Operating Systems

Operating Systems Operating Systems Unit 11: Security

Security • prevent unauthorized access to resources and information maintained by computers • issues: • Guarantee the privacy and integrity of data • Restricting the use of computer resources • Providing resilience against malicious attempts to incapacitate the system COP 5994 - Operating Systems

Security Mechanisms • Encryption: • Transform data into something that an attacker cannot understand (confidentiality) • check whether something has been modified (integrity) • Authentication: • verify the identity of a subject • Authorization: • determine if a subject is permitted to request service • Auditing: • trace subjects and requests • can help catch an attacker COP 5994 - Operating Systems

Encryption • Goal: data readable only to intended reader • Cryptography: • encode and decode data • based on cypher: • function to encode/decode data • ex: substitution cypher, transposition cypher • modern cypher has key • parameter to encoding/decoding function COP 5994 - Operating Systems

Cryptography • issue: key length • 64bit, 128bit, … • symmetric • 1 key for encoding and decoding • problem: key needs to be known to both parties • asymmetric • 2 keys COP 5994 - Operating Systems

Secret-Key Cryptography • symmetric cryptography • one secret key to encrypt / decrypt message • Sender • Encrypts a message using the secret key • Sends encrypted message to the intended recipient • Recipient • Decrypts the message using the same secret key COP 5994 - Operating Systems

Secret-Key Cryptography COP 5994 - Operating Systems

Secret-Key Cryptography: Key distribution • Problem: parties must agree on secret key COP 5994 - Operating Systems

Public-Key Cryptography • Asymmetric: • Employs two inversely related keys: • Public key • Freely distributed • Private key • Kept secret by its owner • If the public key encrypts a message, only the corresponding private key can decrypt it COP 5994 - Operating Systems

Public-Key Cryptography • Scenarios: • sender encrypts message with receivers public key • receiver decrypts message with private key • result: sender has authorized receiver COP 5994 - Operating Systems

Public-Key Cryptography • Scenarios: • sender encrypts message with private key • receiver decrypts message with sender’s public key • result: receiver has authenticated sender COP 5994 - Operating Systems

Full Public-Key Cryptography COP 5994 - Operating Systems

PK-Infrastructure: Certificates • Limitation of public-key cryptography • if users share the same set of keys, it is difficult to establish each party’s identity • Solution: • certify public key • public key is part of certificate • published by certificate authority • certificate authorization hierarchy • rooted at Internet Policy Registration Authority COP 5994 - Operating Systems

Authentication • goal: identify user • unique characteristic of the person • signature • fingerprint, voiceprint, retina scan • ownership of an item • key, badge, id-card, smart card • user knowledge • passwords • personal identification numbers (PINs) • lock combination COP 5994 - Operating Systems

Digital Signatures • The electronic equivalents of written signatures • Authenticate senders’ identities • Idea: • run hash function on document to produce hash value • create signature as encrypted hash value • message is sent with document, signature, hash function • receiver decrypts signature, runs hash function, compare hash values COP 5994 - Operating Systems

Authorization Server: Kerberos • protection against internal security attacks • open-source protocol/server developed at MIT • employs secret-key cryptography • to authenticate users in a network • to maintain the integrity and privacy of network communications • components: • authentication server • Ticket Granting Service COP 5994 - Operating Systems

Kerberos Scenario • Client submits username/password to authentication server • If valid, the authentication server issues a Ticket-Granting Ticket (TGT) encrypted with the client’s secret key • Client sends decrypted TGT to the TGS when requesting a resource. If valid, TGS issues a service ticket encrypted with client’s secret key. • Client decrypts service ticket, which it uses to access network resources COP 5994 - Operating Systems

Authentication: Single Sign-On • Simplifies authentication process • one log in using a single password to access multiple applications across multiple computers • Important to secure single sign-on passwords • examples: • distributed file system • ACM digital library COP 5994 - Operating Systems

Authorization • Discretionary Access Control (DAC) • File owner controls permissions • ex: read, write, execute, access control list • Mandatory Access Control (MAC) • Predefine a central permission scheme COP 5994 - Operating Systems

Access Control Security Models • role based access control (RBAC) • model elements • subject has role has privilege to access object • subject can have multiple roles • role has multiple privileges • privilege defines object access • very flexible COP 5994 - Operating Systems

Auditing • log all system and network activity • host protection • tripwire.org • Intrusion Detection Systems • commercial and open source systems • snort.org, dshield.org, lids.org • detection strategies • statistical anomaly • pattern-matching COP 5994 - Operating Systems

Security Attacks • Crypt-analytic attacks • Viruses and worms • Denial-of-service attacks • Domain name system (DNS) attack • Software exploitation • Buffer overflow • System penetration • Web defacing COP 5994 - Operating Systems

Cryptanalytic Attack • Attempt to decrypt encrypted text • Goal is to determine the key • Encryption algorithm is analyzed to find relations between bits of the encryption key and bits of the encrypted text • Weak statistical trends between encrypted text and keys can be exploited to gain knowledge about the key COP 5994 - Operating Systems

Viruses • executable code • attachment to an e-mail message • hidden within as audio clips, video clips and games • if code is execute, mischief occurs: • file corruption • change application behavior • send emails • erase hard drive, … • replicates itself • via send email COP 5994 - Operating Systems

Virus Types • boot sector virus • controls OS • transient virus • runs with another program • resident virus • operates while OS is active • logic bomb • executes its payload at given time COP 5994 - Operating Systems

Worms • Executable code that spreads by infecting files over a network • Rarely requires any user action to propagate • Does not need to be attached to another program or file to spread • Once a virus or worm is released, it can spread rapidly, often infecting millions of computers worldwide within minutes or hours COP 5994 - Operating Systems

Denial-of-Service (DoS) Attacks • prevent system from servicing legitimate requests • unauthorized traffic saturates a network’s resources, restricting access for legitimate users • typical: flood servers with data packets • attach is carried out by network of computers COP 5994 - Operating Systems

Buffer overflow attacks • occurs when an application sends more data to a buffer than it can hold • can push the additional data into adjacent buffers, corrupting or overwriting existing data • can replace executable code in an application’s stack to alter its behavior • malicious code that will then be able to execute with the same access rights as the application it attacked • depending on the user and application, the attacker may gain access to the entire system COP 5994 - Operating Systems

Attack Prevention and Security Solutions • Firewalls • Antivirus software • Security patches • Secure file systems COP 5994 - Operating Systems

Firewall • Protect against intruders outside the network • Police inbound and outbound traffic for the LAN • Types of firewalls • Packet-filtering firewall • allows only defined traffic • Inspects packets for inconsistencies such as incorrect source address • Application-level gateways • Inspect packets for malicious payloads COP 5994 - Operating Systems

Antivirus Software • Attempts to protect against virus attack • monitor file access • identify and remove viruses • many commercial and open source packages • www.clamav.net COP 5994 - Operating Systems

Detection techniques • Signature scanning • Uses a known virus list • Relies on knowledge about the structure of the computer virus’s code • Can be ineffective against variants and polymorphic viruses • Heuristic scanning • looks for virus-like behavior: • Replication, residence in memory and/or destructive code • can detect viruses that have not yet been identified COP 5994 - Operating Systems

Security Patches • Code releases that address security flaws • Simply releasing a patch for a security flaw is insufficient to improve security • Developers should address security flaws by: • Notifying their users quickly • Providing software that facilitates the process of applying security patches • Example: Hotfixes • Microsoft Automatic Updates COP 5994 - Operating Systems

Secure File Systems • Protect sensitive data regardless of how the data is accessed • Encrypting File System (EFS) • Uses cryptography to protect files and folders in an NTFS file system • Uses secret-key and public-key encryption to secure files COP 5994 - Operating Systems

Secure Communication Protocols • Developed to provide security in several layers of the traditional TCP/IP stack • Secure Sockets Layer (SSL) • common extension to http • Internet Protocol Security (IPSec) • needed for IPv4 • Virtual Private Network (VPN) • uses IPSec channel to virtually extend LAN COP 5994 - Operating Systems

Wireless Security • Wired Equivalent Privacy (WEP) protocol • encrypts transmitted data • prevents unauthorized access to the wireless network • shared single key • Wi-Fi Protected Access (WPA) • provides improved data encryption • uses authentication server • enables user authentication • session key for each user COP 5994 - Operating Systems

Steganography • The practice of hiding information within other information • For example: a message or image, within another image, message or other form of multimedia • Digital watermarks • Used to protect intellectual property • Exploit unused portions of files to store hidden messages, while the digital files maintain their intended semantics COP 5994 - Operating Systems

Agenda for next week: • Project Presentations • Final Exam COP 5994 - Operating Systems

Operating Systems