Public Key Distribution

Public Key Distribution by Azaharul Islam Asik

1. Welcome to My Presentation!!! Prepared By: Md. Azaharul Islam Asik Studying… Dept. of Computer Science and Engineering Jessore University of Science & Technology

2. Public Key Distribution

3. What is Public-Key? In public-key cryptography, everyone has access to everyone’s public-key ; Public keys are available to the public.

4. Distribution of Public Keys It can be considered as using one of: Public announcement Public directory Public key authority Public key certificates

5. Public Announcement Users distribute public keys to recipients or broadcast to community at large. PGP keys to email messages or post to news groups or email list. Major weakness is forgery Anyone can create a key claiming to be someone else and broadcast it. Until is discovered can masquerade as claimed user.

6. Public Announcement A B PUa PUa PUa . . . PUb PUb PUb . . . Figure-1: Public Announcement

7. Public Available Directory Can obtain greater security by registering keys with a public directory Directory must be trusted with properties: contains {name, public-key} entries p articipants register securely with directory p articipants can replace key at any time d irectory is periodically published d irectory can be accessed electronically Still vulnerable to tampering or forgery

8. Public Available Directory Public-Key Directory User B User A PUa PUb Figure-2: Public Key Directory

9. Publicly-Key Authority Improve security by tightening control over distribution of keys directory. Has properties of directory And requires users to know public key for the directory. Then the users interact with directory to obtain any desired public key securely Does require real-time access to directory when keys are needed. May be vulnerable to tampering.

10. Publicly-Key Authority Public-Key Authority A B (1)Request || Time1 (2)E( PRautho , [Pub || Request || Time1]) Figure-3: Public-Key Authority (4)Request || Time2 (5)E( PRautho , [Pub || Request || Time1]) (3)E( PUb , [IDA || N1]) (6)E( PUa , [N1 || N1]) (7)E( PUb , N2)

11. Publicly-Key Certificates Certificates allow key exchange without real time access to public key-authority. A certificate binds identity to public key Usually with other info such as period of validity, rights of use etc With all contents signed by a trusted Public-Key or Certificate Authority (CA) Can be verified by anyone who knows the public-key authorities public-key.

12. Publicly-Key Certificates Certificate Authority A B PUa PUb CA CB CA=E( PRauth , [Time1 || IDA || PUa ]) CB=E( PRauth , [Time2 || IDB || PUb ]) Figure-4: Public-Key Certificates

13. Any Question ? [email protected]

14. Thank You Everyone!!!