Tham khảo tài liệu 'hacker professional ebook part 176', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | cipher near the top and a tiny but accurate model that we can investigate near the bottom. While full-size ciphers can never be exhaustively tested tiny cipher models can be approached experimentally and any flaws in them probably will be present in the full-scale versions we propose to use. Just as mathematics works the same for numbers large or small a backdoor cipher built from fixed construction rules must have the same sort of backdoor whether built large or small. For block ciphers the real block size must be at least 128 bits and the experimental block size probably should be between 8 and 16 bits. Such tiny ciphers can be directly compared to keyed substitution tables of the same size which are the ideal theoretical model of a block cipher. Potentially scalability does far more than just simplify testing Scalability is an enabling technology that supports experimental analysis which is otherwise impossible. Secrecy One of the objectives of cryptography Keeping private information private. Also see trust. In a secret key cipher secrecy implies the use of a strong cipher. Secrecy in communication requires the secure distribution of secret keys to both ends this is the key distribution problem . In a public key cipher the ability to expose keys apparently solves the key distribution problem. But communications secrecy requires that public keys be authenticated certified as belonging to their supposed owner. This must occur to cryptographic levels of assurance because failure leads to immediate vulnerability under a man-in-the-middle attack. The possibility of this sort of attack is very disturbing because it needs little computation and does not involve breaking any cipher which makes all discussion of cipher strength simply irrelevant. Secret Code A coding in which the correspondence between symbol and code value is kept secret. Secret Key Cipher Also called a symmetric cipher or conventional cipher. A cipher in which the exact same key is used to encipher a
