Develop Entropy-Based Password Strength Evaluation

[dfish3r]

Password strength can be measured in entropy of the characters comprising the password string. Develop a Rule that computes password strength in terms of entropy and allow setting threshold values on entropy whereby rule validation fails is the computed entropy is below the threshold.

The computation of entropy should be based on an accepted standard or algorithm. NIST special publication 800-63-1 provides a suitable standard in "Appendix A: Estimating Entropy and Strength":

http://csrc.nist.gov/publications/nistpubs/800-63-1/SP-800-63-1.pdf

[dfish3r]

Fixed in PR #34.