文档介绍：Document serial number【KKGB-LBS98YT-BS8CB-BSUT-BST108】
Plaintext, encryption algorithm, secret key, ciphertext, decryption algorithm.
明文 加密算法 密钥 密文 解密算法
Permutation and substitution.
A stream cipher is one that encrypts a digital data stream one bit or one byte at a time. A block cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length.
Cryptanalysis and brute force.
Ciphertext only. One possible attack under these circumstances is the brute-force approach of trying all possible keys. If the key space is very large, this becomes impractical. Thus, the opponent must rely on an analysis of the ciphertext itself, generally applying various statistical tests to it.
Known analyst may be able to capture one or more plaintext messages as well as their encryptions. With this knowledge, the analyst may be able to deduce the key on the basis of the way in which the known plaintext is transformed.
Chosen plaintext. If the analyst is able to choose the messages to encrypt, the analyst may deliberately pick patterns that can be expected to reveal the structure of the key.