Recognizing and Avoiding Bad Implementations

Identifying insecure password hashing in existing systems requires knowing what to look for. Hash length provides immediate clues: 32 hexadecimal characters indicate MD5, 40 characters suggest SHA-1, and 64 characters imply SHA-256. However, length alone doesn't confirm the algorithm—proper identification requires code review or testing known passwords.

Common implementation mistakes compound algorithmic weaknesses. Using fast hashes with static salts provides minimal improvement over unsalted hashes. Implementing multiple rounds of SHA-256 (often called "SHA-256 crypt") seems secure but lacks memory hardness and standardization. Home-grown combinations like "SHA-256 + MD5" demonstrate fundamental misunderstanding of cryptographic principles.

Modern frameworks increasingly prevent these mistakes by providing secure defaults. However, developers must remain vigilant against outdated tutorials, legacy code examples, and misguided attempts to "improve" security through novel combinations. When implementing password hashing, always use established, purpose-built password hashing functions rather than attempting to secure general-purpose hash functions.

The evidence is overwhelming: MD5, SHA-1, and even SHA-256 are fundamentally inappropriate for password hashing. Their speed, originally a feature, becomes a critical vulnerability in the context of password security. While these algorithms serve important roles in other cryptographic applications, their use for passwords represents a serious security failure. Organizations must migrate away from these algorithms urgently, while developers must understand why these seemingly "cryptographic" functions fail at password protection. The next chapter explores modern password hashing algorithms specifically designed to address these vulnerabilities, providing the security that general-purpose hash functions cannot deliver.## Modern Password Hashing: Bcrypt, Scrypt, and Argon2 Explained

The failures of general-purpose hash functions for password storage drove the development of specialized password hashing algorithms. These modern algorithms—bcrypt, scrypt, and Argon2—incorporate deliberate computational expense and memory requirements to resist attacks that devastate MD5 and SHA implementations. Understanding how these algorithms work, their relative strengths, and appropriate use cases enables developers to implement robust password security that withstands current and emerging threats.