Fundamentals of Computer Security and Cryptography
Computer Security refers to the protection of computer systems and networks from theft, damage, unauthorized access, misuse, or disruption of services. It ensures confidentiality, integrity, and availability of data.
The need for security arises because of increasing cyber threats, sensitive data storage (e.G., financial records, medical data), online transactions, and dependence on cloud services. Without security, systems are vulnerable to data breaches, identity theft, and financial losses.
Security
Data Encryption Standard (DES) and Core Cipher Concepts
Data Encryption Standard (DES) Algorithm Explained
The Data Encryption Standard (DES) is a symmetric-key block cipher developed in the 1970s by IBM and adopted by the US government. It encrypts data in 64-bit blocks using a 56-bit key.
How DES Works
- Initial Permutation (IP): The 64-bit plaintext goes through an initial permutation, which shuffles the bits according to a fixed table.
- Divide into Halves: The permuted text is split into two 32-bit halves: Left (L0) and Right (R0).
- 16 Rounds of Feistel Operations:
Cryptography Fundamentals: Symmetric Ciphers and Block Design
Cryptography and the Symmetric Cipher Model
Cryptography is the science of protecting information by transforming it into a secure format. It ensures data confidentiality, authenticity, integrity, and sometimes non-repudiation during communication or storage.
The Symmetric Cipher Model
In the symmetric cipher model, the same secret key is used for both encryption and decryption of messages.
Key Components of a Symmetric Cipher
- Plaintext (P): The original readable message or data.
- Encryption Algorithm:
Cybersecurity Fundamentals: Authentication, Encryption & Threats
Message Authentication
Message authentication verifies that a message received over a communication channel is from the legitimate sender and has not been altered during transmission. It ensures data integrity, authenticity, and often non-repudiation (in the case of digital signatures).
Goals of Message Authentication
- Authenticity: Confirms that the message came from the stated sender.
- Integrity: Ensures the message has not been changed.
- Non-repudiation (optional): Prevents the sender from denying having
Secure Key Communication: Methods, Protocols, and Security
Secure Key Communications
Three Methods for Secure Key Exchange:
- Trusted Third Party: A central server delegates keys. Every user has a secret key, and the server knows everyone’s keys.
- A → T: { A, B }
- T → A: { Na, Kab, B, {Kab, A}Kb }Ka
- A → B: { Kab }Kb
Problems with Trusted Third Party:
- B doesn’t know who is communicating.
- Replay attack.
- If the server is compromised, it’s a single point of failure, and all user keys are compromised.
- The server can crash due to a denial-of-service attack.
Needham-
Read MoreCryptography Fundamentals: Encryption, Authentication, PKI
Cryptography Fundamentals
1. General Model for Communication
- Alice wants to send a message m to Bob.
- Eve is an adversary who may try to eavesdrop or modify the message.
- The goal of cryptography is to ensure that Eve cannot read or alter the message without authorization.
2. Encryption: Preventing Eavesdropping
- Encryption is used to prevent Eve from reading the message.
Key Concepts:
- Secret Key (Ke): A shared key between Alice and Bob. The longer the key, the higher the security.
- Plaintext (m): The original