linux-kernel - [PATCH v2 05/14] crypto: ecc - For NIST P521 use vli_num

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Date: Thu, 15 Feb 2024 18:14:04 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        herbert@...dor.apana.org.au, davem@...emloft.net
Cc: linux-kernel@...r.kernel.org, saulo.alessandre@....jus.br,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: [PATCH v2 05/14] crypto: ecc - For NIST P521 use vli_num_bits to get number of bits

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@...ux.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