Coca

Abstract

COCA is a fault-tolerant and secure online certification authority that has been built and deployed both in a local area network and in the Internet. Extremely weak assumptions characterize environments in which COCA's protocols execute correctly: no assumption is made about execution speed and message delivery delays; channels are expected to exhibit only intermittent reliability; and with 3t + 1 COCA servers up to t may be faulty or compromised. COCA is the first system to integrate a Byzantine quorum system (used to achieve availability) with proactive recovery (used to defend against mobile adversaries which attack, compromise, and control one replica for a limited period of time before moving on to another). In addition to tackling problems associated with combining fault-tolerance and security, new proactive recovery protocols had to be developed. Experimental results give a quantitative evaluation for the cost and effectiveness of the protocols.

Proactive Byzantine Quorum Systems

“…Some protocols for proactive recovery of servers were proposed in [4,21,13]. Our protocol uses the same assumptions adopted in [4], that presents a protocol for active replication, but does not use threshold cryptography for signatures.…”

“…Our protocol uses the same assumptions adopted in [4], that presents a protocol for active replication, but does not use threshold cryptography for signatures. Other works that use threshold cryptography are COCA [21], that implements a fault-tolerant online certification authority, and CODEX [13], that implements a distributed service for storage and dissemination of secrets. These works employ the APSS [22] proactive secret sharing protocol to update the shares of a service private key.…”

A First Look at Peer-to-Peer Worms: Threats and Defenses

“…Such an infrastructure for distributing and verifying signed updates already exists in many pieces of software for securing automatic software updates. The trusted authority could be implemented using multiple servers [25] to withstand attacks to a fraction of the servers.…”

Multi-Verifier Signatures

“…MACs, however, rely on secret-key setup and do not provide transferability-the property that signed messages accepted by one server and forwarded to other servers will be accepted there too. Transferability is essential in many applications of digital signature schemes (e.g., in distributed systems [7,21,30]). …”