Right from the start Notes/Domino is a secure system. But what is it that makes it so secure? The answer is: applied cryptography that is encryption and signatures! After a short introduction in modern cryptographic methods (without going to much into details), I'll show some of the many places, where cryptography is used in Lotus Notes/Domino to ensure that certain information is accessible only by the intended persons and to prove the integrity and authenticity of data, and how to use/configure this functionality, e. g. the user id file, the (cross) certification, the login process, password recovery, encrypted networking, encrypted emails, documents and fields, signed emails, SSL in the HTTP task, etc.