1. In an evidence based security model that evaluates multiple pieces of evidence using a security policy to determine a set of granted permissions, and wherein one piece of the multiple pieces of evidence is likely to determine whether a first permission is granted, a method for determining a subset of the permissions, comprising steps of: (a) prior to receiving a request to determine whether the first permission is granted, evaluating the one piece of evidence using the security policy, based on the possible values of the one piece of evidence, to determine resultant permissions, and storing the results; and (b) upon receiving a request to determine whether the first permission is granted, wherein the request comprises an instance of the one piece of evidence, querying the stored results to determine whether the first permission is granted.