[gnutls-devel] GnuTLS | server auth: disable TLS 1.3 if no signature algorithm is usable (!987)

[Development of GNU's TLS library]

Merge request https://gitlab.com/gnutls/gnutls/merge_requests/987 was reviewed by Nikos Mavrogiannopoulos

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Nikos Mavrogiannopoulos started a new discussion on lib/auth.c: https://gitlab.com/gnutls/gnutls/merge_requests/987#note_165946553

>  		bool allow_tls13 = 0;
>  		unsigned key_usage;
> +		const gnutls_sign_algorithm_t *sign_algos = gnutls_sign_list();

this is not a thread safe function to call here. I just checked its documentation and it does not seem to mention that fact.

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Nikos Mavrogiannopoulos started a new discussion on lib/auth.c: https://gitlab.com/gnutls/gnutls/merge_requests/987#note_165946554

> -					break;
> +					/* check if the private key is usable for signing in TLS 1.3 */
> +					if (session->security_parameters.entity == GNUTLS_SERVER) {

While that is generic and correct, isn't it an overkill to do for all private keys, and iterate over all signature algorithms? Isn't the problematic case we want to catch, related to RSA private keys? If yes, then what if we only check for them with a fixed RSA-PSS signature?


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