Version B.00 H7076S Module 3 Slides IPSec Overview Version B.00 H7076S Module 3 Slides

IPSec Functionality Confidentiality Eavesdroppers on the network cannot view users’ data. Authentication The claimed sender is in fact the actual sender. Integrity Data has not been altered during transit in the network. Non-repudiation Senders of data cannot claim that they did not send the data. Transparent Network Applications do not need modification to take advantage Security of network security.

Capturing Packets Off the Internet Bad Guy K-CLASS Users in San Francisco Server in Chicago It is trivial to snoop on Internet traffic, including passwords sent over the network. Malicious people exist who actually do these things.

Symmetric Cryptography: Encryption and Decryption Data Key Encrypted Data Encryption Algorithm Data Decryption Algorithm Encrypted Data Key K-CLASS

How ESP Encryption Works ESP = Encapsulating Security Payload Data (aka Payload) IP Hdr TCP Hdr Original IP Packet The same packet after encryption and addition of the ESP Header IP Hdr ESP Hdr TCP Hdr Data (aka Payload) Encrypted The functionality provided by ESP and encryption is confidential.

A Closer Look at ESP An ESP header contain two fields: An ESP header identifier A security parameter index (SPI) value The SPI value is an index into the security association table in memory. The entry in the security association table defines how the packet is encrypted. IP Hdr ESP Hdr TCP Hdr Data (aka Payload) Encrypted ESP 2 Security Association Table in Memory SPI Algorithm Key Lifetime 1 MD5 12505812097 1 day 2 DES 34209482543 1 hour

Authentication: Method Digest Value Data Key Message Digest Value Message Digest Algorithm Message Digest Algorithm Equal? Data Message Digest Value Message Digest Value Data Key K-CLASS

How Authentication Headers Work AH = Authentication Header Data IP Hdr TCP Hdr Original IP Packet The same packet after the addition of the AH header: Data IP Hdr TCP Hdr AH Hdr Authenticated with a Message Digest Value The functionality provided by AH and the message digest is authentication and data integrity.

A Closer Look at AH Headers An AH header contain three fields: An AH header identifier A security parameter index (SPI) value A message digest value The SPI value is an index into the security association table in memory. The entry in the security association table defines how the packet is authenticated. IP Hdr AH Hdr TCP Hdr Data Authenticated AH 1 39475 Security Association Table in Memory SPI Algorithm Key Lifetime 1 MD5 12505812097 1 day 2 DES 34209482543 1 hour

Combined AH and ESP Original IP Packet Data IP Hdr TCP Hdr Original IP Packet The same packet after the addition of the AH header: Data IP Hdr TCP Hdr AH Hdr ESP Hdr Encrypted Authenticated with a Message Digest Value AH 1 39475 ESP 2 Security Association Table in Memory SPI Algorithm Key Lifetime 2 DES 34209482543 1 hour 1 MD5 12505812097 1 day

Symmetric Key Bootstrap Problem K-CLASS K-CLASS ServerA ServerB Security Association Table in ServerA Memory Security Association Table in ServerB Memory SPI Algorithm Key Lifetime 1 ??? ???????????? ???? 2 DES 34209482543 1 hour SPI Algorithm Key Lifetime 1 MD5 12505812097 1 day 2 ??? ???????????? ???? How do systems agree on an initial key? Initial encryption algorithm? Lifetime? How do systems exchange initial key information without the data being stolen by a hacker with a sniffer?

Internet Key Exchange (IKE) Overview iked process iked process Security Association Table Security Association Table SPI Algorithm Key Lifetime 1 ??? ???????????? ???? 2 DES 34209482543 1 hour SPI Algorithm Key Lifetime 1 MD5 12505812097 1 day 2 ??? ???????????? ???? The iked daemon is responsible for : Initially establishing security association table entries with other iked daemons. Agreeing on security algorithms, key values, and key lifetimes with other iked daemons. Maintaining the security association table and agreeing upon new keys when the lifetime for a key expires.

Protecting against an IKED Bluff process iked process iked process SPI Algorithm Key Lifetime 1 ??? ????????? ???? 2 DES 34209483 1 hour Security Association Table SPI Algorithm Key Lifetime 1 ??? ????????? ???? 2 DES 34209483 1 hour Security Association Table Security Association Table SPI Algorithm Key Lifetime 1 ??? ????????? ???? 2 DES 34209483 1 hour I will install IPSec on my system and maybe those customer systems will establish a secure connection with my computer. Conclusion: Need a Primary Authentication Mechanism

Overcoming Security Obstacles Problem: Data packets travel across the network in clear text! Solution: Use IPSec to authenticate (AH) or encrypt (ESP) packets. Problem: How to securely establish IPSec keys Solution: Use Internet Key Exchange (IKE) protocol. Problem: How to securely establish a IKE keys. Solution: Use Diffie-Hellman algorithm. Problem: Diffie-Hellman is prone to “Man-in-the-Middle” attacks. Solution: Use Pre-Shared key authentication or public-key authentication. Problem: Pre-shared keys are not practical; public-keys require authentication. Solution: Use Security Certificates and manage them through a Public Key Infrastructure (PKI)