Both EST and OPC UA allow clients to request new private keys. Both specifications require that encryption be used when returning private key data.
EST allows clients to explicitly request that separate encryption be applied to the private key. The algorithms are specified in the CSR (certificate signing request).
OPC UA allows clients to password protect the key (which uses encryption), however, OPC UA does not allow the client to directly specify the algorithm used. That said, the envelope used to transport private keys can be specified with the PrivateKeyFormat parameter and the set of envelope formats supported by the CertificateManager is published in the Address Space. It is expected that the envelope format will specify the algorithms used either by explicitly encoding the algorithm within the envelope or as part of the definition of the envelope.