summaryrefslogtreecommitdiffabout
path: root/pwmanager/libcrypt/cipher/dsa.c
blob: c3b4c82ef07937db08a58e9eb9acd3b89dd639e6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
/* dsa.c  -  DSA signature scheme
 * Copyright (C) 1998, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
 *
 * This file is part of Libgcrypt.
 *
 * Libgcrypt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser general Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * Libgcrypt is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include "g10lib.h"
#include "mpi.h"
#include "cipher.h"

typedef struct
{
  gcry_mpi_t p;	    /* prime */
  gcry_mpi_t q;	    /* group order */
  gcry_mpi_t g;	    /* group generator */
  gcry_mpi_t y;	    /* g^x mod p */
} DSA_public_key;


typedef struct
{
  gcry_mpi_t p;	    /* prime */
  gcry_mpi_t q;	    /* group order */
  gcry_mpi_t g;	    /* group generator */
  gcry_mpi_t y;	    /* g^x mod p */
  gcry_mpi_t x;	    /* secret exponent */
} DSA_secret_key;


static gcry_mpi_t gen_k (gcry_mpi_t q);
static void test_keys (DSA_secret_key *sk, unsigned qbits);
static int check_secret_key (DSA_secret_key *sk);
static void generate (DSA_secret_key *sk, unsigned nbits,
                      gcry_mpi_t **ret_factors);
static void sign (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t input,
                  DSA_secret_key *skey);
static int verify (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t input,
                   DSA_public_key *pkey);

static void (*progress_cb) (void *,const char *, int, int, int );
static void *progress_cb_data;


void
_gcry_register_pk_dsa_progress (void (*cb) (void *, const char *,
                                            int, int, int),
				void *cb_data)
{
  progress_cb = cb;
  progress_cb_data = cb_data;
}


static void
progress (int c)
{
  if (progress_cb)
    progress_cb (progress_cb_data, "pk_dsa", c, 0, 0);
}


/*
 * Generate a random secret exponent k less than q.
 */
static gcry_mpi_t
gen_k( gcry_mpi_t q )
{
  gcry_mpi_t k = mpi_alloc_secure( mpi_get_nlimbs(q) );
  unsigned int nbits = mpi_get_nbits(q);
  unsigned int nbytes = (nbits+7)/8;
  char *rndbuf = NULL;

  if ( DBG_CIPHER )
    log_debug("choosing a random k ");
  for (;;) 
    {
      if( DBG_CIPHER )
        progress('.');

      if ( !rndbuf || nbits < 32 ) 
        {
          gcry_free(rndbuf);
          rndbuf = gcry_random_bytes_secure( (nbits+7)/8, GCRY_STRONG_RANDOM );
	}
      else
        { /* Change only some of the higher bits.  We could improve
	     this by directly requesting more memory at the first call
	     to get_random_bytes() and use this the here maybe it is
	     easier to do this directly in random.c. */
          char *pp = gcry_random_bytes_secure( 4, GCRY_STRONG_RANDOM );
          memcpy( rndbuf,pp, 4 );
          gcry_free(pp);
	}
      _gcry_mpi_set_buffer( k, rndbuf, nbytes, 0 );
      if ( mpi_test_bit( k, nbits-1 ) )
        mpi_set_highbit( k, nbits-1 );
      else
        {
          mpi_set_highbit( k, nbits-1 );
          mpi_clear_bit( k, nbits-1 );
	}

      if( !(mpi_cmp( k, q ) < 0) ) /* check: k < q */
        {	
          if( DBG_CIPHER )
            progress('+');
          continue; /* no  */
        }
      if( !(mpi_cmp_ui( k, 0 ) > 0) )  /* check: k > 0 */
        {
          if( DBG_CIPHER )
            progress('-');
          continue; /* no */
        }
      break;	/* okay */
    }
  gcry_free(rndbuf);
  if( DBG_CIPHER )
    progress('\n');
  
  return k;
}


static void
test_keys( DSA_secret_key *sk, unsigned qbits )
{
  DSA_public_key pk;
  gcry_mpi_t test = gcry_mpi_new ( qbits  );
  gcry_mpi_t out1_a = gcry_mpi_new ( qbits );
  gcry_mpi_t out1_b = gcry_mpi_new ( qbits );

  pk.p = sk->p;
  pk.q = sk->q;
  pk.g = sk->g;
  pk.y = sk->y;
  gcry_mpi_randomize( test, qbits, GCRY_WEAK_RANDOM );

  sign( out1_a, out1_b, test, sk );
  if( !verify( out1_a, out1_b, test, &pk ) )
    log_fatal("DSA:: sign, verify failed\n");

  gcry_mpi_release ( test );
  gcry_mpi_release ( out1_a );
  gcry_mpi_release ( out1_b );
}



/*
   Generate a DSA key pair with a key of size NBITS.
   Returns: 2 structures filled with all needed values
 	    and an array with the n-1 factors of (p-1)
 */
static void
generate( DSA_secret_key *sk, unsigned nbits, gcry_mpi_t **ret_factors )
{
  gcry_mpi_t p;    /* the prime */
  gcry_mpi_t q;    /* the 160 bit prime factor */
  gcry_mpi_t g;    /* the generator */
  gcry_mpi_t y;    /* g^x mod p */
  gcry_mpi_t x;    /* the secret exponent */
  gcry_mpi_t h, e;  /* helper */
  unsigned qbits;
  byte *rndbuf;

  assert( nbits >= 512 && nbits <= 1024 );

  qbits = 160;
  p = _gcry_generate_elg_prime( 1, nbits, qbits, NULL, ret_factors );
  /* get q out of factors */
  q = mpi_copy((*ret_factors)[0]);
  if( mpi_get_nbits(q) != qbits )
    BUG();

  /* Find a generator g (h and e are helpers).
     e = (p-1)/q */
  e = mpi_alloc( mpi_get_nlimbs(p) );
  mpi_sub_ui( e, p, 1 );
  mpi_fdiv_q( e, e, q );
  g = mpi_alloc( mpi_get_nlimbs(p) );
  h = mpi_alloc_set_ui( 1 ); /* we start with 2 */
  do
    {
      mpi_add_ui( h, h, 1 );
      /* g = h^e mod p */
      gcry_mpi_powm( g, h, e, p );
    } 
  while( !mpi_cmp_ui( g, 1 ) );  /* continue until g != 1 */

  /* Select a random number which has these properties:
   *	 0 < x < q-1
   * This must be a very good random number because this
   * is the secret part. */
  if( DBG_CIPHER )
    log_debug("choosing a random x ");
  assert( qbits >= 160 );
  x = mpi_alloc_secure( mpi_get_nlimbs(q) );
  mpi_sub_ui( h, q, 1 );  /* put q-1 into h */
  rndbuf = NULL;
  do 
    {
      if( DBG_CIPHER )
        progress('.');
      if( !rndbuf )
        rndbuf = gcry_random_bytes_secure( (qbits+7)/8,
                                           GCRY_VERY_STRONG_RANDOM );
      else 
        { /* Change only some of the higher bits (= 2 bytes)*/
          char *r = gcry_random_bytes_secure (2, GCRY_VERY_STRONG_RANDOM);
          memcpy(rndbuf, r, 2 );
          gcry_free(r);
        }

      _gcry_mpi_set_buffer( x, rndbuf, (qbits+7)/8, 0 );
      mpi_clear_highbit( x, qbits+1 );
    } 
  while ( !( mpi_cmp_ui( x, 0 )>0 && mpi_cmp( x, h )<0 ) );
  gcry_free(rndbuf);
  mpi_free( e );
  mpi_free( h );

  /* y = g^x mod p */
  y = mpi_alloc( mpi_get_nlimbs(p) );
  gcry_mpi_powm( y, g, x, p );

  if( DBG_CIPHER ) 
    {
      progress('\n');
      log_mpidump("dsa  p= ", p );
      log_mpidump("dsa  q= ", q );
      log_mpidump("dsa  g= ", g );
      log_mpidump("dsa  y= ", y );
      log_mpidump("dsa  x= ", x );
    }

  /* Copy the stuff to the key structures. */
  sk->p = p;
  sk->q = q;
  sk->g = g;
  sk->y = y;
  sk->x = x;

  /* Now we can test our keys (this should never fail!). */
  test_keys( sk, qbits );
}



/*
   Test whether the secret key is valid.
   Returns: if this is a valid key.
 */
static int
check_secret_key( DSA_secret_key *sk )
{
  int rc;
  gcry_mpi_t y = mpi_alloc( mpi_get_nlimbs(sk->y) );

  gcry_mpi_powm( y, sk->g, sk->x, sk->p );
  rc = !mpi_cmp( y, sk->y );
  mpi_free( y );
  return rc;
}



/*
   Make a DSA signature from HASH and put it into r and s.
 */
static void
sign(gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t hash, DSA_secret_key *skey )
{
  gcry_mpi_t k;
  gcry_mpi_t kinv;
  gcry_mpi_t tmp;

  /* Select a random k with 0 < k < q */
  k = gen_k( skey->q );

  /* r = (a^k mod p) mod q */
  gcry_mpi_powm( r, skey->g, k, skey->p );
  mpi_fdiv_r( r, r, skey->q );

  /* kinv = k^(-1) mod q */
  kinv = mpi_alloc( mpi_get_nlimbs(k) );
  mpi_invm(kinv, k, skey->q );

  /* s = (kinv * ( hash + x * r)) mod q */
  tmp = mpi_alloc( mpi_get_nlimbs(skey->p) );
  mpi_mul( tmp, skey->x, r );
  mpi_add( tmp, tmp, hash );
  mpi_mulm( s , kinv, tmp, skey->q );

  mpi_free(k);
  mpi_free(kinv);
  mpi_free(tmp);
}


/*
   Returns true if the signature composed from R and S is valid.
 */
static int
verify (gcry_mpi_t r, gcry_mpi_t s, gcry_mpi_t hash, DSA_public_key *pkey )
{
  int rc;
  gcry_mpi_t w, u1, u2, v;
  gcry_mpi_t base[3];
  gcry_mpi_t ex[3];

  if( !(mpi_cmp_ui( r, 0 ) > 0 && mpi_cmp( r, pkey->q ) < 0) )
    return 0; /* assertion	0 < r < q  failed */
  if( !(mpi_cmp_ui( s, 0 ) > 0 && mpi_cmp( s, pkey->q ) < 0) )
    return 0; /* assertion	0 < s < q  failed */

  w  = mpi_alloc( mpi_get_nlimbs(pkey->q) );
  u1 = mpi_alloc( mpi_get_nlimbs(pkey->q) );
  u2 = mpi_alloc( mpi_get_nlimbs(pkey->q) );
  v  = mpi_alloc( mpi_get_nlimbs(pkey->p) );

  /* w = s^(-1) mod q */
  mpi_invm( w, s, pkey->q );

  /* u1 = (hash * w) mod q */
  mpi_mulm( u1, hash, w, pkey->q );

  /* u2 = r * w mod q  */
  mpi_mulm( u2, r, w, pkey->q );

  /* v =  g^u1 * y^u2 mod p mod q */
  base[0] = pkey->g; ex[0] = u1;
  base[1] = pkey->y; ex[1] = u2;
  base[2] = NULL;    ex[2] = NULL;
  mpi_mulpowm( v, base, ex, pkey->p );
  mpi_fdiv_r( v, v, pkey->q );

  rc = !mpi_cmp( v, r );

  mpi_free(w);
  mpi_free(u1);
  mpi_free(u2);
  mpi_free(v);

  return rc;
}


/*********************************************
 **************  interface  ******************
 *********************************************/

gcry_err_code_t
_gcry_dsa_generate (int algo, unsigned nbits, unsigned long dummy,
                    gcry_mpi_t *skey, gcry_mpi_t **retfactors)
{
  DSA_secret_key sk;

  generate (&sk, nbits, retfactors);
  skey[0] = sk.p;
  skey[1] = sk.q;
  skey[2] = sk.g;
  skey[3] = sk.y;
  skey[4] = sk.x;

  return GPG_ERR_NO_ERROR;
}


gcry_err_code_t
_gcry_dsa_check_secret_key (int algo, gcry_mpi_t *skey)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  DSA_secret_key sk;

  if ((! skey[0]) || (! skey[1]) || (! skey[2]) || (! skey[3]) || (! skey[4]))
    err = GPG_ERR_BAD_MPI;
  else
    {
      sk.p = skey[0];
      sk.q = skey[1];
      sk.g = skey[2];
      sk.y = skey[3];
      sk.x = skey[4];
      if (! check_secret_key (&sk))
	err = GPG_ERR_BAD_SECKEY;
    }

  return err;
}


gcry_err_code_t
_gcry_dsa_sign (int algo, gcry_mpi_t *resarr, gcry_mpi_t data, gcry_mpi_t *skey)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  DSA_secret_key sk;

  if ((! data)
      || (! skey[0]) || (! skey[1]) || (! skey[2])
      || (! skey[3]) || (! skey[4]))
    err = GPG_ERR_BAD_MPI;
  else
    {
      sk.p = skey[0];
      sk.q = skey[1];
      sk.g = skey[2];
      sk.y = skey[3];
      sk.x = skey[4];
      resarr[0] = mpi_alloc (mpi_get_nlimbs (sk.p));
      resarr[1] = mpi_alloc (mpi_get_nlimbs (sk.p));
      sign (resarr[0], resarr[1], data, &sk);
    }
  return err;
}

gcry_err_code_t
_gcry_dsa_verify (int algo, gcry_mpi_t hash, gcry_mpi_t *data, gcry_mpi_t *pkey,
		  int (*cmp) (void *, gcry_mpi_t), void *opaquev)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  DSA_public_key pk;

  if ((! data[0]) || (! data[1]) || (! hash)
      || (! pkey[0]) || (! pkey[1]) || (! pkey[2]) || (! pkey[3]))
    err = GPG_ERR_BAD_MPI;
  else
    {
      pk.p = pkey[0];
      pk.q = pkey[1];
      pk.g = pkey[2];
      pk.y = pkey[3];
      if (! verify (data[0], data[1], hash, &pk))
	err = GPG_ERR_BAD_SIGNATURE;
    }
  return err;
}


unsigned int
_gcry_dsa_get_nbits (int algo, gcry_mpi_t *pkey)
{
  return mpi_get_nbits (pkey[0]);
}

static char *dsa_names[] =
  {
    "dsa",
    "openpgp-dsa",
    NULL,
  };

gcry_pk_spec_t _gcry_pubkey_spec_dsa =
  {
    "DSA", dsa_names, 
    "pqgy", "pqgyx", "", "rs", "pqgy",
    GCRY_PK_USAGE_SIGN,
    _gcry_dsa_generate,
    _gcry_dsa_check_secret_key,
    NULL,
    NULL,
    _gcry_dsa_sign,
    _gcry_dsa_verify,
    _gcry_dsa_get_nbits,
  };