Abstract: In a portable electronic device, a method of authenticating a document associated with a geographical location is disclosed. A document is provided in the form of digital data, and a hash value is generated from the digital data of said document. Raw GPS data are received from at least one GPS satellite, and then digitally signed by a first private key of the portable electronic device. From the raw GPS data, exact GPS coordinates are calculated. A request for an authentic location stamp is sent to a certification unit, the request containing at least the hash value of the document, the raw GPS data and the exact GPS coordinates, wherein said request is digitally signed by a private key of the portable electronic device. In response to said location stamp request, a nonce value from the certification unit is received, said nonce value being digitally signed by a private key of the certification unit.