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135 .IX Title "bn_internal 3"
136 .TH bn_internal 3 "2016-05-03" "1.0.2h" "OpenSSL"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
142 bn_mul_words, bn_mul_add_words, bn_sqr_words, bn_div_words,
143 bn_add_words, bn_sub_words, bn_mul_comba4, bn_mul_comba8,
144 bn_sqr_comba4, bn_sqr_comba8, bn_cmp_words, bn_mul_normal,
145 bn_mul_low_normal, bn_mul_recursive, bn_mul_part_recursive,
146 bn_mul_low_recursive, bn_mul_high, bn_sqr_normal, bn_sqr_recursive,
147 bn_expand, bn_wexpand, bn_expand2, bn_fix_top, bn_check_top,
148 bn_print, bn_dump, bn_set_max, bn_set_high, bn_set_low \- BIGNUM
149 library internal functions
151 .IX Header "SYNOPSIS"
153 \& #include <openssl/bn.h>
155 \& BN_ULONG bn_mul_words(BN_ULONG *rp, BN_ULONG *ap, int num, BN_ULONG w);
156 \& BN_ULONG bn_mul_add_words(BN_ULONG *rp, BN_ULONG *ap, int num,
158 \& void bn_sqr_words(BN_ULONG *rp, BN_ULONG *ap, int num);
159 \& BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d);
160 \& BN_ULONG bn_add_words(BN_ULONG *rp, BN_ULONG *ap, BN_ULONG *bp,
162 \& BN_ULONG bn_sub_words(BN_ULONG *rp, BN_ULONG *ap, BN_ULONG *bp,
165 \& void bn_mul_comba4(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b);
166 \& void bn_mul_comba8(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b);
167 \& void bn_sqr_comba4(BN_ULONG *r, BN_ULONG *a);
168 \& void bn_sqr_comba8(BN_ULONG *r, BN_ULONG *a);
170 \& int bn_cmp_words(BN_ULONG *a, BN_ULONG *b, int n);
172 \& void bn_mul_normal(BN_ULONG *r, BN_ULONG *a, int na, BN_ULONG *b,
174 \& void bn_mul_low_normal(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n);
175 \& void bn_mul_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n2,
176 \& int dna,int dnb,BN_ULONG *tmp);
177 \& void bn_mul_part_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b,
178 \& int n, int tna,int tnb, BN_ULONG *tmp);
179 \& void bn_mul_low_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b,
180 \& int n2, BN_ULONG *tmp);
181 \& void bn_mul_high(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, BN_ULONG *l,
182 \& int n2, BN_ULONG *tmp);
184 \& void bn_sqr_normal(BN_ULONG *r, BN_ULONG *a, int n, BN_ULONG *tmp);
185 \& void bn_sqr_recursive(BN_ULONG *r, BN_ULONG *a, int n2, BN_ULONG *tmp);
187 \& void mul(BN_ULONG r, BN_ULONG a, BN_ULONG w, BN_ULONG c);
188 \& void mul_add(BN_ULONG r, BN_ULONG a, BN_ULONG w, BN_ULONG c);
189 \& void sqr(BN_ULONG r0, BN_ULONG r1, BN_ULONG a);
191 \& BIGNUM *bn_expand(BIGNUM *a, int bits);
192 \& BIGNUM *bn_wexpand(BIGNUM *a, int n);
193 \& BIGNUM *bn_expand2(BIGNUM *a, int n);
194 \& void bn_fix_top(BIGNUM *a);
196 \& void bn_check_top(BIGNUM *a);
197 \& void bn_print(BIGNUM *a);
198 \& void bn_dump(BN_ULONG *d, int n);
199 \& void bn_set_max(BIGNUM *a);
200 \& void bn_set_high(BIGNUM *r, BIGNUM *a, int n);
201 \& void bn_set_low(BIGNUM *r, BIGNUM *a, int n);
204 .IX Header "DESCRIPTION"
205 This page documents the internal functions used by the OpenSSL
206 \&\fB\s-1BIGNUM\s0\fR implementation. They are described here to facilitate
207 debugging and extending the library. They are \fInot\fR to be used by
209 .SS "The \s-1BIGNUM\s0 structure"
210 .IX Subsection "The BIGNUM structure"
212 \& typedef struct bignum_st BIGNUM;
216 \& BN_ULONG *d; /* Pointer to an array of \*(AqBN_BITS2\*(Aq bit chunks. */
217 \& int top; /* Index of last used d +1. */
218 \& /* The next are internal book keeping for bn_expand. */
219 \& int dmax; /* Size of the d array. */
220 \& int neg; /* one if the number is negative */
225 The integer value is stored in \fBd\fR, a \fImalloc()\fRed array of words (\fB\s-1BN_ULONG\s0\fR),
226 least significant word first. A \fB\s-1BN_ULONG\s0\fR can be either 16, 32 or 64 bits
227 in size, depending on the 'number of bits' (\fB\s-1BITS2\s0\fR) specified in
228 \&\f(CW\*(C`openssl/bn.h\*(C'\fR.
230 \&\fBdmax\fR is the size of the \fBd\fR array that has been allocated. \fBtop\fR
231 is the number of words being used, so for a value of 4, bn.d[0]=4 and
232 bn.top=1. \fBneg\fR is 1 if the number is negative. When a \fB\s-1BIGNUM\s0\fR is
233 \&\fB0\fR, the \fBd\fR field can be \fB\s-1NULL\s0\fR and \fBtop\fR == \fB0\fR.
235 \&\fBflags\fR is a bit field of flags which are defined in \f(CW\*(C`openssl/bn.h\*(C'\fR. The
236 flags begin with \fB\s-1BN_FLG_\s0\fR. The macros BN_set_flags(b,n) and
237 BN_get_flags(b,n) exist to enable or fetch flag(s) \fBn\fR from \fB\s-1BIGNUM\s0\fR
240 Various routines in this library require the use of temporary
241 \&\fB\s-1BIGNUM\s0\fR variables during their execution. Since dynamic memory
242 allocation to create \fB\s-1BIGNUM\s0\fRs is rather expensive when used in
243 conjunction with repeated subroutine calls, the \fB\s-1BN_CTX\s0\fR structure is
244 used. This structure contains \fB\s-1BN_CTX_NUM\s0\fR \fB\s-1BIGNUM\s0\fRs, see
245 \&\fIBN_CTX_start\fR\|(3).
246 .SS "Low-level arithmetic operations"
247 .IX Subsection "Low-level arithmetic operations"
248 These functions are implemented in C and for several platforms in
251 bn_mul_words(\fBrp\fR, \fBap\fR, \fBnum\fR, \fBw\fR) operates on the \fBnum\fR word
252 arrays \fBrp\fR and \fBap\fR. It computes \fBap\fR * \fBw\fR, places the result
253 in \fBrp\fR, and returns the high word (carry).
255 bn_mul_add_words(\fBrp\fR, \fBap\fR, \fBnum\fR, \fBw\fR) operates on the \fBnum\fR
256 word arrays \fBrp\fR and \fBap\fR. It computes \fBap\fR * \fBw\fR + \fBrp\fR, places
257 the result in \fBrp\fR, and returns the high word (carry).
259 bn_sqr_words(\fBrp\fR, \fBap\fR, \fBn\fR) operates on the \fBnum\fR word array
260 \&\fBap\fR and the 2*\fBnum\fR word array \fBap\fR. It computes \fBap\fR * \fBap\fR
261 word-wise, and places the low and high bytes of the result in \fBrp\fR.
263 bn_div_words(\fBh\fR, \fBl\fR, \fBd\fR) divides the two word number (\fBh\fR,\fBl\fR)
264 by \fBd\fR and returns the result.
266 bn_add_words(\fBrp\fR, \fBap\fR, \fBbp\fR, \fBnum\fR) operates on the \fBnum\fR word
267 arrays \fBap\fR, \fBbp\fR and \fBrp\fR. It computes \fBap\fR + \fBbp\fR, places the
268 result in \fBrp\fR, and returns the high word (carry).
270 bn_sub_words(\fBrp\fR, \fBap\fR, \fBbp\fR, \fBnum\fR) operates on the \fBnum\fR word
271 arrays \fBap\fR, \fBbp\fR and \fBrp\fR. It computes \fBap\fR \- \fBbp\fR, places the
272 result in \fBrp\fR, and returns the carry (1 if \fBbp\fR > \fBap\fR, 0
275 bn_mul_comba4(\fBr\fR, \fBa\fR, \fBb\fR) operates on the 4 word arrays \fBa\fR and
276 \&\fBb\fR and the 8 word array \fBr\fR. It computes \fBa\fR*\fBb\fR and places the
279 bn_mul_comba8(\fBr\fR, \fBa\fR, \fBb\fR) operates on the 8 word arrays \fBa\fR and
280 \&\fBb\fR and the 16 word array \fBr\fR. It computes \fBa\fR*\fBb\fR and places the
283 bn_sqr_comba4(\fBr\fR, \fBa\fR, \fBb\fR) operates on the 4 word arrays \fBa\fR and
284 \&\fBb\fR and the 8 word array \fBr\fR.
286 bn_sqr_comba8(\fBr\fR, \fBa\fR, \fBb\fR) operates on the 8 word arrays \fBa\fR and
287 \&\fBb\fR and the 16 word array \fBr\fR.
289 The following functions are implemented in C:
291 bn_cmp_words(\fBa\fR, \fBb\fR, \fBn\fR) operates on the \fBn\fR word arrays \fBa\fR
292 and \fBb\fR. It returns 1, 0 and \-1 if \fBa\fR is greater than, equal and
295 bn_mul_normal(\fBr\fR, \fBa\fR, \fBna\fR, \fBb\fR, \fBnb\fR) operates on the \fBna\fR
296 word array \fBa\fR, the \fBnb\fR word array \fBb\fR and the \fBna\fR+\fBnb\fR word
297 array \fBr\fR. It computes \fBa\fR*\fBb\fR and places the result in \fBr\fR.
299 bn_mul_low_normal(\fBr\fR, \fBa\fR, \fBb\fR, \fBn\fR) operates on the \fBn\fR word
300 arrays \fBr\fR, \fBa\fR and \fBb\fR. It computes the \fBn\fR low words of
301 \&\fBa\fR*\fBb\fR and places the result in \fBr\fR.
303 bn_mul_recursive(\fBr\fR, \fBa\fR, \fBb\fR, \fBn2\fR, \fBdna\fR, \fBdnb\fR, \fBt\fR) operates
304 on the word arrays \fBa\fR and \fBb\fR of length \fBn2\fR+\fBdna\fR and \fBn2\fR+\fBdnb\fR
305 (\fBdna\fR and \fBdnb\fR are currently allowed to be 0 or negative) and the 2*\fBn2\fR
306 word arrays \fBr\fR and \fBt\fR. \fBn2\fR must be a power of 2. It computes
307 \&\fBa\fR*\fBb\fR and places the result in \fBr\fR.
309 bn_mul_part_recursive(\fBr\fR, \fBa\fR, \fBb\fR, \fBn\fR, \fBtna\fR, \fBtnb\fR, \fBtmp\fR)
310 operates on the word arrays \fBa\fR and \fBb\fR of length \fBn\fR+\fBtna\fR and
311 \&\fBn\fR+\fBtnb\fR and the 4*\fBn\fR word arrays \fBr\fR and \fBtmp\fR.
313 bn_mul_low_recursive(\fBr\fR, \fBa\fR, \fBb\fR, \fBn2\fR, \fBtmp\fR) operates on the
314 \&\fBn2\fR word arrays \fBr\fR and \fBtmp\fR and the \fBn2\fR/2 word arrays \fBa\fR
317 bn_mul_high(\fBr\fR, \fBa\fR, \fBb\fR, \fBl\fR, \fBn2\fR, \fBtmp\fR) operates on the
318 \&\fBn2\fR word arrays \fBr\fR, \fBa\fR, \fBb\fR and \fBl\fR (?) and the 3*\fBn2\fR word
321 \&\fIBN_mul()\fR calls \fIbn_mul_normal()\fR, or an optimized implementation if the
322 factors have the same size: \fIbn_mul_comba8()\fR is used if they are 8
323 words long, \fIbn_mul_recursive()\fR if they are larger than
324 \&\fB\s-1BN_MULL_SIZE_NORMAL\s0\fR and the size is an exact multiple of the word
325 size, and \fIbn_mul_part_recursive()\fR for others that are larger than
326 \&\fB\s-1BN_MULL_SIZE_NORMAL\s0\fR.
328 bn_sqr_normal(\fBr\fR, \fBa\fR, \fBn\fR, \fBtmp\fR) operates on the \fBn\fR word array
329 \&\fBa\fR and the 2*\fBn\fR word arrays \fBtmp\fR and \fBr\fR.
331 The implementations use the following macros which, depending on the
332 architecture, may use \*(L"long long\*(R" C operations or inline assembler.
333 They are defined in \f(CW\*(C`bn_lcl.h\*(C'\fR.
335 mul(\fBr\fR, \fBa\fR, \fBw\fR, \fBc\fR) computes \fBw\fR*\fBa\fR+\fBc\fR and places the
336 low word of the result in \fBr\fR and the high word in \fBc\fR.
338 mul_add(\fBr\fR, \fBa\fR, \fBw\fR, \fBc\fR) computes \fBw\fR*\fBa\fR+\fBr\fR+\fBc\fR and
339 places the low word of the result in \fBr\fR and the high word in \fBc\fR.
341 sqr(\fBr0\fR, \fBr1\fR, \fBa\fR) computes \fBa\fR*\fBa\fR and places the low word
342 of the result in \fBr0\fR and the high word in \fBr1\fR.
344 .IX Subsection "Size changes"
345 \&\fIbn_expand()\fR ensures that \fBb\fR has enough space for a \fBbits\fR bit
346 number. \fIbn_wexpand()\fR ensures that \fBb\fR has enough space for an
347 \&\fBn\fR word number. If the number has to be expanded, both macros
348 call \fIbn_expand2()\fR, which allocates a new \fBd\fR array and copies the
349 data. They return \fB\s-1NULL\s0\fR on error, \fBb\fR otherwise.
351 The \fIbn_fix_top()\fR macro reduces \fBa\->top\fR to point to the most
352 significant non-zero word plus one when \fBa\fR has shrunk.
354 .IX Subsection "Debugging"
355 \&\fIbn_check_top()\fR verifies that \f(CW\*(C`((a)\->top >= 0 && (a)\->top
356 <= (a)\->dmax)\*(C'\fR. A violation will cause the program to abort.
358 \&\fIbn_print()\fR prints \fBa\fR to stderr. \fIbn_dump()\fR prints \fBn\fR words at \fBd\fR
359 (in reverse order, i.e. most significant word first) to stderr.
361 \&\fIbn_set_max()\fR makes \fBa\fR a static number with a \fBdmax\fR of its current size.
362 This is used by \fIbn_set_low()\fR and \fIbn_set_high()\fR to make \fBr\fR a read-only
363 \&\fB\s-1BIGNUM\s0\fR that contains the \fBn\fR low or high words of \fBa\fR.
365 If \fB\s-1BN_DEBUG\s0\fR is not defined, \fIbn_check_top()\fR, \fIbn_print()\fR, \fIbn_dump()\fR
366 and \fIbn_set_max()\fR are defined as empty macros.
368 .IX Header "SEE ALSO"