Bennet Yee

Using Secure Coprocessors Degree Type: Ph.D. in Computer Science
Advisor(s): Doug Tygar
Graduated: May 1994

Abstract:

How do we build distributed systems that are secure? Cryptographic techniques can be used to secure the communications between physically separated systems, but this is not enough: we must be able to guarantee the privacy of the cryptographic keys and the integrity of the cryptographic functions, in addition to the integrity of the security kernel and access control databases we have on the machines. Physical security is a central assumption
upon which secure distributed systems are built; without this foundation even the best
cryptosystem or the most secure kernel will crumble. In this thesis, I address the distributed
security problem by proposing the addition of a small, physically secure hardware module,
a secure coprocessor, to standard workstations and PCs. My central axiom is that secure
coprocessors are able to maintain the privacy of the data they process.
This thesis attacks the distributed security problem from multiple sides.
First, I analyze the security properties of existing system components, both at the hardware and
software level. Second, I demonstrate how physical security requirements may be isolated to the secure coprocessor, and showed how security properties may be bootstrapped
using cryptographic techniques from this central nucleus of security within a combined hardware/software architecture. Such isolation has practical advantages: the nucleus of security-relevant modules provide additional separation of concern between functional requirements and security requirement, and the security modules are more centralized and
their properties more easily scrutinized. Third, I demonstrate the feasibility of the secure coprocessor approach, and report on my implementation of this combined architecture on top
of prototype hardware. Fourth, I design, analyze, implement, and measure performance of
cryptographic protocols with super-exponential security for zero-knowledge authentication
and key exchange. These protocols are suitable for use in security critical environments.
Last, I show how secure coprocessors may be used in a fault-tolerant manner while still
maintaining their strong privacy guarantees.

Thesis Committee:
Doug Tygar (Chair)
Rick Rashid
M. Satyanarayanan
Steve White (IBM Research)

James Morris, Head, Computer Science Department
Raj Reddy Dean, School of Computer Science

Keywords:
authentication, coprocessor, cryptography, integrity, privacy, security