Using Elliptic Curve Cryptography

You can control both the priority ordering and range of Elliptic Curves used to negotiate with connecting peers when establishing connections using Elliptic Curve Diffie-Hellman Exchange (ECDHE) or Elliptic Curve Diffie-Hellman (ECDH) cipher suites.

Note: In the 5.0 release, the client selects a group of supported key exchange cipher groups that are used for a Diffie-Hellman key exchange. In previous products this collection used to be referred to as the ECC Curves List.
Important: If you are using any identity or Certificate Authority (CA) certificate that contains an ECC public key. The Key Exchange Cipher Groups used for that key must be specified in the Key Exchange Cipher Groups field in a listener's SSL options (I601) or the MF Directory Server tab (e041).

If the key's key exchange cipher group is not present, no Elliptic Curve Digital Signature Algorithm (ECDSA) cipher suite connections can be established. Any certificate bearing an unconfigured or misconfigured key exchange cipher group is treated as untrusted because its key exchange cipher group is unknown to the system.

To maximize performance, Micro Focus recommends that servers are configured to support at least two groups. Clients will use one of those two groups for its initial key sharing exchange. In a dual certificate configuration and if the connecting client is not configured for ECDSA only, then the RSA identity certificate and any issuing CA chain might still establish a listening endpoint using the alternative certificate and RSA key. In these circumstances ECDHE-RSA or ECDH-RSA cipher suites are used.

When listing key exchange cipher groups, the priority order is read from left to right with the highest priority on the left. Any combination of spaces, commas, and semicolons can be used as separators for key exchange cipher group. By default, the following key exchange cipher groups are used: 

secp521r1;secp384r1;prime256v1;secp256k1;secp224r1;secp224k1;prime192v1

You can specify your preferred key exchange cipher groups in the Key Exchange Cipher Groups field. If key exchange cipher group curves are duplicated in the list, the first example encountered sets its priority position. All subsequent duplicates are ignored. For example, secp521r1 is the highest priority key exchange cipher group. While secp256k1 is the fourth highest priority curve despite also being found at position ten in the list: 

secp521r1;secp384r1;prime256v1,secp256k1,secp224r1;secp224k1;secp521r1;secp384r1;prime256v1;secp256k1;secp224r1;secp224k1;prime192v1

Any specified curve collection replaces the default collection. If no configuration is specified, the default Key Exchange Cipher Groups is the Key Exchange Cipher Groups listed above. The priority order is determined by the cryptographic service provider.

Note: The default collection of elliptic curves is suitable for most users.
Micro Focus recommends you use the following supported ECC Prime Curves:
Note: Only ECC Prime Curves are supported.
Note: secp256r1 is synonymous and interchangeable with prime256v1. Also, secp192r1 is synonymous and interchangeable with prime192v1.

Micro Focus recommends placing X25519 and X448 as the highest priority key exchange groups in your list if you are using TLS v1.3.

To optimize the key exchange cipher groups to have the highest level of security while providing the greatest level of compatibility with clients, Micro Focus recommends you specify the following Key Exchange Cipher Groups: 

secp521r1;brainpoolP512r1;brainpoolP384r1;brainpoolP256r1;secp384r1;prime256v1;secp256k1;secp224k1;secp224r1;prime192v1

Unlike the TLS1.3 Cipher Suites field which is unique to TLS1.3. The Key Exchange Cipher Groups that are specified also control the groups for TLS v1.2 and earlier.

Micro Focus recommends you avoid using the following key exchange cipher groups which are now considered insecure:

Parent topic: Specifying a Server Protocol and Cipher Suite Preference