A computer uses the information included within a digital certificate to obtain a current date and time value from a trusted extrinsic trusted source and the computer compares the obtained current date and time value to a validity period included in the digital certificate to determine if the digital certificate is expired. The information included within the digital certificate specifying an extrinsic source for the current date and time value can be included in an extension of the digital certificate, and the information can specify a plurality of extrinsic sources.