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

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

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

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

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.

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

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

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

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

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

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)

Distributed System Security: RSA Algorithm ● Alice finds two large prime numbers p, q ● Alice computes n=p*q and  =(p-1)*(q-1) ● Alice picks a random number e, between 1 and  -1 such that e is relatively prime to  ● 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)

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

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

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

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

Distributed System Security: Applications ● PGP – “Pretty Good Privacy” – Freeware file and 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

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

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

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 ● Ian Blake, Gadiel Seroussi, Nigel Smart. Elliptic Curves in Cryptography 1999