Before the modern age, cryptography was only used for encryption which is to use a secret key to convert readable text (cleartext) to unintelligible nonsense text (ciphertext). Decryption is then to use the same secret key to recover the text. While encryption still is an important application today, cryptography has several other uses, especially to ensure the authenticity of entities (systems and users), and to ensure the authenticity and integrity of information. This is built into communication protocols on the Internet and other communication technologies. Modern cryptography uses advanced mathematical theory, where the security strength is based on computational hardness assumptions. While it is theoretically possible to break a well-designed cryptographic algorithm, it is infeasible in practice to do so because it would take millions of years with current computers.