Trustworthy Computing under Identity-Based Encryption

We propose a fully functional identity-based encryption scheme (IBE). The scheme has chosen cipher text security in the random oracle model assuming a variant of the computational Diffie-Hellman problem. Our system is based on bilinear maps between groups. The Weil pairing on elliptic curves is an example of such a map. We give precise definitions for secure identity based encryption schemes and give several applications for such systems. Trustworthy computing modules like secure coprocessors (ScP) are already in extensive use today, albeit limited predominantly to scenarios where constraints on cost is not a serious limiting factor. However, inexpensive trustworthy computers are required for many evolving application scenarios. The problem of realizing inexpensive ScPs for large-scale networks consisting of low complexity devices have not received adequate consideration thus far. We introduce two strategies toward realizing low-cost ScPs. The first is the decrypt only when necessary (DOWN) policy, which can substantially improve the ability of low-cost ScPs to protect their secrets. The DOWN policy relies on the ability to operate with fractional parts of secrets. Taking full advantage of the DOWN policy requires consideration of the nature of computations performed with secrets and even the mechanisms employed for distribution of secrets