Line data Source code
1 : /* ecdh.c - ECDH public key operations used in public key glue code
2 : * Copyright (C) 2010, 2011 Free Software Foundation, Inc.
3 : *
4 : * This file is part of GnuPG.
5 : *
6 : * GnuPG is free software; you can redistribute it and/or modify
7 : * it under the terms of the GNU General Public License as published by
8 : * the Free Software Foundation; either version 3 of the License, or
9 : * (at your option) any later version.
10 : *
11 : * GnuPG is distributed in the hope that it will be useful,
12 : * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 : * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 : * GNU General Public License for more details.
15 : *
16 : * You should have received a copy of the GNU General Public License
17 : * along with this program; if not, see <http://www.gnu.org/licenses/>.
18 : */
19 :
20 : #include <config.h>
21 : #include <stdio.h>
22 : #include <stdlib.h>
23 : #include <string.h>
24 : #include <errno.h>
25 :
26 : #include "gpg.h"
27 : #include "util.h"
28 : #include "pkglue.h"
29 : #include "main.h"
30 : #include "options.h"
31 :
32 : /* A table with the default KEK parameters used by GnuPG. */
33 : static const struct
34 : {
35 : unsigned int qbits;
36 : int openpgp_hash_id; /* KEK digest algorithm. */
37 : int openpgp_cipher_id; /* KEK cipher algorithm. */
38 : } kek_params_table[] =
39 : /* Note: Must be sorted by ascending values for QBITS. */
40 : {
41 : { 256, DIGEST_ALGO_SHA256, CIPHER_ALGO_AES },
42 : { 384, DIGEST_ALGO_SHA384, CIPHER_ALGO_AES256 },
43 :
44 : /* Note: 528 is 521 rounded to the 8 bit boundary */
45 : { 528, DIGEST_ALGO_SHA512, CIPHER_ALGO_AES256 }
46 : };
47 :
48 :
49 :
50 : /* Return KEK parameters as an opaque MPI The caller must free the
51 : returned value. Returns NULL and sets ERRNO on error. */
52 : gcry_mpi_t
53 0 : pk_ecdh_default_params (unsigned int qbits)
54 : {
55 : byte *kek_params;
56 : int i;
57 :
58 0 : kek_params = xtrymalloc (4);
59 0 : if (!kek_params)
60 0 : return NULL;
61 0 : kek_params[0] = 3; /* Number of bytes to follow. */
62 0 : kek_params[1] = 1; /* Version for KDF+AESWRAP. */
63 :
64 : /* Search for matching KEK parameter. Defaults to the strongest
65 : possible choices. Performance is not an issue here, only
66 : interoperability. */
67 0 : for (i=0; i < DIM (kek_params_table); i++)
68 : {
69 0 : if (kek_params_table[i].qbits >= qbits
70 0 : || i+1 == DIM (kek_params_table))
71 : {
72 0 : kek_params[2] = kek_params_table[i].openpgp_hash_id;
73 0 : kek_params[3] = kek_params_table[i].openpgp_cipher_id;
74 0 : break;
75 : }
76 : }
77 0 : log_assert (i < DIM (kek_params_table));
78 0 : if (DBG_CRYPTO)
79 0 : log_printhex ("ECDH KEK params are", kek_params, sizeof(kek_params) );
80 :
81 0 : return gcry_mpi_set_opaque (NULL, kek_params, 4 * 8);
82 : }
83 :
84 :
85 : /* Encrypts/decrypts DATA using a key derived from the ECC shared
86 : point SHARED_MPI using the FIPS SP 800-56A compliant method
87 : key_derivation+key_wrapping. If IS_ENCRYPT is true the function
88 : encrypts; if false, it decrypts. PKEY is the public key and PK_FP
89 : the fingerprint of this public key. On success the result is
90 : stored at R_RESULT; on failure NULL is stored at R_RESULT and an
91 : error code returned. */
92 : gpg_error_t
93 48 : pk_ecdh_encrypt_with_shared_point (int is_encrypt, gcry_mpi_t shared_mpi,
94 : const byte pk_fp[MAX_FINGERPRINT_LEN],
95 : gcry_mpi_t data, gcry_mpi_t *pkey,
96 : gcry_mpi_t *r_result)
97 : {
98 : gpg_error_t err;
99 : byte *secret_x;
100 : int secret_x_size;
101 : unsigned int nbits;
102 : const unsigned char *kek_params;
103 : size_t kek_params_size;
104 : int kdf_hash_algo;
105 : int kdf_encr_algo;
106 : unsigned char message[256];
107 : size_t message_size;
108 :
109 48 : *r_result = NULL;
110 :
111 48 : nbits = pubkey_nbits (PUBKEY_ALGO_ECDH, pkey);
112 48 : if (!nbits)
113 0 : return gpg_error (GPG_ERR_TOO_SHORT);
114 :
115 : {
116 : size_t nbytes;
117 :
118 : /* Extract x component of the shared point: this is the actual
119 : shared secret. */
120 48 : nbytes = (mpi_get_nbits (pkey[1] /* public point */)+7)/8;
121 48 : secret_x = xtrymalloc_secure (nbytes);
122 48 : if (!secret_x)
123 0 : return gpg_error_from_syserror ();
124 :
125 48 : err = gcry_mpi_print (GCRYMPI_FMT_USG, secret_x, nbytes,
126 : &nbytes, shared_mpi);
127 48 : if (err)
128 : {
129 0 : xfree (secret_x);
130 0 : log_error ("ECDH ephemeral export of shared point failed: %s\n",
131 : gpg_strerror (err));
132 0 : return err;
133 : }
134 :
135 48 : secret_x_size = (nbits+7)/8;
136 48 : log_assert (nbytes >= secret_x_size);
137 48 : if ((nbytes & 1))
138 : /* Remove the "04" prefix of non-compressed format. */
139 48 : memmove (secret_x, secret_x+1, secret_x_size);
140 48 : if (nbytes - secret_x_size)
141 48 : memset (secret_x+secret_x_size, 0, nbytes-secret_x_size);
142 :
143 48 : if (DBG_CRYPTO)
144 0 : log_printhex ("ECDH shared secret X is:", secret_x, secret_x_size );
145 : }
146 :
147 : /*** We have now the shared secret bytes in secret_x. ***/
148 :
149 : /* At this point we are done with PK encryption and the rest of the
150 : * function uses symmetric key encryption techniques to protect the
151 : * input DATA. The following two sections will simply replace
152 : * current secret_x with a value derived from it. This will become
153 : * a KEK.
154 : */
155 48 : if (!gcry_mpi_get_flag (pkey[2], GCRYMPI_FLAG_OPAQUE))
156 : {
157 0 : xfree (secret_x);
158 0 : return gpg_error (GPG_ERR_BUG);
159 : }
160 48 : kek_params = gcry_mpi_get_opaque (pkey[2], &nbits);
161 48 : kek_params_size = (nbits+7)/8;
162 :
163 48 : if (DBG_CRYPTO)
164 0 : log_printhex ("ecdh KDF params:", kek_params, kek_params_size);
165 :
166 : /* Expect 4 bytes 03 01 hash_alg symm_alg. */
167 48 : if (kek_params_size != 4 || kek_params[0] != 3 || kek_params[1] != 1)
168 : {
169 0 : xfree (secret_x);
170 0 : return gpg_error (GPG_ERR_BAD_PUBKEY);
171 : }
172 :
173 48 : kdf_hash_algo = kek_params[2];
174 48 : kdf_encr_algo = kek_params[3];
175 :
176 48 : if (DBG_CRYPTO)
177 0 : log_debug ("ecdh KDF algorithms %s+%s with aeswrap\n",
178 : openpgp_md_algo_name (kdf_hash_algo),
179 : openpgp_cipher_algo_name (kdf_encr_algo));
180 :
181 48 : if (kdf_hash_algo != GCRY_MD_SHA256
182 30 : && kdf_hash_algo != GCRY_MD_SHA384
183 15 : && kdf_hash_algo != GCRY_MD_SHA512)
184 : {
185 0 : xfree (secret_x);
186 0 : return gpg_error (GPG_ERR_BAD_PUBKEY);
187 : }
188 48 : if (kdf_encr_algo != CIPHER_ALGO_AES
189 30 : && kdf_encr_algo != CIPHER_ALGO_AES192
190 30 : && kdf_encr_algo != CIPHER_ALGO_AES256)
191 : {
192 0 : xfree (secret_x);
193 0 : return gpg_error (GPG_ERR_BAD_PUBKEY);
194 : }
195 :
196 : /* Build kdf_params. */
197 : {
198 : IOBUF obuf;
199 :
200 48 : obuf = iobuf_temp();
201 : /* variable-length field 1, curve name OID */
202 48 : err = gpg_mpi_write_nohdr (obuf, pkey[0]);
203 : /* fixed-length field 2 */
204 48 : iobuf_put (obuf, PUBKEY_ALGO_ECDH);
205 : /* variable-length field 3, KDF params */
206 48 : err = (err ? err : gpg_mpi_write_nohdr (obuf, pkey[2]));
207 : /* fixed-length field 4 */
208 48 : iobuf_write (obuf, "Anonymous Sender ", 20);
209 : /* fixed-length field 5, recipient fp */
210 48 : iobuf_write (obuf, pk_fp, 20);
211 :
212 48 : message_size = iobuf_temp_to_buffer (obuf, message, sizeof message);
213 48 : iobuf_close (obuf);
214 48 : if (err)
215 : {
216 0 : xfree (secret_x);
217 0 : return err;
218 : }
219 :
220 48 : if(DBG_CRYPTO)
221 0 : log_printhex ("ecdh KDF message params are:", message, message_size);
222 : }
223 :
224 : /* Derive a KEK (key wrapping key) using MESSAGE and SECRET_X. */
225 : {
226 : gcry_md_hd_t h;
227 : int old_size;
228 :
229 48 : err = gcry_md_open (&h, kdf_hash_algo, 0);
230 48 : if (err)
231 : {
232 0 : log_error ("gcry_md_open failed for kdf_hash_algo %d: %s",
233 : kdf_hash_algo, gpg_strerror (err));
234 0 : xfree (secret_x);
235 0 : return err;
236 : }
237 48 : gcry_md_write(h, "\x00\x00\x00\x01", 4); /* counter = 1 */
238 48 : gcry_md_write(h, secret_x, secret_x_size); /* x of the point X */
239 48 : gcry_md_write(h, message, message_size);/* KDF parameters */
240 :
241 48 : gcry_md_final (h);
242 :
243 48 : log_assert( gcry_md_get_algo_dlen (kdf_hash_algo) >= 32 );
244 :
245 48 : memcpy (secret_x, gcry_md_read (h, kdf_hash_algo),
246 48 : gcry_md_get_algo_dlen (kdf_hash_algo));
247 48 : gcry_md_close (h);
248 :
249 48 : old_size = secret_x_size;
250 48 : log_assert( old_size >= gcry_cipher_get_algo_keylen( kdf_encr_algo ) );
251 48 : secret_x_size = gcry_cipher_get_algo_keylen( kdf_encr_algo );
252 48 : log_assert( secret_x_size <= gcry_md_get_algo_dlen (kdf_hash_algo) );
253 :
254 : /* We could have allocated more, so clean the tail before returning. */
255 48 : memset (secret_x+secret_x_size, 0, old_size - secret_x_size);
256 48 : if (DBG_CRYPTO)
257 0 : log_printhex ("ecdh KEK is:", secret_x, secret_x_size );
258 : }
259 :
260 : /* And, finally, aeswrap with key secret_x. */
261 : {
262 : gcry_cipher_hd_t hd;
263 : size_t nbytes;
264 :
265 : byte *data_buf;
266 : int data_buf_size;
267 :
268 : gcry_mpi_t result;
269 :
270 48 : err = gcry_cipher_open (&hd, kdf_encr_algo, GCRY_CIPHER_MODE_AESWRAP, 0);
271 48 : if (err)
272 : {
273 0 : log_error ("ecdh failed to initialize AESWRAP: %s\n",
274 : gpg_strerror (err));
275 0 : xfree (secret_x);
276 0 : return err;
277 : }
278 :
279 48 : err = gcry_cipher_setkey (hd, secret_x, secret_x_size);
280 48 : xfree (secret_x);
281 48 : secret_x = NULL;
282 48 : if (err)
283 : {
284 0 : gcry_cipher_close (hd);
285 0 : log_error ("ecdh failed in gcry_cipher_setkey: %s\n",
286 : gpg_strerror (err));
287 0 : return err;
288 : }
289 :
290 48 : data_buf_size = (gcry_mpi_get_nbits(data)+7)/8;
291 48 : if ((data_buf_size & 7) != (is_encrypt ? 0 : 1))
292 : {
293 0 : log_error ("can't use a shared secret of %d bytes for ecdh\n",
294 : data_buf_size);
295 0 : return gpg_error (GPG_ERR_BAD_DATA);
296 : }
297 :
298 48 : data_buf = xtrymalloc_secure( 1 + 2*data_buf_size + 8);
299 48 : if (!data_buf)
300 : {
301 0 : err = gpg_error_from_syserror ();
302 0 : gcry_cipher_close (hd);
303 0 : return err;
304 : }
305 :
306 48 : if (is_encrypt)
307 : {
308 24 : byte *in = data_buf+1+data_buf_size+8;
309 :
310 : /* Write data MPI into the end of data_buf. data_buf is size
311 : aeswrap data. */
312 24 : err = gcry_mpi_print (GCRYMPI_FMT_USG, in,
313 : data_buf_size, &nbytes, data/*in*/);
314 24 : if (err)
315 : {
316 0 : log_error ("ecdh failed to export DEK: %s\n", gpg_strerror (err));
317 0 : gcry_cipher_close (hd);
318 0 : xfree (data_buf);
319 0 : return err;
320 : }
321 :
322 24 : if (DBG_CRYPTO)
323 0 : log_printhex ("ecdh encrypting :", in, data_buf_size );
324 :
325 24 : err = gcry_cipher_encrypt (hd, data_buf+1, data_buf_size+8,
326 : in, data_buf_size);
327 24 : memset (in, 0, data_buf_size);
328 24 : gcry_cipher_close (hd);
329 24 : if (err)
330 : {
331 0 : log_error ("ecdh failed in gcry_cipher_encrypt: %s\n",
332 : gpg_strerror (err));
333 0 : xfree (data_buf);
334 0 : return err;
335 : }
336 24 : data_buf[0] = data_buf_size+8;
337 :
338 24 : if (DBG_CRYPTO)
339 0 : log_printhex ("ecdh encrypted to:", data_buf+1, data_buf[0] );
340 :
341 24 : result = gcry_mpi_set_opaque (NULL, data_buf, 8 * (1+data_buf[0]));
342 24 : if (!result)
343 : {
344 0 : err = gpg_error_from_syserror ();
345 0 : xfree (data_buf);
346 0 : log_error ("ecdh failed to create an MPI: %s\n",
347 : gpg_strerror (err));
348 0 : return err;
349 : }
350 :
351 24 : *r_result = result;
352 : }
353 : else
354 : {
355 : byte *in;
356 : const void *p;
357 :
358 24 : p = gcry_mpi_get_opaque (data, &nbits);
359 24 : nbytes = (nbits+7)/8;
360 24 : if (!p || nbytes > data_buf_size || !nbytes)
361 : {
362 0 : xfree (data_buf);
363 0 : return gpg_error (GPG_ERR_BAD_MPI);
364 : }
365 24 : memcpy (data_buf, p, nbytes);
366 24 : if (data_buf[0] != nbytes-1)
367 : {
368 0 : log_error ("ecdh inconsistent size\n");
369 0 : xfree (data_buf);
370 0 : return gpg_error (GPG_ERR_BAD_MPI);
371 : }
372 24 : in = data_buf+data_buf_size;
373 24 : data_buf_size = data_buf[0];
374 :
375 24 : if (DBG_CRYPTO)
376 0 : log_printhex ("ecdh decrypting :", data_buf+1, data_buf_size);
377 :
378 24 : err = gcry_cipher_decrypt (hd, in, data_buf_size, data_buf+1,
379 : data_buf_size);
380 24 : gcry_cipher_close (hd);
381 24 : if (err)
382 : {
383 0 : log_error ("ecdh failed in gcry_cipher_decrypt: %s\n",
384 : gpg_strerror (err));
385 0 : xfree (data_buf);
386 0 : return err;
387 : }
388 :
389 24 : data_buf_size -= 8;
390 :
391 24 : if (DBG_CRYPTO)
392 0 : log_printhex ("ecdh decrypted to :", in, data_buf_size);
393 :
394 : /* Padding is removed later. */
395 : /* if (in[data_buf_size-1] > 8 ) */
396 : /* { */
397 : /* log_error ("ecdh failed at decryption: invalid padding." */
398 : /* " 0x%02x > 8\n", in[data_buf_size-1] ); */
399 : /* return gpg_error (GPG_ERR_BAD_KEY); */
400 : /* } */
401 :
402 24 : err = gcry_mpi_scan (&result, GCRYMPI_FMT_USG, in, data_buf_size, NULL);
403 24 : xfree (data_buf);
404 24 : if (err)
405 : {
406 0 : log_error ("ecdh failed to create a plain text MPI: %s\n",
407 : gpg_strerror (err));
408 0 : return err;
409 : }
410 :
411 24 : *r_result = result;
412 : }
413 : }
414 :
415 48 : return err;
416 : }
417 :
418 :
419 : static gcry_mpi_t
420 24 : gen_k (unsigned nbits)
421 : {
422 : gcry_mpi_t k;
423 :
424 24 : k = gcry_mpi_snew (nbits);
425 24 : if (DBG_CRYPTO)
426 0 : log_debug ("choosing a random k of %u bits\n", nbits);
427 :
428 24 : gcry_mpi_randomize (k, nbits-1, GCRY_STRONG_RANDOM);
429 :
430 24 : if (DBG_CRYPTO)
431 : {
432 : unsigned char *buffer;
433 0 : if (gcry_mpi_aprint (GCRYMPI_FMT_HEX, &buffer, NULL, k))
434 0 : BUG ();
435 0 : log_debug ("ephemeral scalar MPI #0: %s\n", buffer);
436 0 : gcry_free (buffer);
437 : }
438 :
439 24 : return k;
440 : }
441 :
442 :
443 : /* Generate an ephemeral key for the public ECDH key in PKEY. On
444 : success the generated key is stored at R_K; on failure NULL is
445 : stored at R_K and an error code returned. */
446 : gpg_error_t
447 24 : pk_ecdh_generate_ephemeral_key (gcry_mpi_t *pkey, gcry_mpi_t *r_k)
448 : {
449 : unsigned int nbits;
450 : gcry_mpi_t k;
451 :
452 24 : *r_k = NULL;
453 :
454 24 : nbits = pubkey_nbits (PUBKEY_ALGO_ECDH, pkey);
455 24 : if (!nbits)
456 0 : return gpg_error (GPG_ERR_TOO_SHORT);
457 24 : k = gen_k (nbits);
458 24 : if (!k)
459 0 : BUG ();
460 :
461 24 : *r_k = k;
462 24 : return 0;
463 : }
464 :
465 :
466 :
467 : /* Perform ECDH decryption. */
468 : int
469 24 : pk_ecdh_decrypt (gcry_mpi_t * result, const byte sk_fp[MAX_FINGERPRINT_LEN],
470 : gcry_mpi_t data, gcry_mpi_t shared, gcry_mpi_t * skey)
471 : {
472 24 : if (!data)
473 0 : return gpg_error (GPG_ERR_BAD_MPI);
474 24 : return pk_ecdh_encrypt_with_shared_point (0 /*=decryption*/, shared,
475 : sk_fp, data/*encr data as an MPI*/,
476 : skey, result);
477 : }
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