[PATCH v2 05/14] crypto: ecc - For NIST P521 use vli_num_bits to get number of bits

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,
	Stefan Berger <stefanb@linux.ibm.com>
Subject: [PATCH v2 05/14] crypto: ecc - For NIST P521 use vli_num_bits to get number of bits
Date: Thu, 15 Feb 2024 18:14:04 -0500	[thread overview]
Message-ID: <20240215231414.3857320-6-stefanb@linux.ibm.com> (raw)
In-Reply-To: <20240215231414.3857320-1-stefanb@linux.ibm.com>

In ecc_point_mult use vli_num_bits to determine the number of bits when
using NIST P521. 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>
---
 crypto/ecc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index ea7b28b5e00e..0734cea284a4 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 (ndigits == 9 && !strcmp(curve->name, "nist_521"))
+		num_bits = vli_num_bits(scalar, ndigits);
+	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

