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 MAX_EXTERN_MPI_BITS 16384
24 
mpi_read_from_buffer(const void * xbuffer,unsigned * ret_nread)25 MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
26 {
27 	const uint8_t *buffer = xbuffer;
28 	int i, j;
29 	unsigned nbits, nbytes, nlimbs, nread = 0;
30 	mpi_limb_t a;
31 	MPI val = NULL;
32 
33 	if (*ret_nread < 2)
34 		goto leave;
35 	nbits = buffer[0] << 8 | buffer[1];
36 
37 	if (nbits > MAX_EXTERN_MPI_BITS) {
38 		pr_info("MPI: mpi too large (%u bits)\n", nbits);
39 		goto leave;
40 	}
41 	buffer += 2;
42 	nread = 2;
43 
44 	nbytes = (nbits + 7) / 8;
45 	nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
46 	val = mpi_alloc(nlimbs);
47 	if (!val)
48 		return NULL;
49 	i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
50 	i %= BYTES_PER_MPI_LIMB;
51 	val->nbits = nbits;
52 	j = val->nlimbs = nlimbs;
53 	val->sign = 0;
54 	for (; j > 0; j--) {
55 		a = 0;
56 		for (; i < BYTES_PER_MPI_LIMB; i++) {
57 			if (++nread > *ret_nread) {
58 				printk
59 				    ("MPI: mpi larger than buffer nread=%d ret_nread=%d\n",
60 				     nread, *ret_nread);
61 				goto leave;
62 			}
63 			a <<= 8;
64 			a |= *buffer++;
65 		}
66 		i = 0;
67 		val->d[j - 1] = a;
68 	}
69 
70 leave:
71 	*ret_nread = nread;
72 	return val;
73 }
74 EXPORT_SYMBOL_GPL(mpi_read_from_buffer);
75 
76 /****************
77  * Make an mpi from a character string.
78  */
mpi_fromstr(MPI val,const char * str)79 int mpi_fromstr(MPI val, const char *str)
80 {
81 	int hexmode = 0, sign = 0, prepend_zero = 0, i, j, c, c1, c2;
82 	unsigned nbits, nbytes, nlimbs;
83 	mpi_limb_t a;
84 
85 	if (*str == '-') {
86 		sign = 1;
87 		str++;
88 	}
89 	if (*str == '0' && str[1] == 'x')
90 		hexmode = 1;
91 	else
92 		return -EINVAL;	/* other bases are not yet supported */
93 	str += 2;
94 
95 	nbits = strlen(str) * 4;
96 	if (nbits % 8)
97 		prepend_zero = 1;
98 	nbytes = (nbits + 7) / 8;
99 	nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
100 	if (val->alloced < nlimbs)
101 		if (!mpi_resize(val, nlimbs))
102 			return -ENOMEM;
103 	i = BYTES_PER_MPI_LIMB - nbytes % BYTES_PER_MPI_LIMB;
104 	i %= BYTES_PER_MPI_LIMB;
105 	j = val->nlimbs = nlimbs;
106 	val->sign = sign;
107 	for (; j > 0; j--) {
108 		a = 0;
109 		for (; i < BYTES_PER_MPI_LIMB; i++) {
110 			if (prepend_zero) {
111 				c1 = '0';
112 				prepend_zero = 0;
113 			} else
114 				c1 = *str++;
115 			assert(c1);
116 			c2 = *str++;
117 			assert(c2);
118 			if (c1 >= '0' && c1 <= '9')
119 				c = c1 - '0';
120 			else if (c1 >= 'a' && c1 <= 'f')
121 				c = c1 - 'a' + 10;
122 			else if (c1 >= 'A' && c1 <= 'F')
123 				c = c1 - 'A' + 10;
124 			else {
125 				mpi_clear(val);
126 				return 1;
127 			}
128 			c <<= 4;
129 			if (c2 >= '0' && c2 <= '9')
130 				c |= c2 - '0';
131 			else if (c2 >= 'a' && c2 <= 'f')
132 				c |= c2 - 'a' + 10;
133 			else if (c2 >= 'A' && c2 <= 'F')
134 				c |= c2 - 'A' + 10;
135 			else {
136 				mpi_clear(val);
137 				return 1;
138 			}
139 			a <<= 8;
140 			a |= c;
141 		}
142 		i = 0;
143 
144 		val->d[j - 1] = a;
145 	}
146 
147 	return 0;
148 }
149 EXPORT_SYMBOL_GPL(mpi_fromstr);
150 
151 /****************
152  * Return an allocated buffer with the MPI (msb first).
153  * NBYTES receives the length of this buffer. Caller must free the
154  * return string (This function does return a 0 byte buffer with NBYTES
155  * set to zero if the value of A is zero. If sign is not NULL, it will
156  * be set to the sign of the A.
157  */
mpi_get_buffer(MPI a,unsigned * nbytes,int * sign)158 void *mpi_get_buffer(MPI a, unsigned *nbytes, int *sign)
159 {
160 	uint8_t *p, *buffer;
161 	mpi_limb_t alimb;
162 	int i;
163 	unsigned int n;
164 
165 	if (sign)
166 		*sign = a->sign;
167 	*nbytes = n = a->nlimbs * BYTES_PER_MPI_LIMB;
168 	if (!n)
169 		n++;		/* avoid zero length allocation */
170 	p = buffer = kmalloc(n, GFP_KERNEL);
171 	if (!p)
172 		return NULL;
173 
174 	for (i = a->nlimbs - 1; i >= 0; i--) {
175 		alimb = a->d[i];
176 #if BYTES_PER_MPI_LIMB == 4
177 		*p++ = alimb >> 24;
178 		*p++ = alimb >> 16;
179 		*p++ = alimb >> 8;
180 		*p++ = alimb;
181 #elif BYTES_PER_MPI_LIMB == 8
182 		*p++ = alimb >> 56;
183 		*p++ = alimb >> 48;
184 		*p++ = alimb >> 40;
185 		*p++ = alimb >> 32;
186 		*p++ = alimb >> 24;
187 		*p++ = alimb >> 16;
188 		*p++ = alimb >> 8;
189 		*p++ = alimb;
190 #else
191 #error please implement for this limb size.
192 #endif
193 	}
194 
195 	/* this is sub-optimal but we need to do the shift operation
196 	 * because the caller has to free the returned buffer */
197 	for (p = buffer; !*p && *nbytes; p++, --*nbytes)
198 		;
199 	if (p != buffer)
200 		memmove(buffer, p, *nbytes);
201 
202 	return buffer;
203 }
204 EXPORT_SYMBOL_GPL(mpi_get_buffer);
205 
206 /****************
207  * Use BUFFER to update MPI.
208  */
mpi_set_buffer(MPI a,const void * xbuffer,unsigned nbytes,int sign)209 int mpi_set_buffer(MPI a, const void *xbuffer, unsigned nbytes, int sign)
210 {
211 	const uint8_t *buffer = xbuffer, *p;
212 	mpi_limb_t alimb;
213 	int nlimbs;
214 	int i;
215 
216 	nlimbs = (nbytes + BYTES_PER_MPI_LIMB - 1) / BYTES_PER_MPI_LIMB;
217 	if (RESIZE_IF_NEEDED(a, nlimbs) < 0)
218 		return -ENOMEM;
219 	a->sign = sign;
220 
221 	for (i = 0, p = buffer + nbytes - 1; p >= buffer + BYTES_PER_MPI_LIMB;) {
222 #if BYTES_PER_MPI_LIMB == 4
223 		alimb = (mpi_limb_t) *p--;
224 		alimb |= (mpi_limb_t) *p-- << 8;
225 		alimb |= (mpi_limb_t) *p-- << 16;
226 		alimb |= (mpi_limb_t) *p-- << 24;
227 #elif BYTES_PER_MPI_LIMB == 8
228 		alimb = (mpi_limb_t) *p--;
229 		alimb |= (mpi_limb_t) *p-- << 8;
230 		alimb |= (mpi_limb_t) *p-- << 16;
231 		alimb |= (mpi_limb_t) *p-- << 24;
232 		alimb |= (mpi_limb_t) *p-- << 32;
233 		alimb |= (mpi_limb_t) *p-- << 40;
234 		alimb |= (mpi_limb_t) *p-- << 48;
235 		alimb |= (mpi_limb_t) *p-- << 56;
236 #else
237 #error please implement for this limb size.
238 #endif
239 		a->d[i++] = alimb;
240 	}
241 	if (p >= buffer) {
242 #if BYTES_PER_MPI_LIMB == 4
243 		alimb = *p--;
244 		if (p >= buffer)
245 			alimb |= (mpi_limb_t) *p-- << 8;
246 		if (p >= buffer)
247 			alimb |= (mpi_limb_t) *p-- << 16;
248 		if (p >= buffer)
249 			alimb |= (mpi_limb_t) *p-- << 24;
250 #elif BYTES_PER_MPI_LIMB == 8
251 		alimb = (mpi_limb_t) *p--;
252 		if (p >= buffer)
253 			alimb |= (mpi_limb_t) *p-- << 8;
254 		if (p >= buffer)
255 			alimb |= (mpi_limb_t) *p-- << 16;
256 		if (p >= buffer)
257 			alimb |= (mpi_limb_t) *p-- << 24;
258 		if (p >= buffer)
259 			alimb |= (mpi_limb_t) *p-- << 32;
260 		if (p >= buffer)
261 			alimb |= (mpi_limb_t) *p-- << 40;
262 		if (p >= buffer)
263 			alimb |= (mpi_limb_t) *p-- << 48;
264 		if (p >= buffer)
265 			alimb |= (mpi_limb_t) *p-- << 56;
266 #else
267 #error please implement for this limb size.
268 #endif
269 		a->d[i++] = alimb;
270 	}
271 	a->nlimbs = i;
272 
273 	if (i != nlimbs) {
274 		pr_emerg("MPI: mpi_set_buffer: Assertion failed (%d != %d)", i,
275 		       nlimbs);
276 		BUG();
277 	}
278 	return 0;
279 }
280 EXPORT_SYMBOL_GPL(mpi_set_buffer);
281