🔒Cybersecurity and Cryptography Unit 10 – Crypto Hashes and Message Authentication

What's the Big Deal?

• Crypto hashes and message authentication are essential for ensuring data integrity and authenticity in digital communications
• Help protect against tampering, forgery, and unauthorized access to sensitive information (financial transactions, personal data)
• Enable secure storage of passwords and other credentials by transforming them into irreversible hashes
• Form the foundation for digital signatures, which verify the origin and integrity of messages and documents
• Play a critical role in blockchain technology, ensuring the immutability and integrity of transaction records
• Used in various domains, including cybersecurity, e-commerce, and secure messaging applications
• Provide a reliable means of detecting any unauthorized modifications to data during transmission or storage

Key Concepts

• Cryptographic hash functions: mathematical algorithms that take an input (message) and produce a fixed-size output (hash)
  • One-way functions: computationally infeasible to reverse the hash and obtain the original message
  • Collision resistance: extremely difficult to find two different messages that produce the same hash value
• Message authentication codes (MACs): short pieces of information used to authenticate a message and ensure its integrity
  • Generated using a secret key shared between the sender and the receiver
  • Provide data origin authentication and detect any unauthorized modifications to the message
• Digital signatures: mathematical schemes that demonstrate the authenticity and integrity of a message or document
  • Generated using the sender's private key and verified using the corresponding public key
  • Non-repudiation: the sender cannot deny having sent the message, as the signature is unique to their private key
• Salting: adding random data (salt) to the input before hashing to enhance security against precomputation attacks (rainbow tables)
• Keyed-hash message authentication code (HMAC): a specific type of MAC that involves a cryptographic hash function and a secret key
  • Provides both message authentication and integrity protection
  • Widely used in secure communication protocols (SSL/TLS, IPsec)

How It Works

• Cryptographic hash functions take an input message of arbitrary length and produce a fixed-size output (hash value or digest)
  • The hash value is a unique representation of the input message
  • Even a small change in the input results in a completely different hash value (avalanche effect)
• Message authentication codes (MACs) are generated by combining the message with a secret key and passing it through a MAC algorithm
  • The sender computes the MAC and appends it to the message before sending
  • The receiver recomputes the MAC using the same secret key and compares it with the received MAC to verify the message's authenticity and integrity
• Digital signatures are created using asymmetric cryptography (public-key cryptography)
  • The sender signs the message using their private key, which is kept secret
  • The receiver verifies the signature using the sender's public key, which is widely distributed
  • The signature ensures the message originated from the claimed sender and has not been altered during transmission
• Hashing passwords before storing them in a database adds an extra layer of security
  • Even if the database is compromised, the attacker cannot directly obtain the original passwords
  • Salting the passwords before hashing makes it harder for attackers to use precomputed hash tables (rainbow tables) to crack the passwords

Types and Algorithms

• Commonly used cryptographic hash functions:
  • SHA (Secure Hash Algorithm) family: SHA-1, SHA-256, SHA-512
    • SHA-1 is considered insecure due to potential collisions and should be avoided
    • SHA-256 and SHA-512 are widely used and considered secure for most applications
  • MD5 (Message-Digest Algorithm 5): historically popular but now considered insecure due to collisions
  • BLAKE2: a fast and secure hash function optimized for performance on modern processors
• Message authentication code algorithms:
  • HMAC (Hash-based Message Authentication Code): combines a cryptographic hash function (e.g., SHA-256) with a secret key
    • Widely used in secure communication protocols (SSL/TLS, IPsec)
  • CMAC (Cipher-based Message Authentication Code): based on block ciphers (e.g., AES) instead of hash functions
  • Poly1305: a high-speed message authentication code designed for use with the ChaCha20 stream cipher
• Digital signature algorithms:
  • RSA (Rivest-Shamir-Adleman): based on the difficulty of factoring large integers
    • Widely used for secure email (PGP, S/MIME) and SSL/TLS certificates
  • DSA (Digital Signature Algorithm): based on the discrete logarithm problem
  • ECDSA (Elliptic Curve Digital Signature Algorithm): uses elliptic curve cryptography for more efficient signature generation and verification

Real-World Applications

• Secure communication protocols (SSL/TLS, SSH, IPsec) use hash functions and MACs to ensure data integrity and authenticity
  • SSL/TLS certificates use digital signatures to verify the identity of websites and establish secure connections
• Password storage and verification systems employ hashing to protect user credentials
  • Hashed passwords are stored in databases instead of plaintext to mitigate the impact of data breaches
• File integrity verification uses hash functions to detect changes or tampering
  • Software downloads often provide hash values to ensure the downloaded files have not been corrupted or modified
• Digital signatures are used for signing contracts, legal documents, and software updates
  • Code signing verifies the authenticity and integrity of software, drivers, and firmware updates
• Blockchain technology relies on cryptographic hash functions to ensure the immutability and integrity of transaction records
  • Each block in the chain contains a hash of the previous block, creating a tamper-evident ledger
• Version control systems (Git, Mercurial) use hash functions to identify and track changes in source code repositories
• Secure messaging applications (Signal, WhatsApp) employ end-to-end encryption and message authentication to protect user privacy

Security Considerations

• Choosing the right cryptographic hash function is crucial for maintaining security
  • Avoid using broken or insecure hash functions (MD5, SHA-1) in new applications
  • Use well-established and thoroughly analyzed hash functions (SHA-256, SHA-512, BLAKE2)
• Proper key management is essential for the security of message authentication codes and digital signatures
  • Keep private keys secure and protect them from unauthorized access
  • Regularly rotate keys and revoke compromised keys to minimize the impact of key leaks
• Use salting when hashing passwords to defend against rainbow table attacks
  • Generate a unique random salt for each password and store the salt alongside the hashed password
• Implement secure key exchange mechanisms (Diffie-Hellman, ECDH) to establish shared secrets for message authentication codes
• Regularly update and patch systems to address known vulnerabilities in cryptographic libraries and implementations
• Use secure random number generators for generating keys, salts, and nonces to ensure unpredictability
• Implement rate limiting and account lockout mechanisms to protect against brute-force attacks on password hashes

Common Attacks and Vulnerabilities

• Collision attacks: attempt to find two different messages that produce the same hash value
  • Can lead to forgery and impersonation attacks if the hash function is not collision-resistant
• Length extension attacks: exploit a weakness in some hash functions (MD5, SHA-1) to append data to a message without knowing the original content
  • Can be mitigated by using HMAC or a hash function resistant to length extension attacks (SHA-256, SHA-512)
• Rainbow table attacks: use precomputed hash tables to crack password hashes
  • Salting passwords renders rainbow tables ineffective by making each hash unique
• Side-channel attacks: exploit information leakage (timing, power consumption) to gain insights into secret keys or intermediate values
  • Implement constant-time algorithms and use secure hardware (HSMs) to mitigate side-channel attacks
• Padding oracle attacks: exploit vulnerabilities in the padding scheme used by some encryption and authentication modes (CBC, PKCS#7)
  • Use authenticated encryption modes (GCM, CCM) or encrypt-then-MAC constructions to prevent padding oracle attacks
• Replay attacks: capture and reuse valid messages or authentication codes to impersonate the sender
  • Include unique nonces or timestamps in messages and verify them to detect and prevent replay attacks

Future Trends

• Post-quantum cryptography: developing cryptographic algorithms that are resistant to attacks by quantum computers
  • Quantum computers could break many current public-key cryptosystems (RSA, ECC) in the future
  • Research focuses on lattice-based, code-based, and multivariate cryptography for post-quantum security
• Authenticated encryption modes: combining encryption and authentication into a single, efficient operation
  • Modes like GCM (Galois/Counter Mode) and CCM (Counter with CBC-MAC) provide both confidentiality and integrity protection
  • Increasing adoption in secure communication protocols and applications
• Blockchain and distributed ledger technologies: leveraging cryptographic hash functions for secure, decentralized systems
  • Potential applications in supply chain management, identity verification, and secure data sharing
• Homomorphic encryption: enabling computations on encrypted data without revealing the underlying values
  • Could enable secure cloud computing and privacy-preserving data analysis
• Secure multi-party computation: allowing multiple parties to jointly compute a function while keeping their inputs private
  • Applications in secure voting systems, auctions, and privacy-preserving machine learning
• Verifiable delay functions (VDFs): cryptographic primitives that require a specific amount of time to compute, even with parallel processing
  • Potential use cases in randomness beacons, leader election in consensus protocols, and spam prevention