CrySP Speaker Series on Privacy

This speaker series is made possible by an anonymous charitable donation in memory of cypherpunks and privacy advocates Len Sassaman, Hugh Daniel, Hal Finney, and Caspar Bowden.

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Sieve: Cryptographically Enforced Access Control for User Data in Untrusted Clouds

Frank Wang, MIT

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February 1, 2017 2:30pm, in DC 2585


Modern web services rob users of low-level control over cloud storage—a user’s single logical data set is scattered across multiple storage silos whose access controls are set by web services, not users. The consequence is that users lack the ultimate authority to determine how their data is shared with other web services. In this talk, we introduce Sieve, a new platform which selectively (and securely) exposes user data to web services. Sieve has a user-centric storage model: each user uploads encrypted data to a single cloud store, and by default, only the user knows the decryption keys. Given this storage model, Sieve defines an infrastructure to support rich, legacy web applications. Using attribute-based encryption, Sieve allows users to define intuitively understandable access policies that are cryptographically enforceable. Using key homomorphism, Sieve can reencrypt user data on storage providers in situ, revoking decryption keys from web services without revealing new keys to the storage provider. Using secret sharing and two-factor authentication, Sieve protects cryptographic secrets against the loss of user devices like smartphones and laptops. The result is that users can enjoy rich, legacy web applications, while benefiting from cryptographically strong controls over which data a web service can access.


Frank is a PhD student at MIT focusing on building secure systems. He got his bachelor’s degree from Stanford with a focus on applied cryptography. He runs the MIT security seminar and a summer program for early stage security companies called Cybersecurity Factory. He has interned on the security teams at Google and Facebook as well as consulted on security strategy for various companies. When he is not busy worrying about your security, he enjoys going to art museums and being outdoors.