Distributed Systems
COMP90015 2021 Semester 1
Tutorial 08
Today’s Agenda
- Assignment 2 Q & A
- Questions on Security (partial)
- Demo on File Transfer
- Demo on Git
Assignment 2 Q & A
1. What are the different security threats and methods of attacks in a
distributed system?
Security Threats
Three broad Classes:
Leakage: Acquisition of information by unauthorised recipients
Tampering: Unauthorised alteration of information
Vandalism: Interference with the proper operation of systems
Method of Attacks
Eavesdropping - A form of leakage obtaining private or secret information or
copies of messages without authority.
Masquerading – A form of impersonating assuming the identity of another
user/principal – i.e, sending or receiving messages using the identity of another
principal without their authority.
Message tampering- altering the content of messages in transit man in the middle
attack (tampers with the secure channel mechanism)
Replaying- storing secure messages and sending them at a later date
Denial of service - Vandalism flooding a channel or other resource, denying access
to others
2. List and briefly explain some worst case assumptions when designing a secure
system.
● Networks are insecure.
○ Messages can be looked at, copied, modified and retransmitted,
○ Attackers can obtain information that they should not and can pretend to be a legitimate party.
● The source code is known to the attacker.
○ Knowing the source code can help the attacker discover vulnerabilities.
● Interfaces are exposed
○ Communication interfaces are necessarily open to allow clients to access them.
○ Attackers can send messages to any interface.
● The attacker has unlimited computing resources.
○ Assume that attackers will have access to the largest and most powerful computers projected
in the lifetime of a system.
2. List and briefly explain some worst case assumptions when designing a
secure system.
3. Define encryption and describe the two main types of keys used by encryption
algorithms.
● Encryption
○ process of encoding a message in such a way as to hide its contents.
● Shared secret keys (symmetric)
○ Sender and recipient share knowledge of the key and it must not be revealed to anyone
else.
● Public/private key pairs (asymmetric)
○ The sender uses a public key to encrypt the message.
○ The recipient uses a corresponding private key to decrypt the message.
○ Only the recipient can decrypt the message, because they have the private key.
○ Typically require 100 to 1000 times as much processing power as secret-key algorithms.
3. Define encryption and describe the two main types of keys used by encryption
algorithms.
Code Demo
● Sending/Receiving files with Java Sockets
Demo : Git
For more details: EGitTutorial.pdf




























































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