1. Key Management

2. Authentication Using Public-Key Cryptography  K A +, K B + : public keys Alice Bob K B + (A, R A ) 1 2 K A + (R A, R B,K A,B ) 3 K A,B (R B )  What if K B + is faked?

3. Security Management  Problem: how do you get keys in the first place?  Key distribution: securely associate an entity with a key -Example: Public Key Infrastructure (PKI), a system that manages public key distribution on a wide-scale  Key establishment: establish session keys -Use public key cryptography (we already know how to do it)

4. Components of a PKI

5. Digital Certificate  Signed data structure that binds an entity (E) with its corresponding public key (K E + ) -Signed by a recognized and trusted authority, i.e., Certification Authority (CA) -Provide assurance that a particular public key belongs to a specific entity  How? -CA generates K CA - (E, K E + ) -Everyone can verify signature using K CA +

6. Certification Authority (CA)  People, processes responsible for creation, delivery and management of digital certificates  Organized in a hierarchy (use delegation – see next) CA-1CA-2 Root CA

7. Registration Authority  People, processes and/or tools that are responsible for -Authenticating the identity of new entities (users or computing devices) -Requiring certificates from CA’s.

8. Certificate Repository  A database which is accessible to all users of a PKI, contains: -Digital certificates, -Certificate revocation information -Policy information

9. Example  Alice generates her own key pair. public key Alice private key Alice  Bob generates his own key pair.  Both sent their public key to a CA and receive a digital certificate public key Bob private key Bob

10. Example  Alice gets Bob’s public key from the CA private key Alice public key Bob private key Bob public key Alice  Bob gets Alice’s public key from the CA

11. Certificate Revocation  Process of publicly announcing that a certificate has been revoked and should no longer be used.  Approaches: -Use certificates that automatically time out -Use certificate revocation list

12. Authorization Management

13.  Granting authorization rights  Related with access control which verifies access rights

14. Capabilities (1)  How to grant a capability?  How to verify a capability?

15. Capabilities (2)  Capability: -Unforgeable data structure for a specific resource R -Specify access right the holder has with respect to R  An example: 48 bits24 bits8 bits48 bits Server portObjectRightsCheck

16. Capabilities (3)  Generation of a restricted capability from an owner capability Owner

17. Delegation: Motivation Example  A user Alice has read-only access rights on a large file F  Alice wants to print F on printer P no earlier than 2am -Method A: Alice sends the entire file F to the printer P; -Method B: Alice passes the file name to P and printer P copies the file F to its spooling directory when F is actually needed. -For method B, Alice needs to delegate her read-only access rights on F to printer P

18. Delegation: Neuman Scheme  The general structure of a proxy as used for delegation:

19. Delegation: Neuman Scheme  Using a proxy to delegate and prove ownership of access rights  In practice S + proxy, S - proxy can be a public-private key pair and N can be a nonce