CS283 - Lecture 6 - Part 2 - Additional Topics - Authentication

CS283 - Lecture 6 - Part 2 - Additional Topics - Authentication

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Lecture 6 Part 2 - Additional Topics - WU Authentication GWU CS 172/283 Autumn 2009 All slides from Bishop’s slide set 11/11/2009 CS283-172/Fall06/GWU/Vora/Identity All Slides from Bishop's Slide Set 1
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Basics ¾ Authentication: the binding of identity to a subject ¾ The identity is that of an external entity (e.g. my identity, Matt, etc .) he subject is a computer entity (e g a process ¾ The subject is a computer entity (e.g. a process, etc .) 2 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
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Establishing Identity ¾ Establishing Identity can be based on determining one or more of the following ¾ What the entity knows ( eg. a password) ¾ What the entity has ( eg. a badge, a smart card) ¾ What the entity is ( eg. fingerprints, retinal characteristics) here e entity is ( g In front of a particular terminal) ¾ Where the entity is ( eg . In front of a particular terminal) 3 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
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Authentication System ¾ An authentication system ( A , C , F , L , S ) consists of ¾ A: authentication information that proves identity : omplementary information tored on a computer and ¾ C: complementary information stored on a computer and used to validate authentication information ¾ F: complementation functions ; f : A C ¾ L: authentication functions that verify identity ¾ l: A × C {true, false} ¾ S: selection functions enabling an entity to create or alter information in A or C 4 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
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n Example of an Authentication An Example of an Authentication System ¾ A password system, with passwords stored on line in clear text ¾ A: the set of strings making up passwords ¾ C: = A ¾ F: singleton set of identity function { I } ¾ L: single equality test function { eq } : nction to set/change a password ¾ S: function to set/change a password 5 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
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Passwords ¾ Password Characteristics ¾ A Sequence of characters ¾ Examples: 10 digits, a string of letters, etc . ¾ Generated randomly, by a user or by a computer with user input ¾ A Sequence of words ¾ Examples: pass-phrases ¾ Algorithms xamples: challenge sponse one me passwords ¾ Examples: challenge-response, one-time passwords 6 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
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Password Storage ¾ Store as cleartext ¾ If the password file is compromised => all passwords are vealed revealed ¾ Encipher the password file ¾ The OS still needs to have decipherment and encipherment keys in memory ¾ This reduces to the previous problem tore a one- ay hash of passwords ¾ Store a one way hash of passwords ¾ In this case, if the hash file is read, the attacker must still guess passwords or invert the hash 7 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 06 – Part 2 - Rev 20091103
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Example ¾ UNIX system standard hash function ashes the password into an 11 character string using one ¾ Hashes the password into an 11 character string using one of 4096 hash functions ¾ As an authentication system: = { strings of 8 chars or less } ¾ A { strings of 8 chars or less } |A| = 127 8 6.9 × 10 16
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CS283 - Lecture 6 - Part 2 - Additional Topics - Authentication

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