Cybersecurity Midterm

Confidentiality

Ensures that sensitive information remains private and is only accessible to authorized users.

Symmetric Cryptography

Uses the same key for encryption and decryption; faster and used for bulk encryption (e.g., DES, AES).

Asymmetric Cryptography

Uses a public key for encryption and a private key for decryption; used for key exchange and digital signatures (e.g., RSA, Diffie-Hellman).

Confusion

Obscures the relationship between ciphertext and the key, making it difficult to derive the key.

Diffusion

Ensures that changing one bit in plaintext significantly changes the ciphertext, hiding patterns in the plaintext.

Permutation

Rearranges the order of bits without changing their values.

Substitution

Replaces bits or groups of bits with different values to increase security.

Feistel Cipher

A cryptographic structure that alternates substitution and permutation over multiple rounds, dividing plaintext into two halves and applies a function to one half using a subkey before swapping.

DES Algorithm

Symmetric block cipher with a 64-bit block size and a 56-bit key, applying 16 rounds of Feistel structure.

What makes the DES algorithm weak?

Key size is too short, making it vulnerable to brute-force attacks.

Double DES

Uses two rounds of DES but is vulnerable to the Meet-in-the-Middle Attack, which reduces security. Can be broken from the sides.

Triple DES

Utilizes three rounds of DES for increased security but remains vulnerable to the Meet-in-the-Middle Attack.

AES (Advanced Encryption Standard)

Replaced DES due to stronger security and efficiency, with a block size of 128 bits and variable key sizes (128, 192, 256 bits).

Avalanche Effect

Small changes in input drastically change the output of AES encryption.

Steps per round of AES encryption

Byte Substitution (S-Box) – Non-linear transformation.

Shift Rows – Row-wise cyclic shifts.

Mix Columns – Matrix multiplication for diffusion.

Add Round Key – XOR with round key.

ECB (Electronic Codebook)

A mode of block cipher where each block is encrypted independently, insecure for long messages due to repeating patterns.

CBC (Cipher Block Chaining)

A block cipher mode where each block is XORed with the previous ciphertext block before encryption.

CFB (Cipher Feedback)

Converts a block cipher into a self-synchronizing stream cipher.

OFB (Output Feedback)

Generates keystream blocks before XORing with plaintext, preventing error propagation.

CTR (Counter Mode)

Uses a counter instead of feedback, allowing parallel encryption for speed and efficiency.

Stream Ciphers

Encrypts data one bit or byte at a time, requiring a random keystream that must not be reused. Used in real-time communication and wireless encryption.

Block Cipher

Encrypts data in fixed-size blocks (e.g., 64-bit, 128-bit), utilizing structures like Feistel in DES.

Main differences between block and stream ciphers?

Block: Encrypts data in fixed size blocks (64, 128) and uses Feistel structure.

Stream: Encrypts one bit/byte at a time and required a keystream.

Public Key

Developed to solve key distribution problems, utilizing public-private key pairs for security (RSA and Diffie-Hellman).

Applications: Encryption, digital signatures, key exchange.

Trapdoor One-Way Function

Easy to compute in one direction but hard to reverse without the secret key.

Meet-in-the-Middle Attack

An attack that reduces security, particularly against Double DES.

IV (Initialization Vector) Mistakes

Must be unique and unpredictable to ensure the security of encryption.

Padding (PKCS#5)

Ensures plaintext properly fits the block size for encryption.