public function getEncryptionPublicKey(): EncryptionPublicKey
    {
        $ed25519_pk = $this->getRawKeyMaterial();
        $x25519_pk = \sodium_crypto_sign_ed25519_pk_to_curve25519(
            $ed25519_pk
        );
        return new EncryptionPublicKey(
            new HiddenString($x25519_pk)
        );
    }