6/21/01Team 2 DCS 835 Rev 6/22/011 IP Security (IPSec)  Background –The internet has no centralized technical support. What makes it work is an agreed upon common set of protocols that allow different networks to communicate with one another. TCP/IP protocols developed de facto, although today TCP/IP is formally specified as a de jure standard by the Internet Engineering Task Force (IETF).

6/21/01Team 2 DCS 835 Rev 6/22/012 IP Security (IPSec)  Background (cont’d) –The IETF is open to anyone. The membership requirement is participation in one of the more than 100 working groups. Each group has a working theme. IPSec protocols were developed by the Security working group.

6/21/01Team 2 DCS 835 Rev 6/22/013 IP Security (IPSec)  Background (cont’d) IPSec began as two security protocol proposals: Photuris and SKIP. When the proponents couldn’t reach agreement, ISAKMP, a general-purpose syntax was agreed to. At the same time, a third more complex protocol called Oakley, was proposed. Finally, a document originally titled ISAKMP/Oakley Resolution Document evolved into what is now known as Internet Key Exchange (IKE), the key portion of IPSec.

6/21/01Team 2 DCS 835 Rev 6/22/014 IP Security (IPSec)  Technical Overview –IPSec is a set of protocols devised by the IETF –IPSec offers authentication and privacy services at the IP layer –IPSec can be used with IPv4 and IPv6 –IPSec provides a flexible framework –It is not a single protocol, but provides a set of security algorithms that work within the framework

6/21/01Team 2 DCS 835 Rev 6/22/015 IP Security (IPSec)  Technical Overview (cont’d) The two main pieces of IPSEC are the data packet encodngs (AH and ESP), and the key exchange portion (IKE) IPSec operates “on top of” layer 3 (IP), but “below” layer 4 (TCP or UDP), in that it encrypts each data packet independent of all others. If packets are lost or delayed, layer 4 (the layer that requests retransmission) sees only authenticated data.

6/21/01Team 2 DCS 835 Rev 6/22/016 IP Security (IPSec)  Required Security Algorithms –IPSec defines a minimal set of algorithms that are mandatory.

6/21/01Team 2 DCS 835 Rev 6/22/017 IP Security (IPSec) - Authentication  IPSec Authentication Header IPv4 HEADER AUTHENTICATION HEADER TCP HEADER TCP DATA IPv4 datagram with IPSec authentication header added IPSec uses a separate authentication header The Protocol field in the IP header is set to 51 The receiver gets the information type carried in the datagram from the NEXT HEADER field in the authentication header

6/21/01Team 2 DCS 835 Rev 6/22/018 IP Security (IPSec) - Authentication  IPSec Authentication Header (cont’d) NEXT HEADERPAYLOAD LENRESERVED IPSec authentication header format SECURITY PARAMETERS INDEX SEQUENCE NUMBER AUTHENTICATION DATA (VARIABLE

6/21/01Team 2 DCS 835 Rev 6/22/019 IP Security (IPSec) - Authentication  IPSec Authentication Header (cont’d) –PAYLOAD LEN specifies the length of the authentication header –SEQUENCE NUMBER contains a unique sequence number for each packet sent. –SECURITY PARAMETERS INDEX specifies the security scheme used –AUTHENTICATION DATA contains data for the selected security scheme

6/21/01Team 2 DCS 835 Rev 6/22/0110 IP Security (IPSec) - Authentication  IPSec security schemes can include: –Authentication algorithm –A key (or keys) used by the algorithm –A lifetime for the key –A lifetime for the algorithm –A list of source addresses authorized to use the scheme.

6/21/01Team 2 DCS 835 Rev 6/22/0111 IP Security (IPSec) - Authentication  IPSec Security Association –To save header space, IPSec arranges to have each receiver collect all the details about a security scheme in an abstraction called a Security Association (SA). –Each SA is given a security parameters index (a number that identifies it) –The sender must know the SA of the receiver, and places the value in the security parameters index of each datagram.

6/21/01Team 2 DCS 835 Rev 6/22/0112 IP Security (IPSec) - Authentication  IPSec Security Association (cont’d) –Index values are not global –Each destination creates as many SAs as it needs and assigns an index to each –The destination can assign a lifetime for each SA, and reuse the index after the SA expires

6/21/01Team 2 DCS 835 Rev 6/22/0113 IP Security (IPSec) - Authentication  IPSec Mutable Header Fields –IPSec is designed to ensure that the datagram that is sent is unchanged when it arrives. If the entire datagram were authenticated, this would be impossible, because each intermediate router decrements the time-to-live field and recomputes the checksum –IPSec calls header fields that are changed in transit mutable fields –Therefore IPSec only authenticates immutable fields

6/21/01Team 2 DCS 835 Rev 6/22/0114 IP Security (IPSec) - Privacy  IPSec Encapsulating Security Payload (ESP) IPv4 HEADER ESP HEADER TCP HEADER TCP DATA IPv4 datagram with IPSec ESP added The Protocol field in the IP header is set to 50 ESP uses many of the same features used in the authentication header, but rearranges the order ESP TRAILER ESP AUTH Encrypted Authenticated

6/21/01Team 2 DCS 835 Rev 6/22/0115 IP Security (IPSec) - Privacy  IPSec Encapsulating Security Payload (ESP) 0 – 255 OCTETS OF PADDINGPAD LENGTHNEXT HEADER SECURITY PARAMETERS INDEX SEQUENCE NUMBER ESP AUTHENTICATION DATA (VARIABLE) ESP Header ESP Trailer

6/21/01Team 2 DCS 835 Rev 6/22/0116 IP Security (IPSec) - Privacy  IPSec Encapsulating Security Payload (ESP) –Padding may be required because the NEXT HEADER field is right justified within a 4-octet field. IPSec requires that the AUTH DATA be aligned to the start of a 4-octet boundary

6/21/01Team 2 DCS 835 Rev 6/22/0117 IP Security (IPSec) Tunneling OUTER IP HEADER ESP HEADER INNER IP DATAGRAM (INCLUDING IP HEADER) IPSec tunneling mode with ESP added VPN uses encryption along with IP-in-IP tunneling to keep inter-site data transfers private. The IPSec standard explicitly defines the tunneled versions of the datagrams. ESP TRAILER ESP AUTH Encrypted Authenticated OUTER IP HEADER IPSSec tunneling mode for authentication AUTHENTICATION HEADER INNER IP DATAGRAM (INCLUDING IP HEADER)

6/21/01Team 2 DCS 835 Rev 6/22/0118 References 1.Comer, Douglas E. Internetworking with TCP/IP Vol 1: Principles, Protocols, and Architecture, 4 th ed. Upper Saddle River, N.J.: Prentice Hall, Cisco Systems, IP Security—IPSec Overview, _ov.pdf _ov.pdf 3.Cisco Systems, IPSec Network Security, Release 11.3(3)T. 13t_3/ipsec.pdf 13t_3/ipsec.pdf 4.Zao, Kent, Gahm, Troxel, Condell, Helinck, Yuan, Castineyra. “A Public Key Based Secure Mobile IP”, Wireless Networks Vol. 5, J.C Baltzer AG, 1999, pp Treese, Win. “Putting it Together: Engineering the Net: The IETF”, networker Vol 3 No.1, March, 1999, pp Perlman, Kaufman. “Key Exchange in IPSec: Analysis of IKE”, IEEE Internet Computing, Nov-Dec 2000,