1. Security Management

2. Given Credit Where It Is Due
Most slides are from Scott Shenker and Ion Stoica at University of California, Berkeley
I have modified and added some slides

3. Outline
Key Management
Group management
Authorization management

4. Authentication Using Public-Key Cryptography
KA+, KB+: public keys
KB+(A, RA) 1 2
KA+(RA, RB,KA,B)
Alice
Bob 3
KA,B(RB)
What if KA+ or KB+ is faked?

5. 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)
Diffie-Hellman key exchange

6. Components of a PKI

7. Digital Certificate
Signed data structure that binds an entity (E) with its corresponding public key (KE+)
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 KCA-(E, KE+)
Everyone can verify signature using KCA+

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

9. 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.

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

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

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

13. 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Process of publicly announcing that a certificate has been revoked and should no longer be used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

14. Key Establishment Method 1
What’s your public key?
Bob picks a symmetric key and encrypts it using Alice’s public key
Alice decrypts the symmetric key using her private key
Then sends the key to Alice
Bob encrypts his message using the symmetric key
Then sends the message to Alice
Alice decrypts the message using the symmetric key hi

15. Key Establishment Method 2: Diffie-Hellman Key Exchange
Agree on two numbers n, g; both numbers can be made public!
Alice and Bob pick two secret numbers x and y
n=10, g=7, x=3, g^x mod n = 3;
y=5, g^{xy} mod n = 3;
g^y mod n = 7;
g^{xy} mod n = 3.

16. Outline
Key Management
Group management
Authorization management

17. Secure Group Management
Motivation: offer high availability for security services
How: replicate services
Problem: how to add a new replica to a group without compromising the integrity of the group?

18. Securely Admitting A New Group Member
CKG: secret key used for communication within group
KG+,KG-: public-private key pair to communicate with non-group members
KP,G: secret key
RP: reply pad
T: local time
Notation: [X]Y: X was signed by Y
join request
group admittance
Process in group G
New process

19. Outline
Key Management
Group management
Authorization management

20. Authorization Management
Granting authorization rights
Related with access control which verifies access rights

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

22. Capabilities (2) Capability:
Unforgeable data structure for a specific resource R
Specify access right the holder has with respect to R
Capability in Amoeba (one of the first object-based DS):
48 bits
24 bits
8 bits
Server port
Object
Rights
Check
Amoeba was one of the first object-based distributed systems.

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

24. 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

25. Delegation A wants to delegate an operation on a resource to B
Problem: how does A delegates its access rights to B?
Solutions: A signs (A, B, R)
If B wants to delegate operation to C, C needs to contact A
Avoid this problem using a proxy (Neuman scheme)
Proxy: a token allowing its owner to operate with the same or restricted rights as the entity granting the token

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

27. 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
If Bob wants to delegate some of his access rights to Chuck, how to do that securely without Alice’s involvement?

28. Virus vs. Worm