lib/mpi/mpicoder.c

   1 /* mpicoder.c  -  Coder for the external representation of MPIs
   2  * Copyright (C) 1998, 1999 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 2 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, write to the Free Software
  18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
  19  */
  20
  21 #include "mpi-internal.h"
  22
  23 #define DIM(v) (sizeof(v)/sizeof((v)[0]))
  24 #define MAX_EXTERN_MPI_BITS 16384
  25
  26 static uint8_t asn[15] =        /* Object ID is 1.3.14.3.2.26 */
  27 { 0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03,
  28         0x02, 0x1a, 0x05, 0x00, 0x04, 0x14
  29 };
  30
  31 MPI do_encode_md(const void *sha_buffer, unsigned nbits)
  32 {
  33         int nframe = (nbits + 7) / 8;
  34         uint8_t *frame, *fr_pt;
  35         int i = 0, n;
  36         size_t asnlen = DIM(asn);
  37         MPI a = MPI_NULL;
  38
  39         if (SHA1_DIGEST_LENGTH + asnlen + 4 > nframe)
  40                 pr_info("MPI: can't encode a %d bit MD into a %d bits frame\n",
  41                        (int)(SHA1_DIGEST_LENGTH * 8), (int)nbits);
  42
  43         /* We encode the MD in this way:
  44          *
  45          *       0  A PAD(n bytes)   0  ASN(asnlen bytes)  MD(len bytes)
  46          *
  47          * PAD consists of FF bytes.
  48          */
  49         frame = kmalloc(nframe, GFP_KERNEL);
  50         if (!frame)
  51                 return MPI_NULL;
  52         n = 0;
  53         frame[n++] = 0;
  54         frame[n++] = 1;         /* block type */
  55         i = nframe - SHA1_DIGEST_LENGTH - asnlen - 3;
  56
  57         if (i <= 1) {
  58                 pr_info("MPI: message digest encoding failed\n");
  59                 kfree(frame);
  60                 return a;
  61         }
  62
  63         memset(frame + n, 0xff, i);
  64         n += i;
  65         frame[n++] = 0;
  66         memcpy(frame + n, &asn, asnlen);
  67         n += asnlen;
  68         memcpy(frame + n, sha_buffer, SHA1_DIGEST_LENGTH);
  69         n += SHA1_DIGEST_LENGTH;
  70
  71         i = nframe;
  72         fr_pt = frame;
  73
  74         if (n != nframe) {
  75                 printk
  76                     ("MPI: message digest encoding failed, frame length is wrong\n");
  77                 kfree(frame);
  78                 return a;
  79         }
  80
  81         a = mpi_alloc((nframe + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB);
  82         mpi_set_buffer(a, frame, nframe, 0);
  83         kfree(frame);
  84
  85         return a;
  86 }
  87
  88 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
  89 {
  90         const uint8_t *buffer = xbuffer;
  91         int i, j;
  92         unsigned nbits, nbytes, nlimbs, nread = 0;
  93         mpi_limb_t a;
  94         MPI val = MPI_NULL;
  95
  96         if (*ret_nread < 2)
  97                 goto leave;
  98         nbits = buffer[0] << 8 | buffer[1];
  99
 100         if (nbits > MAX_EXTERN_MPI_BITS) {
 101                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 102                 goto leave;
 103         }
 104         buffer += 2;
 105         nread = 2;
 106
 107         nbytes = (nbits + 7) / 8;
 108         nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
 109         val = mpi_alloc(nlimbs);
 110         if (!val)
 111                 return MPI_NULL;
 112         i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 113         i %= BYTES_PER_MPI_LIMB;
 114         val->nbits = nbits;
 115         j = val->nlimbs = nlimbs;
 116         val->sign = 0;
 117         for (; j > 0; j--) {
 118                 a = 0;
 119                 for (; i < BYTES_PER_MPI_LIMB; i++) {
 120                         if (++nread > *ret_nread) {
 121                                 printk
 122                                     ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
 123                                      nread, *ret_nread);
 124                                 goto leave;
 125                         }
 126                         a <<= 8;
 127                         a |= *buffer++;
 128                 }
 129                 i = 0;
 130                 val->d[j - 1] = a;
 131         }
 132
 133 leave:
 134         *ret_nread = nread;
 135         return val;
 136 }
 137 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 138
 139 /****************
 140  * Make an mpi from a character string.
 141  */
 142 int mpi_fromstr(MPI val, const char *str)
 143 {
 144         int hexmode = 0, sign = 0, prepend_zero = 0, i, j, c, c1, c2;
 145         unsigned nbits, nbytes, nlimbs;
 146         mpi_limb_t a;
 147
 148         if (*str == '-') {
 149                 sign = 1;
 150                 str++;
 151         }
 152         if (*str == '0' && str[1] == 'x')
 153                 hexmode = 1;
 154         else
 155                 return -EINVAL; /* other bases are not yet supported */
 156         str += 2;
 157
 158         nbits = strlen(str) * 4;
 159         if (nbits % 8)
 160                 prepend_zero = 1;
 161         nbytes = (nbits + 7) / 8;
 162         nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
 163         if (val->alloced < nlimbs)
 164                 if (!mpi_resize(val, nlimbs))
 165                         return -ENOMEM;
 166         i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 167         i %= BYTES_PER_MPI_LIMB;
 168         j = val->nlimbs = nlimbs;
 169         val->sign = sign;
 170         for (; j > 0; j--) {
 171                 a = 0;
 172                 for (; i < BYTES_PER_MPI_LIMB; i++) {
 173                         if (prepend_zero) {
 174                                 c1 = '0';
 175                                 prepend_zero = 0;
 176                         } else
 177                                 c1 = *str++;
 178                         assert(c1);
 179                         c2 = *str++;
 180                         assert(c2);
 181                         if (c1 >= '0' && c1 <= '9')
 182                                 c = c1 - '0';
 183                         else if (c1 >= 'a' && c1 <= 'f')
 184                                 c = c1 - 'a' + 10;
 185                         else if (c1 >= 'A' && c1 <= 'F')
 186                                 c = c1 - 'A' + 10;
 187                         else {
 188                                 mpi_clear(val);
 189                                 return 1;
 190                         }
 191                         c <<= 4;
 192                         if (c2 >= '0' && c2 <= '9')
 193                                 c |= c2 - '0';
 194                         else if (c2 >= 'a' && c2 <= 'f')
 195                                 c |= c2 - 'a' + 10;
 196                         else if (c2 >= 'A' && c2 <= 'F')
 197                                 c |= c2 - 'A' + 10;
 198                         else {
 199                                 mpi_clear(val);
 200                                 return 1;
 201                         }
 202                         a <<= 8;
 203                         a |= c;
 204                 }
 205                 i = 0;
 206
 207                 val->d[j - 1] = a;
 208         }
 209
 210         return 0;
 211 }
 212 EXPORT_SYMBOL_GPL(mpi_fromstr);
 213
 214 /****************
 215  * Special function to get the low 8 bytes from an mpi.
 216  * This can be used as a keyid; KEYID is an 2 element array.
 217  * Return the low 4 bytes.
 218  */
 219 u32 mpi_get_keyid(const MPI a, u32 *keyid)
 220 {
 221 #if BYTES_PER_MPI_LIMB == 4
 222         if (keyid) {
 223                 keyid[0] = a->nlimbs >= 2 ? a->d[1] : 0;
 224                 keyid[1] = a->nlimbs >= 1 ? a->d[0] : 0;
 225         }
 226         return a->nlimbs >= 1 ? a->d[0] : 0;
 227 #elif BYTES_PER_MPI_LIMB == 8
 228         if (keyid) {
 229                 keyid[0] = a->nlimbs ? (u32) (a->d[0] >> 32) : 0;
 230                 keyid[1] = a->nlimbs ? (u32) (a->d[0] & 0xffffffff) : 0;
 231         }
 232         return a->nlimbs ? (u32) (a->d[0] & 0xffffffff) : 0;
 233 #else
 234 #error Make this function work with other LIMB sizes
 235 #endif
 236 }
 237
 238 /****************
 239  * Return an allocated buffer with the MPI (msb first).
 240  * NBYTES receives the length of this buffer. Caller must free the
 241  * return string (This function does return a 0 byte buffer with NBYTES
 242  * set to zero if the value of A is zero. If sign is not NULL, it will
 243  * be set to the sign of the A.
 244  */
 245 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 246 {
 247         uint8_t *p, *buffer;
 248         mpi_limb_t alimb;
 249         int i;
 250         unsigned int n;
 251
 252         if (sign)
 253                 *sign = a->sign;
 254         *nbytes = n = a->nlimbs * BYTES_PER_MPI_LIMB;
 255         if (!n)
 256                 n++;            /* avoid zero length allocation */
 257         p = buffer = kmalloc(n, GFP_KERNEL);
 258
 259         for (i = a->nlimbs - 1; i >= 0; i--) {
 260                 alimb = a->d[i];
 261 #if BYTES_PER_MPI_LIMB == 4
 262                 *p++ = alimb >> 24;
 263                 *p++ = alimb >> 16;
 264                 *p++ = alimb >> 8;
 265                 *p++ = alimb;
 266 #elif BYTES_PER_MPI_LIMB == 8
 267                 *p++ = alimb >> 56;
 268                 *p++ = alimb >> 48;
 269                 *p++ = alimb >> 40;
 270                 *p++ = alimb >> 32;
 271                 *p++ = alimb >> 24;
 272                 *p++ = alimb >> 16;
 273                 *p++ = alimb >> 8;
 274                 *p++ = alimb;
 275 #else
 276 #error please implement for this limb size.
 277 #endif
 278         }
 279
 280         /* this is sub-optimal but we need to do the shift operation
 281          * because the caller has to free the returned buffer */
 282         for (p = buffer; !*p && *nbytes; p++, --*nbytes)
 283                 ;
 284         if (p != buffer)
 285                 memmove(buffer, p, *nbytes);
 286
 287         return buffer;
 288 }
 289 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 290
 291 /****************
 292  * Use BUFFER to update MPI.
 293  */
 294 int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
 295 {
 296         const uint8_t *buffer = xbuffer, *p;
 297         mpi_limb_t alimb;
 298         int nlimbs;
 299         int i;
 300
 301         nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
 302         if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
 303                 return -ENOMEM;
 304         a->sign = sign;
 305
 306         for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
 307 #if BYTES_PER_MPI_LIMB == 4
 308                 alimb = (mpi_limb_t) *p--;
 309                 alimb |= (mpi_limb_t) *p-- << 8;
 310                 alimb |= (mpi_limb_t) *p-- << 16;
 311                 alimb |= (mpi_limb_t) *p-- << 24;
 312 #elif BYTES_PER_MPI_LIMB == 8
 313                 alimb = (mpi_limb_t) *p--;
 314                 alimb |= (mpi_limb_t) *p-- << 8;
 315                 alimb |= (mpi_limb_t) *p-- << 16;
 316                 alimb |= (mpi_limb_t) *p-- << 24;
 317                 alimb |= (mpi_limb_t) *p-- << 32;
 318                 alimb |= (mpi_limb_t) *p-- << 40;
 319                 alimb |= (mpi_limb_t) *p-- << 48;
 320                 alimb |= (mpi_limb_t) *p-- << 56;
 321 #else
 322 #error please implement for this limb size.
 323 #endif
 324                 a->d[i++] = alimb;
 325         }
 326         if (p >= buffer) {
 327 #if BYTES_PER_MPI_LIMB == 4
 328                 alimb = *p--;
 329                 if (p >= buffer)
 330                         alimb |= (mpi_limb_t) *p-- << 8;
 331                 if (p >= buffer)
 332                         alimb |= (mpi_limb_t) *p-- << 16;
 333                 if (p >= buffer)
 334                         alimb |= (mpi_limb_t) *p-- << 24;
 335 #elif BYTES_PER_MPI_LIMB == 8
 336                 alimb = (mpi_limb_t) *p--;
 337                 if (p >= buffer)
 338                         alimb |= (mpi_limb_t) *p-- << 8;
 339                 if (p >= buffer)
 340                         alimb |= (mpi_limb_t) *p-- << 16;
 341                 if (p >= buffer)
 342                         alimb |= (mpi_limb_t) *p-- << 24;
 343                 if (p >= buffer)
 344                         alimb |= (mpi_limb_t) *p-- << 32;
 345                 if (p >= buffer)
 346                         alimb |= (mpi_limb_t) *p-- << 40;
 347                 if (p >= buffer)
 348                         alimb |= (mpi_limb_t) *p-- << 48;
 349                 if (p >= buffer)
 350                         alimb |= (mpi_limb_t) *p-- << 56;
 351 #else
 352 #error please implement for this limb size.
 353 #endif
 354                 a->d[i++] = alimb;
 355         }
 356         a->nlimbs = i;
 357
 358         if (i != nlimbs) {
 359                 pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
 360                        nlimbs);
 361                 BUG();
 362         }
 363         return 0;
 364 }
 365 EXPORT_SYMBOL_GPL(mpi_set_buffer);