avoid potential spurious BN_free()

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

diff --git a/crypto/bn/bn_sqrt.c b/crypto/bn/bn_sqrt.c
index 6e70e5c54140fd3d4060a05c196ebfb39ca5f60f..6beaf9e5e5ddfd6da6942c67b045049a7c979ddb 100644 (file)
--- a/crypto/bn/bn_sqrt.c
+++ b/crypto/bn/bn_sqrt.c
@@ -1,4 +1,4 @@
-/* crypto/bn/bn_mod.c */
+/* crypto/bn/bn_sqrt.c */
 /* Written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>
  * and Bodo Moeller for the OpenSSL project. */
 /* ====================================================================
@@ -70,7 +70,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
        BIGNUM *ret = in;
        int err = 1;
        int r;
-       BIGNUM *b, *q, *t, *x, *y;
+       BIGNUM *A, *b, *q, *t, *x, *y;
        int e, i, j;
        
        if (!BN_is_odd(p) || BN_abs_is_word(p, 1))
@@ -83,9 +83,11 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                                goto end;
                        if (!BN_set_word(ret, BN_is_bit_set(a, 0)))
                                {
-                               BN_free(ret);
+                               if (ret != in)
+                                       BN_free(ret);
                                return NULL;
                                }
+                       bn_check_top(ret);
                        return ret;
                        }
 
@@ -101,23 +103,16 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                        goto end;
                if (!BN_set_word(ret, BN_is_one(a)))
                        {
-                       BN_free(ret);
+                       if (ret != in)
+                               BN_free(ret);
                        return NULL;
                        }
+               bn_check_top(ret);
                return ret;
                }
 
-#if 0 /* if BN_mod_sqrt is used with correct input, this just wastes time */
-       r = BN_kronecker(a, p, ctx);
-       if (r < -1) return NULL;
-       if (r == -1)
-               {
-               BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE);
-               return(NULL);
-               }
-#endif
-
        BN_CTX_start(ctx);
+       A = BN_CTX_get(ctx);
        b = BN_CTX_get(ctx);
        q = BN_CTX_get(ctx);
        t = BN_CTX_get(ctx);
@@ -129,6 +124,9 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                ret = BN_new();
        if (ret == NULL) goto end;
 
+       /* A = a mod p */
+       if (!BN_nnmod(A, a, p, ctx)) goto end;
+
        /* now write  |p| - 1  as  2^e*q  where  q  is odd */
        e = 1;
        while (!BN_is_bit_set(p, e))
@@ -147,9 +145,9 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                if (!BN_rshift(q, p, 2)) goto end;
                q->neg = 0;
                if (!BN_add_word(q, 1)) goto end;
-               if (!BN_mod_exp(ret, a, q, p, ctx)) goto end;
+               if (!BN_mod_exp(ret, A, q, p, ctx)) goto end;
                err = 0;
-               goto end;
+               goto vrfy;
                }
        
        if (e == 2)
@@ -180,15 +178,8 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                 * November 1992.)
                 */
 
-               /* make sure that  a  is reduced modulo p */
-               if (a->neg || BN_ucmp(a, p) >= 0)
-                       {
-                       if (!BN_nnmod(x, a, p, ctx)) goto end;
-                       a = x; /* use x as temporary variable */
-                       }
-
                /* t := 2*a */
-               if (!BN_mod_lshift1_quick(t, a, p)) goto end;
+               if (!BN_mod_lshift1_quick(t, A, p)) goto end;
 
                /* b := (2*a)^((|p|-5)/8) */
                if (!BN_rshift(q, p, 3)) goto end;
@@ -203,12 +194,12 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                if (!BN_sub_word(t, 1)) goto end;
 
                /* x = a*b*t */
-               if (!BN_mod_mul(x, a, b, p, ctx)) goto end;
+               if (!BN_mod_mul(x, A, b, p, ctx)) goto end;
                if (!BN_mod_mul(x, x, t, p, ctx)) goto end;
 
                if (!BN_copy(ret, x)) goto end;
                err = 0;
-               goto end;
+               goto vrfy;
                }
        
        /* e > 2, so we really have to use the Tonelli/Shanks algorithm.
@@ -295,11 +286,11 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
        /* x := a^((q-1)/2) */
        if (BN_is_zero(t)) /* special case: p = 2^e + 1 */
                {
-               if (!BN_nnmod(t, a, p, ctx)) goto end;
+               if (!BN_nnmod(t, A, p, ctx)) goto end;
                if (BN_is_zero(t))
                        {
                        /* special case: a == 0  (mod p) */
-                       if (!BN_zero(ret)) goto end;
+                       BN_zero(ret);
                        err = 0;
                        goto end;
                        }
@@ -308,11 +299,11 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                }
        else
                {
-               if (!BN_mod_exp(x, a, t, p, ctx)) goto end;
+               if (!BN_mod_exp(x, A, t, p, ctx)) goto end;
                if (BN_is_zero(x))
                        {
                        /* special case: a == 0  (mod p) */
-                       if (!BN_zero(ret)) goto end;
+                       BN_zero(ret);
                        err = 0;
                        goto end;
                        }
@@ -320,10 +311,10 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
 
        /* b := a*x^2  (= a^q) */
        if (!BN_mod_sqr(b, x, p, ctx)) goto end;
-       if (!BN_mod_mul(b, b, a, p, ctx)) goto end;
+       if (!BN_mod_mul(b, b, A, p, ctx)) goto end;
        
        /* x := a*x    (= a^((q+1)/2)) */
-       if (!BN_mod_mul(x, x, a, p, ctx)) goto end;
+       if (!BN_mod_mul(x, x, A, p, ctx)) goto end;
 
        while (1)
                {
@@ -340,7 +331,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                        {
                        if (!BN_copy(ret, x)) goto end;
                        err = 0;
-                       goto end;
+                       goto vrfy;
                        }
 
 
@@ -371,6 +362,22 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                e = i;
                }
 
+ vrfy:
+       if (!err)
+               {
+               /* verify the result -- the input might have been not a square
+                * (test added in 0.9.8) */
+               
+               if (!BN_mod_sqr(x, ret, p, ctx))
+                       err = 1;
+               
+               if (!err && 0 != BN_cmp(x, A))
+                       {
+                       BNerr(BN_F_BN_MOD_SQRT, BN_R_NOT_A_SQUARE);
+                       err = 1;
+                       }
+               }
+
  end:
        if (err)
                {
@@ -381,5 +388,6 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
                ret = NULL;
                }
        BN_CTX_end(ctx);
+       bn_check_top(ret);
        return ret;
        }