Completar frases Session06-Symmetric EncryptionVersión en línea Subject : Security and Privacy Risks in Computer & Internet Applications Lecturer: Assoc. Prof. Dr. James Joshi Faculty: Graduate School of Information Technology Siam University, Bangkok, Thailand por Prince Parham 1 cryptographic security statistical ciphers Avalanche complex decrypt bits 1 . Block are among the most widely used types of cryptographic algorithms provide secrecy and / or authentication services . 2 . In 1949 Claude Shannon introduced idea of substitution - permutation ( S - P ) networks . S - P networks are based on the two primitive operations we have seen before : substitution ( S - box ) and permutation ( P - box ) while they provide confusion and diffusion of message . 3 . diffusion ? dissipates structure of plaintext over bulk of ciphertext confusion ? makes relationship between ciphertext and key as as possible 4 . Data Encryption Standard ( DES ) has been considerable controversy over its . DES has become widely used , especially in financial applications 5 . Initial Permutation IP : first step of the data computation IP reorders the input data even bits to LH half , odd bits to RH half quite regular in structure ( easy in h / w ) example : IP ( 675a6967 5e5a6b5a ) = ( ffb2194d 004df6fb ) 6 . Effect : key desirable property of an encryption algorithm where a change of one input or key bit results in changing approx half output bits making attempts to " home - in " by guessing keys impossible 7 . 3DES uses 3 keys and 3 DES executions : ( a ) using 3 keys 3DES has an effective key length of 168 bits ( 3 * 56 ) ( b ) follows encrypt - - encrypt ( EDE ) ( c ) the decryption phase is for backwards compatibility with single DE S
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