crypto: ecdh - add public key verification test

According to SP800-56A section 5.6.2.1, the public key to be processed for the ECDH operation shall be checked for appropriateness. When the public key is considered to be an ephemeral key, the partial validation test as defined in SP800-56A section 5.6.2.3.4 can be applied. The partial verification test requires the presence of the field elements of a and b. For the implemented NIST curves, b is defined in FIPS 186-4 appendix D.1.2. The element a is implicitly given with the Weierstrass equation given in D.1.2 where a = p - 3. Without the test, the NIST ACVP testing fails. After adding this check, the NIST ACVP testing passes. Signed-off-by: Stephan Mueller <[email protected]> Signed-off-by: Herbert Xu <[email protected]>
soumdtt · Jul 8, 2018 · ea169a3 · ea169a3
1 parent e4e4730
commit ea169a3
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Showing 2 changed files with 56 additions and 8 deletions.
diff --git a/crypto/ecc.c b/crypto/ecc.c
@@ -1019,6 +1019,36 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits,
 	return ret;
 }
 
+/* SP800-56A section 5.6.2.3.4 partial verification: ephemeral keys only */
+static int ecc_is_pubkey_valid_partial(const struct ecc_curve *curve,
+				       struct ecc_point *pk)
+{
+	u64 yy[ECC_MAX_DIGITS], xxx[ECC_MAX_DIGITS], w[ECC_MAX_DIGITS];
+
+	/* Check 1: Verify key is not the zero point. */
+	if (ecc_point_is_zero(pk))
+		return -EINVAL;
+
+	/* Check 2: Verify key is in the range [1, p-1]. */
+	if (vli_cmp(curve->p, pk->x, pk->ndigits) != 1)
+		return -EINVAL;
+	if (vli_cmp(curve->p, pk->y, pk->ndigits) != 1)
+		return -EINVAL;
+
+	/* Check 3: Verify that y^2 == (x^3 + a·x + b) mod p */
+	vli_mod_square_fast(yy, pk->y, curve->p, pk->ndigits); /* y^2 */
+	vli_mod_square_fast(xxx, pk->x, curve->p, pk->ndigits); /* x^2 */
+	vli_mod_mult_fast(xxx, xxx, pk->x, curve->p, pk->ndigits); /* x^3 */
+	vli_mod_mult_fast(w, curve->a, pk->x, curve->p, pk->ndigits); /* a·x */
+	vli_mod_add(w, w, curve->b, curve->p, pk->ndigits); /* a·x + b */
+	vli_mod_add(w, w, xxx, curve->p, pk->ndigits); /* x^3 + a·x + b */
+	if (vli_cmp(yy, w, pk->ndigits) != 0) /* Equation */
+		return -EINVAL;
+
+	return 0;
+
+}
+
 int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 			      const u64 *private_key, const u64 *public_key,
 			      u64 *secret)
@@ -1046,16 +1076,20 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 		goto out;
 	}
 
+	ecc_swap_digits(public_key, pk->x, ndigits);
+	ecc_swap_digits(&public_key[ndigits], pk->y, ndigits);
+	ret = ecc_is_pubkey_valid_partial(curve, pk);
+	if (ret)
+		goto err_alloc_product;
+
+	ecc_swap_digits(private_key, priv, ndigits);
+
 	product = ecc_alloc_point(ndigits);
 	if (!product) {
 		ret = -ENOMEM;
 		goto err_alloc_product;
 	}
 
-	ecc_swap_digits(public_key, pk->x, ndigits);
-	ecc_swap_digits(&public_key[ndigits], pk->y, ndigits);
-	ecc_swap_digits(private_key, priv, ndigits);
-
 	ecc_point_mult(product, pk, priv, rand_z, curve->p, ndigits);
 
 	ecc_swap_digits(product->x, secret, ndigits);

diff --git a/crypto/ecc_curve_defs.h b/crypto/ecc_curve_defs.h
@@ -13,9 +13,11 @@ struct ecc_curve {
 	struct ecc_point g;
 	u64 *p;
 	u64 *n;
+	u64 *a;
+	u64 *b;
 };
 
-/* NIST P-192 */
+/* NIST P-192: a = p - 3 */
 static u64 nist_p192_g_x[] = { 0xF4FF0AFD82FF1012ull, 0x7CBF20EB43A18800ull,
 				0x188DA80EB03090F6ull };
 static u64 nist_p192_g_y[] = { 0x73F977A11E794811ull, 0x631011ED6B24CDD5ull,
@@ -24,6 +26,10 @@ static u64 nist_p192_p[] = { 0xFFFFFFFFFFFFFFFFull, 0xFFFFFFFFFFFFFFFEull,
 				0xFFFFFFFFFFFFFFFFull };
 static u64 nist_p192_n[] = { 0x146BC9B1B4D22831ull, 0xFFFFFFFF99DEF836ull,
 				0xFFFFFFFFFFFFFFFFull };
+static u64 nist_p192_a[] = { 0xFFFFFFFFFFFFFFFCull, 0xFFFFFFFFFFFFFFFEull,
+				0xFFFFFFFFFFFFFFFEull };
+static u64 nist_p192_b[] = { 0xFEB8DEECC146B9B1ull, 0x0FA7E9AB72243049ull,
+				0x64210519E59C80E7ull };
 static struct ecc_curve nist_p192 = {
 	.name = "nist_192",
 	.g = {
@@ -32,10 +38,12 @@ static struct ecc_curve nist_p192 = {
 		.ndigits = 3,
 	},
 	.p = nist_p192_p,
-	.n = nist_p192_n
+	.n = nist_p192_n,
+	.a = nist_p192_a,
+	.b = nist_p192_b
 };
 
-/* NIST P-256 */
+/* NIST P-256: a = p - 3 */
 static u64 nist_p256_g_x[] = { 0xF4A13945D898C296ull, 0x77037D812DEB33A0ull,
 				0xF8BCE6E563A440F2ull, 0x6B17D1F2E12C4247ull };
 static u64 nist_p256_g_y[] = { 0xCBB6406837BF51F5ull, 0x2BCE33576B315ECEull,
@@ -44,6 +52,10 @@ static u64 nist_p256_p[] = { 0xFFFFFFFFFFFFFFFFull, 0x00000000FFFFFFFFull,
 				0x0000000000000000ull, 0xFFFFFFFF00000001ull };
 static u64 nist_p256_n[] = { 0xF3B9CAC2FC632551ull, 0xBCE6FAADA7179E84ull,
 				0xFFFFFFFFFFFFFFFFull, 0xFFFFFFFF00000000ull };
+static u64 nist_p256_a[] = { 0xFFFFFFFFFFFFFFFCull, 0x00000000FFFFFFFFull,
+				0x0000000000000000ull, 0xFFFFFFFF00000001ull };
+static u64 nist_p256_b[] = { 0x3BCE3C3E27D2604Bull, 0x651D06B0CC53B0F6ull,
+				0xB3EBBD55769886BCull, 0x5AC635D8AA3A93E7ull };
 static struct ecc_curve nist_p256 = {
 	.name = "nist_256",
 	.g = {
@@ -52,7 +64,9 @@ static struct ecc_curve nist_p256 = {
 		.ndigits = 4,
 	},
 	.p = nist_p256_p,
-	.n = nist_p256_n
+	.n = nist_p256_n,
+	.a = nist_p256_a,
+	.b = nist_p256_b
 };
 
 #endif