Cryptographic Protocols By: Kirti Chawla

Set of rules that ensure that source, transit Introduction Needs & Necessity Standard Protocols An Example Looking Back Set of rules that ensure that source, transit and destination exchanges and retains information in secure way.

Information is not confined We need to exchange information Introduction Needs & Necessity Standard Protocols An Example Looking Back Information is not confined We need to exchange information Standard means of exchanging information

Key exchange protocols Introduction Needs & Necessity Standard Protocols An Example Looking Back Categories Examples Secret sharing Key exchange protocols Identity Authentication protocols Presence of Secret Zero-knowledge proofs Channel Subliminal channel Group Secrets Secure multiparty computation

Key exchange protocols Introduction Needs & Necessity Standard Protocols An Example Looking Back Sender Receiver A key that should be kept secret It is required to be shared Should be valid for a session only

Authentication protocols Introduction Needs & Necessity Standard Protocols An Example Looking Back Home Mobile You need to access resource that are displaced You need to prove your identity without physical relocation Should be time-bound access to resources

Prove possession of secret but don’t divulge it Zero knowledge proofs Introduction Needs & Necessity Standard Protocols An Example Looking Back A Q User Challenger/System Prove possession of secret but don’t divulge it A basic element called trust is there, although however minimum Access to resource based upon this proof

Secret has to go under the eyes of Scrutinizer Subliminal channel Introduction Needs & Necessity Standard Protocols An Example Looking Back Scrutinizer Sender Receiver Secret has to go under the eyes of Scrutinizer The message should appear “innocuous” to Scrutinizer Sender and receiver know the scheme to get secret

Secure multiparty computation Introduction Needs & Necessity Standard Protocols An Example Looking Back Sender Receiver Each member has secret that should not be shared All know the combined result No member can stop or delay any information that’s circulating

Security Protocols Kerberos IPSec SSL/HTTPS Introduction Needs & Necessity Standard Protocols An Example Looking Back Security Protocols Kerberos IPSec SSL/HTTPS

IPSec Introduction Needs & Necessity Standard Protocols An Example Looking Back A set of rules for protecting data at IP layer. It supports both authentication and security of data-packets originating from IP based network. Transport IP-Header Payload Tunnel IP-Header IP-Header Payload

Transport with AH header Authentication Introduction Needs & Necessity Standard Protocols An Example Looking Back IPSec supports authentication by non-repudiation of payload and/or complete packet. The header is called AH or Authentication Header. Transport with AH header IP-header AH-header Payload Tunnel with AH header IP-Header AH-header IP-header Payload

Transport with ESP header Security Introduction Needs & Necessity Standard Protocols An Example Looking Back IPSec supports security by encrypting of payload and/or complete packet. The header is called ESP or Encapsulated Security Payload. Transport with ESP header IP-header ESP-header Payload Tunnel with ESP header IP-Header ESP-header IP-header Payload

Security Associations Introduction Needs & Necessity Standard Protocols An Example Looking Back Security Association is collection of facts that allows two parties to maintain a secure session. All security associations contain certain parameters and destination address. Security Association Database Authentication & security algorithms used Keys used for both algorithms Lifetime of key Lifetime of SA Sensitivity level Structure of SA

How it works ? Authentication Introduction Needs & Necessity Standard Protocols An Example Looking Back Authentication Public Network Security Public Network

Kerberos Introduction Needs & Necessity Standard Protocols An Example Looking Back It’s authentication protocol, which allows controlled and legitimate usage of resources by it’s users.

Components Introduction Needs & Necessity Standard Protocols An Example Looking Back A User who wishes to use some resources on network A Key Distribution Center that gives user a session key, when he logs in. An Authentication Server which authenticates user. A Ticket Granting Server which allows usage of multiple resources on network.

… 1 2 N How it works ? Introduction Needs & Necessity Standard Protocols An Example Looking Back … User AS KDC 1 2 N TGS

Realms Introduction Needs & Necessity Standard Protocols An Example Looking Back KDC Network 2 Network 1 TGS TGS AS AS AS User Network 3 Network N TGS AS TGS

SSL/HTTPS Introduction Needs & Necessity Standard Protocols An Example Looking Back It’s a session or application level protocol to ensure security. SSL is Secure Socket Layer and HTTPS is Secure Hyper Text Transfer Protocol.

Components Introduction Needs & Necessity Standard Protocols An Example Looking Back A User who wishes to use some resources or communicate with other user. A User or Server who wishes to communicate (to provide some service) with above user needs to prove his identity. A Hacker

How it works ? Introduction Needs & Necessity Standard Protocols An Example Looking Back Hello Cert Prove MAC User Server Hacker

A user needs to carry information on the go from incumbent system. Introduction Needs & Necessity Standard Protocols An Example Looking Back A user needs to carry information on the go from incumbent system. Information needs to be authenticated before it leaves incumbent system. A component in system provides mechanism of authenticating information after scrutiny based upon following measures: 1. Ask information bearer of the source of information. 2. Scrutinize based upon information at hand and their persistent knowledge.

How it works ? 2 User 3 Policy Implementer 1 Authenticating component Introduction Needs & Necessity Standard Protocols An Example Looking Back 2 User Policy Implementer 3 1 Authenticating component

Are you familiar with the protocol in previous slide ? Introduction Needs & Necessity Standard Protocols An Example Looking Back Are you familiar with the protocol in previous slide ?