tailieunhanh - Symmetric Encryption Algorithms

Block ciphers are among the most widely used types of cryptographic algorithms provide secrecy and/or authentication services in particular will introduce DES (Data Encryption Standard) | Symmetric Encryption Algorithms CS-480b Dick Steflik Text – Network Security Essentials – Wm. Stallings Lecture slides by Lawrie Brown Edited by Dick Steflik Symmetric Cipher Model Plaintext Encryption Algorithm Secret Key (known to sender and receiver) Ciphertext Decryption Algorithm Plaintext Message Encryption Algorithm Secret Key Plaintext Message Decryption Algorithm Secret Key Transmitted Ciphertext Modern Block Ciphers Block ciphers are among the most widely used types of cryptographic algorithms provide secrecy and/or authentication services in particular will introduce DES (Data Encryption Standard) Modern block ciphers are widely used to provide encryption of quantities of information, and/or a cryptographic checksum to ensure the contents have not been altered. We continue to use block ciphers because they are comparatively fast, and because we know a fair amount about how to design them. Block Cipher Principles most symmetric block ciphers are based on a Feistel Cipher Structure needed since must be able to decrypt ciphertext to recover messages efficiently block ciphers look like an extremely large substitution would need table of 264 entries for a 64-bit block instead create from smaller building blocks using idea of a product cipher An arbitrary reversible substitution cipher for a large block size is not practical, however, from an implementation and performance point of view. In general, for an n-bit general substitution block cipher, the size of the key is n x 2n. For a 64-bit block, which is a desirable length to thwart statistical attacks, the key size is 64 x 264 = 270 = 1021 bits. Claude Shannon and Substitution-Permutation Ciphers in 1949 Claude Shannon introduced idea of substitution-permutation (S-P) networks modern substitution-transposition product cipher these form the basis of modern block ciphers S-P networks are based on the two primitive cryptographic operations we have seen before: substitution (S-box) permutation (P-box) provide . | Symmetric Encryption Algorithms CS-480b Dick Steflik Text – Network Security Essentials – Wm. Stallings Lecture slides by Lawrie Brown Edited by Dick Steflik Symmetric Cipher Model Plaintext Encryption Algorithm Secret Key (known to sender and receiver) Ciphertext Decryption Algorithm Plaintext Message Encryption Algorithm Secret Key Plaintext Message Decryption Algorithm Secret Key Transmitted Ciphertext Modern Block Ciphers Block ciphers are among the most widely used types of cryptographic algorithms provide secrecy and/or authentication services in particular will introduce DES (Data Encryption Standard) Modern block ciphers are widely used to provide encryption of quantities of information, and/or a cryptographic checksum to ensure the contents have not been altered. We continue to use block ciphers because they are comparatively fast, and because we know a fair amount about how to design them. Block Cipher Principles most symmetric block ciphers are based on a Feistel Cipher .