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 <linux/bitops.h>
  22 #include <linux/count_zeros.h>
  23 #include <linux/byteorder/generic.h>
  24 #include <linux/scatterlist.h>
  25 #include <linux/string.h>
  26 #include "mpi-internal.h"
  27
  28 #define MAX_EXTERN_SCAN_BYTES (16*1024*1024)
  29 #define MAX_EXTERN_MPI_BITS 16384
  30
  31 /**
  32  * mpi_read_raw_data - Read a raw byte stream as a positive integer
  33  * @xbuffer: The data to read
  34  * @nbytes: The amount of data to read
  35  */
  36 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
  37 {
  38         const uint8_t *buffer = xbuffer;
  39         int i, j;
  40         unsigned nbits, nlimbs;
  41         mpi_limb_t a;
  42         MPI val = NULL;
  43
  44         while (nbytes > 0 && buffer[0] == 0) {
  45                 buffer++;
  46                 nbytes--;
  47         }
  48
  49         nbits = nbytes * 8;
  50         if (nbits > MAX_EXTERN_MPI_BITS) {
  51                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  52                 return NULL;
  53         }
  54         if (nbytes > 0)
  55                 nbits -= count_leading_zeros(buffer[0]) - (BITS_PER_LONG - 8);
  56
  57         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
  58         val = mpi_alloc(nlimbs);
  59         if (!val)
  60                 return NULL;
  61         val->nbits = nbits;
  62         val->sign = 0;
  63         val->nlimbs = nlimbs;
  64
  65         if (nbytes > 0) {
  66                 i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
  67                 i %= BYTES_PER_MPI_LIMB;
  68                 for (j = nlimbs; j > 0; j--) {
  69                         a = 0;
  70                         for (; i < BYTES_PER_MPI_LIMB; i++) {
  71                                 a <<= 8;
  72                                 a |= *buffer++;
  73                         }
  74                         i = 0;
  75                         val->d[j - 1] = a;
  76                 }
  77         }
  78         return val;
  79 }
  80 EXPORT_SYMBOL_GPL(mpi_read_raw_data);
  81
  82 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
  83 {
  84         const uint8_t *buffer = xbuffer;
  85         unsigned int nbits, nbytes;
  86         MPI val;
  87
  88         if (*ret_nread < 2)
  89                 return ERR_PTR(-EINVAL);
  90         nbits = buffer[0] << 8 | buffer[1];
  91
  92         if (nbits > MAX_EXTERN_MPI_BITS) {
  93                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
  94                 return ERR_PTR(-EINVAL);
  95         }
  96
  97         nbytes = DIV_ROUND_UP(nbits, 8);
  98         if (nbytes + 2 > *ret_nread) {
  99                 pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
 100                                 nbytes, *ret_nread);
 101                 return ERR_PTR(-EINVAL);
 102         }
 103
 104         val = mpi_read_raw_data(buffer + 2, nbytes);
 105         if (!val)
 106                 return ERR_PTR(-ENOMEM);
 107
 108         *ret_nread = nbytes + 2;
 109         return val;
 110 }
 111 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
 112
 113 /****************
 114  * Fill the mpi VAL from the hex string in STR.
 115  */
 116 int mpi_fromstr(MPI val, const char *str)
 117 {
 118         int sign = 0;
 119         int prepend_zero = 0;
 120         int i, j, c, c1, c2;
 121         unsigned int nbits, nbytes, nlimbs;
 122         mpi_limb_t a;
 123
 124         if (*str == '-') {
 125                 sign = 1;
 126                 str++;
 127         }
 128
 129         /* Skip optional hex prefix.  */
 130         if (*str == '0' && str[1] == 'x')
 131                 str += 2;
 132
 133         nbits = strlen(str);
 134         if (nbits > MAX_EXTERN_SCAN_BYTES) {
 135                 mpi_clear(val);
 136                 return -EINVAL;
 137         }
 138         nbits *= 4;
 139         if ((nbits % 8))
 140                 prepend_zero = 1;
 141
 142         nbytes = (nbits+7) / 8;
 143         nlimbs = (nbytes+BYTES_PER_MPI_LIMB-1) / BYTES_PER_MPI_LIMB;
 144
 145         if (val->alloced < nlimbs)
 146                 mpi_resize(val, nlimbs);
 147
 148         i = BYTES_PER_MPI_LIMB - (nbytes % BYTES_PER_MPI_LIMB);
 149         i %= BYTES_PER_MPI_LIMB;
 150         j = val->nlimbs = nlimbs;
 151         val->sign = sign;
 152         for (; j > 0; j--) {
 153                 a = 0;
 154                 for (; i < BYTES_PER_MPI_LIMB; i++) {
 155                         if (prepend_zero) {
 156                                 c1 = '0';
 157                                 prepend_zero = 0;
 158                         } else
 159                                 c1 = *str++;
 160
 161                         if (!c1) {
 162                                 mpi_clear(val);
 163                                 return -EINVAL;
 164                         }
 165                         c2 = *str++;
 166                         if (!c2) {
 167                                 mpi_clear(val);
 168                                 return -EINVAL;
 169                         }
 170                         if (c1 >= '0' && c1 <= '9')
 171                                 c = c1 - '0';
 172                         else if (c1 >= 'a' && c1 <= 'f')
 173                                 c = c1 - 'a' + 10;
 174                         else if (c1 >= 'A' && c1 <= 'F')
 175                                 c = c1 - 'A' + 10;
 176                         else {
 177                                 mpi_clear(val);
 178                                 return -EINVAL;
 179                         }
 180                         c <<= 4;
 181                         if (c2 >= '0' && c2 <= '9')
 182                                 c |= c2 - '0';
 183                         else if (c2 >= 'a' && c2 <= 'f')
 184                                 c |= c2 - 'a' + 10;
 185                         else if (c2 >= 'A' && c2 <= 'F')
 186                                 c |= c2 - 'A' + 10;
 187                         else {
 188                                 mpi_clear(val);
 189                                 return -EINVAL;
 190                         }
 191                         a <<= 8;
 192                         a |= c;
 193                 }
 194                 i = 0;
 195                 val->d[j-1] = a;
 196         }
 197
 198         return 0;
 199 }
 200 EXPORT_SYMBOL_GPL(mpi_fromstr);
 201
 202 MPI mpi_scanval(const char *string)
 203 {
 204         MPI a;
 205
 206         a = mpi_alloc(0);
 207         if (!a)
 208                 return NULL;
 209
 210         if (mpi_fromstr(a, string)) {
 211                 mpi_free(a);
 212                 return NULL;
 213         }
 214         mpi_normalize(a);
 215         return a;
 216 }
 217 EXPORT_SYMBOL_GPL(mpi_scanval);
 218
 219 static int count_lzeros(MPI a)
 220 {
 221         mpi_limb_t alimb;
 222         int i, lzeros = 0;
 223
 224         for (i = a->nlimbs - 1; i >= 0; i--) {
 225                 alimb = a->d[i];
 226                 if (alimb == 0) {
 227                         lzeros += sizeof(mpi_limb_t);
 228                 } else {
 229                         lzeros += count_leading_zeros(alimb) / 8;
 230                         break;
 231                 }
 232         }
 233         return lzeros;
 234 }
 235
 236 /**
 237  * mpi_read_buffer() - read MPI to a bufer provided by user (msb first)
 238  *
 239  * @a:          a multi precision integer
 240  * @buf:        bufer to which the output will be written to. Needs to be at
 241  *              leaset mpi_get_size(a) long.
 242  * @buf_len:    size of the buf.
 243  * @nbytes:     receives the actual length of the data written on success and
 244  *              the data to-be-written on -EOVERFLOW in case buf_len was too
 245  *              small.
 246  * @sign:       if not NULL, it will be set to the sign of a.
 247  *
 248  * Return:      0 on success or error code in case of error
 249  */
 250 int mpi_read_buffer(MPI a, uint8_t *buf, unsigned buf_len, unsigned *nbytes,
 251                     int *sign)
 252 {
 253         uint8_t *p;
 254 #if BYTES_PER_MPI_LIMB == 4
 255         __be32 alimb;
 256 #elif BYTES_PER_MPI_LIMB == 8
 257         __be64 alimb;
 258 #else
 259 #error please implement for this limb size.
 260 #endif
 261         unsigned int n = mpi_get_size(a);
 262         int i, lzeros;
 263
 264         if (!buf || !nbytes)
 265                 return -EINVAL;
 266
 267         if (sign)
 268                 *sign = a->sign;
 269
 270         lzeros = count_lzeros(a);
 271
 272         if (buf_len < n - lzeros) {
 273                 *nbytes = n - lzeros;
 274                 return -EOVERFLOW;
 275         }
 276
 277         p = buf;
 278         *nbytes = n - lzeros;
 279
 280         for (i = a->nlimbs - 1 - lzeros / BYTES_PER_MPI_LIMB,
 281                         lzeros %= BYTES_PER_MPI_LIMB;
 282                 i >= 0; i--) {
 283 #if BYTES_PER_MPI_LIMB == 4
 284                 alimb = cpu_to_be32(a->d[i]);
 285 #elif BYTES_PER_MPI_LIMB == 8
 286                 alimb = cpu_to_be64(a->d[i]);
 287 #else
 288 #error please implement for this limb size.
 289 #endif
 290                 memcpy(p, (u8 *)&alimb + lzeros, BYTES_PER_MPI_LIMB - lzeros);
 291                 p += BYTES_PER_MPI_LIMB - lzeros;
 292                 lzeros = 0;
 293         }
 294         return 0;
 295 }
 296 EXPORT_SYMBOL_GPL(mpi_read_buffer);
 297
 298 /*
 299  * mpi_get_buffer() - Returns an allocated buffer with the MPI (msb first).
 300  * Caller must free the return string.
 301  * This function does return a 0 byte buffer with nbytes set to zero if the
 302  * value of A is zero.
 303  *
 304  * @a:          a multi precision integer.
 305  * @nbytes:     receives the length of this buffer.
 306  * @sign:       if not NULL, it will be set to the sign of the a.
 307  *
 308  * Return:      Pointer to MPI buffer or NULL on error
 309  */
 310 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
 311 {
 312         uint8_t *buf;
 313         unsigned int n;
 314         int ret;
 315
 316         if (!nbytes)
 317                 return NULL;
 318
 319         n = mpi_get_size(a);
 320
 321         if (!n)
 322                 n++;
 323
 324         buf = kmalloc(n, GFP_KERNEL);
 325
 326         if (!buf)
 327                 return NULL;
 328
 329         ret = mpi_read_buffer(a, buf, n, nbytes, sign);
 330
 331         if (ret) {
 332                 kfree(buf);
 333                 return NULL;
 334         }
 335         return buf;
 336 }
 337 EXPORT_SYMBOL_GPL(mpi_get_buffer);
 338
 339 /**
 340  * mpi_write_to_sgl() - Funnction exports MPI to an sgl (msb first)
 341  *
 342  * This function works in the same way as the mpi_read_buffer, but it
 343  * takes an sgl instead of u8 * buf.
 344  *
 345  * @a:          a multi precision integer
 346  * @sgl:        scatterlist to write to. Needs to be at least
 347  *              mpi_get_size(a) long.
 348  * @nbytes:     the number of bytes to write.  Leading bytes will be
 349  *              filled with zero.
 350  * @sign:       if not NULL, it will be set to the sign of a.
 351  *
 352  * Return:      0 on success or error code in case of error
 353  */
 354 int mpi_write_to_sgl(MPI a, struct scatterlist *sgl, unsigned nbytes,
 355                      int *sign)
 356 {
 357         u8 *p, *p2;
 358 #if BYTES_PER_MPI_LIMB == 4
 359         __be32 alimb;
 360 #elif BYTES_PER_MPI_LIMB == 8
 361         __be64 alimb;
 362 #else
 363 #error please implement for this limb size.
 364 #endif
 365         unsigned int n = mpi_get_size(a);
 366         struct sg_mapping_iter miter;
 367         int i, x, buf_len;
 368         int nents;
 369
 370         if (sign)
 371                 *sign = a->sign;
 372
 373         if (nbytes < n)
 374                 return -EOVERFLOW;
 375
 376         nents = sg_nents_for_len(sgl, nbytes);
 377         if (nents < 0)
 378                 return -EINVAL;
 379
 380         sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
 381         sg_miter_next(&miter);
 382         buf_len = miter.length;
 383         p2 = miter.addr;
 384
 385         while (nbytes > n) {
 386                 i = min_t(unsigned, nbytes - n, buf_len);
 387                 memset(p2, 0, i);
 388                 p2 += i;
 389                 nbytes -= i;
 390
 391                 buf_len -= i;
 392                 if (!buf_len) {
 393                         sg_miter_next(&miter);
 394                         buf_len = miter.length;
 395                         p2 = miter.addr;
 396                 }
 397         }
 398
 399         for (i = a->nlimbs - 1; i >= 0; i--) {
 400 #if BYTES_PER_MPI_LIMB == 4
 401                 alimb = a->d[i] ? cpu_to_be32(a->d[i]) : 0;
 402 #elif BYTES_PER_MPI_LIMB == 8
 403                 alimb = a->d[i] ? cpu_to_be64(a->d[i]) : 0;
 404 #else
 405 #error please implement for this limb size.
 406 #endif
 407                 p = (u8 *)&alimb;
 408
 409                 for (x = 0; x < sizeof(alimb); x++) {
 410                         *p2++ = *p++;
 411                         if (!--buf_len) {
 412                                 sg_miter_next(&miter);
 413                                 buf_len = miter.length;
 414                                 p2 = miter.addr;
 415                         }
 416                 }
 417         }
 418
 419         sg_miter_stop(&miter);
 420         return 0;
 421 }
 422 EXPORT_SYMBOL_GPL(mpi_write_to_sgl);
 423
 424 /*
 425  * mpi_read_raw_from_sgl() - Function allocates an MPI and populates it with
 426  *                           data from the sgl
 427  *
 428  * This function works in the same way as the mpi_read_raw_data, but it
 429  * takes an sgl instead of void * buffer. i.e. it allocates
 430  * a new MPI and reads the content of the sgl to the MPI.
 431  *
 432  * @sgl:        scatterlist to read from
 433  * @nbytes:     number of bytes to read
 434  *
 435  * Return:      Pointer to a new MPI or NULL on error
 436  */
 437 MPI mpi_read_raw_from_sgl(struct scatterlist *sgl, unsigned int nbytes)
 438 {
 439         struct sg_mapping_iter miter;
 440         unsigned int nbits, nlimbs;
 441         int x, j, z, lzeros, ents;
 442         unsigned int len;
 443         const u8 *buff;
 444         mpi_limb_t a;
 445         MPI val = NULL;
 446
 447         ents = sg_nents_for_len(sgl, nbytes);
 448         if (ents < 0)
 449                 return NULL;
 450
 451         sg_miter_start(&miter, sgl, ents, SG_MITER_ATOMIC | SG_MITER_FROM_SG);
 452
 453         lzeros = 0;
 454         len = 0;
 455         while (nbytes > 0) {
 456                 while (len && !*buff) {
 457                         lzeros++;
 458                         len--;
 459                         buff++;
 460                 }
 461
 462                 if (len && *buff)
 463                         break;
 464
 465                 sg_miter_next(&miter);
 466                 buff = miter.addr;
 467                 len = miter.length;
 468
 469                 nbytes -= lzeros;
 470                 lzeros = 0;
 471         }
 472
 473         miter.consumed = lzeros;
 474
 475         nbytes -= lzeros;
 476         nbits = nbytes * 8;
 477         if (nbits > MAX_EXTERN_MPI_BITS) {
 478                 sg_miter_stop(&miter);
 479                 pr_info("MPI: mpi too large (%u bits)\n", nbits);
 480                 return NULL;
 481         }
 482
 483         if (nbytes > 0)
 484                 nbits -= count_leading_zeros(*buff) - (BITS_PER_LONG - 8);
 485
 486         sg_miter_stop(&miter);
 487
 488         nlimbs = DIV_ROUND_UP(nbytes, BYTES_PER_MPI_LIMB);
 489         val = mpi_alloc(nlimbs);
 490         if (!val)
 491                 return NULL;
 492
 493         val->nbits = nbits;
 494         val->sign = 0;
 495         val->nlimbs = nlimbs;
 496
 497         if (nbytes == 0)
 498                 return val;
 499
 500         j = nlimbs - 1;
 501         a = 0;
 502         z = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
 503         z %= BYTES_PER_MPI_LIMB;
 504
 505         while (sg_miter_next(&miter)) {
 506                 buff = miter.addr;
 507                 len = miter.length;
 508
 509                 for (x = 0; x < len; x++) {
 510                         a <<= 8;
 511                         a |= *buff++;
 512                         if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
 513                                 val->d[j--] = a;
 514                                 a = 0;
 515                         }
 516                 }
 517                 z += x;
 518         }
 519
 520         return val;
 521 }
 522 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);
 523
 524 /* Perform a two's complement operation on buffer P of size N bytes.  */
 525 static void twocompl(unsigned char *p, unsigned int n)
 526 {
 527         int i;
 528
 529         for (i = n-1; i >= 0 && !p[i]; i--)
 530                 ;
 531         if (i >= 0) {
 532                 if ((p[i] & 0x01))
 533                         p[i] = (((p[i] ^ 0xfe) | 0x01) & 0xff);
 534                 else if ((p[i] & 0x02))
 535                         p[i] = (((p[i] ^ 0xfc) | 0x02) & 0xfe);
 536                 else if ((p[i] & 0x04))
 537                         p[i] = (((p[i] ^ 0xf8) | 0x04) & 0xfc);
 538                 else if ((p[i] & 0x08))
 539                         p[i] = (((p[i] ^ 0xf0) | 0x08) & 0xf8);
 540                 else if ((p[i] & 0x10))
 541                         p[i] = (((p[i] ^ 0xe0) | 0x10) & 0xf0);
 542                 else if ((p[i] & 0x20))
 543                         p[i] = (((p[i] ^ 0xc0) | 0x20) & 0xe0);
 544                 else if ((p[i] & 0x40))
 545                         p[i] = (((p[i] ^ 0x80) | 0x40) & 0xc0);
 546                 else
 547                         p[i] = 0x80;
 548
 549                 for (i--; i >= 0; i--)
 550                         p[i] ^= 0xff;
 551         }
 552 }
 553
 554 int mpi_print(enum gcry_mpi_format format, unsigned char *buffer,
 555                         size_t buflen, size_t *nwritten, MPI a)
 556 {
 557         unsigned int nbits = mpi_get_nbits(a);
 558         size_t len;
 559         size_t dummy_nwritten;
 560         int negative;
 561
 562         if (!nwritten)
 563                 nwritten = &dummy_nwritten;
 564
 565         /* Libgcrypt does no always care to set clear the sign if the value
 566          * is 0.  For printing this is a bit of a surprise, in particular
 567          * because if some of the formats don't support negative numbers but
 568          * should be able to print a zero.  Thus we need this extra test
 569          * for a negative number.
 570          */
 571         if (a->sign && mpi_cmp_ui(a, 0))
 572                 negative = 1;
 573         else
 574                 negative = 0;
 575
 576         len = buflen;
 577         *nwritten = 0;
 578         if (format == GCRYMPI_FMT_STD) {
 579                 unsigned char *tmp;
 580                 int extra = 0;
 581                 unsigned int n;
 582
 583                 tmp = mpi_get_buffer(a, &n, NULL);
 584                 if (!tmp)
 585                         return -EINVAL;
 586
 587                 if (negative) {
 588                         twocompl(tmp, n);
 589                         if (!(*tmp & 0x80)) {
 590                                 /* Need to extend the sign.  */
 591                                 n++;
 592                                 extra = 2;
 593                         }
 594                 } else if (n && (*tmp & 0x80)) {
 595                         /* Positive but the high bit of the returned buffer is set.
 596                          * Thus we need to print an extra leading 0x00 so that the
 597                          * output is interpreted as a positive number.
 598                          */
 599                         n++;
 600                         extra = 1;
 601                 }
 602
 603                 if (buffer && n > len) {
 604                         /* The provided buffer is too short. */
 605                         kfree(tmp);
 606                         return -E2BIG;
 607                 }
 608                 if (buffer) {
 609                         unsigned char *s = buffer;
 610
 611                         if (extra == 1)
 612                                 *s++ = 0;
 613                         else if (extra)
 614                                 *s++ = 0xff;
 615                         memcpy(s, tmp, n-!!extra);
 616                 }
 617                 kfree(tmp);
 618                 *nwritten = n;
 619                 return 0;
 620         } else if (format == GCRYMPI_FMT_USG) {
 621                 unsigned int n = (nbits + 7)/8;
 622
 623                 /* Note:  We ignore the sign for this format.  */
 624                 /* FIXME: for performance reasons we should put this into
 625                  * mpi_aprint because we can then use the buffer directly.
 626                  */
 627
 628                 if (buffer && n > len)
 629                         return -E2BIG;
 630                 if (buffer) {
 631                         unsigned char *tmp;
 632
 633                         tmp = mpi_get_buffer(a, &n, NULL);
 634                         if (!tmp)
 635                                 return -EINVAL;
 636                         memcpy(buffer, tmp, n);
 637                         kfree(tmp);
 638                 }
 639                 *nwritten = n;
 640                 return 0;
 641         } else if (format == GCRYMPI_FMT_PGP) {
 642                 unsigned int n = (nbits + 7)/8;
 643
 644                 /* The PGP format can only handle unsigned integers.  */
 645                 if (negative)
 646                         return -EINVAL;
 647
 648                 if (buffer && n+2 > len)
 649                         return -E2BIG;
 650
 651                 if (buffer) {
 652                         unsigned char *tmp;
 653                         unsigned char *s = buffer;
 654
 655                         s[0] = nbits >> 8;
 656                         s[1] = nbits;
 657
 658                         tmp = mpi_get_buffer(a, &n, NULL);
 659                         if (!tmp)
 660                                 return -EINVAL;
 661                         memcpy(s+2, tmp, n);
 662                         kfree(tmp);
 663                 }
 664                 *nwritten = n+2;
 665                 return 0;
 666         } else if (format == GCRYMPI_FMT_SSH) {
 667                 unsigned char *tmp;
 668                 int extra = 0;
 669                 unsigned int n;
 670
 671                 tmp = mpi_get_buffer(a, &n, NULL);
 672                 if (!tmp)
 673                         return -EINVAL;
 674
 675                 if (negative) {
 676                         twocompl(tmp, n);
 677                         if (!(*tmp & 0x80)) {
 678                                 /* Need to extend the sign.  */
 679                                 n++;
 680                                 extra = 2;
 681                         }
 682                 } else if (n && (*tmp & 0x80)) {
 683                         n++;
 684                         extra = 1;
 685                 }
 686
 687                 if (buffer && n+4 > len) {
 688                         kfree(tmp);
 689                         return -E2BIG;
 690                 }
 691
 692                 if (buffer) {
 693                         unsigned char *s = buffer;
 694
 695                         *s++ = n >> 24;
 696                         *s++ = n >> 16;
 697                         *s++ = n >> 8;
 698                         *s++ = n;
 699                         if (extra == 1)
 700                                 *s++ = 0;
 701                         else if (extra)
 702                                 *s++ = 0xff;
 703                         memcpy(s, tmp, n-!!extra);
 704                 }
 705                 kfree(tmp);
 706                 *nwritten = 4+n;
 707                 return 0;
 708         } else if (format == GCRYMPI_FMT_HEX) {
 709                 unsigned char *tmp;
 710                 int i;
 711                 int extra = 0;
 712                 unsigned int n = 0;
 713
 714                 tmp = mpi_get_buffer(a, &n, NULL);
 715                 if (!tmp)
 716                         return -EINVAL;
 717                 if (!n || (*tmp & 0x80))
 718                         extra = 2;
 719
 720                 if (buffer && 2*n + extra + negative + 1 > len) {
 721                         kfree(tmp);
 722                         return -E2BIG;
 723                 }
 724                 if (buffer) {
 725                         unsigned char *s = buffer;
 726
 727                         if (negative)
 728                                 *s++ = '-';
 729                         if (extra) {
 730                                 *s++ = '0';
 731                                 *s++ = '0';
 732                         }
 733
 734                         for (i = 0; i < n; i++) {
 735                                 unsigned int c = tmp[i];
 736
 737                                 *s++ = (c >> 4) < 10 ? '0'+(c>>4) : 'A'+(c>>4)-10;
 738                                 c &= 15;
 739                                 *s++ = c < 10 ? '0'+c : 'A'+c-10;
 740                         }
 741                         *s++ = 0;
 742                         *nwritten = s - buffer;
 743                 } else {
 744                         *nwritten = 2*n + extra + negative + 1;
 745                 }
 746                 kfree(tmp);
 747                 return 0;
 748         } else
 749                 return -EINVAL;
 750 }
 751 EXPORT_SYMBOL_GPL(mpi_print);