Change BN_mod_sqrt() so that it verifies that the input value is

really the square of the return value.

diff --git a/CHANGES b/CHANGES
index 1ce30313e45b200cf8627b0a42b1580eba66d053..26c84b059622e47e227d2830a8529a86251afcfb 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,11 @@
 
  Changes between 0.9.7 and 0.9.8  [xx XXX 2002]
 
+  *) Change BN_mod_sqrt() so that it verifies that the input value
+     is really the square of the return value.  (Previously,
+     BN_mod_sqrt would show GIGO behaviour.)
+     [Bodo Moeller]
+
   *) Add named elliptic curves over binary fields from X9.62, SECG,
      and WAP/WTLS; add OIDs that were still missing.
 

diff --git a/crypto/bn/bn_sqrt.c b/crypto/bn/bn_sqrt.c
index e2a1105dc838b2f29b3867f06f653d08a90f368f..52dbc68a131e8859a4f77f0ef06317b1880b1689 100644 (file)
--- a/crypto/bn/bn_sqrt.c
+++ b/crypto/bn/bn_sqrt.c
@@ -72,7 +72,7 @@ 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))
@@ -120,6 +120,7 @@ BIGNUM *BN_mod_sqrt(BIGNUM *in, const BIGNUM *a, const BIGNUM *p, BN_CTX *ctx)
 #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);
@@ -131,6 +132,9 @@ 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))
@@ -149,9 +153,9 @@ 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)
@@ -182,15 +186,8 @@ 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;
@@ -205,12 +202,12 @@ 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.
@@ -297,7 +294,7 @@ 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) */
@@ -310,7 +307,7 @@ 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) */
@@ -322,10 +319,10 @@ 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)
                {
@@ -342,7 +339,7 @@ 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;
                        }
 
 
@@ -373,6 +370,22 @@ 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)
                {

diff --git a/crypto/ec/ecp_smpl.c b/crypto/ec/ecp_smpl.c
index 70fed912a23e1a018a55425584408879cca724a0..97ff8eb61a7bcc0817c4ffb5e96d88d59e452d0e 100644 (file)
--- a/crypto/ec/ecp_smpl.c
+++ b/crypto/ec/ecp_smpl.c
@@ -705,8 +705,6 @@ int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *po
                        ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES, ERR_R_BN_LIB);
                goto err;
                }
-       /* If tmp1 is not a square (i.e. there is no point on the curve with
-        * our x), then y now is a nonsense value too */
 
        if (y_bit != BN_is_odd(y))
                {
@@ -720,6 +718,7 @@ int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *po
                        if (kron == 1)
                                ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES, EC_R_INVALID_COMPRESSION_BIT);
                        else
+                               /* BN_mod_sqrt() should have cought this error (not a square) */
                                ECerr(EC_F_EC_GFP_SIMPLE_SET_COMPRESSED_COORDINATES, EC_R_INVALID_COMPRESSED_POINT);
                        goto err;
                        }