IPsec  IPsec (IP security)  Security for transmission over IP networks The InternetThe Internet Internal corporate IP networksInternal corporate IP networks IP packets sent over public switched data networks (PSDN)IP packets sent over public switched data networks (PSDN) Local Network Internet Local Network

IPsec  Why do we need IPsec? IP has no securityIP has no security Add security to create a virtual private network (VPN) to give secure communication over the Internet or another IP networkAdd security to create a virtual private network (VPN) to give secure communication over the Internet or another IP network Local Network Internet Local Network

IPsec  Genesis Being created by the Internet Engineering Task ForceBeing created by the Internet Engineering Task Force For both IP version 4 and IP version 6For both IP version 4 and IP version 6

IPsec  Two Modes of operation  Tunnel Mode IPsec server at each siteIPsec server at each site Secures messages going through the InternetSecures messages going through the Internet Local Network Internet Local Network Secure Communication IPsec Server

IPsec  Tunnel Mode Hosts operate in their usual wayHosts operate in their usual way  Tunnel mode IPsec is transparent to the hosts No security within the site networksNo security within the site networks Local Network Internet Local Network Secure Communication IPsec Server

IPsec  Two Modes of operation  Transport Mode End-to-end security between the hostsEnd-to-end security between the hosts Security within site networks as wellSecurity within site networks as well Requires hosts to implement IPsecRequires hosts to implement IPsec Local Network Internet Local Network Secure Communication

IPsec  Transport Mode Adds a security header to IP packetAdds a security header to IP packet After the main IP headerAfter the main IP header Source and destination addresses of hosts can be learned by interceptorSource and destination addresses of hosts can be learned by interceptor Only the original data field is protectedOnly the original data field is protected Protected Original Data Field Original IP Header Transport Security Header

IPsec  Tunnel Mode Adds a security header before the original IP headerAdds a security header before the original IP header Has IP addresses of the source and destination IPsec servers only, not those of the source and destination hostsHas IP addresses of the source and destination IPsec servers only, not those of the source and destination hosts Protects the main IP headerProtects the main IP header Protected Original Data Field Protected Original IP Header Tunnel Security Header

IPsec  Can combine the two modes Transport mode for end-to-end securityTransport mode for end-to-end security Plus tunnel mode to hide the IP addresses of the source and destination hosts during passage through the InternetPlus tunnel mode to hide the IP addresses of the source and destination hosts during passage through the Internet Local Network Internet Local Network Tunnel Mode Transport Mode

IPsec  Two forms of protection  Encapsulating Security Protocol (ESP) security provides confidentiality as well as authentication  Authentication Header (AH) security provides authentication but not confidentiality Useful where encryption is forbidden by lawUseful where encryption is forbidden by law Provides slightly better authentication by providing authentication over a slightly larger part of the message, but this is rarely decisiveProvides slightly better authentication by providing authentication over a slightly larger part of the message, but this is rarely decisive

IPsec  Modes and protection methods can be applied in any combination Tunnel Mode Transport Mode ESPSupportedSupported AHSupportedSupported

IPsec  Security Associations (SAs) are agreements between two hosts or two IPsec servers, depending on the mode  “Contracts” for how security will be performed  Negotiated  Governs subsequent transmissions Host AHost B Negotiate Security Association

IPsec  Security Associations (SAs) can be asymmetrical Different strengths in the two directionsDifferent strengths in the two directions For instance, clients and servers may have different security needsFor instance, clients and servers may have different security needs Host AHost B SA for messages From A to B SA for messages From B to A

IPsec Policies may limit what SAs can be negotiated To ensure that adequately strong SAs for the organization’s threatsTo ensure that adequately strong SAs for the organization’s threats Gives uniformity to negotiation decisionsGives uniformity to negotiation decisions Host AHost B Security Association Negotiations Limited By Policies

IPsec  First, two parties negotiate IKE (Internet Key Exchange) Security Associations IKE is not IPsec-specificIKE is not IPsec-specific Can be used in other security protocolsCan be used in other security protocols Host AHost B Communication Governed by IKE SA

IPsec  Under the protection of communication governed by this IKE SA, negotiate IPsec-specific security associations Host AHost B Communication Governed by IKE SA IPsec SA Negotiation

IPsec  Process of Creating IKE SAs (and other SAs) Negotiate security parameters within policy limitationsNegotiate security parameters within policy limitations Authenticate the parties using SA-agreed methodsAuthenticate the parties using SA-agreed methods Exchange a symmetric session key using SA-agreed methodExchange a symmetric session key using SA-agreed method Communicate securely with confidentiality, message-by-message authentication, and message integrity using SA-agreed methodCommunicate securely with confidentiality, message-by-message authentication, and message integrity using SA-agreed method

IPsec  IPsec has mandatory security algorithms Uses them as defaults if no other algorithm is negotiatedUses them as defaults if no other algorithm is negotiated Other algorithms may be negotiatedOther algorithms may be negotiated But these mandatory algorithms MUST be supportedBut these mandatory algorithms MUST be supported

IPsec  Diffie-Hellman Key Agreement To agree upon a symmetric session key to be used for confidentiality during this sessionTo agree upon a symmetric session key to be used for confidentiality during this session Also does authenticationAlso does authentication Party AParty B

IPsec  Diffie-Hellman Key Agreement Each party sends the other a nonce (random number)Each party sends the other a nonce (random number) The nonces will almost certainly be differentThe nonces will almost certainly be different Nonces are not sent confidentiallyNonces are not sent confidentially Party AParty B Nonce B Nonce A

IPsec  Diffie-Hellman Key Agreement From the different nonces, each party will be able to compute the same symmetric session key for subsequent useFrom the different nonces, each party will be able to compute the same symmetric session key for subsequent use No exchange of the key; instead, agreement on the keyNo exchange of the key; instead, agreement on the key Party AParty B Symmetric Key From nonces, independently compute same symmetric session key