"代换-置换网络：现代密码学基础"

对称密码学是密码学中的一个重要分支，通过代换-置换网络实现加密和解密的过程。在代换过程中，二进制字通过S-boxes进行替换，而在置换过程中，通过P-boxes对二进制字的顺序进行重新排列。代换-置换网络是现代密码学的基础，其思想形成了现代密码算法的基础。Shannon在1949年的文章中首次提出了代换-置换网络的思想，这种密码操作模式的发展成为了现代形式的代换-置换乘积密码。在这种密码算法中，S-P网络是基于代换和置换这两种基本的密码运算构成的。通过S-P网络，密码可以得到更高的安全性，防止信息被未授权的人员获取。DES预热代换-置换网络的算法设计就是一个经典的代换-置换网络的例子，通过代换和置换两种基本操作，实现了对明文的加密，并且具有较高的安全性。代换-置换网络的思想使得密码算法更加复杂和安全，为信息安全的保护提供了重要的技术支持。Symmetric cryptography is a branch of cryptography that uses substitution-permutation networks to achieve encryption and decryption processes. In the substitution process, binary words are replaced by S-boxes, while in the permutation process, the order of the binary words is rearranged through P-boxes. The substitution-permutation network is the foundation of modern cryptography, and its idea forms the basis of modern cryptographic algorithms. Shannon first proposed the idea of substitution-permutation network in his article in 1949, and the development of this mode of operation has become the modern form of substitution-permutation product cipher. In this type of code algorithm, S-P networks are based on substitution and permutation, the two basic cryptographic operations. Through S-P networks, passwords can be more secure to prevent information from being accessed by unauthorized individuals. The design of the DES preheating substitution-permutation network algorithm is a classic example of a substitution-permutation network that uses two basic operations, substitution and permutation, to encrypt plaintext and has high security. The idea of substitution-permutation networks makes cipher algorithms more complex and secure, providing important technical support for the protection of information security.