Fix for CVE-2014-0076

[openssl.git] / crypto / bn / bn_lib.c

diff --git a/crypto/bn/bn_lib.c b/crypto/bn/bn_lib.c
index 5470fbe6ef374721ef58c1fb801ef34f7a3e7f8f..5461e6ee7dbee4d84e346fb6ee232dda1a00a916 100644 (file)
--- a/crypto/bn/bn_lib.c
+++ b/crypto/bn/bn_lib.c
@@ -139,25 +139,6 @@ const BIGNUM *BN_value_one(void)
        return(&const_one);
        }
 
-char *BN_options(void)
-       {
-       static int init=0;
-       static char data[16];
-
-       if (!init)
-               {
-               init++;
-#ifdef BN_LLONG
-               BIO_snprintf(data,sizeof data,"bn(%d,%d)",
-                            (int)sizeof(BN_ULLONG)*8,(int)sizeof(BN_ULONG)*8);
-#else
-               BIO_snprintf(data,sizeof data,"bn(%d,%d)",
-                            (int)sizeof(BN_ULONG)*8,(int)sizeof(BN_ULONG)*8);
-#endif
-               }
-       return(data);
-       }
-
 int BN_num_bits_word(BN_ULONG l)
        {
        static const unsigned char bits[256]={
@@ -843,3 +824,55 @@ int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b,
                }
        return bn_cmp_words(a,b,cl);
        }
+
+/* 
+ * Constant-time conditional swap of a and b.  
+ * a and b are swapped if condition is not 0.  The code assumes that at most one bit of condition is set.
+ * nwords is the number of words to swap.  The code assumes that at least nwords are allocated in both a and b,
+ * and that no more than nwords are used by either a or b.
+ * a and b cannot be the same number
+ */
+void BN_consttime_swap(BN_ULONG condition, BIGNUM *a, BIGNUM *b, int nwords)
+       {
+       BN_ULONG t;
+       int i;
+
+       bn_wcheck_size(a, nwords);
+       bn_wcheck_size(b, nwords);
+
+       assert(a != b);
+       assert((condition & (condition - 1)) == 0);
+       assert(sizeof(BN_ULONG) >= sizeof(int));
+
+       condition = ((condition - 1) >> (BN_BITS2 - 1)) - 1;
+
+       t = (a->top^b->top) & condition;
+       a->top ^= t;
+       b->top ^= t;
+
+#define BN_CONSTTIME_SWAP(ind) \
+       do { \
+               t = (a->d[ind] ^ b->d[ind]) & condition; \
+               a->d[ind] ^= t; \
+               b->d[ind] ^= t; \
+       } while (0)
+
+
+       switch (nwords) {
+       default:
+               for (i = 10; i < nwords; i++) 
+                       BN_CONSTTIME_SWAP(i);
+               /* Fallthrough */
+       case 10: BN_CONSTTIME_SWAP(9); /* Fallthrough */
+       case 9: BN_CONSTTIME_SWAP(8); /* Fallthrough */
+       case 8: BN_CONSTTIME_SWAP(7); /* Fallthrough */
+       case 7: BN_CONSTTIME_SWAP(6); /* Fallthrough */
+       case 6: BN_CONSTTIME_SWAP(5); /* Fallthrough */
+       case 5: BN_CONSTTIME_SWAP(4); /* Fallthrough */
+       case 4: BN_CONSTTIME_SWAP(3); /* Fallthrough */
+       case 3: BN_CONSTTIME_SWAP(2); /* Fallthrough */
+       case 2: BN_CONSTTIME_SWAP(1); /* Fallthrough */
+       case 1: BN_CONSTTIME_SWAP(0);
+       }
+#undef BN_CONSTTIME_SWAP
+}