20-771: Computer Security Lecture 3: SSL

1. 20-771: Computer SecurityLecture 3: SSL Robert Thibadeau School of Computer Science Carnegie Mellon University Institute for eCommerce, Fall 2000

2. Today’s lecture • Review • SSL, SET • Break (10 min) • X.509v3

3. This Week Chapters 3-4-5 WS Homework – Discussion Groups Threads for Windows 2000 Quiz – Chapters 3-4-5

4. Our Class Client Applications Server Applications SSL Web Client Security Web Server Security Security Assurance Applications Security Server Applications WINDOWS 2000 Proxy/Router Applications – Put in Hardware! (buy CISCO) Client Security Server Security Path Security - Physical security Proxy/Router Security - Kind of Server Host Security Whole Facility / Internet Security – Protocols/Policy/Publicity Technology The Law How To Integrity/Privacy/Authenticate/Authorize/Record Cryptography

5. Fundamental Elements of Security : IPAAA • Integrity • Privacy • Authentication • Authorization • Auditability

6. Cryptography • A key is just the parameter that makes a program do something to the plaintext or the cyphertext that is very hard to discover. • Symmetric Cryptography = Private Key Systems • Great for the Privacy Function, Hiding Secrets • One Way Hashes = Digest Functions = Integrity Checkers = Password Storage • Great for Integrity Checking, Hiding Secrets • Public Key Cryptography = Public/Private Key Pairs = RSA Patent (sept 21) • Private Reads, Public Writes : Send Secret to Authentic Person • Private Writes, Public Reads = Signing: Authenticate Writer, no secret • Certificates : Signing, used for Authorization • CA : Authority who guarantees Authentication • Where to hide Private Keys? Key Escrow, Smart Cards, Floppy • PKI – the total system of keys, CA

7. Internet Cryptographic Protocols • Cybercash : Electronic Funds Transactions, RFC1898 • DNSSEC : Domain Name System, RFC2065 • IPSec : Packet-Level Encryption, RFC2401 • PCT : TCP/IP-level Encryption • PGP : E-Mail, RFC2015 • S/MIME : E-Mail, RFC2311,RFC2634 • S-HTTP : Web Browsing, RFC2660 • SET : Electronic Funds Transactions • SSL : TCP/IP-level Encryption, Netscape • SSH : Remote Login • http://search.ietf.org/internet-drafts/draft-ietf-secsh-transport-07.txt • http://search.ietf.org/internet-drafts/draft-provos-secsh-dh-group-exchange-00.txt • TLS : TCP/IP-level Encryption, RFC2246

8. Secure Socket Layer History • SSL 1.0 Netscape 1994 • S-HTTP (web only) • SSL 2.0 Netscape (buggy) • PCT Microsoft (loser) 1996 • SSL 3.0 Netscape • TLS 1.0 IETF (now dominant) 1999

9. SSL • “TLS, more commonly known as SSL” • RFC2246 : TLS Protocol Version 1.0 1/99 • RFC2487 : SMTP over TLS • RFC2712 : Adding Kerberos to TLS • RFC2716 : PPP TLS • RFC2817 : Upgrading to TLS within HTTP/1.1 • RFC2818 : HTTP over TLS • RFC2830 : TLS for Lightweight Directory Access Protocol (LDAP) • The Lock or Non-broken Key on Your Browser • Get the picture? (yes, we like it)

10. Protocol Stack TELNET HTTP SMTP NNTP SSL Interface : Port N FTP Transport - TCP Internet - IP Network Interface – EtherNet/etc. Physical Layer

11. SSL • Crypto Solves the Problems – You just need to select among good alternatives for each task. • The “cypher suite” • X.509 Certificates (1991) too. • First, cypher suite agreement between the TCP peers.

12. SSL Components Establishing Symmetric SessionKey DIFFIE-HILLMAN RSA Public Key for Authentication Session Encryption with Symmetric Key for Privacy TRIPLE-DES/CBC RC4 RC3 RC2 Message Message Digest for Checking on Message Integrity SHA MD5

13. SSL Cipher Suites

14. SSL Encrypts • ALL Browser-Server and Server-Browser except which-browser is talking to which-server • URL of requested document • Contents of requested document • Contents of any submitted form fill-outs • Cookies sent from browser to server • Cookies sent from server to browser • Contents of HTTP header • Javascript communications • Etc. ??NetShow—cause that’s UDP??

15. What Could Replace SSL? TELNET HTTP SMTP NNTP SSL Interface : Port N FTP Transport - TCP IPSec Internet - IP Network Interface – EtherNet/etc. Physical Layer

16. IPSec Does Not • Authenticate Participants • But then, neither does SSL in practice • Its does authenticate computers … not done by SSL except during session. SSL can’t stop a proxy.

17. 1. Client says Hello & Stuff 2. Server says Hello & Stuff 3. Server sends Certificate 4. (opt) Server requests client Certificate 5. Client sends Certificate 6. Client sends ClientKeyExchange 7. Client sends a Certificate Verify message 8. Both send ChangeCipherSpec Messages 9. Both send Finished Messages SSL Transaction message

18. Rules of Thumb • Always get 128 Bit Browsers • This is called “US” as opposed to “International” Even though it really means the opposite!!!!!!! • 128 bits is really really good for securing your transaction against spies • Unfortunately, hides employee behavior. • Unfortunately, false sense of security: • Most theft of credit cards is by the employees of credit card processing operations including retailer, clearing, etc. • Do you really trust Amazon? Read their privacy statement at http://www.amazon.com/privacy-notice

19. SET • Authentication : All parties use certificates including customer, merchant, bank, merchant’s bank. • Confidentiality : Encrypted and Private • Message Integrity : Can’t be tampered • Linkage : Verification of encrypted attachments (blind forwarding)

20. Set Protocol Supports all Features of Credit Card System • Cardholder registration • Merchant registration • Purchase requests • Payment authorizations • Payment capture (funds transfer) • Chargebacks (refunds to customers) • Credits • Credit reversals • Debit Card (check card) transactions • Real-time, batch, installment payments, etc.

21. Problems with SET • Risk Management leads Banks to use Intermediaries • Intermediaries have access to the credit card purchasing information • This is where most theft occurs. • To be adopted SET really needs to be accompanied with a change in credit card processing. • BUT: the rate of Internet Charge Backs is HUGE! (Particularly on download purchases and subscriptions). Retailers are now being fined in the hope of reducing this. • SET does not create a non-repudiatable confirmation of the successful obtaining and use of the product sold. It hides critical information from the retailer!

22. BREAK! Lincoln Stein

23. X.509v3 Certificates • More generally used than SSL • Used by SSL • Used by nearly every major computer security system • From Older Standards Groups • ISO/ITU • International Standards Organization/ANSI • International Telecommunications Union (was CCITT – fax, TIFF) • Part of United Nations as of 1988 • ASN.1 (Abstract Syntax Notation 1) – see www.asn1.com • This is instead of BNF and is pretty arcane, but includes encoding rules (DER) • SGML (predecessor of HTML) used this, X.10 Financial Systems. • Object Identifier • Tree starting with world, down through countries, companies, etc., www.hyperstamps.com fun • Your international phone number is a legal Object Identifier • It is a felony in nearly every country of the world to counterfeit an ISO issued Object Identifiers

24. X.509v3 Where to Get • You have to pay 34 Swiss Francs! • www.itu.org -- search on X.509 • But WAIT! X.509v4 is out, but not yet published! • Those typical Swiss…always getting rich • No, this is how nearly all older standards bodies have worked – they sell copies of their standards • Buy them. They are like the RFCs and the W3 Specifications. They will make you one of the few real experts.

25. What is X.509? • A means of authenticating a “directory” • Uses public/private key exclusively (and that means RSA for all practical purposes … Sept 21, remember?) • A means for chaining certificate authorities • Didn’t work, people really just chain certificates • The information about who you are is hashed and signed so this can be compared with the plaintext about who you are in the certificate • Serial Number : an Object Identifier – It’s a FELONY to copy this even in IRAQ!!!

26. X.509 Basic Form Certificate Serial Number Public Key for Authentication RSA DateTime and Expiration Sept 21, 2000! Who you are Message Message Digest for Checking on Message Integrity SHA MD5

27. Concepts behind X.509 • user certificate; public key certificate; certificate: • The public keys of a user, together with some other information, rendered unforgeable by encipherment with the private key of the certification authority which issued it. • certification path: • An ordered sequence of certificates of objects in the directory information tree which, together with the public key of the initial object in the path, can be processed to obtain that of the final object in the path.

28. X.509 Nomenclature

29. Certificate Definition Certificate ::= SIGNED{SEQUENCE{ version version Default v1, serialNumber CertificateSerialNumber, signature AlgorithmIdentifier, issuer Name, validity Validity, subject Name, subjectPublicKeyInfo SubjectPublicKeyInfo, issuerUniqueIdentifier ObjectIdentifier, - v3 subjectUniqueIdentifier ObjectIdentifier, - v3 extensions Extensions, }}

30. Certificate Defined (cont) Version :== Integer (for v1, v2, v3) CertificateSerialNumber ::= Integer AlgorithmIdentifier ::= SEQUENCE{ ..stuff about crypto } Validity ::= SEQUENCE { notBefore Time, notAfter Time} SubjectPublicKeyInfo ::= SEQUENCE { algorithm AlgorithmIdentifier, subjectPublicKey BITSTRING } Time ::= CHOICE { utcTime UTCTime, generalizedTime GeneralizedTime } Extensions ::== SEQUENCE OF extensions like, critical TrueORFalse – v3

31. Date Time • Great Security Technique for Authentication • Challenge-Response, let mother nature be the challenge. • Very hard to defeat since you have to crack the code too quickly … can be used to put a time limit on things. This is used by many certificates. • Kerberos uses this in issuing “tickets” for a time. • Great Security Technique for Auditability • Hash the date-time and sign it. • Requires an authority or both members of transaction to maintain copy (you can’t deny your signature even if you “fix” your copy!)

32. X.509 certificate types • For people • For web sites • For companies • For organizations inside companies • For software • Etc. etc. etc. • You could have X.509 certificates that certify a toaster made a piece of toast. http://dollar.ecom.cmu.edu/sec/509.doc

33. What’s Wrong with Them • Classic HORRIBLE USER INTERFACE ASSOCIATED WITH GOOD CRYPTOGRAPHY • You have to apply to a root CA for one • They invade your privacy! • They make you PAY! • They make them last only one Year! • And you pay again. • Hey…their cost is a few cpu seconds… • Homework: Go to Thawte (www.verisign.com) and get a free personal certificate for your mail browser (outlook, eudora, or netscape). • See what I mean?

34. Better root CAs • There should not be a commercial monopoly here. • Social Security Admin could issue free personal certificates FOR LIFE. • This would make your private key very private • Needs to be on a smart card you don’t lose • Would make Certificate Revocation Work! • Now, each individual person can become a CA! • He can establish expirations suitable to him • He does not himself expire. • Same for each company (IRS or United Nations through ASN.1 Object Identifiers maintained by United Nations.) • September 21, 2000!!! Wanna be a root CA?

35. SSL • What does SSL stand for? • Does SSL use X.509v3 Certificates? • When is the client and server authenticated in SSL? • Can SSL perform a secure transaction without server authentication? • Do browsers by default come configured for low grade, exportable, security?