public function getEncryptionSecretKey(): EncryptionSecretKey
    {
        $ed25519_sk = $this->getRawKeyMaterial();
        $x25519_sk = \sodium_crypto_sign_ed25519_sk_to_curve25519(
            $ed25519_sk
        );
        return new EncryptionSecretKey(
            new HiddenString($x25519_sk)
        );
    }