Distributed System Security - Distributed Operating Systems - Lecture Slides, Slides of Computer Science

Download Distributed System Security - Distributed Operating Systems - Lecture Slides and more Slides Computer Science in PDF only on Docsity!

Distributed System Security

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

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

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.

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 Docsity.com

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 KeDocsity.com

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

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)

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

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: 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

Applications

● PGP

• “Pretty Good Privacy”
• Freeware file and e-mail encryption program
• 128-bit RSA Public Key Encryption & 128-bit MD digest function

● Secure Sockets Layer (SSL)

• Operating system and encryption algorithm independent network protocol layer

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