🔐Cryptography Unit 10 – Applied Cryptography

Key Concepts and Terminology

• Cryptography involves the study and practice of secure communication in the presence of adversaries
• Plaintext refers to the original, unencrypted message or data
• Ciphertext is the encrypted version of the plaintext, transformed using a cryptographic algorithm
• Encryption is the process of converting plaintext into ciphertext to protect its confidentiality
• Decryption reverses the encryption process, converting ciphertext back into plaintext
• Cryptographic keys are secret values used in conjunction with algorithms to encrypt and decrypt data
  • Symmetric keys are used for both encryption and decryption in symmetric cryptography
  • Public and private key pairs are used in asymmetric (public-key) cryptography
• Cryptographic hash functions produce fixed-size digests (hash values) from arbitrary-length inputs
  • Hash functions are designed to be one-way and collision-resistant

Cryptographic Algorithms and Protocols

• Symmetric encryption algorithms use the same key for both encryption and decryption
  • Examples include AES (Advanced Encryption Standard) and DES (Data Encryption Standard)
• Asymmetric encryption algorithms, also known as public-key cryptography, use a pair of keys: a public key for encryption and a private key for decryption
  • RSA (Rivest-Shamir-Adleman) and ECC (Elliptic Curve Cryptography) are widely used asymmetric algorithms
• Cryptographic protocols define a sequence of steps and rules for secure communication between parties
• Key exchange protocols, such as Diffie-Hellman, enable secure establishment of shared secret keys over insecure channels
• Digital signature schemes, like DSA (Digital Signature Algorithm), provide authentication, integrity, and non-repudiation
• Cryptographic hash functions, including SHA-256 and SHA-3, generate fixed-size digests for data integrity and verification purposes

Encryption Techniques and Methods

• Block ciphers operate on fixed-size blocks of plaintext and ciphertext
  • Examples include AES, which uses 128-bit blocks, and DES, which uses 64-bit blocks
• Stream ciphers encrypt plaintext one bit or byte at a time, generating a pseudorandom keystream
  • RC4 is a widely used stream cipher, although it has known vulnerabilities
• Padding schemes, such as PKCS#7, are used to ensure the plaintext length is a multiple of the block size
• Block cipher modes of operation define how blocks are encrypted and linked together
  • ECB (Electronic Codebook) mode encrypts each block independently, which can lead to patterns in the ciphertext
  • CBC (Cipher Block Chaining) mode XORs each plaintext block with the previous ciphertext block before encryption
  • CTR (Counter) mode combines a nonce and a counter to generate a unique keystream for each block
• Authenticated encryption modes, like GCM (Galois/Counter Mode), provide both confidentiality and integrity

Digital Signatures and Authentication

• Digital signatures provide authentication, integrity, and non-repudiation for digital documents and messages
• The signer uses their private key to generate a signature on the message or hash of the message
• The signature can be verified using the signer's public key to ensure the message originated from the claimed signer and has not been tampered with
• Digital certificates, issued by trusted Certificate Authorities (CAs), bind a public key to an identity
  • X.509 is a widely used standard for digital certificates
• Public Key Infrastructure (PKI) establishes a framework for managing digital certificates and enabling secure communication
• Message Authentication Codes (MACs) provide message integrity without non-repudiation
  • HMAC (Hash-based MAC) combines a cryptographic hash function with a secret key

Key Management and Distribution

• Key management involves the secure generation, storage, distribution, and destruction of cryptographic keys
• Key generation techniques ensure keys have sufficient randomness and are generated securely
  • Pseudorandom number generators (PRNGs) and hardware random number generators (HRNGs) are used for key generation
• Key storage requires protecting keys from unauthorized access and tampering
  • Hardware security modules (HSMs) provide secure key storage and cryptographic operations
• Key distribution protocols, such as Diffie-Hellman, enable secure key exchange over insecure channels
• Key rotation involves regularly replacing keys to limit the impact of key compromise
• Key revocation mechanisms, like certificate revocation lists (CRLs), allow for invalidation of compromised or expired keys

Cryptanalysis and Attack Methods

• Cryptanalysis is the study of techniques for breaking or weakening cryptographic systems
• Brute-force attacks involve exhaustively trying all possible key combinations until the correct key is found
  • The security of a cryptographic system depends on the key size and the computational power available to attackers
• Differential cryptanalysis analyzes how differences in plaintext pairs affect differences in ciphertext pairs
• Linear cryptanalysis exploits linear approximations of the cipher's components to recover the key
• Side-channel attacks exploit physical characteristics of the cryptographic implementation
  • Timing attacks observe variations in execution time to infer information about the key or plaintext
  • Power analysis attacks measure power consumption to extract sensitive information
• Quantum computing poses a threat to certain cryptographic algorithms, particularly those based on integer factorization (RSA) and discrete logarithms (Diffie-Hellman, ECC)
  • Post-quantum cryptography aims to develop algorithms resistant to quantum attacks

Real-World Applications and Use Cases

• Secure communication protocols, like HTTPS and SSL/TLS, rely on cryptography to protect data transmitted over networks
  • HTTPS encrypts web traffic between clients and servers using a combination of symmetric and asymmetric cryptography
• Secure storage solutions, such as full disk encryption, protect data at rest using cryptographic techniques
  • BitLocker and FileVault are examples of disk encryption software
• Digital rights management (DRM) systems use cryptography to control access to and usage of copyrighted digital content
• Cryptocurrencies, like Bitcoin and Ethereum, utilize cryptographic primitives for secure transactions and consensus mechanisms
  • Blockchain technology relies on cryptographic hash functions and digital signatures for integrity and authentication
• Secure messaging applications, such as Signal and WhatsApp, employ end-to-end encryption to protect user privacy

Security Considerations and Best Practices

• Use well-established and thoroughly reviewed cryptographic algorithms and protocols
  • Avoid custom or proprietary algorithms that have not undergone extensive scrutiny
• Select appropriate key sizes to ensure adequate security based on the expected lifetime of the protected data
  • NIST recommends using AES with at least 128-bit keys and RSA with at least 2048-bit keys
• Properly manage and protect cryptographic keys throughout their lifecycle
  • Use secure key generation techniques and store keys securely
  • Regularly rotate and revoke keys to minimize the impact of key compromise
• Implement secure random number generators for key generation and other cryptographic purposes
  • Avoid using weak or predictable sources of randomness
• Use authenticated encryption modes to provide both confidentiality and integrity for encrypted data
• Properly validate and verify digital signatures to prevent forgery and ensure data integrity
• Keep cryptographic libraries and implementations up to date with the latest security patches and best practices
• Regularly audit and test cryptographic systems for vulnerabilities and weaknesses