \
49 } \
50 while (0)
51
52# define sha256_process_bytes(buf, len, ctxp, nss_ctxp) \
53 NSSLOWHASH_Update (nss_ctxp, (const unsigned char *) buf, len)
54
55# define sha256_finish_ctx(ctxp, nss_ctxp, result) \
56 do \
57 { \
58 unsigned int ret; \
59 NSSLOWHASH_End (nss_ctxp, result, &ret, sizeof (result)); \
60 assert (ret == sizeof (result)); \
61 NSSLOWHASH_Destroy (nss_ctxp); \
62 nss_ctxp = NULL; \
63 } \
64 while (0)
65#else
66# define sha256_init_ctx(ctxp, nss_ctxp) \
67 __sha256_init_ctx (ctxp)
68
69# define sha256_process_bytes(buf, len, ctxp, nss_ctxp) \
70 __sha256_process_bytes(buf, len, ctxp)
71
72# define sha256_finish_ctx(ctxp, nss_ctxp, result) \
73 __sha256_finish_ctx (ctxp, result)
74#endif
75
76
77/* Define our magic string to mark salt for SHA256 "encryption"
78 replacement. */
79static const char sha256_salt_prefix[] = "$5$";
80
81/* Prefix for optional rounds specification. */
82static const char sha256_rounds_prefix[] = "rounds=";
83
84/* Maximum salt string length. */
85#define SALT_LEN_MAX 16
86/* Default number of rounds if not explicitly specified. */
87#define ROUNDS_DEFAULT 5000
88/* Minimum number of rounds. */
89#define ROUNDS_MIN 1000
90/* Maximum number of rounds. */
91#define ROUNDS_MAX 999999999
92
93
94/* Prototypes for local functions. */
95extern char *__sha256_crypt_r (const char *key, const char *salt,
96 char *buffer, int buflen);
97extern char *__sha256_crypt (const char *key, const char *salt);
98
99
100char *
101__sha256_crypt_r (const char *key, const char *salt, char *buffer, int buflen)
102{
103 unsigned char alt_result[32]
104 __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
105 unsigned char temp_result[32]
106 __attribute__ ((__aligned__ (__alignof__ (uint32_t))));
107 size_t salt_len;
108 size_t key_len;
109 size_t cnt;
110 char *cp;
111 char *copied_key = NULL;
112 char *copied_salt = NULL;
113 char *p_bytes;
114 char *s_bytes;
115 /* Default number of rounds. */
116 size_t rounds = ROUNDS_DEFAULT;
117 bool rounds_custom = false;
118 size_t alloca_used = 0;
119 char *free_key = NULL;
120 char *free_pbytes = NULL;
121
122 /* Find beginning of salt string. The prefix should normally always
123 be present. Just in case it is not. */
124 if (strncmp (sha256_salt_prefix, salt, sizeof (sha256_salt_prefix) - 1) == 0)
125 /* Skip salt prefix. */
126 salt += sizeof (sha256_salt_prefix) - 1;
127
128 if (strncmp (salt, sha256_rounds_prefix, sizeof (sha256_rounds_prefix) - 1)
129 == 0)
130 {
131 const char *num = salt + sizeof (sha256_rounds_prefix) - 1;
132 char *endp;
133 unsigned long int srounds = strtoul (num, &endp, 10);
134 if (*endp == '$')
135 {
136 salt = endp + 1;
137 rounds = MAX (ROUNDS_MIN, MIN (srounds, ROUNDS_MAX));
138 rounds_custom = true;
139 }
140 }
141
142 salt_len = MIN (strcspn (salt, "$"), SALT_LEN_MAX);
143 key_len = strlen (key);
144
145 if ((key - (char *) 0) % __alignof__ (uint32_t) != 0)
146 {
147 char *tmp;
148
149 if (__libc_use_alloca (alloca_used + key_len + __alignof__ (uint32_t)))
150 tmp = alloca_account (key_len + __alignof__ (uint32_t), alloca_used);
151 else
152 {
153 free_key = tmp = (char *) malloc (key_len + __alignof__ (uint32_t));
154 if (tmp == NULL)
155 return NULL;
156 }
157
158 key = copied_key =
159 memcpy (tmp + __alignof__ (uint32_t)
160 - (tmp - (char *) 0) % __alignof__ (uint32_t),
161 key, key_len);
162 assert ((key - (char *) 0) % __alignof__ (uint32_t) == 0);
163 }
164
165 if ((salt - (char *) 0) % __alignof__ (uint32_t) != 0)
166 {
167 char *tmp = (char *) alloca (salt_len + __alignof__ (uint32_t));
168 alloca_used += salt_len + __alignof__ (uint32_t);
169 salt = copied_salt =
170 memcpy (tmp + __alignof__ (uint32_t)
171 - (tmp - (char *) 0) % __alignof__ (uint32_t),
172 salt, salt_len);
173 assert ((salt - (char *) 0) % __alignof__ (uint32_t) == 0);
174 }
175
176#ifdef USE_NSS
177 /* Initialize libfreebl3. */
178 NSSLOWInitContext *nss_ictx = NSSLOW_Init ();
179 if (nss_ictx == NULL)
180 {
181 free (free_key);
182 return NULL;
183 }
184 NSSLOWHASHContext *nss_ctx = NULL;
185 NSSLOWHASHContext *nss_alt_ctx = NULL;
186#else
187 struct sha256_ctx ctx;
188 struct sha256_ctx alt_ctx;
189#endif
190
191 /* Prepare for the real work. */
192 sha256_init_ctx (&ctx, nss_ctx);
193
194 /* Add the key string. */
195 sha256_process_bytes (key, key_len, &ctx, nss_ctx);
196
197 /* The last part is the salt string. This must be at most 16
198 characters and it ends at the first `$' character. */
199 sha256_process_bytes (salt, salt_len, &ctx, nss_ctx);
200
201
202 /* Compute alternate SHA256 sum with input KEY, SALT, and KEY. The
203 final result will be added to the first context. */
204 sha256_init_ctx (&alt_ctx, nss_alt_ctx);
205
206 /* Add key. */
207 sha256_process_bytes (key, key_len, &alt_ctx, nss_alt_ctx);
208
209 /* Add salt. */
210 sha256_process_bytes (salt, salt_len, &alt_ctx, nss_alt_ctx);
211
212 /* Add key again. */
213 sha256_process_bytes (key, key_len, &alt_ctx, nss_alt_ctx);
214
215 /* Now get result of this (32 bytes) and add it to the other
216 context. */
217 sha256_finish_ctx (&alt_ctx, nss_alt_ctx, alt_result);
218
219 /* Add for any character in the key one byte of the alternate sum. */
220 for (cnt = key_len; cnt > 32; cnt -= 32)
221 sha256_process_bytes (alt_result, 32, &ctx, nss_ctx);
222 sha256_process_bytes (alt_result, cnt, &ctx, nss_ctx);
223
224 /* Take the binary representation of the length of the key and for every
225 1 add the alternate sum, for every 0 the key. */
226 for (cnt = key_len; cnt > 0; cnt >>= 1)
227 if ((cnt & 1) != 0)
228 sha256_process_bytes (alt_result, 32, &ctx, nss_ctx);
229 else
230 sha256_process_bytes (key, key_len, &ctx, nss_ctx);
231
232 /* Create intermediate result. */
233 sha256_finish_ctx (&ctx, nss_ctx, alt_result);
234
235 /* Start computation of P byte sequence. */
236 sha256_init_ctx (&alt_ctx, nss_alt_ctx);
237
238 /* For every character in the password add the entire password. */
239 for (cnt = 0; cnt < key_len; ++cnt)
240 sha256_process_bytes (key, key_len, &alt_ctx, nss_alt_ctx);
241
242 /* Finish the digest. */
243 sha256_finish_ctx (&alt_ctx, nss_alt_ctx, temp_result);
244
245 /* Create byte sequence P. */
246 if (__libc_use_alloca (alloca_used + key_len))
247 cp = p_bytes = (char *) alloca (key_len);
248 else
249 {
250 free_pbytes = cp = p_bytes = (char *)malloc (key_len);
251 if (free_pbytes == NULL)
252 {
253 free (free_key);
254 return NULL;
255 }
256 }
257
258 for (cnt = key_len; cnt >= 32; cnt -= 32)
259 cp = mempcpy (cp, temp_result, 32);
260 memcpy (cp, temp_result, cnt);
261
262 /* Start computation of S byte sequence. */
263 sha256_init_ctx (&alt_ctx, nss_alt_ctx);
264
265 /* For every character in the password add the entire password. */
266 for (cnt = 0; cnt < 16 + alt_result[0]; ++cnt)
267 sha256_process_bytes (salt, salt_len, &alt_ctx, nss_alt_ctx);
268
269 /* Finish the digest. */
270 sha256_finish_ctx (&alt_ctx, nss_alt_ctx, temp_result);
271
272 /* Create byte sequence S. */
273 cp = s_bytes = alloca (salt_len);
274 for (cnt = salt_len; cnt >= 32; cnt -= 32)
275 cp = mempcpy (cp, temp_result, 32);
276 memcpy (cp, temp_result, cnt);
277
278 /* Repeatedly run the collected hash value through SHA256 to burn
279 CPU cycles. */
280 for (cnt = 0; cnt < rounds; ++cnt)
281 {
282 /* New context. */
283 sha256_init_ctx (&ctx, nss_ctx);
284
285 /* Add key or last result. */
286 if ((cnt & 1) != 0)
287 sha256_process_bytes (p_bytes, key_len, &ctx, nss_ctx);
288 else
289 sha256_process_bytes (alt_result, 32, &ctx, nss_ctx);
290
291 /* Add salt for numbers not divisible by 3. */
292 if (cnt % 3 != 0)
293 sha256_process_bytes (s_bytes, salt_len, &ctx, nss_ctx);
294
295 /* Add key for numbers not divisible by 7. */
296 if (cnt % 7 != 0)
297 sha256_process_bytes (p_bytes, key_len, &ctx, nss_ctx);
298
299 /* Add key or last result. */
300 if ((cnt & 1) != 0)
301 sha256_process_bytes (alt_result, 32, &ctx, nss_ctx);
302 else
303 sha256_process_bytes (p_bytes, key_len, &ctx, nss_ctx);
304
305 /* Create intermediate result. */
306 sha256_finish_ctx (&ctx, nss_ctx, alt_result);
307 }
308
309#ifdef USE_NSS
310 /* Free libfreebl3 resources. */
311 NSSLOW_Shutdown (nss_ictx);
312#endif
313
314 /* Now we can construct the result string. It consists of three
315 parts. */
316 cp = __stpncpy (buffer, sha256_salt_prefix, MAX (0, buflen));
317 buflen -= sizeof (sha256_salt_prefix) - 1;
318
319 if (rounds_custom)
320 {
321 int n = __snprintf (cp, MAX (0, buflen), "%s%zu$",
322 sha256_rounds_prefix, rounds);
323 cp += n;
324 buflen -= n;
325 }
326
327 cp = __stpncpy (cp, salt, MIN ((size_t) MAX (0, buflen), salt_len));
328 buflen -= MIN ((size_t) MAX (0, buflen), salt_len);
329
330 if (buflen > 0)
331 {
332 *cp++ = '$';
333 --buflen;
334 }
335
336 __b64_from_24bit (&cp, &buflen,
337 alt_result[0], alt_result[10], alt_result[20], 4);
338 __b64_from_24bit (&cp, &buflen,
339 alt_result[21], alt_result[1], alt_result[11], 4);
340 __b64_from_24bit (&cp, &buflen,
341 alt_result[12], alt_result[22], alt_result[2], 4);
342 __b64_from_24bit (&cp, &buflen,
343 alt_result[3], alt_result[13], alt_result[23], 4);
344 __b64_from_24bit (&cp, &buflen,
345 alt_result[24], alt_result[4], alt_result[14], 4);
346 __b64_from_24bit (&cp, &buflen,
347 alt_result[15], alt_result[25], alt_result[5], 4);
348 __b64_from_24bit (&cp, &buflen,
349 alt_result[6], alt_result[16], alt_result[26], 4);
350 __b64_from_24bit (&cp, &buflen,
351 alt_result[27], alt_result[7], alt_result[17], 4);
352 __b64_from_24bit (&cp, &buflen,
353 alt_result[18], alt_result[28], alt_result[8], 4);
354 __b64_from_24bit (&cp, &buflen,
355 alt_result[9], alt_result[19], alt_result[29], 4);
356 __b64_from_24bit (&cp, &buflen,
357 0, alt_result[31], alt_result[30], 3);
358 if (buflen <= 0)
359 {
360 __set_errno (ERANGE);
361 buffer = NULL;
362 }
363 else
364 *cp = '\0'; /* Terminate the string. */
365
366 /* Clear the buffer for the intermediate result so that people
367 attaching to processes or reading core dumps cannot get any
368 information. We do it in this way to clear correct_words[]
369 inside the SHA256 implementation as well. */
370#ifndef USE_NSS
371 __sha256_init_ctx (&ctx);
372 __sha256_finish_ctx (&ctx, alt_result);
373 explicit_bzero (&ctx, sizeof (ctx));
374 explicit_bzero (&alt_ctx, sizeof (alt_ctx));
375#endif
376 explicit_bzero (temp_result, sizeof (temp_result));
377 explicit_bzero (p_bytes, key_len);
378 explicit_bzero (s_bytes, salt_len);
379 if (copied_key != NULL)
380 explicit_bzero (copied_key, key_len);
381 if (copied_salt != NULL)
382 explicit_bzero (copied_salt, salt_len);
383
384 free (free_key);
385 free (free_pbytes);
386 return buffer;
387}
388
389#ifndef _LIBC
390# define libc_freeres_ptr(decl) decl
391#endif
392libc_freeres_ptr (static char *buffer);
393
394/* This entry point is equivalent to the `crypt' function in Unix
395 libcs. */
396char *
397__sha256_crypt (const char *key, const char *salt)
398{
399 /* We don't want to have an arbitrary limit in the size of the
400 password. We can compute an upper bound for the size of the
401 result in advance and so we can prepare the buffer we pass to
402 `sha256_crypt_r'. */
403 static int buflen;
404 int needed = (sizeof (sha256_salt_prefix) - 1
405 + sizeof (sha256_rounds_prefix) + 9 + 1
406 + strlen (salt) + 1 + 43 + 1);
407
408 if (buflen < needed)
409 {
410 char *new_buffer = (char *) realloc (buffer, needed);
411 if (new_buffer == NULL)
412 return NULL;
413
414 buffer = new_buffer;
415 buflen = needed;
416 }
417
418 return __sha256_crypt_r (key, salt, buffer, buflen);
419}
420
421#ifndef _LIBC
422static void
423__attribute__ ((__destructor__))
424free_mem (void)
425{
426 free (buffer);
427}
428#endif
429

source code of glibc/crypt/sha256-crypt.c