4.2 Iteration Count
An iteration count has traditionally served the purpose of increasing
the cost of producing keys from a password, thereby also increasing
the difficulty of attack. For the methods in this document, a minimum
of 1000 iterations is recommended. This will increase the cost of
exhaustive search for passwords significantly, without a noticeable
impact in the cost of deriving individual keys.
https://www.ietf.org/rfc/rfc2898.txt