Methods, apparatus and systems for generating a trusted digital time stamp as well as a public time source. It includes, an apparatus for receiving and recording public time information and a method for verifying a digital time stamp. A method for generating a trusted digital time stamp includes: obtaining a first time information and a corresponding random code from a public time source; and generating a digital time stamp using a first time information and random code. A method for verifying a digital time stamp includes: recording time information and corresponding random codes transmitted by a public time source; retrieving time information and a random code contained in the time stamp; and comparing a retrieved random code from the time stamp with one of the recorded random codes that corresponds to a time information in the time stamp, if they are consistent, the time stamp is determined to be trusted, otherwise the time stamp is determined to be not trusted.