A method and system for managing public key certificates is provided. A user purchases a block of unallocated time. When the user requests a certificate, the user specifies a life span for the certificate. A certificate is generated, and the life span of the certificate is deducted from the block of unallocated time. If the user revokes a certificate, the remaining lifetime of the revoked certificate is added back to the block of unallocated time. This allows certificates to be revoked without loss of purchased time, and gives the user more flexibility at requesting and revoking certificates.