tls: Stop hardcoding 2048 bit RSA key length

[martinpitt]

These are rejected as "too weak" by the "FUTURE" crypto policy. Let the tools decide about appropriate defaults rather.

Thanks to Renaud Métrich for finding this!

https://issues.redhat.com/browse/RHEL-78645

[martinpitt]

I tested this command:

#     openssl req -x509 \
        -days 365 \
        -newkey rsa \
        -keyout key \
        -keyform PEM \
        -nodes \
        -out cert \
        -outform PEM \
        -subj "/CN=localhost" \
        -config - \
        -extensions v3_req << EOF
    [ req ]
    req_extensions = v3_req
    extensions = v3_req
    distinguished_name = req_distinguished_name
    [ req_distinguished_name ]
    [ v3_req ]
    subjectAltName=IP:127.0.0.1,DNS:localhost
    basicConstraints = critical, CA:TRUE
    keyUsage = critical, digitalSignature,cRLSign,keyCertSign,keyEncipherment,keyAgreement
    extendedKeyUsage = serverAuth
EOF

and then checked the key length. On Debian 12 (our oldest supported release), Fedora 41, and even RHEL 8.10. The default already is 2048 bits, so for the default crypto policy there is no change.

[martinpitt]

The f41/revdeps failure is unrelated and tracked in cockpit-project/cockpit-podman#1999

https://artifacts.dev.testing-farm.io/2386b322-90d8-4923-831d-981d7481306d/

[jelly]

As not all distros have crypto policies, I looked at the default for key-strength, its 2048 for sscg

[jelly]

according to the man page also defaults to 2028