Abstract: A digital certificate is formed from a digitized representation of a unique biological feature of a registrant, for example, the registrant's chromosomal DNA. The digital representation is signed with the registrant's private encryption key and transmitted to a certificate authority. The registrant's identity is verified at a remote registration terminal. When the registrant's identity has been verified the certificate authority forms the certificate by encrypting the digital signature with the certificate authority'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.