SecurityThe Security Environment ThreatsIntrudersAccidental Data LossBasics of CryptographySecret-Key CryptographyPublic-Key CryptographyOne-Way FunctionsDigital SignaturesUser AuthenticationAuthentication Using PasswordsSlide 12Slide 13Authentication Using a Physical ObjectAuthentication Using BiometricsCountermeasuresOperating System Security Trojan HorsesLogin SpoofingLogic BombsTrap DoorsBuffer OverflowGeneric Security AttacksFamous Security FlawsDesign Principles for SecurityNetwork SecurityVirus Damage ScenariosHow Viruses Work (1)How Viruses Work (2)How Viruses Work (3)How Viruses Work (4)How Viruses SpreadAntivirus and Anti-Antivirus TechniquesSlide 33Slide 34The Internet WormMobile Code (1) SandboxingMobile Code (2)Mobile Code (3)Java Security (1)Java Security (2)Protection Mechanisms Protection Domains (1)Protection Domains (2)Protection Domains (3)Access Control Lists (1)Access Control Lists (2)Capabilities (1)Capabilities (2)Trusted Systems Trusted Computing BaseFormal Models of Secure SystemsMultilevel Security (1)Multilevel Security (2)Orange Book Security (1)Orange Book Security (2)Covert Channels (1)Covert Channels (2)Covert Channels (3)1SecurityChapter 99.1 The security environment 9.2 Basics of cryptography 9.3 User authentication 9.4 Attacks from inside the system 9.5 Attacks from outside the system 9.6 Protection mechanisms 9.7 Trusted systems2The Security EnvironmentThreatsSecurity goals and threats3IntrudersCommon Categories1. Casual prying by nontechnical users2. Snooping by insiders3. Determined attempt to make money4. Commercial or military espionage4Accidental Data LossCommon Causes1. Acts of God-fires, floods, wars2. Hardware or software errors-CPU malfunction, bad disk, program bugs3. Human errors-data entry, wrong tape mounted5Basics of CryptographyRelationship between the plaintext and the ciphertext6•Monoalphabetic substitution–each letter replaced by different letter•Given the encryption key, –easy to find decryption key•Secret-key crypto called symmetric-key cryptoSecret-Key Cryptography7Public-Key Cryptography•All users pick a public key/private key pair–publish the public key–private key not published•Public key is the encryption key–private key is the decryption key8One-Way Functions•Function such that given formula for f(x)–easy to evaluate y = f(x)•But given y–computationally infeasible to find x9Digital Signatures•Computing a signature block•What the receiver gets(b)10User AuthenticationBasic Principles. Authentication must identify:1. Something the user knows2. Something the user has3. Something the user isThis is done before user can use the system11Authentication Using Passwords(a) A successful login(b) Login rejected after name entered(c) Login rejected after name and password typed12Authentication Using Passwords•How a cracker broke into LBL–a U.S. Dept. of Energy research lab13Authentication Using PasswordsThe use of salt to defeat precomputation of encrypted passwordsSaltPassword,,,,14Authentication Using a Physical Object•Magnetic cards–magnetic stripe cards–chip cards: stored value cards, smart cards15Authentication Using BiometricsA device for measuring finger length.16Countermeasures•Limiting times when someone can log in•Automatic callback at number prespecified•Limited number of login tries•A database of all logins•Simple login name/password as a trap–security personnel notified when attacker bites17Operating System SecurityTrojan Horses•Free program made available to unsuspecting user–Actually contains code to do harm•Place altered version of utility program on victim's computer–trick user into running that program18Login Spoofing(a) Correct login screen(b) Phony login screen19Logic Bombs•Company programmer writes program–potential to do harm–OK as long as he/she enters password daily–ff programmer fired, no password and bomb explodes20Trap Doors(a) Normal code. (b) Code with a trapdoor inserted21Buffer Overflow•(a) Situation when main program is running•(b) After program A called•(c) Buffer overflow shown in gray22Generic Security AttacksTypical attacks•Request memory, disk space, tapes and just read•Try illegal system calls•Start a login and hit DEL, RUBOUT, or BREAK•Try modifying complex OS structures•Try to do specified DO NOTs•Convince a system programmer to add a trap door•Beg admin's sec’y to help a poor user who forgot password23Famous Security FlawsThe TENEX – password problem(a) (b) (c)24Design Principles for Security1. System design should be public2. Default should be n access3. Check for current authority4. Give each process least privilege possible5. Protection mechanism should be-simple-uniform-in lowest layers of system6. Scheme should be psychologically acceptableAnd … keep it simple25Network Security•External threat–code transmitted to target machine–code executed there, doing damage•Goals of virus writer–quickly spreading virus–difficult to detect–hard to get rid of•Virus = program can reproduce itself–attach its code to another program–additionally, do harm26Virus Damage Scenarios•Blackmail•Denial of service as long as virus runs•Permanently damage hardware•Target a competitor's computer–do harm–espionage•Intra-corporate dirty tricks–sabotage another corporate officer's files27How Viruses Work (1)•Virus written in assembly language•Inserted into another program–use tool called a “dropper”•Virus dormant until program executed–then infects other programs–eventually executes its “payload”28How Viruses Work (2)Recursive procedure that finds executable files on a UNIX systemVirus couldinfect them all29How Viruses Work (3)•An executable program•With a virus at the front•With the virus at the end•With a virus spread over free space within program30How Viruses Work (4)•After virus has captured interrupt, trap vectors•After OS has retaken printer interrupt vector•After virus has noticed loss of printer interrupt vector and recaptured it31How Viruses Spread•Virus placed where likely to be copied•When copied–infects programs on hard drive, floppy–may try to spread over LAN•Attach to innocent looking email–when it runs, use mailing list to replicate32Antivirus and Anti-Antivirus Techniques(a) A program(b) Infected program(c) Compressed infected program(d) Encrypted virus(e) Compressed virus with encrypted compression code33Antivirus and