Plutus is a cryptographic storage system that enables secure file sharing without placing much trust on the file servers. In particular, it makes novel use of cryptographic primitives to protect and share files. Plutus features highly scalable key management while allowing individual users to retain direct control over who gets access to their files. We explain the mechanisms in Plutus to reduce the number of cryptographic keys exchanged between users by using filegroups, distinguish file read and write access, handle user revocation efficiently, and allow an untrusted server to authorize file writes. We have built a prototype of Plutus on OpenAFS. Measurements of this prototype show that Plutus achieves strong security with overhead comparable to systems that encrypt all network traffic.

We describe a general architecture for intrusion-tolerant enterprise systems and the implementation of an intrusion-tolerant Web server as a specific instance. The architecture comprises functionally redundant COTS servers running on diverse operating systems and platforms, hardened intrusion-tolerance proxies that mediate client requests and verify the behavior of servers and other proxies, and monitoring and alert management components based on the EMERALD intrusion-detection framework. Integrity and availability are maintained by dynamically adapting the system configuration in response to intrusions or other faults. The dynamic configuration specifies the servers assigned to each client request, the agreement protocol used to validate server replies, and the resources spent on monitoring and detection. Alerts trigger increasingly strict regimes to ensure continued service, with graceful degradation of performance, even if some servers or proxies are compromised or faulty. The system returns to less stringent regimes as threats diminish. Servers and proxies can be isolated, repaired, and reinserted without interrupting service.

Abstract. Though conventional block cipher is widely used in Peer-to-Peer storage systems, it is insufficient to ensure the confidentiality of long-term archive data because of the inherent Peer-to-Peer storage vulnerability that data is stored on other untrusted peers. There are two potential security weak spots: (1) sensitive data may be exposed from the encrypted data stored on an adversary peer when the weakness of block cipher is discovered or there is a leakage of secret key; (2) even when a user realizes the security threats, he/she cannot destroy the encrypted data stored on an adversary peer to minimizing the loss. This paper proposes a novel secure erasure code (SEC) scheme to solve the above security problems. The SEC scheme encodes the sensitive data into several fragments, and then stores the fragments onto different peers. In theory, SEC ensures unconditional confidentiality at the fragment level, which means that an adversary cannot obtain any portion of sensitive data from local stored encrypted fragment even if he/she has the secret key and infinite computation power. By leveraging the large scale property of Peer-to-Peer systems, SEC further makes it infeasible for the adversary to collect enough fragments for decrypting. SEC can be used alone or together with block cipher to solve these potential security problems. The performance results show that the SEC scheme is practical for the real-world applications. 1

Plutus is a cryptographic storage system that enables secure file sharing without placing much trust on the file servers. In particular, it makes novel use of cryptographic primitives to protect and share files. Plutus features highly scalable key management while allowing individual users to retain direct control over who gets access to their files. We explain the mechanisms in Plutus to reduce the number of cryptographic keys exchanged between users by using filegroups, distinguish file read and write access, handle user revocation efficiently, and allow an untrusted server to authorize file writes. We have built a prototype of Plutus on OpenAFS. Measurements of this prototype show that Plutus achieves strong security with overhead comparable to systems that encrypt all network traffic.

We describe a general architecture for intrusion-tolerant enterprise systems and the implementation of an intrusion-tolerant Web server as a specific instance. The architecture comprises functionally redundant COTS servers running on diverse operating systems and platforms, hardened intrusion-tolerance proxies that mediate client requests and verify the behavior of servers and other proxies, and monitoring and alert management components based on the EMERALD intrusion-detection framework. Integrity and availability are maintained by dynamically adapting the system configuration in response to intrusions or other faults. The dynamic configuration specifies the servers assigned to each client request, the agreement protocol used to validate server replies, and the resources spent on monitoring and detection. Alerts trigger increasingly strict regimes to ensure continued service, with graceful degradation of performance, even if some servers or proxies are compromised or faulty. The system returns to less stringent regimes as threats diminish. Servers and proxies can be isolated, repaired, and reinserted without interrupting service.

Abstract—This paper presents a recursive computational multisecret sharing technique that hides k − 2 secrets of size b each into n shares of a single secret S of size b, such that any k of the n shares suffice to recreate the secret S as well as all the hidden secrets. This may act as a steganographic channel to transmit hidden information or used for authentication and verification of shares and the secret itself. Further, such a recursive technique may be used as a computational secret sharing technique that has potential applications in secure and reliable storage of information on the Web, in sensor networks and information dispersal schemes. The presented technique, unlike previous computational techniques, does not require the use of any encryption key or storage of public information. I.

This paper presents a k-threshold secret sharing technique that distributes a secret S into shares of size |S| k−1 |S|, where |S | denotes the secret size. This bound is close to the optimal bound of

Abstract. Sensitive electronic data may be required to remain confidential for long periods of time. Yet encryption under a computationally secure cryptosystem cannot provide a guarantee of long term confidentiality, due to potential advances in computing power or cryptanalysis. Long term confidentiality is ensured by information theoretically secure ciphers, but at the expense of impractical key agreement and key management. We overview known methods to alleviate these problems, whilst retaining some form of information theoretic security relevant for long term confidentiality.