Month: March 2017

SoK: Cryptographically Protected Database Search

Excited to announce that our paper on protected database search will be appear at 2017 IEEE Security and Privacy.

Joint work with Mayank Varia, Arkady Yerukhimovich, Emily Shen, Ariel Hamlin, Vijay Gadepally, Richard Shay, John, Darby Mitchell, and Robert K. Cunningham


Protected database search systems cryptographically isolate the roles of reading from, writing to, and administering the database. This separation limits unnecessary administrator access and protects data in the case of system breaches. Since protected search was introduced in 2000, the area has grown rapidly; systems are offered by academia, start-ups, and established companies.

However, there is no best protected search system or set of techniques. Design of such systems is a balancing act between security, functionality, performance, and usability. This challenge is made more difficult by ongoing database specialization, as some users will want the functionality of SQL, NoSQL, or NewSQL databases. This database evolution will continue, and the protected search community should be able to quickly provide functionality consistent with newly invented databases.

At the same time, the community must accurately and clearly characterize the tradeoffs between different approaches. To address these challenges, we provide the following contributions:

1) An identification of the important primitive operations across database paradigms. We find there are a small number of \emph{base} operations that can be used and combined to support a large number of database paradigms.

2) An evaluation of the current state of protected search systems in implementing these base operations. This evaluation describes the main approaches and tradeoffs for each base operation. Furthermore, it puts protected search in the context of unprotected search, identifying key gaps in functionality.

3) An analysis of attacks against protected search for different base queries.

4) A roadmap and tools for transforming a protected search system into a protected database, including an open-source performance evaluation platform and initial user opinions of protected search.

Public Key Cryptography with Noisy Private Keys

New Paper: Public Key Cryptography with Noisy Private Keys

Abstract: Passwords bootstrap symmetric and asymmetric cryptography, tying keys to an individual user. Biometrics are intended to strengthen this tie. Unfortunately, biometrics exhibit noise between repeated readings. Fuzzy extractors (Dodis et al., Eurocrypt 2004) derive stable symmetric keys from noisy sources.

We ask if it is also possible for noisy sources to directly replace private keys in asymmetric cryptosystems. We propose a new primitive called public-key cryptosystems with noisy keys. Such a cryptosystem functions when the private key varies according to some metric. An intuitive solution is to combine a fuzzy extractor with a public key cryptosystem. Unfortunately, fuzzy extractors need static helper information to account for noise. This helper information creates fundamental limitations on the resulting cryptosytems.

To overcome these limitations, we directly construct public-key encryption and digital signature algorithms with noisy keys. The core of our constructions is a computational version of the fuzzy vault (Juels and Sudan, Designs, Codes, and Cryptography 2006). Security of our schemes is based on graded encoding schemes (Garg et al., Eurocrypt 2013, Garg et al., TCC 2016). Importantly, our public-key encryption algorithm is based on a weaker model of grading encoding. If functional encryption or indistinguishable obfuscation exist in this weaker model, they also exist in the standard model.

In addition, we use the computational fuzzy vault to construct the first reusable fuzzy extractor (Boyen, CCS 2004) supporting a linear fraction of errors.

Joint work with Charles Herder, Marten van Dijk, and Srinivas Devadas