March 2005 1R. Smith - University of St Thomas - Minnesota

QMCS 490 - Class TodayQMCS 490 - Class Today

• ““Enigma” recap and finishEnigma” recap and finish• The quiz/surveyThe quiz/survey• Next homework assignmentNext homework assignment• Desktop Crypto implementationsDesktop Crypto implementations

March 2005 2R. Smith - University of St Thomas - Minnesota

Homework AssignmentHomework Assignment

• Look up some things in Chapter 5Look up some things in Chapter 5• Use Moore’s Law to guess how large of a Use Moore’s Law to guess how large of a

crypto key a DES Cracker-style computer can crypto key a DES Cracker-style computer can crack in a given year.crack in a given year.

• Turn the calculation around and guess the year Turn the calculation around and guess the year in which such a machine will be able to crack a in which such a machine will be able to crack a key of a given size.key of a given size.

• Print out Chapters 1 and 2. Look at pretty Print out Chapters 1 and 2. Look at pretty picture and diagrams. Read a few stories. Bring picture and diagrams. Read a few stories. Bring them to class on Monday.them to class on Monday.

March 2005 3R. Smith - University of St Thomas - Minnesota

Desktop Crypto ImplementationsDesktop Crypto Implementations

• File encryptionFile encryption– User controlled; sharing and separation on computerUser controlled; sharing and separation on computer

• Volume encryptionVolume encryption– Device driver encrypts data written to the driveDevice driver encrypts data written to the drive– Can’t boot without a password/phrase/keyCan’t boot without a password/phrase/key– Users can steal from each otherUsers can steal from each other– Everything is safe if stolen (and key is unknown)Everything is safe if stolen (and key is unknown)

• Hard drive encryptionHard drive encryption– Fast crypto built into hard driveFast crypto built into hard drive– Users can steal from each otherUsers can steal from each other– Crypto is harder to disableCrypto is harder to disable– Problem: how do we handle the key?Problem: how do we handle the key?

March 2005 4R. Smith - University of St Thomas - Minnesota

Software Crypto DilemmasSoftware Crypto Dilemmas

• How do we keep the crypto safe?How do we keep the crypto safe?– What can ‘they’ subvertWhat can ‘they’ subvert

• Subversion examplesSubversion examples– File encryptionFile encryption– Hard drive encryptionHard drive encryption

• Access control protectionsAccess control protections

March 2005 5R. Smith - University of St Thomas - Minnesota

Access Control for this classAccess Control for this class

• For Access Control ExamplesFor Access Control Examples• Three elements to considerThree elements to consider

– Operating system – always has full accessOperating system – always has full access– Owner (usually the creator) – always has full accessOwner (usually the creator) – always has full access– Everyone else – access may be restrictedEveryone else – access may be restricted

• To specify access on a file or other assetTo specify access on a file or other asset– Identify the ownerIdentify the owner– Identify permissions granted to everyone else, if anyIdentify permissions granted to everyone else, if any

• Access permissions to grantAccess permissions to grant– Read, write – usual meaningRead, write – usual meaning– Execute – if executable, may be executed by other usersExecute – if executable, may be executed by other users– Search – for directories: can’t read but can search Search – for directories: can’t read but can search

March 2005 6R. Smith - University of St Thomas - Minnesota

Access Control for CryptoAccess Control for Crypto

• Who owns the executable?Who owns the executable?• Who can modify it?Who can modify it?• Who owns keys?Who owns keys?

March 2005 7R. Smith - University of St Thomas - Minnesota

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