Public key infrastructure

A PKI (30) includes an off-line registration authority (38) that issues a first unsigned certificate (60) to a subject (34) that binds a public key (62) of the subject to long-term identification information (63) related to the subject and maintains a certificate database (40) of unsigned certificates in which it stores the first unsigned certificate. An on-line credentials server (42) issues a short-term disposable certificate (70) to the subject that binds the public key of the subject from the first unsigned certificate to the long-term identification information related to the subject from the first unsigned certificate. The credentials server maintains a table (44) that contains entries corresponding to valid unsigned certificates stored in the certificate database. The subject presents the short-term disposable certificate to a verifier (36) for authentication and demonstrates that the subject has knowledge of a private key corresponding to the public key (46) in the short-term disposable certificate.