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Web Security

Web Security. Sandy Kutin CSPP 532 8/7/01. Web security: an overview. Company wants to build web site Online purchasing Requests for service or support Viewing data files online How do we make this process secure? Confidentiality Authentication Usual answer: cryptography.

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Web Security

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  1. Web Security Sandy Kutin CSPP 532 8/7/01

  2. Web security: an overview • Company wants to build web site • Online purchasing • Requests for service or support • Viewing data files online • How do we make this process secure? • Confidentiality • Authentication • Usual answer: cryptography

  3. Applications TCP IP TCP/IP in 60 seconds • Computers communicate via packets, not connection • Packets are directed from machine to machine • Smart nodes, stupid network • Contrasts with phone network • Internet Protocol controls this movement • Transfer Control Protocol: packets at destination • Could insert cryptography at any layer

  4. Applications TCP IPsec IPsec • IPsec works at IP level • Transparent to applications • Slows everything down • Some say it’s the future, some say it’s not • If every packet is encrypted: negates performance-optimization, firewalls

  5. Applications SSL Record TCP IP HaSSLe-free Solution • Secure Sockets Layer (SSL) • Works at TCP level • Developed by Netscape • “Applications” now includes: • Handshake, Alert, Cipher Spec Change • Packets encoded by SSL Record Protocol • Implemented in web server, browser • Successor: Transport Layer Security (TLS)

  6. LoSSLess Communication • SSL Record Protocol: • 1. Fragment data into blocks; can compress • 2. Append MAC to each block: • MAC = H(K | pad2 | H(K | pad1 | info | data)) • H could be MD5 or SHA-1; similar to HMAC • info includes sequencing, length information • 3. Encrypt each block (symmetric) • 4. Append header, send fragment

  7. BusineSSLike Handshake • How do we establish a session key? • 1. Client says “hello”: version, random number • 2. Server says “hello”: same, includes key exchange method, optional certificate • 3. Client initiates key exchange (may just generate master, send it using RSA) • 4. Both sides compute various keys from master, random numbers in hello messages • 5. Confirmation messages

  8. HelpleSSLy Hoping • So, does SSL secure our site? • Confidential, authenticated transactions are important, but not the only issue • Threat model: who might attack, and how • Steal customer data (credit cards) • Steal private corporate data • Deface web site • Denial of Service: prevent us from working • SSL has nothing to do with any of these

  9. Trial Separation • How do we keep corporate data secure? • Solution: keep it separate • Only mix information when you have to: use a floppy, or a laptop • Partial solution: restrict web server’s access privileges (e.g., firewall, DMZ) • OK if data flow is mostly to the server • What about credit card numbers?

  10. Bob Alice Stallings, page 464 (from the web site)

  11. SET, I project • Secure Electronic Transaction (SET) • MasterCard, Visa • Alice sends Bob order, encrypted card info • Bob forward card info to MC/Visa • MC/Visa pays Bob • Bob never gets card number • Credit card company never gets order information

  12. Building a Better MouSETrap • OI = order info (include time), OIMD = H(OI) • PI = payment info (& time), PIMD = H(PI) • Alice signs (OIMD | PIMD) (SHA-1, RSA) • Alice sends Bob OI, ECC(PI), PIMD, sig S • Bob compute OIMD, checks signature S • Bob sends OIMD, ECC(PI), S to MC/Visa • They decrypt, check PI, check signature S • They transfer funds, Bob ships item to Alice

  13. Improving our MindSET • Think outside the box • Q: How do we store credit card numbers? • A: Store them so we can’t read them • Application-level solutions: harder to implement, but better targeted to problems • Cryptography is only part of the solution • Any system can be broken • Build a threat model, measure costs

  14. Breaking and Entering • Enemy could break in • Could corrupt data (deface web site) • Could steal data (including passwords) • Could gain control of system • Firewalls help, but there’s always a way in • Keep data separate whenever possible • Educate users about viruses, Trojan horses • Install patches as often as you can

  15. Intruder Alert • Home security: locks stop easy attacks • Better: door, window alarms • (as long as they don’t go through the walls) • Even better: motion detectors • Alarms don’t stop anything directly, but they alert the authorities • Fear of alarms forces criminals to hurry, make mistakes

  16. Law and Order • Deterrent to robbery: fear of prosecution • After a crime, police gather fingerprints, DNA, eyewitnesses • Not aimed at stopping crime or recovering goods, but at punishing criminals • Hard to do in computer crime; criminals often minors or foreign nationals

  17. Intrusion Detection • No matter what systems and protocols we use, people will break in if they want • Hard to defend against determined teenagers with nothing else to do • Solution: monitor system, detect intrusions, watch for unusual activity • Honeypots: trap intruders • Gather evidence; maybe prosecute • At the very least, close off the holes

  18. Denial of Service Attacks • One approach: break in, crash the server • Another: flood the server with bad requests • Distributed Denial of Service (DDoS): • Take over PCs around the country/world • Use them to overload a site • Only solution: have hardware routers detect bad packets • Almost impossible; Windows XP may make it worse

  19. Here’s looking at you, KiDDoS • In the real world: to attack, you have to put yourself at risk. Not on the Internet. • In the real world: attackers must learn skills. Not on the Internet. • One person discovers a hole, writes a script; now “script kiddies” can use it • Patches don’t work. Attackers will always be ahead of users. • Beta testing doesn’t uncover security holes

  20. Gibson Research Corporation • Steve Gibson’s GRC.com: security • Attacked, repeatedly, by DDoSs. No defense. “Nothing more than the whim of a 13-year old hacker is required to knock any user, site, or server right off the Internet.” • Solution: Distributed Responsibility • Owners responsible for their machines • ISPs responsible for their routers • Software writers responsible for bugs

  21. EXPensive Problem • Attackers usually spoof source IP addresses, to conceal their location • Easy to do in UNIX (as root) • Not possible in Windows 9x/ME, but possible in Windows 2000/XP • Microsoft says: we’re fixing a bug • Gibson says: there’s no legitimate reason home users would need this feature

  22. Bruce Schneier: Counterpane • Author of “Applied Cryptography” • Feels only monitoring, intrusion detection, active response can do any good • Counterpane.com: corporate security • Solution: Insurance • Insure against damages from attacks • Lower rates for following good practices

  23. Recommended Reading • Secret-sharing: • Schneier, Sections 3.7, 23.2 • SSL, SET: Stallings, Chapter 14 • General security: • Stallings, Chapters 15-16 • www.grc.com/dos/ • www.counterpane.com

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