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 == '' && 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 = '';
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 >= '' && c1 <= '9')
171 c = c1 - '';
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 >= '' && c2 <= '9')
182 c |= c2 - '';
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 buffer provided by user (msb first)
238 *
239 * @a: a multi precision integer
240 * @buf: buffer to which the output will be written to. Needs to be at
241 * least 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 = min_t(unsigned, miter.length, nbytes);
508 nbytes -= len;
509
510 for (x = 0; x < len; x++) {
511 a <<= 8;
512 a |= *buff++;
513 if (((z + x + 1) % BYTES_PER_MPI_LIMB) == 0) {
514 val->d[j--] = a;
515 a = 0;
516 }
517 }
518 z += x;
519 }
520
521 return val;
522 }
523 EXPORT_SYMBOL_GPL(mpi_read_raw_from_sgl);
524
525 /* Perform a two's complement operation on buffer P of size N bytes. */
526 static void twocompl(unsigned char *p, unsigned int n)
527 {
528 int i;
529
530 for (i = n-1; i >= 0 && !p[i]; i--)
531 ;
532 if (i >= 0) {
533 if ((p[i] & 0x01))
534 p[i] = (((p[i] ^ 0xfe) | 0x01) & 0xff);
535 else if ((p[i] & 0x02))
536 p[i] = (((p[i] ^ 0xfc) | 0x02) & 0xfe);
537 else if ((p[i] & 0x04))
538 p[i] = (((p[i] ^ 0xf8) | 0x04) & 0xfc);
539 else if ((p[i] & 0x08))
540 p[i] = (((p[i] ^ 0xf0) | 0x08) & 0xf8);
541 else if ((p[i] & 0x10))
542 p[i] = (((p[i] ^ 0xe0) | 0x10) & 0xf0);
543 else if ((p[i] & 0x20))
544 p[i] = (((p[i] ^ 0xc0) | 0x20) & 0xe0);
545 else if ((p[i] & 0x40))
546 p[i] = (((p[i] ^ 0x80) | 0x40) & 0xc0);
547 else
548 p[i] = 0x80;
549
550 for (i--; i >= 0; i--)
551 p[i] ^= 0xff;
552 }
553 }
554
555 int mpi_print(enum gcry_mpi_format format, unsigned char *buffer,
556 size_t buflen, size_t *nwritten, MPI a)
557 {
558 unsigned int nbits = mpi_get_nbits(a);
559 size_t len;
560 size_t dummy_nwritten;
561 int negative;
562
563 if (!nwritten)
564 nwritten = &dummy_nwritten;
565
566 /* Libgcrypt does no always care to set clear the sign if the value
567 * is 0. For printing this is a bit of a surprise, in particular
568 * because if some of the formats don't support negative numbers but
569 * should be able to print a zero. Thus we need this extra test
570 * for a negative number.
571 */
572 if (a->sign && mpi_cmp_ui(a, 0))
573 negative = 1;
574 else
575 negative = 0;
576
577 len = buflen;
578 *nwritten = 0;
579 if (format == GCRYMPI_FMT_STD) {
580 unsigned char *tmp;
581 int extra = 0;
582 unsigned int n;
583
584 tmp = mpi_get_buffer(a, &n, NULL);
585 if (!tmp)
586 return -EINVAL;
587
588 if (negative) {
589 twocompl(tmp, n);
590 if (!(*tmp & 0x80)) {
591 /* Need to extend the sign. */
592 n++;
593 extra = 2;
594 }
595 } else if (n && (*tmp & 0x80)) {
596 /* Positive but the high bit of the returned buffer is set.
597 * Thus we need to print an extra leading 0x00 so that the
598 * output is interpreted as a positive number.
599 */
600 n++;
601 extra = 1;
602 }
603
604 if (buffer && n > len) {
605 /* The provided buffer is too short. */
606 kfree(tmp);
607 return -E2BIG;
608 }
609 if (buffer) {
610 unsigned char *s = buffer;
611
612 if (extra == 1)
613 *s++ = 0;
614 else if (extra)
615 *s++ = 0xff;
616 memcpy(s, tmp, n-!!extra);
617 }
618 kfree(tmp);
619 *nwritten = n;
620 return 0;
621 } else if (format == GCRYMPI_FMT_USG) {
622 unsigned int n = (nbits + 7)/8;
623
624 /* Note: We ignore the sign for this format. */
625 /* FIXME: for performance reasons we should put this into
626 * mpi_aprint because we can then use the buffer directly.
627 */
628
629 if (buffer && n > len)
630 return -E2BIG;
631 if (buffer) {
632 unsigned char *tmp;
633
634 tmp = mpi_get_buffer(a, &n, NULL);
635 if (!tmp)
636 return -EINVAL;
637 memcpy(buffer, tmp, n);
638 kfree(tmp);
639 }
640 *nwritten = n;
641 return 0;
642 } else if (format == GCRYMPI_FMT_PGP) {
643 unsigned int n = (nbits + 7)/8;
644
645 /* The PGP format can only handle unsigned integers. */
646 if (negative)
647 return -EINVAL;
648
649 if (buffer && n+2 > len)
650 return -E2BIG;
651
652 if (buffer) {
653 unsigned char *tmp;
654 unsigned char *s = buffer;
655
656 s[0] = nbits >> 8;
657 s[1] = nbits;
658
659 tmp = mpi_get_buffer(a, &n, NULL);
660 if (!tmp)
661 return -EINVAL;
662 memcpy(s+2, tmp, n);
663 kfree(tmp);
664 }
665 *nwritten = n+2;
666 return 0;
667 } else if (format == GCRYMPI_FMT_SSH) {
668 unsigned char *tmp;
669 int extra = 0;
670 unsigned int n;
671
672 tmp = mpi_get_buffer(a, &n, NULL);
673 if (!tmp)
674 return -EINVAL;
675
676 if (negative) {
677 twocompl(tmp, n);
678 if (!(*tmp & 0x80)) {
679 /* Need to extend the sign. */
680 n++;
681 extra = 2;
682 }
683 } else if (n && (*tmp & 0x80)) {
684 n++;
685 extra = 1;
686 }
687
688 if (buffer && n+4 > len) {
689 kfree(tmp);
690 return -E2BIG;
691 }
692
693 if (buffer) {
694 unsigned char *s = buffer;
695
696 *s++ = n >> 24;
697 *s++ = n >> 16;
698 *s++ = n >> 8;
699 *s++ = n;
700 if (extra == 1)
701 *s++ = 0;
702 else if (extra)
703 *s++ = 0xff;
704 memcpy(s, tmp, n-!!extra);
705 }
706 kfree(tmp);
707 *nwritten = 4+n;
708 return 0;
709 } else if (format == GCRYMPI_FMT_HEX) {
710 unsigned char *tmp;
711 int i;
712 int extra = 0;
713 unsigned int n = 0;
714
715 tmp = mpi_get_buffer(a, &n, NULL);
716 if (!tmp)
717 return -EINVAL;
718 if (!n || (*tmp & 0x80))
719 extra = 2;
720
721 if (buffer && 2*n + extra + negative + 1 > len) {
722 kfree(tmp);
723 return -E2BIG;
724 }
725 if (buffer) {
726 unsigned char *s = buffer;
727
728 if (negative)
729 *s++ = '-';
730 if (extra) {
731 *s++ = '';
732 *s++ = '';
733 }
734
735 for (i = 0; i < n; i++) {
736 unsigned int c = tmp[i];
737
738 *s++ = (c >> 4) < 10 ? ''+(c>>4) : 'A'+(c>>4)-10;
739 c &= 15;
740 *s++ = c < 10 ? ''+c : 'A'+c-10;
741 }
742 *s++ = 0;
743 *nwritten = s - buffer;
744 } else {
745 *nwritten = 2*n + extra + negative + 1;
746 }
747 kfree(tmp);
748 return 0;
749 } else
750 return -EINVAL;
751 }
752 EXPORT_SYMBOL_GPL(mpi_print);
753
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