private function getEncryptionKey(string $sessionId): string
    {
        return (string) openssl_digest($this->appKey . $sessionId, $this->hashAlgorithm);
    }
private function getEncryptionKey(string $sessionId): string
    {
        return (string) openssl_digest($this->appKey . $sessionId, $this->hashAlgorithm);
    }
private function getEncryptionKey ( string $ sessionId ) : string { return ( string ) openssl_digest ( $ this -> appKey . $ sessionId , $ this -> hashAlgorithm ) ; }
Calculates the key to be used in the session encryption.

@param  string $sessionId Id of the session
@return string Encryption key
Calculates the key to be used in the session encryption .