linux-kernel - [PATCH v2 11/14] crypto: Add nbits field to ecc

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Message-ID: <20240215231414.3857320-12-stefanb@linux.ibm.com>
Date: Thu, 15 Feb 2024 18:14:10 -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 11/14] crypto: Add nbits field to ecc_curve structure

Add the number of bits a curve has to the ecc_curve definition. This field
only needs to be set for curves that don't fill up all bytes in their
digits, such as NIST P521 which has only 9 bits in the most significant
digit. This field will be used to determine the number of bytes a curve
requires for its key coordinates for example.

Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
---
 crypto/ecc_curve_defs.h    | 1 +
 include/crypto/ecc_curve.h | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/crypto/ecc_curve_defs.h b/crypto/ecc_curve_defs.h
index 93a47a5d460a..09a221657c31 100644
--- a/crypto/ecc_curve_defs.h
+++ b/crypto/ecc_curve_defs.h
@@ -119,6 +119,7 @@ static u64 nist_p521_b[] = { 0xef451fd46b503f00ull, 0x3573df883d2c34f1ull,
 				0x051ull };
 static struct ecc_curve nist_p521 = {
 	.name = "nist_521",
+	.nbits = 521,
 	.g = {
 		.x = nist_p521_g_x,
 		.y = nist_p521_g_y,
diff --git a/include/crypto/ecc_curve.h b/include/crypto/ecc_curve.h
index 70964781eb68..337a44956926 100644
--- a/include/crypto/ecc_curve.h
+++ b/include/crypto/ecc_curve.h
@@ -23,6 +23,8 @@ struct ecc_point {
  * struct ecc_curve - definition of elliptic curve
  *
  * @name:	Short name of the curve.
+ * @nbits:      Curves that do not use all bits in their ndigits must specify
+ *              their number of bits here, otherwise can leave at 0.
  * @g:		Generator point of the curve.
  * @p:		Prime number, if Barrett's reduction is used for this curve
  *		pre-calculated value 'mu' is appended to the @p after ndigits.
@@ -34,6 +36,7 @@ struct ecc_point {
  */
 struct ecc_curve {
 	char *name;
+	unsigned int nbits;
 	struct ecc_point g;
 	u64 *p;
 	u64 *n;
-- 
2.43.0