PBKDF2

PBKDF2 stands for Password-Based Key Derivation Function 2. It is a cryptographic function designed to derive keys from passwords, providing a way to produce cryptographic material that is harder to guess than the original password. PBKDF2 is specified in PKCS #5 v2.0 and described in RFC 2898. It takes four main inputs: a password, a salt, an iteration count, and a desired key length, and it outputs a derived key of the specified length.

The function uses a pseudorandom function, typically an HMAC with a chosen hash function (for example HMAC-SHA1 or HMAC-SHA256). It applies this PRF repeatedly to the password and salt to generate blocks, which are XORed together to form the final derived key. The salt protects against precomputed attacks such as rainbow tables, and the iteration count increases the computational workload, slowing down offline attacks.

Security considerations for PBKDF2 depend on password strength, salt randomness, and an appropriate iteration count. Modern guidance recommends using a high iteration count that your environment can tolerate, often in the tens or hundreds of thousands, or more, depending on the chosen hash function and hardware capabilities. A unique, high-entropy salt should be used for each password and stored alongside the derived key or hash. While PBKDF2 remains widely supported and interoperable, newer schemes such as Argon2 are favored for new designs due to memory-hardness properties.

Common applications include password storage for authentication systems and deriving keys for encryption from user passwords. PBKDF2 remains a standard option, but its effectiveness hinges on strong passwords and proper parameter choices.