security1-clement

security1-clement - Network Security Cryptography...

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Network Security
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Cryptography Cryptography functions Secret key (e.g., DES) Public key (e.g., RSA) Message digest (e.g., MD5) Security services Privacy: preventing unauthorized release of information Authentication: verifying identity of the remote participant Integrity: making sure message has not been altered
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DES Data Encryption Standard (DES) 56 bit key, insecure Triple DES is secure, but supplanted by AES Advanced Encryption Standard ( AES ) Specified for US Government contracts Neither are provably secure
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Encryption Algorithms Private Key (DES) 64-bit key (56-bits + 8-bit parity) 16 rounds Round 1 Round 2 Round 16 . plain text Initial Permutation Final Permutation 56bit Key Encrypt w/ Secret Key Decrypt w/ Secret Key plaintext plaintext ciphertext
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Each round Function F and generation of K i for each round not shown Repeat for larger messages L i -1 R i 1 L i R i F + i K cipher 1 block 1 DES + IV cipher block DES + 2 2 cipher block DES + 3 3 cipher block DES + 4 4
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AES operates on a 4×4 array of bytes , termed the state For encryption, each round of AES consists of four stages: AddRoundKey - each byte of the state is combined with the derived cipher key SubBytes - a non-linear substitution step where each byte is replaced with another according to a lookup table . ShiftRows - a transposition step where each row of the state is shifted cyclically a certain number of steps. MixColumns
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This note was uploaded on 03/02/2012 for the course C S 360 taught by Professor Clement,m during the Winter '08 term at BYU.

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security1-clement - Network Security Cryptography...

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