Hello,

The interface of the Diffie-Hellman (DHM) module is modeled on the way it's used in TLS, which is a bit different from the classical presentation. You can find code examples in programs/pkey/dh_client.c and programs/pkey/dh_server.c .

Elliptic-curve Diffie-Hellman (provided by the ECDH module) has similar security properties and is significantly faster. If you don't need interoperability with legacy software that only supports classical (finite-field) Diffie-Hellman, you should use ECDH rather than DHM. With the ECDH module, you can use either the same TLS-inspired interface as the DHM module, or a more classical interface for which there is a usage example in psa_crypto.c in the function psa_key_agreement_ecdh.

Hope this helps,