INF 123 SW Arch, dist sys & interop Lecture 14

INF 123 SW Arch, dist sys & interopLecture 14 Prof. Crista Lopes

Objectives • Understanding threats to security in decentralized systems • Understanding basic mechanisms for security on the Internet • Firewalls • SSL/TLS • HTTPS

Decentralization • No centralized authority to coordinate and control entities • Independent peers, with possibly conflicting goals, interact with each other and make local autonomous decisions • Presence of malicious peers in open decentralized applications • Need for measures to protect peers against malicious attacks

Security • “The protection afforded to an automated information system in order to attain the applicable objectives of preserving the integrity, availability and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications).” • National Institute of Standards and Technology

Security Computer systems include the people using the computers. Many security threats exploit the human [good] nature.

Security • Confidentiality • Preserving the confidentiality of information means preventing unauthorized parties from accessing the information or perhaps even being aware of the existence of the information. I.e., secrecy. • Integrity • Maintaining the integrity of information means that only authorized parties can manipulate the information and do so only in authorized ways. • Availability • Resources are available if they are accessible by authorized parties on all appropriate occasions.

Trust • Who do you trust? For what functions? • Trust is not a binary concept! Nor static! • If trust is high • Security measures can be lowered • If trust is low • Security measures must be ramped up Blind trust No trust

Trust & Security • What security measures? • Security is not necessarily machine-bound • Depending on many tradeoffs • Security measures can be technological • Upon limited trust • Security measures may be social • Punitive measures for breach of trust Social measures Computer measures

Computer Security Well-Known Threats Well-Known Solutions

Computer Security in Practice • A never-ending game of Vulnerability; Attack; Fix; Repeat • There’s no such thing as a completely secure system • Know your system’s goals and requirements, set security investment accordingly

Integrity of Computer Systems • Firewalls • “part of a computer system or network that is designed to block unauthorized access while permitting authorized communications. It is a device or set of devices which is configured to permit or deny computer applications based upon a set of rules and other criteria.” • Basic task is to regulate some of the flow of traffic between computer networks of different trust levels. • Software and/or hardware

Firewalls: The problem • Computers inside a local area network (LAN) run applications that assume a high-level of trust within that LAN, but that trust does not hold wrt the rest of the Internet

Types of Firewalls • Packet filters: Operate at UDP/TCP/IP level • Traffic filtering based on properties such as:Source IP address & port, Destination IP address & portApplication-level protocols, … • Application-layer • Knowledge of services (WWW, FTP, Naspter) • May have knowledge of users • On inspecting all packets for improper content, firewalls can restrict or prevent the spread of networked computer worms and trojans

Integrity Threat: Botnets Bots are installed on victims’ computers via unsuspecting acts like installing goodies, unziping files, etc. Bots talk to master using unsuspecting channels such as IRC, Twitter, IM, etc. Very hard to fight

Confidentiality of Data • Cryptography • Steganography • On the Internet • Secure Socket Layer / Transport Layer Security • HTTPS

Cryptography • Encryption: converts human-parseable information into unintelligible gibberish • Decryption: the opposite • Cypher: pair of algorithms for encrypting and decrypting information • Ancient “art” used prominently in WWII

MD5 Hashes • Message Digest algorithm 5 • Transforms an arbitrary-length message into a 128-bit value • One way function • Used widely for everyday cryptography • Proved not very secure, collisions

MD5 Hashes • MD5("The quick brown fox jumps over the lazy dog") = 9e107d9d372bb6826bd81d3542a419d6 • MD5("The quick brown fox jumps over the lazy dog.") = e4d909c290d0fb1ca068ffaddf22cbd0

Typical MD5 use • Password encryption for storage and network • Example: OpenSim passwords • http://beta.opensimulator.org/node/56

Dictionary Attack • Attempt at deciphering passwords by using words from a dictionary • Brute-force or probabilistic • Given 9e107d9d372bb6826bd81d3542a419d6 • Try MD5(words) and compare the hash

Dictionary Attack Counter-Measure • Salts: append MD5(password) with an arbitrary (long) number, and hash that • Result = MD5(MD5(password) : salt) • Need to keep the salt around for password verification • Example: OpenSim passwords

Main Lesson about Passwords • Avoid transmitting and storing naked passwords! • Next: transmitting confidential data over the Internet

Remember Wifi? POST /wifi/login HTTP/1.1 Hostname: … Content-Type: … Content-Length: … METHOD=login&firstname=foo&lastname=bar&password=hereismypassword Naked transmission!

Attacks • Eavesdropping • Remember all routing that happens on the Internet • Man-in-the-middle • Malicious server pretends to be target server

Encryption of data • JavaScript-encrypt before sending • Application overhead • Use Transport Layer Security (TLS)

SSL/TLS • Extra pieces of transport-layer protocol for negotiating cyphers and ensuring authentication of the server • Bottom line: • Payload data is encrypted before sending, decrypted upon reception

HTTPS = HTTP + SSL/TLS POST /wifi/login HTTP/1.1 Hostname: … Content-Type: … Content-Length: … METHOD=login&firstname=foo&lastname=bar&password=hereismypassword Unintelligible gibberish

HTTPS = HTTP + SSL/TLS • https:// instead of http:// • Uses port 443 by default instead of port 80

INF 123 SW Arch, dist sys & interop Lecture 14