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
Cryptography: Ciphers, Security, and MAC
Miscellaneous: Secret (Symmetric), Public (Asymmetric).
Math:
- XOR (a ⊕ b) is 0 if the values are the same, 1 if they are different. c = (x ⊕ k) is random and independent of the original X.
- Addition: Given x is a binary string of length n, and a is an integer, then (a+x) is the n least significant bits of the binary encoding of adding the values a and x.
- Given n bits, Pr[any one string] = 1/2n.
Classical Ciphers/Principles:
- Shift: Shifts all letters by the same amount (key). It can be cracked by brute-