As paper-based communication and transaction mechanisms are replaced by automated ones, traditional forms of security such as photographs and handwritten signatures are becoming outdated. Most security experts believe that digital certificates offer the best technology for safeguarding electronic communications. They are already widely used for authenticating and encrypting email and software, and eventually will be built into any device or piece of software that must be able to communicate securely. There is a serious problem, however, with this unavoidable trend: unless drastic measures are taken, everyone will be forced to communicate via what will be the most pervasive electronic surveillance tool ever built. There will also be abundant opportunity for misuse of digital certificates by hackers, unscrupulous employees, government agencies, financial institutions, insurance companies, and so on.In this book Stefan Brands proposes cryptographic building blocks for the design of digital certificates that preserve privacy without sacrificing security. Such certificates function in much the same way as cinema tickets or subway tokens: anyone can establish their validity and the data they specify, but no more than that. Furthermore, different actions by the same person cannot be linked. Certificate holders have control over what information is disclosed, and to whom. Subsets of the proposed cryptographic building blocks can be used in combination, allowing a cookbook approach to the design of public key infrastructures. Potential applications include electronic cash, electronic postage, digital rights management, pseudonyms for online chat rooms, health care information storage, electronic voting, and even electronic gambling.