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most promising approach to improving password security allow users to select own password but have system verify it is acceptable ▫ simple rule enforcement (see earlier slide) ▫ compare against dictionary of bad passwords ▫ use algorithmic (markov model or bloom filter) to detect poor choices

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Internet Security Association and Key Management Protocol provides framework for key management defines procedures and packet formats to establish, negotiate, modify, & delete SAs independent of key exchange protocol, encryption alg, & authentication method

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merchant sends payment gateway a payment capture request gateway checks request then causes funds to be transferred to merchants account notifies merchant using capture response

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Does not rely on certificate authorities in PGP every user is own CA ▫ can sign keys for users they know directly (certificates are like X.509) forms a “web of trust” ▫ trust keys have signed ▫ can trust keys others have signed if have a chain of signatures to them key ring includes trust indicators users can also revoke their keys

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(Step 1) Key generation: Every entity generates a public-private key pair ▫ choose a random private key ▫ compute the public key (Step 2) Registration: Every entity should ▫ provide proof of their identity (to the CA) (Step 3) Obtain certificate from the CA ▫ CA signs a certificate which binds the identity of A to A’s public key

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Sheart of the algorithm processing message in 1024-bit blocks consists of 80 rounds ▫ updating a 512-bit buffer ▫ using a 64-bit value Wt derived from the current message block ▫ and a round constant based on cube root of first 80 prime numbers

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Based on the difficulty of discrete log problem (like DH) All entities agree on a prime p (say 200 digits long) and a generator g Alice chooses a random value a as her private key (a < p also has typically the same number of digits as p) Alice compute α = ga mod p as her public key

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Shave considered: ▫ Symmetric cipher model and terminology ▫ Classical ciphers ▫ Modern cipher techniques  block vs stream ciphers  Feistel cipher design & structure  DES details & strength ▫ Differential & Linear Cryptanaly

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Symmetric Cipher Model Classical Substitution Ciphers ▫ Caesar Cipher ▫ Monoalphabetic Cipher ▫ Playfair Cipher ▫ Polyalphabetic Ciphers ▫ Vigenère Cipher Cryptanalysis using letter frequencies

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DoS attack or DDoS is an attempt to make a computer resource unavailable to its intended users. Methods of attack ▫ ICMP flood ▫ Teardrop Attacks ▫ Peer-to-peer attacks

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