March R. Smith - University of St Thomas - Minnesota CISC Class Today HomeworkHomework Project ScheduleProject Schedule LabLab RecapRecap Protecting packet integrityProtecting packet integrity IPSECIPSEC

Recap Protocols and LayeringProtocols and Layering –The funnel Lots of ApplicationsLots of Applications Narrow middle for the “protocol stack”Narrow middle for the “protocol stack” Lots of device drivers for different network hardwareLots of device drivers for different network hardware Network EncryptionNetwork Encryption –Link vs Network vs Application Different protection afforded at different layersDifferent protection afforded at different layers –Let’s bring up Wireshark for a moment March R. Smith - University of St Thomas - Minnesota

Project Schedule April 20: Next MondayApril 20: Next Monday –Project Proposal DUE –You want to start working on the project NOW –You want to have your team in place ASAP April 27: Twelve Days from TodayApril 27: Twelve Days from Today –Project OUTLINE Due –The outline is a bit of work If you’re a group, figure out how to divide it upIf you’re a group, figure out how to divide it up Hand in combined outline and combined reference listHand in combined outline and combined reference list –It counts for a chunk of the assignment (20% or so) –DON’T MESS IT UP March R. Smith - University of St Thomas - Minnesota

The Lab How are people doing?How are people doing? –Due Next Wednesday –Don’t get wrapped around the Loopback: Where to do itWhere to do it –Lab down the hall – OSS 429 When to do itWhen to do it –Do I need to schedule some time? –Do enough people have card access? 12/21/2015 4R. Smith - University of St Thomas - Minnesota

Protecting Packet Integrity Tools at our disposalTools at our disposal –Encryption, checksums, CRCs, one-way hash ThreatsThreats –Fabricating new packets – forgery –Changing packet contents – tricking the application –Changing packet addresses – redirecting the packet March R. Smith - University of St Thomas - Minnesota

Checksums for packet protection Incorporating a secret for protectionIncorporating a secret for protection March R. Smith - University of St Thomas - Minnesota

Attacking the simple checksum The checksum isn’t sensitive to positionThe checksum isn’t sensitive to position March R. Smith - University of St Thomas - Minnesota

Practical problems The secret information isn’t very muchThe secret information isn’t very much –Trial-and-error can generate a working checksum The checksum isn’t very sensitiveThe checksum isn’t very sensitive –Obvious errors aren’t detected –Designed to detect simple, random errors –Not really designed to protect against clever people What tool(s) can improve this?What tool(s) can improve this? March R. Smith - University of St Thomas - Minnesota

Keyed Hash Use one-way hash with a shared secretUse one-way hash with a shared secret –Hash included in message –Recipient verifies the message with the shared secret March R. Smith - University of St Thomas - Minnesota

Issues with Keyed Hashes One-way hashes aren’t perfectOne-way hashes aren’t perfect –Research has found ways to fiddle with them –In particular, some aren’t sensitive enough to ‘truncation’ Alternative #1: put secret on front and backAlternative #1: put secret on front and back –Initial strategy used in the IPSEC protocols Still sensitive to other hash vulnerabilitiesStill sensitive to other hash vulnerabilities –Designers sought a way to cover weaknesses –Apply hash multiple times to cover various problems March R. Smith - University of St Thomas - Minnesota

Keyed Hash on Steroids - HMAC State of the art in keyed hashingState of the art in keyed hashing March R. Smith - University of St Thomas - Minnesota

IP Security Protocol – IPSEC Security protection that’s IP routableSecurity protection that’s IP routable We authenticate the IP addressesWe authenticate the IP addresses We encrypt everything inside the IP headerWe encrypt everything inside the IP header March R. Smith - University of St Thomas - Minnesota

Separate Headers AH – Authentication HeaderAH – Authentication Header –Keeps the packet intact ESP – Encapsulating Security PayloadESP – Encapsulating Security Payload –A ‘generic’ security format, originally just for encryption –Now does both encryption and authentication March R. Smith - University of St Thomas - Minnesota

Practical question for network geeks What parts of the IP packet MUST be modified?What parts of the IP packet MUST be modified? What happens during routing?What happens during routing? MAC addressingMAC addressing Hop-per-hopHop-per-hop March R. Smith - University of St Thomas - Minnesota

Authentication Header – ‘AH’ Protects unchanging bits of the IP headerProtects unchanging bits of the IP header “SPI” – Security Parameter Index“SPI” – Security Parameter Index –Identifies the keying and hash algorithm to use March R. Smith - University of St Thomas - Minnesota

March R. Smith - University of St Thomas - Minnesota That’s it Questions?Questions? Creative Commons License This work is licensed under the Creative Commons Attribution-Share Alike 3.0 United States License. To view a copy of this license, visit or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA.