a digital certificate is formed from a digitized representation of a unique biological feature of a registrant , for example , the registrant &# 39 ; s chromosomal dna . the digital representation is signed with the registrant &# 39 ; s private encryption key and transmitted to a certificate authority . the registrant &# 39 ; s identity is verified at a remote registration terminal . when the registrant &# 39 ; s identity has been verified the certificate authority forms the certificate by encrypting the digital signature with the certificate authority &# 39 ; s own encrypting key . the certificate is also held in a publicly available directory . the certificate is used to authenticate an electronic document by appending the certificate to the electronic document . the document and the certificate are then transmitted to a receiving terminal . the identity of the transmitting party can be verified by inspecting the certificate . in the event the sending party denies sending the document , the biological feature can be extracted from the certificate and directly compared with the actual biological feature of the sending party .