<PackageReference Include="BouncyCastle.Cryptography" Version="2.7.0" />

Org.BouncyCastle.Crypto.Agreement.X448Agreement

public sealed class X448Agreement : IRawAgreement
X448 (RFC 7748) Diffie-Hellman raw agreement. Init takes the local X448PrivateKeyParameters; CalculateAgreement writes the 56-byte shared secret derived against the peer's X448PublicKeyParameters.
public int AgreementSize { get; }

Length in bytes of the shared secret produced by the agreement (56).

public X448Agreement()

public void CalculateAgreement(ICipherParameters publicKey, byte[] buf, int off)

Perform the agreement against publicKey and write the shared secret into buf starting at off.

public void Init(ICipherParameters parameters)

Capture the local private key used for subsequent agreements.