e5574168 |
1 | /* |
2 | * Bignum routines for RSA and DH and stuff. |
3 | */ |
4 | |
5 | #include <stdio.h> |
6 | #include <stdlib.h> |
7 | #include <string.h> |
8 | |
9 | #include "ssh.h" |
10 | |
7cca0d81 |
11 | unsigned short bnZero[1] = { 0 }; |
12 | unsigned short bnOne[2] = { 1, 1 }; |
e5574168 |
13 | |
7d6ee6ff |
14 | /* |
15 | * The Bignum format is an array of `unsigned short'. The first |
16 | * element of the array counts the remaining elements. The |
17 | * remaining elements express the actual number, base 2^16, _least_ |
18 | * significant digit first. (So it's trivial to extract the bit |
19 | * with value 2^n for any n.) |
20 | * |
21 | * All Bignums in this module are positive. Negative numbers must |
22 | * be dealt with outside it. |
23 | * |
24 | * INVARIANT: the most significant word of any Bignum must be |
25 | * nonzero. |
26 | */ |
27 | |
7cca0d81 |
28 | Bignum Zero = bnZero, One = bnOne; |
e5574168 |
29 | |
30 | Bignum newbn(int length) { |
31 | Bignum b = malloc((length+1)*sizeof(unsigned short)); |
32 | if (!b) |
33 | abort(); /* FIXME */ |
34 | memset(b, 0, (length+1)*sizeof(*b)); |
35 | b[0] = length; |
36 | return b; |
37 | } |
38 | |
7cca0d81 |
39 | Bignum copybn(Bignum orig) { |
40 | Bignum b = malloc((orig[0]+1)*sizeof(unsigned short)); |
41 | if (!b) |
42 | abort(); /* FIXME */ |
43 | memcpy(b, orig, (orig[0]+1)*sizeof(*b)); |
44 | return b; |
45 | } |
46 | |
e5574168 |
47 | void freebn(Bignum b) { |
48 | /* |
49 | * Burn the evidence, just in case. |
50 | */ |
51 | memset(b, 0, sizeof(b[0]) * (b[0] + 1)); |
52 | free(b); |
53 | } |
54 | |
55 | /* |
56 | * Compute c = a * b. |
57 | * Input is in the first len words of a and b. |
58 | * Result is returned in the first 2*len words of c. |
59 | */ |
9400cf6f |
60 | static void internal_mul(unsigned short *a, unsigned short *b, |
61 | unsigned short *c, int len) |
e5574168 |
62 | { |
63 | int i, j; |
64 | unsigned long ai, t; |
65 | |
9400cf6f |
66 | for (j = 0; j < 2*len; j++) |
67 | c[j] = 0; |
e5574168 |
68 | |
69 | for (i = len - 1; i >= 0; i--) { |
70 | ai = a[i]; |
71 | t = 0; |
72 | for (j = len - 1; j >= 0; j--) { |
73 | t += ai * (unsigned long) b[j]; |
74 | t += (unsigned long) c[i+j+1]; |
75 | c[i+j+1] = (unsigned short)t; |
76 | t = t >> 16; |
77 | } |
78 | c[i] = (unsigned short)t; |
79 | } |
80 | } |
81 | |
6e522441 |
82 | static void internal_add_shifted(unsigned short *number, |
83 | unsigned n, int shift) { |
9400cf6f |
84 | int word = 1 + (shift / 16); |
85 | int bshift = shift % 16; |
6e522441 |
86 | unsigned long addend; |
9400cf6f |
87 | |
88 | addend = n << bshift; |
89 | |
90 | while (addend) { |
91 | addend += number[word]; |
6e522441 |
92 | number[word] = (unsigned short) addend & 0xFFFF; |
9400cf6f |
93 | addend >>= 16; |
94 | word++; |
95 | } |
96 | } |
97 | |
e5574168 |
98 | /* |
99 | * Compute a = a % m. |
9400cf6f |
100 | * Input in first alen words of a and first mlen words of m. |
101 | * Output in first alen words of a |
102 | * (of which first alen-mlen words will be zero). |
e5574168 |
103 | * The MSW of m MUST have its high bit set. |
9400cf6f |
104 | * Quotient is accumulated in the `quotient' array, which is a Bignum |
105 | * rather than the internal bigendian format. Quotient parts are shifted |
106 | * left by `qshift' before adding into quot. |
e5574168 |
107 | */ |
9400cf6f |
108 | static void internal_mod(unsigned short *a, int alen, |
109 | unsigned short *m, int mlen, |
110 | unsigned short *quot, int qshift) |
e5574168 |
111 | { |
112 | unsigned short m0, m1; |
113 | unsigned int h; |
114 | int i, k; |
115 | |
e5574168 |
116 | m0 = m[0]; |
9400cf6f |
117 | if (mlen > 1) |
118 | m1 = m[1]; |
119 | else |
120 | m1 = 0; |
e5574168 |
121 | |
9400cf6f |
122 | for (i = 0; i <= alen-mlen; i++) { |
e5574168 |
123 | unsigned long t; |
9400cf6f |
124 | unsigned int q, r, c, ai1; |
e5574168 |
125 | |
126 | if (i == 0) { |
127 | h = 0; |
128 | } else { |
129 | h = a[i-1]; |
130 | a[i-1] = 0; |
131 | } |
132 | |
9400cf6f |
133 | if (i == alen-1) |
134 | ai1 = 0; |
135 | else |
136 | ai1 = a[i+1]; |
137 | |
e5574168 |
138 | /* Find q = h:a[i] / m0 */ |
139 | t = ((unsigned long) h << 16) + a[i]; |
140 | q = t / m0; |
141 | r = t % m0; |
142 | |
143 | /* Refine our estimate of q by looking at |
144 | h:a[i]:a[i+1] / m0:m1 */ |
145 | t = (long) m1 * (long) q; |
9400cf6f |
146 | if (t > ((unsigned long) r << 16) + ai1) { |
e5574168 |
147 | q--; |
148 | t -= m1; |
149 | r = (r + m0) & 0xffff; /* overflow? */ |
150 | if (r >= (unsigned long)m0 && |
9400cf6f |
151 | t > ((unsigned long) r << 16) + ai1) |
e5574168 |
152 | q--; |
153 | } |
154 | |
9400cf6f |
155 | /* Subtract q * m from a[i...] */ |
e5574168 |
156 | c = 0; |
9400cf6f |
157 | for (k = mlen - 1; k >= 0; k--) { |
e5574168 |
158 | t = (long) q * (long) m[k]; |
159 | t += c; |
160 | c = t >> 16; |
161 | if ((unsigned short) t > a[i+k]) c++; |
162 | a[i+k] -= (unsigned short) t; |
163 | } |
164 | |
165 | /* Add back m in case of borrow */ |
166 | if (c != h) { |
167 | t = 0; |
9400cf6f |
168 | for (k = mlen - 1; k >= 0; k--) { |
e5574168 |
169 | t += m[k]; |
170 | t += a[i+k]; |
171 | a[i+k] = (unsigned short)t; |
172 | t = t >> 16; |
173 | } |
9400cf6f |
174 | q--; |
e5574168 |
175 | } |
9400cf6f |
176 | if (quot) |
177 | internal_add_shifted(quot, q, qshift + 16 * (alen-mlen-i)); |
e5574168 |
178 | } |
179 | } |
180 | |
181 | /* |
182 | * Compute (base ^ exp) % mod. |
183 | * The base MUST be smaller than the modulus. |
184 | * The most significant word of mod MUST be non-zero. |
185 | * We assume that the result array is the same size as the mod array. |
186 | */ |
187 | void modpow(Bignum base, Bignum exp, Bignum mod, Bignum result) |
188 | { |
189 | unsigned short *a, *b, *n, *m; |
190 | int mshift; |
191 | int mlen, i, j; |
192 | |
193 | /* Allocate m of size mlen, copy mod to m */ |
194 | /* We use big endian internally */ |
195 | mlen = mod[0]; |
196 | m = malloc(mlen * sizeof(unsigned short)); |
197 | for (j = 0; j < mlen; j++) m[j] = mod[mod[0] - j]; |
198 | |
199 | /* Shift m left to make msb bit set */ |
200 | for (mshift = 0; mshift < 15; mshift++) |
201 | if ((m[0] << mshift) & 0x8000) break; |
202 | if (mshift) { |
203 | for (i = 0; i < mlen - 1; i++) |
204 | m[i] = (m[i] << mshift) | (m[i+1] >> (16-mshift)); |
205 | m[mlen-1] = m[mlen-1] << mshift; |
206 | } |
207 | |
208 | /* Allocate n of size mlen, copy base to n */ |
209 | n = malloc(mlen * sizeof(unsigned short)); |
210 | i = mlen - base[0]; |
211 | for (j = 0; j < i; j++) n[j] = 0; |
212 | for (j = 0; j < base[0]; j++) n[i+j] = base[base[0] - j]; |
213 | |
214 | /* Allocate a and b of size 2*mlen. Set a = 1 */ |
215 | a = malloc(2 * mlen * sizeof(unsigned short)); |
216 | b = malloc(2 * mlen * sizeof(unsigned short)); |
217 | for (i = 0; i < 2*mlen; i++) a[i] = 0; |
218 | a[2*mlen-1] = 1; |
219 | |
220 | /* Skip leading zero bits of exp. */ |
221 | i = 0; j = 15; |
222 | while (i < exp[0] && (exp[exp[0] - i] & (1 << j)) == 0) { |
223 | j--; |
224 | if (j < 0) { i++; j = 15; } |
225 | } |
226 | |
227 | /* Main computation */ |
228 | while (i < exp[0]) { |
229 | while (j >= 0) { |
9400cf6f |
230 | internal_mul(a + mlen, a + mlen, b, mlen); |
231 | internal_mod(b, mlen*2, m, mlen, NULL, 0); |
e5574168 |
232 | if ((exp[exp[0] - i] & (1 << j)) != 0) { |
9400cf6f |
233 | internal_mul(b + mlen, n, a, mlen); |
234 | internal_mod(a, mlen*2, m, mlen, NULL, 0); |
e5574168 |
235 | } else { |
236 | unsigned short *t; |
237 | t = a; a = b; b = t; |
238 | } |
239 | j--; |
240 | } |
241 | i++; j = 15; |
242 | } |
243 | |
244 | /* Fixup result in case the modulus was shifted */ |
245 | if (mshift) { |
246 | for (i = mlen - 1; i < 2*mlen - 1; i++) |
247 | a[i] = (a[i] << mshift) | (a[i+1] >> (16-mshift)); |
248 | a[2*mlen-1] = a[2*mlen-1] << mshift; |
9400cf6f |
249 | internal_mod(a, mlen*2, m, mlen, NULL, 0); |
e5574168 |
250 | for (i = 2*mlen - 1; i >= mlen; i--) |
251 | a[i] = (a[i] >> mshift) | (a[i-1] << (16-mshift)); |
252 | } |
253 | |
254 | /* Copy result to buffer */ |
255 | for (i = 0; i < mlen; i++) |
256 | result[result[0] - i] = a[i+mlen]; |
257 | |
258 | /* Free temporary arrays */ |
259 | for (i = 0; i < 2*mlen; i++) a[i] = 0; free(a); |
260 | for (i = 0; i < 2*mlen; i++) b[i] = 0; free(b); |
261 | for (i = 0; i < mlen; i++) m[i] = 0; free(m); |
262 | for (i = 0; i < mlen; i++) n[i] = 0; free(n); |
263 | } |
7cca0d81 |
264 | |
265 | /* |
266 | * Compute (p * q) % mod. |
267 | * The most significant word of mod MUST be non-zero. |
268 | * We assume that the result array is the same size as the mod array. |
269 | */ |
270 | void modmul(Bignum p, Bignum q, Bignum mod, Bignum result) |
271 | { |
272 | unsigned short *a, *n, *m, *o; |
273 | int mshift; |
274 | int pqlen, mlen, i, j; |
275 | |
276 | /* Allocate m of size mlen, copy mod to m */ |
277 | /* We use big endian internally */ |
278 | mlen = mod[0]; |
279 | m = malloc(mlen * sizeof(unsigned short)); |
280 | for (j = 0; j < mlen; j++) m[j] = mod[mod[0] - j]; |
281 | |
282 | /* Shift m left to make msb bit set */ |
283 | for (mshift = 0; mshift < 15; mshift++) |
284 | if ((m[0] << mshift) & 0x8000) break; |
285 | if (mshift) { |
286 | for (i = 0; i < mlen - 1; i++) |
287 | m[i] = (m[i] << mshift) | (m[i+1] >> (16-mshift)); |
288 | m[mlen-1] = m[mlen-1] << mshift; |
289 | } |
290 | |
291 | pqlen = (p[0] > q[0] ? p[0] : q[0]); |
292 | |
293 | /* Allocate n of size pqlen, copy p to n */ |
294 | n = malloc(pqlen * sizeof(unsigned short)); |
295 | i = pqlen - p[0]; |
296 | for (j = 0; j < i; j++) n[j] = 0; |
297 | for (j = 0; j < p[0]; j++) n[i+j] = p[p[0] - j]; |
298 | |
299 | /* Allocate o of size pqlen, copy q to o */ |
300 | o = malloc(pqlen * sizeof(unsigned short)); |
301 | i = pqlen - q[0]; |
302 | for (j = 0; j < i; j++) o[j] = 0; |
303 | for (j = 0; j < q[0]; j++) o[i+j] = q[q[0] - j]; |
304 | |
305 | /* Allocate a of size 2*pqlen for result */ |
306 | a = malloc(2 * pqlen * sizeof(unsigned short)); |
307 | |
308 | /* Main computation */ |
9400cf6f |
309 | internal_mul(n, o, a, pqlen); |
310 | internal_mod(a, pqlen*2, m, mlen, NULL, 0); |
7cca0d81 |
311 | |
312 | /* Fixup result in case the modulus was shifted */ |
313 | if (mshift) { |
314 | for (i = 2*pqlen - mlen - 1; i < 2*pqlen - 1; i++) |
315 | a[i] = (a[i] << mshift) | (a[i+1] >> (16-mshift)); |
316 | a[2*pqlen-1] = a[2*pqlen-1] << mshift; |
9400cf6f |
317 | internal_mod(a, pqlen*2, m, mlen, NULL, 0); |
7cca0d81 |
318 | for (i = 2*pqlen - 1; i >= 2*pqlen - mlen; i--) |
319 | a[i] = (a[i] >> mshift) | (a[i-1] << (16-mshift)); |
320 | } |
321 | |
322 | /* Copy result to buffer */ |
323 | for (i = 0; i < mlen; i++) |
324 | result[result[0] - i] = a[i+2*pqlen-mlen]; |
325 | |
326 | /* Free temporary arrays */ |
327 | for (i = 0; i < 2*pqlen; i++) a[i] = 0; free(a); |
328 | for (i = 0; i < mlen; i++) m[i] = 0; free(m); |
329 | for (i = 0; i < pqlen; i++) n[i] = 0; free(n); |
330 | for (i = 0; i < pqlen; i++) o[i] = 0; free(o); |
331 | } |
332 | |
333 | /* |
9400cf6f |
334 | * Compute p % mod. |
335 | * The most significant word of mod MUST be non-zero. |
336 | * We assume that the result array is the same size as the mod array. |
337 | * We optionally write out a quotient. |
338 | */ |
339 | void bigmod(Bignum p, Bignum mod, Bignum result, Bignum quotient) |
340 | { |
341 | unsigned short *n, *m; |
342 | int mshift; |
343 | int plen, mlen, i, j; |
344 | |
345 | /* Allocate m of size mlen, copy mod to m */ |
346 | /* We use big endian internally */ |
347 | mlen = mod[0]; |
348 | m = malloc(mlen * sizeof(unsigned short)); |
349 | for (j = 0; j < mlen; j++) m[j] = mod[mod[0] - j]; |
350 | |
351 | /* Shift m left to make msb bit set */ |
352 | for (mshift = 0; mshift < 15; mshift++) |
353 | if ((m[0] << mshift) & 0x8000) break; |
354 | if (mshift) { |
355 | for (i = 0; i < mlen - 1; i++) |
356 | m[i] = (m[i] << mshift) | (m[i+1] >> (16-mshift)); |
357 | m[mlen-1] = m[mlen-1] << mshift; |
358 | } |
359 | |
360 | plen = p[0]; |
361 | /* Ensure plen > mlen */ |
362 | if (plen <= mlen) plen = mlen+1; |
363 | |
364 | /* Allocate n of size plen, copy p to n */ |
365 | n = malloc(plen * sizeof(unsigned short)); |
366 | for (j = 0; j < plen; j++) n[j] = 0; |
367 | for (j = 1; j <= p[0]; j++) n[plen-j] = p[j]; |
368 | |
369 | /* Main computation */ |
370 | internal_mod(n, plen, m, mlen, quotient, mshift); |
371 | |
372 | /* Fixup result in case the modulus was shifted */ |
373 | if (mshift) { |
374 | for (i = plen - mlen - 1; i < plen - 1; i++) |
375 | n[i] = (n[i] << mshift) | (n[i+1] >> (16-mshift)); |
376 | n[plen-1] = n[plen-1] << mshift; |
377 | internal_mod(n, plen, m, mlen, quotient, 0); |
378 | for (i = plen - 1; i >= plen - mlen; i--) |
379 | n[i] = (n[i] >> mshift) | (n[i-1] << (16-mshift)); |
380 | } |
381 | |
382 | /* Copy result to buffer */ |
383 | for (i = 1; i <= result[0]; i++) { |
384 | int j = plen-i; |
385 | result[i] = j>=0 ? n[j] : 0; |
386 | } |
387 | |
388 | /* Free temporary arrays */ |
389 | for (i = 0; i < mlen; i++) m[i] = 0; free(m); |
390 | for (i = 0; i < plen; i++) n[i] = 0; free(n); |
391 | } |
392 | |
393 | /* |
7cca0d81 |
394 | * Decrement a number. |
395 | */ |
396 | void decbn(Bignum bn) { |
397 | int i = 1; |
398 | while (i < bn[0] && bn[i] == 0) |
399 | bn[i++] = 0xFFFF; |
400 | bn[i]--; |
401 | } |
402 | |
403 | /* |
404 | * Read an ssh1-format bignum from a data buffer. Return the number |
405 | * of bytes consumed. |
406 | */ |
407 | int ssh1_read_bignum(unsigned char *data, Bignum *result) { |
408 | unsigned char *p = data; |
409 | Bignum bn; |
410 | int i; |
411 | int w, b; |
412 | |
413 | w = 0; |
414 | for (i=0; i<2; i++) |
415 | w = (w << 8) + *p++; |
416 | |
417 | b = (w+7)/8; /* bits -> bytes */ |
418 | w = (w+15)/16; /* bits -> words */ |
419 | |
a52f067e |
420 | if (!result) /* just return length */ |
421 | return b + 2; |
422 | |
7cca0d81 |
423 | bn = newbn(w); |
424 | |
425 | for (i=1; i<=w; i++) |
426 | bn[i] = 0; |
427 | for (i=b; i-- ;) { |
428 | unsigned char byte = *p++; |
429 | if (i & 1) |
430 | bn[1+i/2] |= byte<<8; |
431 | else |
432 | bn[1+i/2] |= byte; |
433 | } |
434 | |
435 | *result = bn; |
436 | |
437 | return p - data; |
438 | } |
5c58ad2d |
439 | |
440 | /* |
441 | * Return the bit count of a bignum, for ssh1 encoding. |
442 | */ |
443 | int ssh1_bignum_bitcount(Bignum bn) { |
444 | int bitcount = bn[0] * 16 - 1; |
445 | |
446 | while (bitcount >= 0 && (bn[bitcount/16+1] >> (bitcount % 16)) == 0) |
447 | bitcount--; |
448 | return bitcount + 1; |
449 | } |
450 | |
451 | /* |
452 | * Return the byte length of a bignum when ssh1 encoded. |
453 | */ |
454 | int ssh1_bignum_length(Bignum bn) { |
455 | return 2 + (ssh1_bignum_bitcount(bn)+7)/8; |
456 | } |
457 | |
458 | /* |
459 | * Return a byte from a bignum; 0 is least significant, etc. |
460 | */ |
461 | int bignum_byte(Bignum bn, int i) { |
462 | if (i >= 2*bn[0]) |
463 | return 0; /* beyond the end */ |
464 | else if (i & 1) |
465 | return (bn[i/2+1] >> 8) & 0xFF; |
466 | else |
467 | return (bn[i/2+1] ) & 0xFF; |
468 | } |
469 | |
470 | /* |
9400cf6f |
471 | * Return a bit from a bignum; 0 is least significant, etc. |
472 | */ |
473 | int bignum_bit(Bignum bn, int i) { |
474 | if (i >= 16*bn[0]) |
475 | return 0; /* beyond the end */ |
476 | else |
477 | return (bn[i/16+1] >> (i%16)) & 1; |
478 | } |
479 | |
480 | /* |
481 | * Set a bit in a bignum; 0 is least significant, etc. |
482 | */ |
483 | void bignum_set_bit(Bignum bn, int bitnum, int value) { |
484 | if (bitnum >= 16*bn[0]) |
485 | abort(); /* beyond the end */ |
486 | else { |
487 | int v = bitnum/16+1; |
488 | int mask = 1 << (bitnum%16); |
489 | if (value) |
490 | bn[v] |= mask; |
491 | else |
492 | bn[v] &= ~mask; |
493 | } |
494 | } |
495 | |
496 | /* |
5c58ad2d |
497 | * Write a ssh1-format bignum into a buffer. It is assumed the |
498 | * buffer is big enough. Returns the number of bytes used. |
499 | */ |
500 | int ssh1_write_bignum(void *data, Bignum bn) { |
501 | unsigned char *p = data; |
502 | int len = ssh1_bignum_length(bn); |
503 | int i; |
504 | int bitc = ssh1_bignum_bitcount(bn); |
505 | |
506 | *p++ = (bitc >> 8) & 0xFF; |
507 | *p++ = (bitc ) & 0xFF; |
508 | for (i = len-2; i-- ;) |
509 | *p++ = bignum_byte(bn, i); |
510 | return len; |
511 | } |
9400cf6f |
512 | |
513 | /* |
514 | * Compare two bignums. Returns like strcmp. |
515 | */ |
516 | int bignum_cmp(Bignum a, Bignum b) { |
517 | int amax = a[0], bmax = b[0]; |
518 | int i = (amax > bmax ? amax : bmax); |
519 | while (i) { |
520 | unsigned short aval = (i > amax ? 0 : a[i]); |
521 | unsigned short bval = (i > bmax ? 0 : b[i]); |
522 | if (aval < bval) return -1; |
523 | if (aval > bval) return +1; |
524 | i--; |
525 | } |
526 | return 0; |
527 | } |
528 | |
529 | /* |
530 | * Right-shift one bignum to form another. |
531 | */ |
532 | Bignum bignum_rshift(Bignum a, int shift) { |
533 | Bignum ret; |
534 | int i, shiftw, shiftb, shiftbb, bits; |
535 | unsigned short ai, ai1; |
536 | |
537 | bits = ssh1_bignum_bitcount(a) - shift; |
538 | ret = newbn((bits+15)/16); |
539 | |
540 | if (ret) { |
541 | shiftw = shift / 16; |
542 | shiftb = shift % 16; |
543 | shiftbb = 16 - shiftb; |
544 | |
545 | ai1 = a[shiftw+1]; |
546 | for (i = 1; i <= ret[0]; i++) { |
547 | ai = ai1; |
548 | ai1 = (i+shiftw+1 <= a[0] ? a[i+shiftw+1] : 0); |
549 | ret[i] = ((ai >> shiftb) | (ai1 << shiftbb)) & 0xFFFF; |
550 | } |
551 | } |
552 | |
553 | return ret; |
554 | } |
555 | |
556 | /* |
557 | * Non-modular multiplication and addition. |
558 | */ |
559 | Bignum bigmuladd(Bignum a, Bignum b, Bignum addend) { |
560 | int alen = a[0], blen = b[0]; |
561 | int mlen = (alen > blen ? alen : blen); |
562 | int rlen, i, maxspot; |
563 | unsigned short *workspace; |
564 | Bignum ret; |
565 | |
566 | /* mlen space for a, mlen space for b, 2*mlen for result */ |
567 | workspace = malloc(mlen * 4 * sizeof(unsigned short)); |
568 | for (i = 0; i < mlen; i++) { |
569 | workspace[0*mlen + i] = (mlen-i <= a[0] ? a[mlen-i] : 0); |
570 | workspace[1*mlen + i] = (mlen-i <= b[0] ? b[mlen-i] : 0); |
571 | } |
572 | |
573 | internal_mul(workspace+0*mlen, workspace+1*mlen, workspace+2*mlen, mlen); |
574 | |
575 | /* now just copy the result back */ |
576 | rlen = alen + blen + 1; |
577 | if (addend && rlen <= addend[0]) |
578 | rlen = addend[0] + 1; |
579 | ret = newbn(rlen); |
580 | maxspot = 0; |
581 | for (i = 1; i <= ret[0]; i++) { |
582 | ret[i] = (i <= 2*mlen ? workspace[4*mlen - i] : 0); |
583 | if (ret[i] != 0) |
584 | maxspot = i; |
585 | } |
586 | ret[0] = maxspot; |
587 | |
588 | /* now add in the addend, if any */ |
589 | if (addend) { |
590 | unsigned long carry = 0; |
591 | for (i = 1; i <= rlen; i++) { |
592 | carry += (i <= ret[0] ? ret[i] : 0); |
593 | carry += (i <= addend[0] ? addend[i] : 0); |
6e522441 |
594 | ret[i] = (unsigned short) carry & 0xFFFF; |
9400cf6f |
595 | carry >>= 16; |
596 | if (ret[i] != 0 && i > maxspot) |
597 | maxspot = i; |
598 | } |
599 | } |
600 | ret[0] = maxspot; |
601 | |
602 | return ret; |
603 | } |
604 | |
605 | /* |
606 | * Non-modular multiplication. |
607 | */ |
608 | Bignum bigmul(Bignum a, Bignum b) { |
609 | return bigmuladd(a, b, NULL); |
610 | } |
611 | |
612 | /* |
613 | * Convert a (max 16-bit) short into a bignum. |
614 | */ |
615 | Bignum bignum_from_short(unsigned short n) { |
616 | Bignum ret; |
617 | |
618 | ret = newbn(2); |
619 | ret[1] = n & 0xFFFF; |
620 | ret[2] = (n >> 16) & 0xFFFF; |
621 | ret[0] = (ret[2] ? 2 : 1); |
622 | return ret; |
623 | } |
624 | |
625 | /* |
626 | * Add a long to a bignum. |
627 | */ |
628 | Bignum bignum_add_long(Bignum number, unsigned long addend) { |
629 | Bignum ret = newbn(number[0]+1); |
630 | int i, maxspot = 0; |
631 | unsigned long carry = 0; |
632 | |
633 | for (i = 1; i <= ret[0]; i++) { |
634 | carry += addend & 0xFFFF; |
635 | carry += (i <= number[0] ? number[i] : 0); |
636 | addend >>= 16; |
6e522441 |
637 | ret[i] = (unsigned short) carry & 0xFFFF; |
9400cf6f |
638 | carry >>= 16; |
639 | if (ret[i] != 0) |
640 | maxspot = i; |
641 | } |
642 | ret[0] = maxspot; |
643 | return ret; |
644 | } |
645 | |
646 | /* |
647 | * Compute the residue of a bignum, modulo a (max 16-bit) short. |
648 | */ |
649 | unsigned short bignum_mod_short(Bignum number, unsigned short modulus) { |
9400cf6f |
650 | unsigned long mod, r; |
651 | int i; |
652 | |
653 | r = 0; |
654 | mod = modulus; |
655 | for (i = number[0]; i > 0; i--) |
656 | r = (r * 65536 + number[i]) % mod; |
6e522441 |
657 | return (unsigned short) r; |
9400cf6f |
658 | } |
659 | |
660 | static void diagbn(char *prefix, Bignum md) { |
661 | int i, nibbles, morenibbles; |
662 | static const char hex[] = "0123456789ABCDEF"; |
663 | |
664 | printf("%s0x", prefix ? prefix : ""); |
665 | |
666 | nibbles = (3 + ssh1_bignum_bitcount(md))/4; if (nibbles<1) nibbles=1; |
667 | morenibbles = 4*md[0] - nibbles; |
668 | for (i=0; i<morenibbles; i++) putchar('-'); |
669 | for (i=nibbles; i-- ;) |
670 | putchar(hex[(bignum_byte(md, i/2) >> (4*(i%2))) & 0xF]); |
671 | |
672 | if (prefix) putchar('\n'); |
673 | } |
674 | |
675 | /* |
676 | * Greatest common divisor. |
677 | */ |
678 | Bignum biggcd(Bignum av, Bignum bv) { |
679 | Bignum a = copybn(av); |
680 | Bignum b = copybn(bv); |
681 | |
682 | diagbn("a = ", a); |
683 | diagbn("b = ", b); |
684 | while (bignum_cmp(b, Zero) != 0) { |
685 | Bignum t = newbn(b[0]); |
686 | bigmod(a, b, t, NULL); |
687 | diagbn("t = ", t); |
688 | while (t[0] > 1 && t[t[0]] == 0) t[0]--; |
689 | freebn(a); |
690 | a = b; |
691 | b = t; |
692 | } |
693 | |
694 | freebn(b); |
695 | return a; |
696 | } |
697 | |
698 | /* |
699 | * Modular inverse, using Euclid's extended algorithm. |
700 | */ |
701 | Bignum modinv(Bignum number, Bignum modulus) { |
702 | Bignum a = copybn(modulus); |
703 | Bignum b = copybn(number); |
704 | Bignum xp = copybn(Zero); |
705 | Bignum x = copybn(One); |
706 | int sign = +1; |
707 | |
708 | while (bignum_cmp(b, One) != 0) { |
709 | Bignum t = newbn(b[0]); |
710 | Bignum q = newbn(a[0]); |
711 | bigmod(a, b, t, q); |
712 | while (t[0] > 1 && t[t[0]] == 0) t[0]--; |
713 | freebn(a); |
714 | a = b; |
715 | b = t; |
716 | t = xp; |
717 | xp = x; |
718 | x = bigmuladd(q, xp, t); |
719 | sign = -sign; |
720 | freebn(t); |
721 | } |
722 | |
723 | freebn(b); |
724 | freebn(a); |
725 | freebn(xp); |
726 | |
727 | /* now we know that sign * x == 1, and that x < modulus */ |
728 | if (sign < 0) { |
729 | /* set a new x to be modulus - x */ |
730 | Bignum newx = newbn(modulus[0]); |
731 | unsigned short carry = 0; |
732 | int maxspot = 1; |
733 | int i; |
734 | |
735 | for (i = 1; i <= newx[0]; i++) { |
736 | unsigned short aword = (i <= modulus[0] ? modulus[i] : 0); |
737 | unsigned short bword = (i <= x[0] ? x[i] : 0); |
738 | newx[i] = aword - bword - carry; |
739 | bword = ~bword; |
740 | carry = carry ? (newx[i] >= bword) : (newx[i] > bword); |
741 | if (newx[i] != 0) |
742 | maxspot = i; |
743 | } |
744 | newx[0] = maxspot; |
745 | freebn(x); |
746 | x = newx; |
747 | } |
748 | |
749 | /* and return. */ |
750 | return x; |
751 | } |
6e522441 |
752 | |
753 | /* |
754 | * Render a bignum into decimal. Return a malloced string holding |
755 | * the decimal representation. |
756 | */ |
757 | char *bignum_decimal(Bignum x) { |
758 | int ndigits, ndigit; |
759 | int i, iszero; |
760 | unsigned long carry; |
761 | char *ret; |
762 | unsigned short *workspace; |
763 | |
764 | /* |
765 | * First, estimate the number of digits. Since log(10)/log(2) |
766 | * is just greater than 93/28 (the joys of continued fraction |
767 | * approximations...) we know that for every 93 bits, we need |
768 | * at most 28 digits. This will tell us how much to malloc. |
769 | * |
770 | * Formally: if x has i bits, that means x is strictly less |
771 | * than 2^i. Since 2 is less than 10^(28/93), this is less than |
772 | * 10^(28i/93). We need an integer power of ten, so we must |
773 | * round up (rounding down might make it less than x again). |
774 | * Therefore if we multiply the bit count by 28/93, rounding |
775 | * up, we will have enough digits. |
776 | */ |
777 | i = ssh1_bignum_bitcount(x); |
778 | ndigits = (28*i + 92)/93; /* multiply by 28/93 and round up */ |
779 | ndigits++; /* allow for trailing \0 */ |
780 | ret = malloc(ndigits); |
781 | |
782 | /* |
783 | * Now allocate some workspace to hold the binary form as we |
784 | * repeatedly divide it by ten. Initialise this to the |
785 | * big-endian form of the number. |
786 | */ |
787 | workspace = malloc(sizeof(unsigned short) * x[0]); |
788 | for (i = 0; i < x[0]; i++) |
789 | workspace[i] = x[x[0] - i]; |
790 | |
791 | /* |
792 | * Next, write the decimal number starting with the last digit. |
793 | * We use ordinary short division, dividing 10 into the |
794 | * workspace. |
795 | */ |
796 | ndigit = ndigits-1; |
797 | ret[ndigit] = '\0'; |
798 | do { |
799 | iszero = 1; |
800 | carry = 0; |
801 | for (i = 0; i < x[0]; i++) { |
802 | carry = (carry << 16) + workspace[i]; |
803 | workspace[i] = (unsigned short) (carry / 10); |
804 | if (workspace[i]) |
805 | iszero = 0; |
806 | carry %= 10; |
807 | } |
808 | ret[--ndigit] = (char)(carry + '0'); |
809 | } while (!iszero); |
810 | |
811 | /* |
812 | * There's a chance we've fallen short of the start of the |
813 | * string. Correct if so. |
814 | */ |
815 | if (ndigit > 0) |
816 | memmove(ret, ret+ndigit, ndigits-ndigit); |
817 | |
818 | /* |
819 | * Done. |
820 | */ |
821 | return ret; |
822 | } |