Commit 6fb60a84 authored by Bodo Möller's avatar Bodo Möller
Browse files

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

really the square of the return value.
parent 5af7d1a3

CHANGES

+5 −0
Original line number Diff line number Diff line
@@ -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.

crypto/bn/bn_sqrt.c

+31 −18
Original line number Diff line number Diff line
@@ -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)

		{

crypto/ec/ecp_smpl.c

+1 −2
Original line number Diff line number Diff line
@@ -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;

			}