Git-commit: ea169a30a6bf6782a05a51d2b9cf73db151eab8b
From: Stephan Mueller <smueller@chronox.de>
Date: Mon, 25 Jun 2018 12:00:18 +0200
Subject: [PATCH] crypto: ecdh - add public key verification test
Patch-mainline: v4.19-rc1
References: bsc#1155331

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 <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Torsten Duwe <duwe@suse.de>
---
 crypto/ecc.c            | 42 ++++++++++++++++++++++++++++++++++++++----
 crypto/ecc_curve_defs.h | 22 ++++++++++++++++++----
 2 files changed, 56 insertions(+), 8 deletions(-)

--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -966,6 +966,36 @@ out:
 	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 u8 *private_key, unsigned int private_key_len,
 		       const u8 *public_key, unsigned int public_key_len,
@@ -993,16 +1023,20 @@ int crypto_ecdh_shared_secret(unsigned i
 		goto out;
 	}
 
+	ecc_swap_digits((const u64 *)public_key, pk->x, ndigits);
+	ecc_swap_digits((const u64 *)&public_key[nbytes], pk->y, ndigits);
+	ret = ecc_is_pubkey_valid_partial(curve, pk);
+	if (ret)
+		goto err_alloc_product;
+
+	ecc_swap_digits((const u64 *)private_key, priv, ndigits);
+
 	product = ecc_alloc_point(ndigits);
 	if (!product) {
 		ret = -ENOMEM;
 		goto err_alloc_product;
 	}
 
-	ecc_swap_digits((const u64 *)public_key, pk->x, ndigits);
-	ecc_swap_digits((const u64 *)&public_key[nbytes], pk->y, ndigits);
-	ecc_swap_digits((const u64 *)private_key, priv, ndigits);
-
 	ecc_point_mult(product, pk, priv, rand_z, curve->p, ndigits);
 
 	ecc_swap_digits(product->x, (u64 *)secret, ndigits);
--- a/crypto/ecc_curve_defs.h
+++ b/crypto/ecc_curve_defs.h
@@ -12,9 +12,11 @@ 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,
@@ -23,6 +25,10 @@ static u64 nist_p192_p[] = { 0xFFFFFFFFF
 				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 = {
@@ -31,10 +37,12 @@ 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,
@@ -43,6 +51,10 @@ static u64 nist_p256_p[] = { 0xFFFFFFFFF
 				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 = {
@@ -51,7 +63,9 @@ 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
