linux-kernel - [PATCH v8 07/13] crypto: ecc - Add special case for NIST P521 in ecc_point

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Date: Thu,  4 Apr 2024 10:18:50 -0400
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, lukas@...ner.de,
        bbhushan2@...vell.com, jarkko@...nel.org,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: [PATCH v8 07/13] crypto: ecc - Add special case for NIST P521 in ecc_point_mult

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.

Tested-by: Lukas Wunner <lukas@...ner.de>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
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 90a8c7ea9095..fe2ae2d4185c 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -1320,7 +1320,10 @@ 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)	/* NIST P521 */
+		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