method and apparatus for determining that a first unit of data associated with a first party has not been modified since a specified point in time . a method includes the steps of providing the first unit of data and generating a second unit of data from the first unit of data , the second unit of data being expressive of an information content of the first unit of data . the method further includes a step of generating a time indication for specifying a point in time , the time indication being generated with time generation means having a time is settable by a second party other than the first party . that is , the time generation means is secured and cannot be altered or changed by the first party . the method further includes a step of encrypting the second unit of data and the generated time indication to generate a third unit of data . the method includes as an additional step a step of validating the first unit of data to ensure that the first unit of data has not been modified since the specified point in time .