Key authentication

Abstract: An automatic control system for a tube expander tool of the type having a hydraulically powered rotary tool which is advanced and retracted by a reversible linear motor. Operation of automatic cycling is initiated by a manual control whereas axial movement of the tool can be interrupted at any time by operating a hold control while rotation of the tool continues as long as necessary to iron out excess metal or to reposition the tube in the bore should this be desirable. The tool is maintained under constant load at all times by load sensor means in the tool advancing circuit and operable to vary the rate of tool advance to maintain a desired constant load and to prevent overloading. Accordingly, the rate of tool advance varies inversely as the load on the tool.

Abstract: A new simple password exponential key exchange method (SPEKE) is described. It belongs to an exclusive class of methods which provide authentication and key establishment over an insecure channel using only a small password, without risk of offline dictionary attack. SPEKE and the closely-related Diffie-Hellman Encrypted Key Exchange (DH-EKE) are examined in light of both known and new attacks, along with sufficient preventive constraints. Although SPEKE and DH-EKE are similar, the constraints are different. The class of strong password-only methods is compared to other authentication schemes. Benefits, limitations, and tradeoffs between efficiency and security are discussed. These methods are important for several uses, including replacement of obsolete systems, and building hybrid two-factor systems where independent password-only and key-based methods can survive a single event of either key theft or password compromise.

Abstract: The distribution of cryptographic keys has always been a major problem in applications with many users. Solutions were found for closed user groups and small open systems. These are, however, not efficient for large networks. We propose an identity-based approach to that problem which is simple and applicable to networks of arbitrary size. With the solution proposed, the user group can, furthermore, be extended at will. Each new user needs only to visit a key authentication center (KAC) once and is from then on able to exchange authenticated keys with each other user of the network. We expect this type of approach, which was originally conceived for authentication and signatures, to play an increasing role in the solution of all types of key distribution problems.

Abstract: We construct a public key encryption scheme in which there is one public encryption key, but many private decryption keys. If some digital content (e.g., a music clip) is encrypted using the public key and distributed through a broadcast channel, then each legitimate user can decrypt using its own private key. Furthermore, if a coalition of users collude to create a new decryption key then there is an effcient algorithm to trace the new key to its creators. Hence, our system provides a simple and effcient solution to the "traitor tracing problem". Our tracing algorithm is deterministic, and catches all active traitors while never accusing innocent users, although it is only partially "black box". A minor modification to the scheme enables it to resist an adaptive chosen ciphertext attack. Our techniques apply error correcting codes to the discrete log representation problem.