Line data Source code
1 : /*-------------------------------------------------------------------------
2 : * scram-common.c
3 : * Shared frontend/backend code for SCRAM authentication
4 : *
5 : * This contains the common low-level functions needed in both frontend and
6 : * backend, for implement the Salted Challenge Response Authentication
7 : * Mechanism (SCRAM), per IETF's RFC 5802.
8 : *
9 : * Portions Copyright (c) 2017-2025, PostgreSQL Global Development Group
10 : *
11 : * IDENTIFICATION
12 : * src/common/scram-common.c
13 : *
14 : *-------------------------------------------------------------------------
15 : */
16 : #ifndef FRONTEND
17 : #include "postgres.h"
18 : #else
19 : #include "postgres_fe.h"
20 : #endif
21 :
22 : #include "common/base64.h"
23 : #include "common/hmac.h"
24 : #include "common/scram-common.h"
25 : #ifndef FRONTEND
26 : #include "miscadmin.h"
27 : #endif
28 : #include "port/pg_bswap.h"
29 :
30 : /*
31 : * Calculate SaltedPassword.
32 : *
33 : * The password should already be normalized by SASLprep. Returns 0 on
34 : * success, -1 on failure with *errstr pointing to a message about the
35 : * error details.
36 : */
37 : int
38 246 : scram_SaltedPassword(const char *password,
39 : pg_cryptohash_type hash_type, int key_length,
40 : const char *salt, int saltlen, int iterations,
41 : uint8 *result, const char **errstr)
42 : {
43 246 : int password_len = strlen(password);
44 246 : uint32 one = pg_hton32(1);
45 : int i,
46 : j;
47 : uint8 Ui[SCRAM_MAX_KEY_LEN];
48 : uint8 Ui_prev[SCRAM_MAX_KEY_LEN];
49 246 : pg_hmac_ctx *hmac_ctx = pg_hmac_create(hash_type);
50 :
51 246 : if (hmac_ctx == NULL)
52 : {
53 0 : *errstr = pg_hmac_error(NULL); /* returns OOM */
54 0 : return -1;
55 : }
56 :
57 : /*
58 : * Iterate hash calculation of HMAC entry using given salt. This is
59 : * essentially PBKDF2 (see RFC2898) with HMAC() as the pseudorandom
60 : * function.
61 : */
62 :
63 : /* First iteration */
64 492 : if (pg_hmac_init(hmac_ctx, (uint8 *) password, password_len) < 0 ||
65 492 : pg_hmac_update(hmac_ctx, (uint8 *) salt, saltlen) < 0 ||
66 492 : pg_hmac_update(hmac_ctx, (uint8 *) &one, sizeof(uint32)) < 0 ||
67 246 : pg_hmac_final(hmac_ctx, Ui_prev, key_length) < 0)
68 : {
69 0 : *errstr = pg_hmac_error(hmac_ctx);
70 0 : pg_hmac_free(hmac_ctx);
71 0 : return -1;
72 : }
73 :
74 246 : memcpy(result, Ui_prev, key_length);
75 :
76 : /* Subsequent iterations */
77 921852 : for (i = 2; i <= iterations; i++)
78 : {
79 : #ifndef FRONTEND
80 : /*
81 : * Make sure that this is interruptible as scram_iterations could be
82 : * set to a large value.
83 : */
84 561082 : CHECK_FOR_INTERRUPTS();
85 : #endif
86 :
87 1843212 : if (pg_hmac_init(hmac_ctx, (uint8 *) password, password_len) < 0 ||
88 1843212 : pg_hmac_update(hmac_ctx, (uint8 *) Ui_prev, key_length) < 0 ||
89 921606 : pg_hmac_final(hmac_ctx, Ui, key_length) < 0)
90 : {
91 0 : *errstr = pg_hmac_error(hmac_ctx);
92 0 : pg_hmac_free(hmac_ctx);
93 0 : return -1;
94 : }
95 :
96 30412998 : for (j = 0; j < key_length; j++)
97 29491392 : result[j] ^= Ui[j];
98 921606 : memcpy(Ui_prev, Ui, key_length);
99 : }
100 :
101 246 : pg_hmac_free(hmac_ctx);
102 246 : return 0;
103 : }
104 :
105 :
106 : /*
107 : * Calculate hash for a NULL-terminated string. (The NULL terminator is
108 : * not included in the hash). Returns 0 on success, -1 on failure with *errstr
109 : * pointing to a message about the error details.
110 : */
111 : int
112 300 : scram_H(const uint8 *input, pg_cryptohash_type hash_type, int key_length,
113 : uint8 *result, const char **errstr)
114 : {
115 : pg_cryptohash_ctx *ctx;
116 :
117 300 : ctx = pg_cryptohash_create(hash_type);
118 300 : if (ctx == NULL)
119 : {
120 0 : *errstr = pg_cryptohash_error(NULL); /* returns OOM */
121 0 : return -1;
122 : }
123 :
124 600 : if (pg_cryptohash_init(ctx) < 0 ||
125 600 : pg_cryptohash_update(ctx, input, key_length) < 0 ||
126 300 : pg_cryptohash_final(ctx, result, key_length) < 0)
127 : {
128 0 : *errstr = pg_cryptohash_error(ctx);
129 0 : pg_cryptohash_free(ctx);
130 0 : return -1;
131 : }
132 :
133 300 : pg_cryptohash_free(ctx);
134 300 : return 0;
135 : }
136 :
137 : /*
138 : * Calculate ClientKey. Returns 0 on success, -1 on failure with *errstr
139 : * pointing to a message about the error details.
140 : */
141 : int
142 194 : scram_ClientKey(const uint8 *salted_password,
143 : pg_cryptohash_type hash_type, int key_length,
144 : uint8 *result, const char **errstr)
145 : {
146 194 : pg_hmac_ctx *ctx = pg_hmac_create(hash_type);
147 :
148 194 : if (ctx == NULL)
149 : {
150 0 : *errstr = pg_hmac_error(NULL); /* returns OOM */
151 0 : return -1;
152 : }
153 :
154 388 : if (pg_hmac_init(ctx, salted_password, key_length) < 0 ||
155 388 : pg_hmac_update(ctx, (uint8 *) "Client Key", strlen("Client Key")) < 0 ||
156 194 : pg_hmac_final(ctx, result, key_length) < 0)
157 : {
158 0 : *errstr = pg_hmac_error(ctx);
159 0 : pg_hmac_free(ctx);
160 0 : return -1;
161 : }
162 :
163 194 : pg_hmac_free(ctx);
164 194 : return 0;
165 : }
166 :
167 : /*
168 : * Calculate ServerKey. Returns 0 on success, -1 on failure with *errstr
169 : * pointing to a message about the error details.
170 : */
171 : int
172 234 : scram_ServerKey(const uint8 *salted_password,
173 : pg_cryptohash_type hash_type, int key_length,
174 : uint8 *result, const char **errstr)
175 : {
176 234 : pg_hmac_ctx *ctx = pg_hmac_create(hash_type);
177 :
178 234 : if (ctx == NULL)
179 : {
180 0 : *errstr = pg_hmac_error(NULL); /* returns OOM */
181 0 : return -1;
182 : }
183 :
184 468 : if (pg_hmac_init(ctx, salted_password, key_length) < 0 ||
185 468 : pg_hmac_update(ctx, (uint8 *) "Server Key", strlen("Server Key")) < 0 ||
186 234 : pg_hmac_final(ctx, result, key_length) < 0)
187 : {
188 0 : *errstr = pg_hmac_error(ctx);
189 0 : pg_hmac_free(ctx);
190 0 : return -1;
191 : }
192 :
193 234 : pg_hmac_free(ctx);
194 234 : return 0;
195 : }
196 :
197 :
198 : /*
199 : * Construct a SCRAM secret, for storing in pg_authid.rolpassword.
200 : *
201 : * The password should already have been processed with SASLprep, if necessary!
202 : *
203 : * The result is palloc'd or malloc'd, so caller is responsible for freeing it.
204 : *
205 : * On error, returns NULL and sets *errstr to point to a message about the
206 : * error details.
207 : */
208 : char *
209 104 : scram_build_secret(pg_cryptohash_type hash_type, int key_length,
210 : const char *salt, int saltlen, int iterations,
211 : const char *password, const char **errstr)
212 : {
213 : uint8 salted_password[SCRAM_MAX_KEY_LEN];
214 : uint8 stored_key[SCRAM_MAX_KEY_LEN];
215 : uint8 server_key[SCRAM_MAX_KEY_LEN];
216 : char *result;
217 : char *p;
218 : int maxlen;
219 : int encoded_salt_len;
220 : int encoded_stored_len;
221 : int encoded_server_len;
222 : int encoded_result;
223 :
224 : /* Only this hash method is supported currently */
225 : Assert(hash_type == PG_SHA256);
226 :
227 : Assert(iterations > 0);
228 :
229 : /* Calculate StoredKey and ServerKey */
230 104 : if (scram_SaltedPassword(password, hash_type, key_length,
231 : salt, saltlen, iterations,
232 104 : salted_password, errstr) < 0 ||
233 104 : scram_ClientKey(salted_password, hash_type, key_length,
234 104 : stored_key, errstr) < 0 ||
235 104 : scram_H(stored_key, hash_type, key_length,
236 104 : stored_key, errstr) < 0 ||
237 104 : scram_ServerKey(salted_password, hash_type, key_length,
238 : server_key, errstr) < 0)
239 : {
240 : /* errstr is filled already here */
241 : #ifdef FRONTEND
242 0 : return NULL;
243 : #else
244 0 : elog(ERROR, "could not calculate stored key and server key: %s",
245 : *errstr);
246 : #endif
247 : }
248 :
249 : /*----------
250 : * The format is:
251 : * SCRAM-SHA-256$<iteration count>:<salt>$<StoredKey>:<ServerKey>
252 : *----------
253 : */
254 104 : encoded_salt_len = pg_b64_enc_len(saltlen);
255 104 : encoded_stored_len = pg_b64_enc_len(key_length);
256 104 : encoded_server_len = pg_b64_enc_len(key_length);
257 :
258 104 : maxlen = strlen("SCRAM-SHA-256") + 1
259 : + 10 + 1 /* iteration count */
260 : + encoded_salt_len + 1 /* Base64-encoded salt */
261 104 : + encoded_stored_len + 1 /* Base64-encoded StoredKey */
262 104 : + encoded_server_len + 1; /* Base64-encoded ServerKey */
263 :
264 : #ifdef FRONTEND
265 2 : result = malloc(maxlen);
266 2 : if (!result)
267 : {
268 0 : *errstr = _("out of memory");
269 0 : return NULL;
270 : }
271 : #else
272 102 : result = palloc(maxlen);
273 : #endif
274 :
275 104 : p = result + sprintf(result, "SCRAM-SHA-256$%d:", iterations);
276 :
277 : /* salt */
278 104 : encoded_result = pg_b64_encode(salt, saltlen, p, encoded_salt_len);
279 104 : if (encoded_result < 0)
280 : {
281 0 : *errstr = _("could not encode salt");
282 : #ifdef FRONTEND
283 0 : free(result);
284 0 : return NULL;
285 : #else
286 0 : elog(ERROR, "%s", *errstr);
287 : #endif
288 : }
289 104 : p += encoded_result;
290 104 : *(p++) = '$';
291 :
292 : /* stored key */
293 104 : encoded_result = pg_b64_encode((char *) stored_key, key_length, p,
294 : encoded_stored_len);
295 104 : if (encoded_result < 0)
296 : {
297 0 : *errstr = _("could not encode stored key");
298 : #ifdef FRONTEND
299 0 : free(result);
300 0 : return NULL;
301 : #else
302 0 : elog(ERROR, "%s", *errstr);
303 : #endif
304 : }
305 :
306 104 : p += encoded_result;
307 104 : *(p++) = ':';
308 :
309 : /* server key */
310 104 : encoded_result = pg_b64_encode((char *) server_key, key_length, p,
311 : encoded_server_len);
312 104 : if (encoded_result < 0)
313 : {
314 0 : *errstr = _("could not encode server key");
315 : #ifdef FRONTEND
316 0 : free(result);
317 0 : return NULL;
318 : #else
319 0 : elog(ERROR, "%s", *errstr);
320 : #endif
321 : }
322 :
323 104 : p += encoded_result;
324 104 : *(p++) = '\0';
325 :
326 : Assert(p - result <= maxlen);
327 :
328 104 : return result;
329 : }
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