# Encryption and Decryption ## What is Encryption Encryption is the process of converting readable data, called plaintext, into an unreadable scrambled form, called ciphertext, using a mathematical algorithm and a key. The resulting ciphertext appears as random gibberish to anyone who does not have the correct decryption key. Encryption is used to protect the confidentiality of data whether it is stored on a disk or transmitted over a network. Even if an attacker intercepts or steals encrypted data, they cannot understand it without the key. ## What is Decryption Decryption is the reverse process of encryption, converting ciphertext back into the original plaintext using the appropriate key. The person or system that has the correct decryption key can decrypt the ciphertext and recover the original data. The security of encrypted data depends entirely on keeping the decryption key secret from unauthorized parties. ## How Encryption Works Encryption algorithms take the plaintext and the encryption key as inputs and produce the ciphertext as output. Modern encryption algorithms are designed to be computationally infeasible to break without the key, even if the attacker knows exactly which algorithm was used. This property, called Kerckhoffs's principle, means that security depends on the key alone. The algorithm can be public, but the key must be kept secret. A well-designed algorithm cannot be broken by examining patterns in the ciphertext because the output should appear random. ## Types of Encryption Symmetric encryption uses the same key for both encryption and decryption. The key must be shared securely between the communicating parties before encrypted communication can begin. Symmetric encryption is fast and efficient, making it suitable for encrypting large amounts of data. AES is the current standard symmetric encryption algorithm. Asymmetric encryption uses a mathematically related pair of keys, a public key and a private key. Data encrypted with the public key can only be decrypted with the private key. Asymmetric encryption is slower than symmetric encryption but solves the key distribution problem because the public key can be shared openly. ## Encryption in Practice In practice, most secure communication systems combine both types of encryption. Asymmetric encryption is used to securely exchange a symmetric session key. Then symmetric encryption is used for the actual data transfer because it is much faster. This is exactly how TLS works for HTTPS connections. The TLS handshake uses asymmetric cryptography to authenticate the server and exchange a session key. The session key is then used with symmetric encryption for all subsequent data transfer.