[PATCH] crypto: Limit MODULE_SIG_KEY_TYPE_ECDSA to SHA384 or SHA512

[Dimitri John Ledkov]

NIST FIPS 186-5 states that it is recommended that the security
strength associated with the bit length of n and the security strength
of the hash function be the same, or higher upon agreement. Given NIST
P384 curve is used, force using either SHA384 or SHA512.

Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@xxxxxxxxxxxxx>
---
 certs/Kconfig | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/certs/Kconfig b/certs/Kconfig
index 1f109b0708..84582de66b 100644
--- a/certs/Kconfig
+++ b/certs/Kconfig
@@ -30,9 +30,11 @@ config MODULE_SIG_KEY_TYPE_RSA
 config MODULE_SIG_KEY_TYPE_ECDSA
 	bool "ECDSA"
 	select CRYPTO_ECDSA
+	depends on MODULE_SIG_SHA384 || MODULE_SIG_SHA512
 	help
-	 Use an elliptic curve key (NIST P384) for module signing. Consider
-	 using a strong hash like sha256 or sha384 for hashing modules.
+	 Use an elliptic curve key (NIST P384) for module signing. Use
+	 a strong hash of same or higher bit length, i.e. sha384 or
+	 sha512 for hashing modules.
 
 	 Note: Remove all ECDSA signing keys, e.g. certs/signing_key.pem,
 	 when falling back to building Linux 5.14 and older kernels.
-- 
2.34.1