EVALUATING THE PREDICTABILITY OF A PASS PHRASE

Computer readable storage medium, computer-implemented method, and computer system for identifying substring repetition in a pass phrase. A sub-string index is generated. The number of bits required to represent each character in the pass phrase is determined. An entropy value is assigned to each character in the pass phrase in accordance with a probability function that assigns highest probabilities at boundaries of an interval for the entropy of a character, or that assigns lowest probabilities when a ratio of a number of pass phrase characters to pass phrase length is equal to a ratio of a size the interval to a sum of interval sizes. A total entropy value for the pass phrase is computed to provide an indication of pass phrase quality.