Crypto_Networking

# Crypto_Networking - ECE 445: Communication Networks...

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1 Security for Wired and Wireless Systems ECE 445: Communication Networks Security for Wired and Wireless Systems

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2 Security for Wired and Wireless Systems ECE 445: Communication Networks A Few Definitions Cryptology: The general study of methods for securing information against disclosure to unauthorized parties. This study includes Cryptography and Cryptanalysis . Cryptosystem: A machine that obscures the contents of a message so that only the intended recipient can read the message. Cryptography: The study of the various techniques for constructing cryptosystems. Cryptanalysis: The study of the various means of breaking cryptosystems.
3 Security for Wired and Wireless Systems ECE 445: Communication Networks Motivations for Cryptology Privacy: The communication channel is to be secured against passive listeners. - military applications - commercial applications - government applications Authentication: The communication channel is to be secure against active interference (e.g. altered or forged messages). - banking - commercial transactions - military orders - treaty verification

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4 Security for Wired and Wireless Systems ECE 445: Communication Networks The Classical Cryptosystem Encryption Decryption Unsecure Channel Secure Channel User A Key Generator User B The same key is used for both encryption and decryption, and must therefore be kept secret. Unfortunately, the secret key must be communicated by some means to the intended recipient of the encrypted message. - courier - external (public key?) cryptosystem
5 Security for Wired and Wireless Systems ECE 445: Communication Networks An NP-Hard Problem Problem: Given k binary polynomials p 1 , p 2 , . .. , p k in n variables x 1 , . .. , x k , determine whether these polynomials have a common zero ( z 1 , . .. , z k ). As k and n increase, this problem rapidly becomes intractable. Theorem: The problem of deciding whether algebraic equations modulo-2 have a solution is NP-hard. Partial Proof: Use solution as certificate. x 1 x 4 x 6 + x 2 x 4 x 5 - 1 = 0 x 1 x 2 + x 2 x 3 + x 3 x 4 - 1 = 0 x 1 x 3 + x 4 x 5 + x 1 x 6 - 1 = 0 Solution ( x 1 ,..., x 6 ) = (1,0,1,1,1,1)

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6 Security for Wired and Wireless Systems ECE 445: Communication Networks The Data Encryption Standard The US National Bureau of standard hoped to develop a one-chip commercial cryptosystem whose security was beyond reproach. RFP: Request for Proposals (1973 - 1974). IBM won with variation of Lucifer cipher. DES published as commercial standard by NBS in 1977. Lucifer had a 128 bit key. DES has an effective key length of 56 bits, which has caused a major controversy. More on that later.
7 Security for Wired and Wireless Systems ECE 445: Communication Networks Lucifer: The Basic Approach 1. Break message up into 2 n -bit blocks, each block to be treated separately. 2.

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## This note was uploaded on 09/01/2008 for the course ECE 4450 taught by Professor Wicker during the Spring '07 term at Cornell University (Engineering School).

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Crypto_Networking - ECE 445: Communication Networks...

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