| Ancient Times | Simple Substitution Ciphers (e.g. Caesar) | These are the earliest types of ciphers, where characters in a message are shifted or substituted with other characters. This was used for secret military or political communication. |
| Middle Ages | Transposition and Advanced Substitution | As societies needed more secure communication, letter shuffling (transposition) and advanced substitution (e.g. Vigenère) were introduced. |
| Early Modern Period | Mechanical Encryption Machines | The evolution of technology saw the creation of mechanical machines for encryption. Notably the Enigma machine, which used rotating disks to scramble messages in complex ways. |
| World War to Cold War | Electromechanical Encrypting | Involves a combination of electrical and mechanical processes to encrypt information. A more complex level of cryptography, making it harder to decipher without the exact keys and settings. |
| Late 20th Century | Symmetric Key Algorithms (e.g. DES, AES) | The key used to encrypt a message is the same key that decrypts it. This brought about the digital age of cryptography, enabling secure electronic communications. |
| Late 20th Century to Present | Asymmetric Key Algorithms (e.g. RSA, DH, ECC) | A pair of keys are used: one public key to encrypt the message, and a corresponding private key to decrypt it. This has become the foundation for secure online transactions. |
| Present | Quantum Cryptography | With the dawn of quantum computing come both threats and possibilities. Quantum cryptography aims to use the principles of quantum mechanics to establish more secure cryptographic systems. |
