[PATCH v5 06/12] crypto: ecc - Add special case for NIST P521 in ecc_point_mult

From: Stefan Berger <stefanb@linux.ibm.com>
To: keyrings@vger.kernel.org, linux-crypto@vger.kernel.org,
	herbert@gondor.apana.org.au, davem@davemloft.net
Cc: linux-kernel@vger.kernel.org, saulo.alessandre@tse.jus.br,
	lukas@wunner.de, Stefan Berger <stefanb@linux.ibm.com>
Subject: [PATCH v5 06/12] crypto: ecc - Add special case for NIST P521 in ecc_point_mult
Date: Wed,  6 Mar 2024 17:22:51 -0500	[thread overview]
Message-ID: <20240306222257.979304-7-stefanb@linux.ibm.com> (raw)
In-Reply-To: <20240306222257.979304-1-stefanb@linux.ibm.com>

In ecc_point_mult use the number of bits of the NIST P521 curve + 2. The
change is required specifically for NIST P521 to pass mathematical tests
on the public key.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Tested-by: Lukas Wunner <lukas@wunner.de>
---
 crypto/ecc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index 373660e7b19d..55fd390d3386 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1326,7 +1326,10 @@ static void ecc_point_mult(struct ecc_point *result,
 	carry = vli_add(sk[0], scalar, curve->n, ndigits);
 	vli_add(sk[1], sk[0], curve->n, ndigits);
 	scalar = sk[!carry];
-	num_bits = sizeof(u64) * ndigits * 8 + 1;
+	if (curve->nbits == 521)
+		num_bits = curve->nbits + 2;
+	else
+		num_bits = sizeof(u64) * ndigits * 8 + 1;
 
 	vli_set(rx[1], point->x, ndigits);
 	vli_set(ry[1], point->y, ndigits);
-- 
2.43.0

