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Application Layer

Application Layer. Overall objective Facilitate end-user requirements Case Study: Internet E-mail WWW Multimedia Remote Login File transfer Require support protocols to assist applications. Issues. Security Network Complexity Network Mgt. Global Naming System. Security.

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Application Layer

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  1. Application Layer • Overall objective • Facilitate end-user requirements • Case Study: Internet • E-mail • WWW • Multimedia • Remote Login • File transfer • Require support protocols to assist applications. Hugh Melvin, Dept. IT, NUI,G

  2. Issues • Security • Network Complexity • Network Mgt. • Global Naming System Hugh Melvin, Dept. IT, NUI,G

  3. Security • Increasingly important Issue • Multi-faceted • Can be built into all layers • Phy : Fibre optic • Network : Firewall • App. Layer: • Cryptography/ Encyyption • Anti-virus protection • Intrusion Detection Products (Anti-hacking) Hugh Melvin, Dept. IT, NUI,G

  4. Cryptography ED • E:Encryption • D: Decryption • C = EK (P) …k = encr. key • P = DK (C) …k = decr. key Plaintext Ciphertext Plaintext Hugh Melvin, Dept. IT, NUI,G

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  6. Encryption Methods • Substitution vs Transposition Ciphers Substitution Cipher (SC) • Replace each plaintext entity with another • Eg. abcdef….. repl with qwerty… • Can use statistical properties of language to break • deduce that e t etc.. Hugh Melvin, Dept. IT, NUI,G

  7. Encryption Methods Transposition Cipher (TC) • reorder plaintext entities • use of key • easy to detect a TC by stats.  need to guess key length Hugh Melvin, Dept. IT, NUI,G

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  9. Encryption algorithms • Secret vs Public Key. Secret Key • End users share a secret key • Same key used for encr./decr. • Secure key distribution is main concern • Eg. DES (Data Encryption Standard), IDEA • Use of Product Ciphers (P-box, S-box) Hugh Melvin, Dept. IT, NUI,G

  10. Product Ciphers P-box • Transposition stage • Eg. 11000000  00101000 (reorder) S-box • Substitution using decoder/P-box/encoder • Eg. 111  011 Can be implemented v. quickly Hugh Melvin, Dept. IT, NUI,G

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  12. DES • 64 bit blocks • 56 bit key • 16 iterations : each uses a diff section of the key • iteration : (left inputXORfn(right input and key section)) Hugh Melvin, Dept. IT, NUI,G

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  14. Successor to DES ? • DES adopted by US in 1977 • Modifications to improve performance (Triple DES) • Inadequate due to computing power • 2001: New Advanced Encryption Standard (AES) standard (Dept. Commerce NIST) • Based on Rijndael algorithm • Rijmen & Daemem • 128,192 & 256 bit keys • Faster than Triple DES • www.nist.gov/aes Hugh Melvin, Dept. IT, NUI,G

  15. Public Key • Different keys used for encr./decr. • encr. key public • decr. key private => no key distribution security concerns • but… difficult to satisfy reqds. • Eg. RSA (Rivest, Shamir and Adleman) Hugh Melvin, Dept. IT, NUI,G

  16. RSA • C = Pe mod n … (e,n) = public key • P = Cd mod n … (d,n) = private key • Based on factoring of large numbers • Computationally intensive => slow to impl. • Used a lot to distribute Secret Keys…Secret Key then used for data transfer. Hugh Melvin, Dept. IT, NUI,G

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  18. http:///www.rsasecurity.com Hugh Melvin, Dept. IT, NUI,G

  19. PKI: Public Key Infrastructure • System of components to secure online transactions • Authentication • Encryption • Based on Digital Certificates & Public-key encryption • PKI System Components • Registration Authority • Certificate Authority • Directory Hugh Melvin, Dept. IT, NUI,G

  20. PKI • Digital Certificate • Attachment to Transaction • Authenticate identity of sender • Authenticate Certificate issuer • Provide Public encryption keys Hugh Melvin, Dept. IT, NUI,G

  21. PKI • Registration Authority • Filters certificate requests • If OK passes onto CA • Certificate Authority • Issues certificates from a directory • Directory • Database of certificates and public keys Hugh Melvin, Dept. IT, NUI,G

  22. PKI • Different vendors • Baltimore Technologies/ RSASecurity/ VeriSign • Interoperability issues • Different Standards • X.509 (www.itu.int/itudoc/itu-t/rec/x/x500up/x509.html) • PKIX (www.ietf.org/html.charters/pkix-charter.html) • Security of Private Key critical • Potential Use of Smart Card technology Hugh Melvin, Dept. IT, NUI,G

  23. Global naming system • Internet: ?00 million hosts • Unique IP address..need for IPv6 • Also require unique hostname for user-friendliness =>danger of name conflict/clash on global scale • Require Mgt. of naming system • DNS (Domain Name System) Hugh Melvin, Dept. IT, NUI,G

  24. DNS • Hierarchical domain based sys. • Distributed database • Maps host names, e-mail addresses and URLs to Resource Records which includes IP address • Typically > 1 DNS Server • Windows • Control Panel => Network => Protocols => Properties => DNS • Also ipconfig /all Hugh Melvin, Dept. IT, NUI,G

  25. Hierarchical Domain Sys. Top level: generic or country • .com = commercial • .edu = educational • .org = non-profit organisation • .ie = Ireland Hugh Melvin, Dept. IT, NUI,G

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  27. Distributed Database (Directory Info. Base DIB) • Distributed sys. of name servers • Local name servers maintain records for local domain..and redirects queries (using UDP) for remote hosts • Resource records: • IP address • Time-to-live (caching) ..etc Hugh Melvin, Dept. IT, NUI,G

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  30. Internet Applications • WWW/HTTP • FTP • Telnet • E-mail • Internet based Multimedia • Webcast • MBone • Protocols: RTP, UDP, SIP,RSVP Hugh Melvin, Dept. IT, NUI,G

  31. WWW (World Wide Web) • Application that runs on the Internet • client-server system • Client Browser : fetches pages, interprets formatting and displays page on screen. Fetches page by establishing a TCP connection to the machine where page is located (web page server). Hugh Melvin, Dept. IT, NUI,G

  32. WWW • Web server: Server process listens to port 80 for incoming TCP connections from clients. • HTTP : Hyper Text Transfer Protocol .. protocol that defines the format of requests and replies in the client/server model.. Hugh Melvin, Dept. IT, NUI,G

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  35. URL • Uniform Resource Locator • Each web page must be individually named (worldwide) • Each page assigned an URL • 3 parts • Where page is located…DNS of machine that contains the web page … • What page is locally called … • How to access it… HTTP protocol Hugh Melvin, Dept. IT, NUI,G

  36. URL • Course notes on Geminga HOW WHERE WHAT http://www.it.nuigalway.ie/staff/h_melvin/hm_main.html Hugh Melvin, Dept. IT, NUI,G

  37. Example netstat -r Active Connections Proto Local Address Foreign Address State TCP bibio:1651 geminga.nuigalway.ie:telnet ESTABLISHED TCP bibio:1693 standards.ieee.org:80 ESTABLISHED TCP bibio:1688 bodkin.nuigalway.ie:pop3 TIME_WAIT TCP bibio:1699 geminga.nuigalway.ie:80 ESTABLISHED • Two TCP Geminga connections (Telnet/WWW) • One WWW connection to IEEE (port 80) • TCP email connection to bodkin Hugh Melvin, Dept. IT, NUI,G

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