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Unformatted text preview: If password file compromised, all passwords revealed •  Encipher file –  Need to have decipherment, encipherment keys in memory –  Reduces to previous problem •  Store one- way hash of password –  If file read, aCacker must s'll guess passwords or invert the hash 18 Unix Password Hash Example •  Original UNIX system standard hash func'on –  Hashes password into 13 char string –  As authen'ca'on system: –  Authen'ca'on informa'on is strings of 8 characters or fewer –  System stores hash with user’s iden'ty in password file –  Hash is complementa'on informa'on –  Verifica'on func'on is hash on password and comparison with stored hash 19 Dic'onary ACacks •  Trial- and- error from a list of poten'al passwords –  Off- line (type 1): know func'ons and registered informa'on, and repeatedly try different guesses g ∈ A un'l the list is done or passwords guessed •  Examples: crack, john- the- ripper –  On- line (type 2): have access to verifica'on func'ons. Try guesses un'l one succeeds. –  Examples: trying to log in by guessing a password –  True story : early authen'ca'on system, checked password character- by- character, flagged error immediately with 1st character not in password 20 Preven'ng ACacks •  How to prevent this: –  Hide informa'on so that either authen'ca'on input, authen'ca'on func'ons, or stored verifica'on informa'on cannot be found. Prevents obvious aCack from above •  Example: UNIX/Linux shadow password files –  Hides hashed passwords where only root has access –  Block access to all verifica'on methods •...
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This note was uploaded on 02/03/2014 for the course ECE 422 taught by Professor Nicol during the Fall '08 term at University of Illinois, Urbana Champaign.

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