Chapter 30
Chapter 30: Cryptography (Detailed Notes)
Overview
Cryptography is the science of securing communication through techniques of transforming messages into secure formats. It plays a key role in network security, ensuring confidentiality, integrity, authentication, and non-repudiation of data .
Key Concepts and Definitions
Plaintext and Ciphertext:
Plaintext: The original message before transformation.
Ciphertext: The encrypted message after transformation. Encryption algorithms convert plaintext into ciphertext, and decryption algorithms reverse this process .
Cipher: A combination of encryption and decryption algorithms used to secure communication .
Key: A number or set of numbers used by encryption and decryption algorithms. Cryptography relies heavily on the use of keys for securing information .
Categories of Cryptography
Symmetric-Key Cryptography:
The same key is used by both the sender and the receiver for encryption and decryption. Symmetric-key cryptography is efficient for large-scale data encryption.
However, a challenge is distributing keys securely among multiple parties. The more entities involved, the greater the complexity in managing keys .
Asymmetric-Key Cryptography:
Uses a pair of keys: a public key for encryption and a private key for decryption. This method eliminates the problem of key distribution faced in symmetric-key cryptography.
RSA Algorithm: A popular asymmetric algorithm that uses two large prime numbers to create public and private keys .
Symmetric-Key Cryptography
Traditional Ciphers: Substitution and transposition ciphers were used historically, replacing or rearranging characters in plaintext. Though simple, these methods are not secure by modern standards .
DES (Data Encryption Standard): A symmetric-key encryption method widely used for decades. DES operates using a 56-bit key and undergoes 16 rounds of encryption. Due to its shorter key size, it has been largely replaced by newer standards like AES .
Triple DES (3DES): An extension of DES that increases key size to improve security by applying DES three times with different keys .
AES (Advanced Encryption Standard): A more modern and secure encryption algorithm using block ciphers with a key size of 128, 192, or 256 bits. It is considered highly secure and efficient .
Asymmetric-Key Cryptography
RSA (Rivest-Shamir-Adleman): One of the most common public-key encryption systems. RSA uses large prime numbers to generate keys. Although secure, it is slower than symmetric-key algorithms, so it is often used for encrypting smaller data or to secure session keys in hybrid encryption schemes .
Diffie-Hellman: A key exchange protocol that enables two parties to establish a shared secret over an insecure channel without revealing the key. It is vulnerable to man-in-the-middle attacks unless additional authentication is applied .
Modern Ciphers and Modes of Operation
Block Ciphers and Stream Ciphers: Encryption techniques like DES and AES divide data into blocks (block ciphers) or operate bit by bit (stream ciphers).
Modes of Operation: Techniques that deploy ciphers include ECB (Electronic Codebook), CBC (Cipher Block Chaining), CFB (Cipher Feedback), and OFB (Output Feedback). These modes dictate how the encryption algorithm processes large sets of data .
Key Management
Symmetric-Key Distribution: Managing keys between parties is difficult in symmetric-key cryptography due to the need for secure communication of the key itself. Large groups require complex key management systems .
Key Distribution Center (KDC): A trusted third-party service that manages and distributes keys among users to reduce the complexity of key management .
Attacks and Security Concerns
Man-in-the-Middle Attack: In Diffie-Hellman key exchanges, an attacker can intercept messages between two parties and establish their own key with each party, making them think they are communicating securely with one another .
Brute Force Attack: Symmetric ciphers like DES can be broken with brute force attacks due to relatively small key sizes, which is why DES was replaced by AES .
These concepts are critical for understanding network security, which is explored in more depth in subsequent chapters.
Last updated