Yuri A not many people have asked for this so it hasn't gotten prioritized. I will take this as a design consideration as we look at revamping the CA and server/agent SSL interactions.
ECC is desirable for agents because it requires less CPU and power than RSA for the same effective level of security. I've moved this to Coremunity and implemented a PR enabling the agent to use EC keys, which is compatible when servers are using RSA keys. We will need to file additional tickets if/when we add server support.
An agent may be configured to use elliptic curve (EC) private keys using the `key_type=ec` puppet setting. By default, puppet will use the `prime256v1` elliptic curve, but an alternate curve may be specified using the `named_curve` puppet setting, provided ruby and openssl support it. See OpenSSL::PKey::EC.builtin_curves for a list of supported curves. Note the `key_type` and `named_curve` settings are ignored if the agent already has a private key. Also the settings only control the type of private key that the agent generates. It does not affect which curve is selected in the TLS protocol.