Hash Functions in the Broader Security Context

While inappropriate for direct password hashing, general-purpose cryptographic hash functions play crucial roles in complete password systems. They generate random salts, derive encryption keys, and create secure tokens. HMAC (Hash-based Message Authentication Code) uses hash functions to provide authenticated encryption. Understanding these broader applications helps build comprehensive security systems.

Password-based key derivation functions (PBKDFs) use hash functions as building blocks while adding iterations to increase computational cost. PBKDF2, for example, applies a pseudorandom function (typically HMAC-SHA256) thousands of times. This approach transforms fast hash functions into slower key derivation functions suitable for password-based encryption, demonstrating how proper construction can adapt general-purpose primitives for specific security needs.

The future of hash functions continues evolving with SHA-3 (Keccak) offering different internal construction and security trade-offs. Post-quantum cryptography research explores hash-based signatures that may remain secure against quantum computers. These developments ensure hash functions will continue playing vital roles in cryptography, even as their direct use for password storage remains inappropriate.

Understanding cryptographic hash functions provides the foundation for implementing secure password storage. Their one-way property and avalanche effect make them essential building blocks, but their speed makes direct use dangerous for passwords. This knowledge enables recognizing both proper and improper uses of hash functions in security systems. As we proceed to examine specific password hashing algorithms, remember that these specialized functions build upon general hash functions while adding crucial protections against the unique threats passwords face. The evolution from simple hash functions to modern password hashing algorithms represents decades of learning from attacks and adapting to advancing computational capabilities.## Password Hashing Algorithms: MD5, SHA, and Why They're Not Enough

The history of password hashing is littered with algorithms that once seemed secure but now offer minimal protection against modern attacks. MD5 and SHA family algorithms, despite their cryptographic pedigree and continued presence in legacy systems, fail catastrophically when used for password storage. Understanding why these widely-deployed algorithms are inadequate—and recognizing their continued misuse—is crucial for anyone responsible for authentication systems. This chapter examines these popular but problematic algorithms, demonstrating through practical examples why they must be abandoned for password security.