Distributed System Security

1. 4/22/04 CPSC 550 Brian Williams Distributed System Security

2. Distributed System Security: Goals • Complete Protection Against All Possible Attacks • Attacks: • Leakage • Attacker intecepts message he/she is unauthorized to access • Tampering • Attacker intercepts and alters a network message, giving benefit to the attacker • Vandalism • Attacker intercepts and alters a network message, but without benefit to the attacker

3. Distributed System Security: Goals System Security reduces to data encryption Attacker Encryption Computer 2 Computer 1

4. Distributed System Security: Definitions • Public Key – Encryption key that is well-known and/or not hidden from third parties • Private Key – Encryption key that is known only by the message sender and/or receiver • Public Key Encryption – An encryption scheme that make use of a public key • Secret Key Encryption – An encryption scheme that implores only private keys

5. Distributed System Security: Definitions • One Way Function – A one-to-one mathematical function that is easily computable, but whose inverse is very difficult to compute • Secure Digest Function – A function that takes an argument M, and returns a fixed length “digest” V, such that V1 is probably much different than V2, for distinct M1, M2.

6. Distributed System Security:Naming Conventions • Alice – First participant in network communication • Bob – Second participant in network communication • Carol – Third Participant (when applicable) • Dave – Fourth Participant (when applicable) • Eve – Eavesdropper • Mallory – Malicious Attacker • Sara – A Server

7. Distributed System Security: Structure • Always prepare for worst-case scenarios • We Assume • Our System Interfaces are exposed • Attacker can send message to any address on the network • Our Network is insecure • Attacker can spoof the address of any message he/she sends with any address value • Our algorithms and their source code are availible to the attackers • Attackers have the best computing equipment made during the lifetime of our system

8. Distributed System Security: Structure (2) • Private Key Encryption • Alice & Bob share knowledge of a secret key K • Alice encrypts her message M, with E(M,K) • Bob decrypts Alices message by D(E(M,K)) = M • Public Key Encryption • Bob creates two keys, Kd and Ke • Bob sends Alice Ke • Alice encrypts her message with E(M,Ke) • Bob decrypts the message with D(E(M,Ke),Kd) = M • Mallory cannot find Kd, even though she knows Ke

9. Distributed System Security: History • Encryption algorithms date back as far as the Ancient Greeks • Military commanders needed to hide their plans from the enemy • National Bureau of Standards calls for official encryption algorithm in 1973 • Adopts “Lucifer” algorithm in 1976 • Now known as Data Encryption Standard (DES) • National Security Agency restricts key sizes to 56 bits

10. Distributed System Security: History • Researchers at Stanford announce Diffie-Hellman-Merkle algorithm in 1976 • Allows for secret key exchange over an insecure channel • Ronald Rivest, Adi Shamir and Leonard Adleman announce RSA algorithm in 1997 • First public key encryption algorithm

11. Distributed System Security:Diffie-Hellman-Merkle Algorithm • Alice and Bob generate seperate and secret keys Ka and Kb • Alice generates another number g, and sends it to Bob • Alice computers g^Ka (mod n) and sends it Bob, while Bob computers g^Kb (mod n) and sends it to Alice • Alice computes (g^Kb)^Ka (mod n) and Bob computes (g^Ka)^Kb (mod n)

12. Distributed System Security:RSA Algorithm • Alice finds two large prime numbers p, q • Alice computes n=p*q and f=(p-1)*(q-1) • Alice picks a random number e, between 1 andf-1 such that e is relatively prime to f • Alice computes d, where e*d = 1 (mod n) • Alice sends e and n to Bob • Bob encrypts his message as E=M^e (mod n) • Alice decrypts his message with D = E^d (mod n)

13. Distributed System Security: Remaining Vunerabilities • Remaing System Vunerabilities • 1) Mallory can still send messages to Bob, spoofed with Alice's address • 2) Mallory can copy messages that Alice sent, and replay them to Bob at a later time • 3) Mallory can intercept the messages containing the initial key exchange and replace Alice's messages with her own

14. Distributed System Security: Vunerablity Solutions • Attack 1: Spoofed messages • Bob attaches a checksum to the end of all his messages before encrypting them • Attack 2: Message Replay • Bob attaches a timestamp to each of his messages • Attack 3: Man-in-the-Middle • Bob and Alice must be able to authenticate each other's first unencrypted messages

15. Distributed System Security:Man-in-the-Middle Attack • Digital Signature • Bob encrypts his message with his private key • Alice et. al. can decrypt the message with Bob's public key • Only Bob has the private key needed to encrypt the message, so the message must have been from Bob • Digital Certificate • Trusted Authority distributes public keys, which they have digitally signed

16. Distributed System Security: Features • Security • System trust is reduced to • Trust in Trusted Authority • Encryption Algorithm • Passwords don't need to be transmitted • Verify identity through “challenges” • Hybrid Methods • Speed of Secret Key with convenience of Public Key

17. Distributed System Security: Applications • PGP • “Pretty Good Privacy” • Freeware file and e-mail encryption program • 128-bit RSA Public Key Encryption & 128-bit MD5 digest function • Secure Sockets Layer (SSL) • Operating system and encryption algorithm independent network protocol layer

18. Distributed System Security: Significant Points • Today's Systems are strong • Virtually unbounded levels of encryption through increased key size • New encryption methods based on the properties of elliptic curves are faster and stronger for a given key size • Trusted authorities and digital signatures insure identity of data sources

19. Distributed System Security: Signficant Points • Weakest Security Link Today: the User • Ignorance of Security Issues • Complacency towards Security • Focus must be on education of end users • Users must understand their role in security • Users must not become complacent towards security issues

20. Distributed System Security:References • George Coulouris, Jean Dollimore, Tim Kingberg. Distributed Systems: Concepts and Design 2001 • Rita C. Summers. Secure Computing 1997 • Simon Singh. The Code Book 1999 • Alan O. Freier, Philip Karlton, Paul C. Kocher, The SSL Protocol Version 3.0 1996 http://wp.netscape.com/eng/ssl3/draft302.txt • Ian Blake, Gadiel Seroussi, Nigel Smart. Elliptic Curves in Cryptography 1999