Laude Shannon and Substitution-Permutation Claude shannon introduced idea of substitution permutation(s-P)networks in 1949 paper form basis of modern block ciphers S-P nets are based on the two primitive cryptographic operations seen before substitution(s-box) permutation(P-box provide confusion diffusion of message key 復大软件学院 LiT
LiJT 11 Claude Shannon and Substitution-Permutation • Claude Shannon introduced idea of substitutionpermutation (S-P) networks in 1949 paper • form basis of modern block ciphers • S-P nets are based on the two primitive cryptographic operations seen before: – substitution (S-box) – permutation (P-box) • provide confusion & diffusion of message & key
to Confusion and Diffusion cipher needs to completely obscure statistical properties of original message a one-time pad does this more practically Shannon suggested combining s &p elements to obtain diffusion -dissipates statistical structure of plaintext over bulk of ciphertext confusion - makes relationship between ciphertext and key as complex as possible 12 復大软件学院 LiT
LiJT 12 Confusion and Diffusion • cipher needs to completely obscure statistical properties of original message • a one-time pad does this • more practically Shannon suggested combining S & P elements to obtain: • diffusion – dissipates statistical structure of plaintext over bulk of ciphertext • confusion – makes relationship between ciphertext and key as complex as possible
Shannon理论 Shannon提出利用扰乱( Confusion)和扩 散( Diffusion)交替的方法来构造乘积密码 密码(SPN, Substitution permutation Network:替代-置换网络) 目的为了使基于统计的分析方法不易或者 不能实现 Shannon理论是现代分组密码算法的基础 復大软件学院 LiT
LiJT 13 Shannon理论 • Shannon提出利用扰乱（Confusion）和扩 散（Diffusion）交替的方法来构造乘积密码 密码（SPN, Substitution Permutation Network：替代-置换网络） • 目的为了使基于统计的分析方法不易或者 不能实现 • Shannon理论是现代分组密码算法的基础