Cryptographic hash function with a 128-bit (16-byte) hash value
PBKDF2 (Password-Based Key Derivation Function 2) is a key derivation function that is part of RSA Laboratories' Public-Key Cryptography Standards (PKCS) series.
"So we can use pbkdf2 with sha512 to gain a very significant advantage over the phpass algorithm mainly because sha512 is a harder algorithm with more computation than md5"
from question "Is this a good hashing password function in PHP? If not, why not?"