linux-kernel - [PATCH v6 12/13] crypto: asymmetric_keys - Adjust signature size calculation for NIST P521

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240312183618.1211745-13-stefanb@linux.vnet.ibm.com>
Date: Tue, 12 Mar 2024 14:36:17 -0400
From: Stefan Berger <stefanb@...ux.vnet.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 v6 12/13] crypto: asymmetric_keys - Adjust signature size calculation for NIST P521

From: Stefan Berger <stefanb@...ux.ibm.com>

Adjust the calculation of the maximum signature size for support of
NIST P521. While existing curves may prepend a 0 byte to their coordinates
(to make the number positive), NIST P521 will not do this since only the
first bit in the most significant byte is used.

If the encoding of the x & y coordinates requires at least 128 bytes then
an additional byte is needed for the encoding of the length. Take this into
account when calculating the maximum signature size.

Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
Reviewed-by: Lukas Wunner <lukas@...ner.de>
Tested-by: Lukas Wunner <lukas@...ner.de>
---
 crypto/asymmetric_keys/public_key.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/crypto/asymmetric_keys/public_key.c b/crypto/asymmetric_keys/public_key.c
index e5f22691febd..16cc0be28929 100644
--- a/crypto/asymmetric_keys/public_key.c
+++ b/crypto/asymmetric_keys/public_key.c
@@ -233,6 +233,7 @@ static int software_key_query(const struct kernel_pkey_params *params,
 	info->key_size = len * 8;
 
 	if (strncmp(pkey->pkey_algo, "ecdsa", 5) == 0) {
+		int slen = len;
 		/*
 		 * ECDSA key sizes are much smaller than RSA, and thus could
 		 * operate on (hashed) inputs that are larger than key size.
@@ -246,8 +247,19 @@ static int software_key_query(const struct kernel_pkey_params *params,
 		 * Verify takes ECDSA-Sig (described in RFC 5480) as input,
 		 * which is actually 2 'key_size'-bit integers encoded in
 		 * ASN.1.  Account for the ASN.1 encoding overhead here.
+		 *
+		 * NIST P192/256/384 may prepend a '0' to a coordinate to
+		 * indicate a positive integer. NIST P521 never needs it.
 		 */
-		info->max_sig_size = 2 * (len + 3) + 2;
+		if (strcmp(pkey->pkey_algo, "ecdsa-nist-p521") != 0)
+			slen += 1;
+		/* Length of encoding the x & y coordinates */
+		slen = 2 * (slen + 2);
+		/*
+		 * If coordinate encoding takes at least 128 bytes then an
+		 * additional byte for length encoding is needed.
+		 */
+		info->max_sig_size = 1 + (slen >= 128) + 1 + slen;
 	} else {
 		info->max_data_size = len;
 		info->max_sig_size = len;
-- 
2.43.0