PBKDF2 (part of the PKCS#5 standard) is a secure password hashing
 algorithm that uses the techniques of "key strengthening" to make the
 complexity of a brute-force attack arbitrarily high. The Crypt::PBKDF2
 module supports SHA-1, SHA-2 and SHA-3 as the underlying hash functions
 natively and can also use arbitrary Digest-compatible classes. It
 allows for an arbitrary number of iterations of the hashing function,
 and a nearly unlimited output hash size (up to 2**32 - 1 times the size
 of the output of the backend hash). The hash is salted, as any password
 hash should be, and the salt may also be of arbitrary size.