Proprietary Certificates

Certificates play an essential role in public-key cryptography, and are likely to become a cornerstone of commerce-relaxed applications. Traditional certificates, however, are not secure against certificate lending, i.e., a situation in which a certificate holder voluntarily shares with others the rights bestowed upon him through a certificate. This type of abuse is a concern in several types of applications, such as those related to digital rights management. In this paper, we introduce the notion of proprietary and collateral certificates. We present a scheme whereby one certificate, known as a proprietary certificate, may be linked to another, known as a collateral certificate. If the owner of the proprietary certificate shares the associated private key, then the private key of the collateral certificate is simultaneously divulged