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)
        );
    }
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)
        );
    }
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 ) ) ; }
Get an encryption secret key from a signing secret key.

@return EncryptionSecretKey
@throws InvalidKey
@throws \TypeError
Get an encryption secret key from a signing secret key .