lib/libcrypto/bn/bn_lcl.h

   1 /* $OpenBSD: bn_lcl.h,v 1.27 2017/01/25 06:15:44 beck Exp $ */
   2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   3  * All rights reserved.
   4  *
   5  * This package is an SSL implementation written
   6  * by Eric Young (eay@cryptsoft.com).
   7  * The implementation was written so as to conform with Netscapes SSL.
   8  *
   9  * This library is free for commercial and non-commercial use as long as
  10  * the following conditions are aheared to.  The following conditions
  11  * apply to all code found in this distribution, be it the RC4, RSA,
  12  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  13  * included with this distribution is covered by the same copyright terms
  14  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  15  *
  16  * Copyright remains Eric Young's, and as such any Copyright notices in
  17  * the code are not to be removed.
  18  * If this package is used in a product, Eric Young should be given attribution
  19  * as the author of the parts of the library used.
  20  * This can be in the form of a textual message at program startup or
  21  * in documentation (online or textual) provided with the package.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 3. All advertising materials mentioning features or use of this software
  32  *    must display the following acknowledgement:
  33  *    "This product includes cryptographic software written by
  34  *     Eric Young (eay@cryptsoft.com)"
  35  *    The word 'cryptographic' can be left out if the rouines from the library
  36  *    being used are not cryptographic related :-).
  37  * 4. If you include any Windows specific code (or a derivative thereof) from
  38  *    the apps directory (application code) you must include an acknowledgement:
  39  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  40  *
  41  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  42  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  43  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  44  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  45  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  46  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  47  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  48  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  49  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  50  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  51  * SUCH DAMAGE.
  52  *
  53  * The licence and distribution terms for any publically available version or
  54  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  55  * copied and put under another distribution licence
  56  * [including the GNU Public Licence.]
  57  */
  58 /* ====================================================================
  59  * Copyright (c) 1998-2000 The OpenSSL Project.  All rights reserved.
  60  *
  61  * Redistribution and use in source and binary forms, with or without
  62  * modification, are permitted provided that the following conditions
  63  * are met:
  64  *
  65  * 1. Redistributions of source code must retain the above copyright
  66  *    notice, this list of conditions and the following disclaimer.
  67  *
  68  * 2. Redistributions in binary form must reproduce the above copyright
  69  *    notice, this list of conditions and the following disclaimer in
  70  *    the documentation and/or other materials provided with the
  71  *    distribution.
  72  *
  73  * 3. All advertising materials mentioning features or use of this
  74  *    software must display the following acknowledgment:
  75  *    "This product includes software developed by the OpenSSL Project
  76  *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
  77  *
  78  * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
  79  *    endorse or promote products derived from this software without
  80  *    prior written permission. For written permission, please contact
  81  *    openssl-core@openssl.org.
  82  *
  83  * 5. Products derived from this software may not be called "OpenSSL"
  84  *    nor may "OpenSSL" appear in their names without prior written
  85  *    permission of the OpenSSL Project.
  86  *
  87  * 6. Redistributions of any form whatsoever must retain the following
  88  *    acknowledgment:
  89  *    "This product includes software developed by the OpenSSL Project
  90  *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
  91  *
  92  * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
  93  * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  94  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  95  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
  96  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  97  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  98  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  99  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 100  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 101  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 102  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 103  * OF THE POSSIBILITY OF SUCH DAMAGE.
 104  * ====================================================================
 105  *
 106  * This product includes cryptographic software written by Eric Young
 107  * (eay@cryptsoft.com).  This product includes software written by Tim
 108  * Hudson (tjh@cryptsoft.com).
 109  *
 110  */
 111
 112 #ifndef HEADER_BN_LCL_H
 113 #define HEADER_BN_LCL_H
 114
 115 #include <openssl/opensslconf.h>
 116
 117 #include <openssl/bn.h>
 118
 119 __BEGIN_HIDDEN_DECLS
 120
 121 /*
 122  * BN_window_bits_for_exponent_size -- macro for sliding window mod_exp functions
 123  *
 124  *
 125  * For window size 'w' (w >= 2) and a random 'b' bits exponent,
 126  * the number of multiplications is a constant plus on average
 127  *
 128  *    2^(w-1) + (b-w)/(w+1);
 129  *
 130  * here  2^(w-1)  is for precomputing the table (we actually need
 131  * entries only for windows that have the lowest bit set), and
 132  * (b-w)/(w+1)  is an approximation for the expected number of
 133  * w-bit windows, not counting the first one.
 134  *
 135  * Thus we should use
 136  *
 137  *    w >= 6  if        b > 671
 138  *     w = 5  if  671 > b > 239
 139  *     w = 4  if  239 > b >  79
 140  *     w = 3  if   79 > b >  23
 141  *    w <= 2  if   23 > b
 142  *
 143  * (with draws in between).  Very small exponents are often selected
 144  * with low Hamming weight, so we use  w = 1  for b <= 23.
 145  */
 146 #define BN_window_bits_for_exponent_size(b) \
 147                 ((b) > 671 ? 6 : \
 148                  (b) > 239 ? 5 : \
 149                  (b) >  79 ? 4 : \
 150                  (b) >  23 ? 3 : 1)
 151
 152
 153 /* BN_mod_exp_mont_consttime is based on the assumption that the
 154  * L1 data cache line width of the target processor is at least
 155  * the following value.
 156  */
 157 #define MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH      ( 64 )
 158 #define MOD_EXP_CTIME_MIN_CACHE_LINE_MASK       (MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH - 1)
 159
 160 /* Window sizes optimized for fixed window size modular exponentiation
 161  * algorithm (BN_mod_exp_mont_consttime).
 162  *
 163  * To achieve the security goals of BN_mode_exp_mont_consttime, the
 164  * maximum size of the window must not exceed
 165  * log_2(MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH).
 166  *
 167  * Window size thresholds are defined for cache line sizes of 32 and 64,
 168  * cache line sizes where log_2(32)=5 and log_2(64)=6 respectively. A
 169  * window size of 7 should only be used on processors that have a 128
 170  * byte or greater cache line size.
 171  */
 172 #if MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH == 64
 173
 174 #  define BN_window_bits_for_ctime_exponent_size(b) \
 175                 ((b) > 937 ? 6 : \
 176                  (b) > 306 ? 5 : \
 177                  (b) >  89 ? 4 : \
 178                  (b) >  22 ? 3 : 1)
 179 #  define BN_MAX_WINDOW_BITS_FOR_CTIME_EXPONENT_SIZE    (6)
 180
 181 #elif MOD_EXP_CTIME_MIN_CACHE_LINE_WIDTH == 32
 182
 183 #  define BN_window_bits_for_ctime_exponent_size(b) \
 184                 ((b) > 306 ? 5 : \
 185                  (b) >  89 ? 4 : \
 186                  (b) >  22 ? 3 : 1)
 187 #  define BN_MAX_WINDOW_BITS_FOR_CTIME_EXPONENT_SIZE    (5)
 188
 189 #endif
 190
 191
 192 /* Pentium pro 16,16,16,32,64 */
 193 /* Alpha       16,16,16,16.64 */
 194 #define BN_MULL_SIZE_NORMAL                     (16) /* 32 */
 195 #define BN_MUL_RECURSIVE_SIZE_NORMAL            (16) /* 32 less than */
 196 #define BN_SQR_RECURSIVE_SIZE_NORMAL            (16) /* 32 */
 197 #define BN_MUL_LOW_RECURSIVE_SIZE_NORMAL        (32) /* 32 */
 198 #define BN_MONT_CTX_SET_SIZE_WORD               (64) /* 32 */
 199
 200 #if !defined(OPENSSL_NO_ASM) && !defined(OPENSSL_NO_INLINE_ASM)
 201 /*
 202  * BN_UMULT_HIGH section.
 203  *
 204  * No, I'm not trying to overwhelm you when stating that the
 205  * product of N-bit numbers is 2*N bits wide:-) No, I don't expect
 206  * you to be impressed when I say that if the compiler doesn't
 207  * support 2*N integer type, then you have to replace every N*N
 208  * multiplication with 4 (N/2)*(N/2) accompanied by some shifts
 209  * and additions which unavoidably results in severe performance
 210  * penalties. Of course provided that the hardware is capable of
 211  * producing 2*N result... That's when you normally start
 212  * considering assembler implementation. However! It should be
 213  * pointed out that some CPUs (most notably Alpha, PowerPC and
 214  * upcoming IA-64 family:-) provide *separate* instruction
 215  * calculating the upper half of the product placing the result
 216  * into a general purpose register. Now *if* the compiler supports
 217  * inline assembler, then it's not impossible to implement the
 218  * "bignum" routines (and have the compiler optimize 'em)
 219  * exhibiting "native" performance in C. That's what BN_UMULT_HIGH
 220  * macro is about:-)
 221  *
 222  *                                      <appro@fy.chalmers.se>
 223  */
 224 # if defined(__alpha)
 225 #  if defined(__GNUC__) && __GNUC__>=2
 226 #   define BN_UMULT_HIGH(a,b)   ({      \
 227         BN_ULONG ret;           \
 228         asm ("umulh     %1,%2,%0"       \
 229              : "=r"(ret)                \
 230              : "r"(a), "r"(b));         \
 231         ret;                    })
 232 #  endif        /* compiler */
 233 # elif defined(_ARCH_PPC) && defined(_LP64)
 234 #  if defined(__GNUC__) && __GNUC__>=2
 235 #   define BN_UMULT_HIGH(a,b)   ({      \
 236         BN_ULONG ret;           \
 237         asm ("mulhdu    %0,%1,%2"       \
 238              : "=r"(ret)                \
 239              : "r"(a), "r"(b));         \
 240         ret;                    })
 241 #  endif        /* compiler */
 242 # elif defined(__x86_64) || defined(__x86_64__)
 243 #  if defined(__GNUC__) && __GNUC__>=2
 244 #   define BN_UMULT_HIGH(a,b)   ({      \
 245         BN_ULONG ret,discard;   \
 246         asm ("mulq      %3"             \
 247              : "=a"(discard),"=d"(ret)  \
 248              : "a"(a), "g"(b)           \
 249              : "cc");                   \
 250         ret;                    })
 251 #   define BN_UMULT_LOHI(low,high,a,b)  \
 252         asm ("mulq      %3"             \
 253                 : "=a"(low),"=d"(high)  \
 254                 : "a"(a),"g"(b)         \
 255                 : "cc");
 256 #  endif
 257 # elif defined(__mips) && defined(_LP64)
 258 #  if defined(__GNUC__) && __GNUC__>=2
 259 #   if __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 4) /* "h" constraint is no more since 4.4 */
 260 #     define BN_UMULT_HIGH(a,b)          (((__uint128_t)(a)*(b))>>64)
 261 #     define BN_UMULT_LOHI(low,high,a,b) ({     \
 262         __uint128_t ret=(__uint128_t)(a)*(b);   \
 263         (high)=ret>>64; (low)=ret;       })
 264 #   else
 265 #     define BN_UMULT_HIGH(a,b) ({      \
 266         BN_ULONG ret;           \
 267         asm ("dmultu    %1,%2"          \
 268              : "=h"(ret)                \
 269              : "r"(a), "r"(b) : "l");   \
 270         ret;                    })
 271 #     define BN_UMULT_LOHI(low,high,a,b)\
 272         asm ("dmultu    %2,%3"          \
 273              : "=l"(low),"=h"(high)     \
 274              : "r"(a), "r"(b));
 275 #    endif
 276 #  endif
 277 # endif         /* cpu */
 278 #endif          /* OPENSSL_NO_ASM */
 279
 280 /*************************************************************
 281  * Using the long long type
 282  */
 283 #define Lw(t)    (((BN_ULONG)(t))&BN_MASK2)
 284 #define Hw(t)    (((BN_ULONG)((t)>>BN_BITS2))&BN_MASK2)
 285
 286 #ifdef BN_DEBUG_RAND
 287 #define bn_clear_top2max(a) \
 288         { \
 289         int      ind = (a)->dmax - (a)->top; \
 290         BN_ULONG *ftl = &(a)->d[(a)->top-1]; \
 291         for (; ind != 0; ind--) \
 292                 *(++ftl) = 0x0; \
 293         }
 294 #else
 295 #define bn_clear_top2max(a)
 296 #endif
 297
 298 #ifdef BN_LLONG
 299 #define mul_add(r,a,w,c) { \
 300         BN_ULLONG t; \
 301         t=(BN_ULLONG)w * (a) + (r) + (c); \
 302         (r)= Lw(t); \
 303         (c)= Hw(t); \
 304         }
 305
 306 #define mul(r,a,w,c) { \
 307         BN_ULLONG t; \
 308         t=(BN_ULLONG)w * (a) + (c); \
 309         (r)= Lw(t); \
 310         (c)= Hw(t); \
 311         }
 312
 313 #define sqr(r0,r1,a) { \
 314         BN_ULLONG t; \
 315         t=(BN_ULLONG)(a)*(a); \
 316         (r0)=Lw(t); \
 317         (r1)=Hw(t); \
 318         }
 319
 320 #elif defined(BN_UMULT_LOHI)
 321 #define mul_add(r,a,w,c) {              \
 322         BN_ULONG high,low,ret,tmp=(a);  \
 323         ret =  (r);                     \
 324         BN_UMULT_LOHI(low,high,w,tmp);  \
 325         ret += (c);                     \
 326         (c) =  (ret<(c))?1:0;           \
 327         (c) += high;                    \
 328         ret += low;                     \
 329         (c) += (ret<low)?1:0;           \
 330         (r) =  ret;                     \
 331         }
 332
 333 #define mul(r,a,w,c)    {               \
 334         BN_ULONG high,low,ret,ta=(a);   \
 335         BN_UMULT_LOHI(low,high,w,ta);   \
 336         ret =  low + (c);               \
 337         (c) =  high;                    \
 338         (c) += (ret<low)?1:0;           \
 339         (r) =  ret;                     \
 340         }
 341
 342 #define sqr(r0,r1,a)    {               \
 343         BN_ULONG tmp=(a);               \
 344         BN_UMULT_LOHI(r0,r1,tmp,tmp);   \
 345         }
 346
 347 #elif defined(BN_UMULT_HIGH)
 348 #define mul_add(r,a,w,c) {              \
 349         BN_ULONG high,low,ret,tmp=(a);  \
 350         ret =  (r);                     \
 351         high=  BN_UMULT_HIGH(w,tmp);    \
 352         ret += (c);                     \
 353         low =  (w) * tmp;               \
 354         (c) =  (ret<(c))?1:0;           \
 355         (c) += high;                    \
 356         ret += low;                     \
 357         (c) += (ret<low)?1:0;           \
 358         (r) =  ret;                     \
 359         }
 360
 361 #define mul(r,a,w,c)    {               \
 362         BN_ULONG high,low,ret,ta=(a);   \
 363         low =  (w) * ta;                \
 364         high=  BN_UMULT_HIGH(w,ta);     \
 365         ret =  low + (c);               \
 366         (c) =  high;                    \
 367         (c) += (ret<low)?1:0;           \
 368         (r) =  ret;                     \
 369         }
 370
 371 #define sqr(r0,r1,a)    {               \
 372         BN_ULONG tmp=(a);               \
 373         (r0) = tmp * tmp;               \
 374         (r1) = BN_UMULT_HIGH(tmp,tmp);  \
 375         }
 376
 377 #else
 378 /*************************************************************
 379  * No long long type
 380  */
 381
 382 #define LBITS(a)        ((a)&BN_MASK2l)
 383 #define HBITS(a)        (((a)>>BN_BITS4)&BN_MASK2l)
 384 #define L2HBITS(a)      (((a)<<BN_BITS4)&BN_MASK2)
 385
 386 #define mul64(l,h,bl,bh) \
 387         { \
 388         BN_ULONG m,m1,lt,ht; \
 389  \
 390         lt=l; \
 391         ht=h; \
 392         m =(bh)*(lt); \
 393         lt=(bl)*(lt); \
 394         m1=(bl)*(ht); \
 395         ht =(bh)*(ht); \
 396         m=(m+m1)&BN_MASK2; if (m < m1) ht+=L2HBITS((BN_ULONG)1); \
 397         ht+=HBITS(m); \
 398         m1=L2HBITS(m); \
 399         lt=(lt+m1)&BN_MASK2; if (lt < m1) ht++; \
 400         (l)=lt; \
 401         (h)=ht; \
 402         }
 403
 404 #define sqr64(lo,ho,in) \
 405         { \
 406         BN_ULONG l,h,m; \
 407  \
 408         h=(in); \
 409         l=LBITS(h); \
 410         h=HBITS(h); \
 411         m =(l)*(h); \
 412         l*=l; \
 413         h*=h; \
 414         h+=(m&BN_MASK2h1)>>(BN_BITS4-1); \
 415         m =(m&BN_MASK2l)<<(BN_BITS4+1); \
 416         l=(l+m)&BN_MASK2; if (l < m) h++; \
 417         (lo)=l; \
 418         (ho)=h; \
 419         }
 420
 421 #define mul_add(r,a,bl,bh,c) { \
 422         BN_ULONG l,h; \
 423  \
 424         h= (a); \
 425         l=LBITS(h); \
 426         h=HBITS(h); \
 427         mul64(l,h,(bl),(bh)); \
 428  \
 429         /* non-multiply part */ \
 430         l=(l+(c))&BN_MASK2; if (l < (c)) h++; \
 431         (c)=(r); \
 432         l=(l+(c))&BN_MASK2; if (l < (c)) h++; \
 433         (c)=h&BN_MASK2; \
 434         (r)=l; \
 435         }
 436
 437 #define mul(r,a,bl,bh,c) { \
 438         BN_ULONG l,h; \
 439  \
 440         h= (a); \
 441         l=LBITS(h); \
 442         h=HBITS(h); \
 443         mul64(l,h,(bl),(bh)); \
 444  \
 445         /* non-multiply part */ \
 446         l+=(c); if ((l&BN_MASK2) < (c)) h++; \
 447         (c)=h&BN_MASK2; \
 448         (r)=l&BN_MASK2; \
 449         }
 450 #endif /* !BN_LLONG */
 451
 452 void bn_mul_normal(BN_ULONG *r, BN_ULONG *a, int na, BN_ULONG *b, int nb);
 453 void bn_mul_comba8(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b);
 454 void bn_mul_comba4(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b);
 455 void bn_sqr_normal(BN_ULONG *r, const BN_ULONG *a, int n, BN_ULONG *tmp);
 456 void bn_sqr_comba8(BN_ULONG *r, const BN_ULONG *a);
 457 void bn_sqr_comba4(BN_ULONG *r, const BN_ULONG *a);
 458 int bn_cmp_words(const BN_ULONG *a, const BN_ULONG *b, int n);
 459 int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b,
 460     int cl, int dl);
 461 void bn_mul_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n2,
 462     int dna, int dnb, BN_ULONG *t);
 463 void bn_mul_part_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b,
 464     int n, int tna, int tnb, BN_ULONG *t);
 465 void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t);
 466 void bn_mul_low_normal(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n);
 467 void bn_mul_low_recursive(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, int n2,
 468     BN_ULONG *t);
 469 void bn_mul_high(BN_ULONG *r, BN_ULONG *a, BN_ULONG *b, BN_ULONG *l, int n2,
 470     BN_ULONG *t);
 471 BN_ULONG bn_add_part_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
 472     int cl, int dl);
 473 BN_ULONG bn_sub_part_words(BN_ULONG *r, const BN_ULONG *a, const BN_ULONG *b,
 474     int cl, int dl);
 475 int bn_mul_mont(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp, const BN_ULONG *np, const BN_ULONG *n0, int num);
 476
 477 #define bn_wexpand(a,words) (((words) <= (a)->dmax)?(a):bn_expand2((a),(words)))
 478 BIGNUM *bn_expand2(BIGNUM *a, int words);
 479 BIGNUM *bn_expand(BIGNUM *a, int bits);
 480
 481 BIGNUM *bn_dup_expand(const BIGNUM *a, int words); /* unused */
 482
 483 /* Bignum consistency macros
 484  * There is one "API" macro, bn_fix_top(), for stripping leading zeroes from
 485  * bignum data after direct manipulations on the data. There is also an
 486  * "internal" macro, bn_check_top(), for verifying that there are no leading
 487  * zeroes. Unfortunately, some auditing is required due to the fact that
 488  * bn_fix_top() has become an overabused duct-tape because bignum data is
 489  * occasionally passed around in an inconsistent state. So the following
 490  * changes have been made to sort this out;
 491  * - bn_fix_top()s implementation has been moved to bn_correct_top()
 492  * - if BN_DEBUG isn't defined, bn_fix_top() maps to bn_correct_top(), and
 493  *   bn_check_top() is as before.
 494  * - if BN_DEBUG *is* defined;
 495  *   - bn_check_top() tries to pollute unused words even if the bignum 'top' is
 496  *     consistent. (ed: only if BN_DEBUG_RAND is defined)
 497  *   - bn_fix_top() maps to bn_check_top() rather than "fixing" anything.
 498  * The idea is to have debug builds flag up inconsistent bignums when they
 499  * occur. If that occurs in a bn_fix_top(), we examine the code in question; if
 500  * the use of bn_fix_top() was appropriate (ie. it follows directly after code
 501  * that manipulates the bignum) it is converted to bn_correct_top(), and if it
 502  * was not appropriate, we convert it permanently to bn_check_top() and track
 503  * down the cause of the bug. Eventually, no internal code should be using the
 504  * bn_fix_top() macro. External applications and libraries should try this with
 505  * their own code too, both in terms of building against the openssl headers
 506  * with BN_DEBUG defined *and* linking with a version of OpenSSL built with it
 507  * defined. This not only improves external code, it provides more test
 508  * coverage for openssl's own code.
 509  */
 510
 511 #ifdef BN_DEBUG
 512
 513 /* We only need assert() when debugging */
 514 #include <assert.h>
 515
 516 #ifdef BN_DEBUG_RAND
 517 #define bn_pollute(a) \
 518         do { \
 519                 const BIGNUM *_bnum1 = (a); \
 520                 if(_bnum1->top < _bnum1->dmax) { \
 521                         unsigned char _tmp_char; \
 522                         /* We cast away const without the compiler knowing, any \
 523                          * *genuinely* constant variables that aren't mutable \
 524                          * wouldn't be constructed with top!=dmax. */ \
 525                         BN_ULONG *_not_const; \
 526                         memcpy(&_not_const, &_bnum1->d, sizeof(BN_ULONG*)); \
 527                         arc4random_buf(&_tmp_char, 1); \
 528                         memset((unsigned char *)(_not_const + _bnum1->top), _tmp_char, \
 529                                 (_bnum1->dmax - _bnum1->top) * sizeof(BN_ULONG)); \
 530                 } \
 531         } while(0)
 532 #else
 533 #define bn_pollute(a)
 534 #endif
 535
 536 #define bn_check_top(a) \
 537         do { \
 538                 const BIGNUM *_bnum2 = (a); \
 539                 if (_bnum2 != NULL) { \
 540                         assert((_bnum2->top == 0) || \
 541                                 (_bnum2->d[_bnum2->top - 1] != 0)); \
 542                         bn_pollute(_bnum2); \
 543                 } \
 544         } while(0)
 545
 546 #define bn_fix_top(a)           bn_check_top(a)
 547
 548 #define bn_check_size(bn, bits) bn_wcheck_size(bn, ((bits+BN_BITS2-1))/BN_BITS2)
 549 #define bn_wcheck_size(bn, words) \
 550         do { \
 551                 const BIGNUM *_bnum2 = (bn); \
 552                 assert(words <= (_bnum2)->dmax && words >= (_bnum2)->top); \
 553         } while(0)
 554
 555 #else /* !BN_DEBUG */
 556
 557 #define bn_pollute(a)
 558 #define bn_check_top(a)
 559 #define bn_fix_top(a)           bn_correct_top(a)
 560 #define bn_check_size(bn, bits)
 561 #define bn_wcheck_size(bn, words)
 562
 563 #endif
 564
 565 #define bn_correct_top(a) \
 566         { \
 567         BN_ULONG *ftl; \
 568         int tmp_top = (a)->top; \
 569         if (tmp_top > 0) \
 570                 { \
 571                 for (ftl= &((a)->d[tmp_top-1]); tmp_top > 0; tmp_top--) \
 572                         if (*(ftl--)) break; \
 573                 (a)->top = tmp_top; \
 574                 } \
 575         bn_pollute(a); \
 576         }
 577
 578 BN_ULONG bn_mul_add_words(BN_ULONG *rp, const BN_ULONG *ap, int num, BN_ULONG w);
 579 BN_ULONG bn_mul_words(BN_ULONG *rp, const BN_ULONG *ap, int num, BN_ULONG w);
 580 void     bn_sqr_words(BN_ULONG *rp, const BN_ULONG *ap, int num);
 581 BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d);
 582 BN_ULONG bn_add_words(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp, int num);
 583 BN_ULONG bn_sub_words(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp, int num);
 584
 585 int BN_bntest_rand(BIGNUM *rnd, int bits, int top, int bottom);
 586
 587 /* Explicitly const time / non-const time versions for internal use */
 588 int BN_mod_exp_ct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
 589     const BIGNUM *m, BN_CTX *ctx);
 590 int BN_mod_exp_nonct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
 591     const BIGNUM *m, BN_CTX *ctx);
 592 int BN_mod_exp_mont_ct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
 593     const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
 594 int BN_mod_exp_mont_nonct(BIGNUM *r, const BIGNUM *a, const BIGNUM *p,
 595     const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
 596 int BN_div_nonct(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
 597     BN_CTX *ctx);
 598 int BN_div_ct(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
 599     BN_CTX *ctx);
 600 #define BN_mod_ct(rem,m,d,ctx) BN_div_ct(NULL,(rem),(m),(d),(ctx))
 601 #define BN_mod_nonct(rem,m,d,ctx) BN_div_nonct(NULL,(rem),(m),(d),(ctx))
 602 BIGNUM *BN_mod_inverse_ct(BIGNUM *ret, const BIGNUM *a, const BIGNUM *n,
 603     BN_CTX *ctx);
 604 BIGNUM *BN_mod_inverse_nonct(BIGNUM *ret, const BIGNUM *a, const BIGNUM *n,
 605     BN_CTX *ctx);
 606 int     BN_gcd_ct(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
 607 int     BN_gcd_nonct(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
 608 __END_HIDDEN_DECLS
 609 #endif