1. Cryptographic Protocols
By:
Kirti Chawla

2. 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.

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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

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

16. 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.

17. 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.

18. … 1 2 N How it works ? Introduction Needs & Necessity
Standard Protocols
An Example
Looking Back …
User AS
KDC 1 2 N
TGS

19. 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

20. 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.

21. 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

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

23. 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.

24. 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

25. 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 ?