[Busec] BUsec next week: Georg Fuchsbauer (Mon 1PM) Ben Fuller (Thurs 10AM)

Sharon Goldberg goldbe at cs.bu.edu
Fri May 10 13:57:37 EDT 2013


Hope you semester has ended well!  Next week we'll host two seminars.
Georg Fuchsbauer will be visiting from IST Austria and will tell us
about cryptographically-enforced role-based access control, on Monday
at 1PM.  (Note unusual time!)

On Thursday, our own Ben Fuller will tell us about new work on
Computational Fuzzy extractors.  Thursday 10AM, with lunch provided.

See you there,

BUsec Calendar:  http://www.bu.edu/cs/busec/
 BUsec Mailing list:  http://cs-mailman.bu.edu/mailman/listinfo/busec
 How to get to BU from MIT:  Try the CT2 bus or MIT's "Boston Daytime
 Shuttle" http://web.mit.edu/facilities/transportation/shuttles/daytime_boston.html

Cryptographically Enforced RBAC
Georg Fuchsbauer, IST Austria
Monday May 13, 1-2.30PM

Cryptographic access control promises to offer easily distributed
trust and broader applicability, while reducing reliance on low-level
online monitors. Traditional implementations of cryptographic access
control rely on simple cryptographic primitives, whereas recent
endeavors employ primitives with richer functionality and security
guarantees. Worryingly, few of the existing cryptographic
access-control schemes come with precise guarantees, the gap between
the policy specification and the implementation being analyzed only
informally, if at all.

In this paper we begin addressing this shortcoming.  Unlike prior work
that targeted ad-hoc policy specification, we look at the
well-established Role-Based Access Control (RBAC) model, as used in a
typical file system. In short, we provide a precise syntax for a
computational version of RBAC, offer rigorous definitions for
cryptographic policy enforcement of a large class of RBAC security
policies, and demonstrate that an implementation based on
attribute-based encryption meets our security notions.

We view our main contribution as being at the conceptual level.
Although we work with RBAC for concreteness, our general methodology
could guide future research for uses of cryptography in other
access-control models.

Computational Fuzzy Extractors
Ben Fuller, BU.
Thursday May 16, 10AM

Fuzzy extractors derive strong keys from noisy sources.  Their
security is defined information-theoretically, which limits the length
of the derived key, sometimes making it too short to be useful. We ask
whether it is possible to obtain longer keys by considering
computational security, and show the following.

- Negative Result: Noise tolerance in fuzzy extractors is usually
achieved using an information-reconciliation component called "secure
sketch." The security of this component, which directly affects the
length of the resulting key, is subject to lower bounds from coding
theory.  We show that, even when defined computationally, secure
sketches are still subject to the same lower bounds.

- Positive Result: We show that the negative result can be overcome by
analyzing computational fuzzy extractors directly.  Namely, we show
how to build a computational fuzzy extractor whose output key length
equals the entropy of the source (this is impossible in the
information-theoretic setting). Our construction is based on the
hardness of the Learning with Errors (LWE) problem, and is secure when
the noisy source is uniform or symbol-fixing (that is, each dimension
is either uniform or fixed). As part of the security proof, we show
that the decision version of LWE is secure when a small number of
dimensions has no error.

Joint work with Xianrui Meng and Leonid Reyzin.

Sharon Goldberg
Computer Science, Boston University

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