Shannon's Characteristics of "Good" Ciphers Claude Shannon, a pioneer in information theory, outlined five essential characteristics for a good cipher: 1. Unconditionally Secure: A cipher is considered unconditionally secure if it cannot be broken even with unlimited computational resources. This level of security is extremely difficult, if not impossible, to achieve in practice. 2. Computationally Secure: A cipher is considered computationally secure if it is impractical to break using currently available technology. This means that the time and computational resources required to decrypt the ciphertext would be prohibitively expensive. 3. Confidentiality: A good cipher should maintain the confidentiality of the plaintext, ensuring that only authorized parties can decrypt the ciphertext. 4. Integrity: A good cipher should preserve the integrity of the data, preventing unauthorized modifications or alterations. 5. Authenticity: A good cipher should provide mechanisms for verifying the authenticity of the sender and ensuring that the message has not been tampered with. Additional Considerations: ● Efficiency: A cipher should be efficient to encrypt and decrypt, especially for large amounts of data. ● Key Management: A good cipher should have a robust key management system to ensure the security of the encryption keys. ● Resistance to Attacks: A cipher should be resistant to various types of attacks, such as brute-force attacks, frequency analysis, and known-plaintext attacks. By adhering to these characteristics, a cipher can provide a high level of security and protect sensitive information from unauthorized access.