PBKDF2 Key Derivation/Verification

PBKDF2 (Password-Based Key Derivation Function 2) is defined in RFC 8018. It raises attack cost with repeated HMAC rounds and is widely used for password-based key derivation.

PBKDF2 is used in password storage, file encryption, and protocol key derivation. It is especially useful where NIST/FIPS compatibility is required.

How It Works

PBKDF2 takes password, salt, iterations, and output length, then repeatedly applies HMAC and combines output blocks.

• Input password, salt, iteration count, and target key length
• Run HMAC using password as key and salt+counter as message
• Repeat rounds and XOR intermediate outputs per block
• Concatenate blocks to obtain the final derived key

OWASP Iteration Guidance (2023)

Recommended iteration counts differ by hash algorithm. Tune values against security goals and performance budget.

Common Use Cases

• Deriving AES/ChaCha20 keys from user passphrases
• Password verification in authentication systems
• Master-password key derivation in password managers
• Disk encryption and secure container key generation

PBKDF2 vs Bcrypt vs Argon2

• PBKDF2 offers strong standards and broad compliance support
• Bcrypt remains common in legacy stacks
• Argon2 provides stronger memory hardness for new systems

Security Best Practices

• Use unique salts with at least 16 bytes
• Store salt with the derived key; salt is not secret
• Increase iterations over time as hardware improves
• Prefer Argon2id for new systems, keep PBKDF2 for compliance scenarios