[Busec] [charles-river-crypto-day] Reminder: Charles River Crypto Day, Dec 5 @ BU

Nir Bitansky nbitansky at gmail.com
Mon Dec 1 10:08:34 EST 2014




Please join us for the next installment of Crypto Day 
<https://bostoncryptoday.wordpress.com/> on Friday, December 5 at Boston 
University.

Location: 111 Cummington Mall <https://goo.gl/maps/Y5Quk> Room 180. 
[directions] <http://www.bu.edu/hic/directions/>

Parking: There’s a pay lot <http://www.bu.edu/maps/?id=2307> across the 
street and 4-hour meters on Bay State Road.

The schedule and abstracts can be found below. 
Hope to see you there!

Yael, Vinod, Daniel, and Nir 

p.s.: if someone forwarded to you this email, and you would like to join 
the mailing list for future announcements send an email to 
charles-river-crypto-day+subscribe at googlegroups.com
Schedule9:30 – 10:00.Introduction/Coffee10:00 – 11:00.
Yuval Ishai, Technion
*Circuits Resilient to Additive Attacks, with Applications to Secure 
Computation*
11:30 – 12:30.Omer Paneth, Boston University
*Publicly-Verifiable Non-Interactive Arguments for Delegating Computations*12:30 
– 2:00.Lunch (provided)2:00 – 3:00.Elaine Shi, University of Maryland
*Programs to Circuits: Towards a Programming Language for Cryptography*3:30 
– 4:30.Sergey Gorbunov, MIT
*Leveled Fully Homomorphic Signatures from Standard Lattices*

Thanks: NSF Frontier Grant: Modular Approach to Cloud Security (MACS), 
Hariri Institute for Computing and Center for RISCS.

Special thanks to Leo Reyzin, Debbie Lehto, and Lauren Dupee for help with 
organization
Abstracts:

*Speaker: Yuval Ishai *
*Title: Circuits Resilient to Additive Attacks, with Applications to Secure 
Computation*

We study the question of protecting arithmetic circuits against additive 
attacks that can add an arbitrary fixed value to each wire in the circuit. 
We show how to transform an arithmetic circuit C into a functionally 
equivalent, randomized circuit C’ of comparable size, such that the effect 
of any additive attack on the wires of C’ can be simulated (up to a small 
statistical distance) by an additive attack on just the inputs and outputs 
of C.

Our study of this question is motivated by the goal of simplifying and 
improving protocols for secure multiparty computation (MPC). It is 
typically the case that securing MPC protocols against active adversaries 
is much more difficult than securing them against passive adversaries. We 
observe that in simple MPC protocols that were designed to protect circuit 
evaluation only against passive adversaries, the effect of any active 
adversary corresponds precisely to an additive attack on the circuit’s 
wires. Thus, to securely evaluate a circuit C in the presence of active 
adversaries, it suffices to apply the passive-case protocol to a 
corresponding circuit C’ which is secure against additive attacks. We use 
this methodology to simplify feasibility results and obtain efficiency 
improvements in several standard MPC models.

Joint work with Daniel Genkin, Manoj Prabhakaran, Amit Sahai, and Eran 
Tromer.

*Speaker: Omer Paneth *
*Title: Publicly-Verifiable Non-Interactive Arguments for Delegating 
Computations*

We construct publicly verifiable non-interactive arguments that can be used 
to delegate polynomial time computations. These computationally sound proof 
systems are completely non-interactive in the common reference string 
model. The verifier’s running time is nearly-linear in the input length, 
and poly-logarithmic in the complexity of the delegated computation. Our 
protocol is based on graded encoding schemes, introduced by Garg, Gentry 
and Halevi (Eurocrypt 2012). Security is proved under a falsifiable and 
arguably simple cryptographic assumption about graded encodings. All prior 
publicly verifiable non-interactive argument systems were based on 
non-falsifiable knowledge assumptions. Our new result builds on the 
beautiful recent work of Kalai, Raz and Rothblum (STOC 2014), who 
constructed privately verifiable 2-message arguments. While building on 
their techniques, our protocols avoid no-signaling PCPs, and we obtain a 
simplified and modular analysis.

As a second contribution, we also construct a publicly verifiable 
non-interactive argument for (logspace-uniform) computations of bounded 
depth. The verifier’s complexity grows with the depth of the circuit. This 
second protocol is adaptively sound, and its security is based on a 
falsifiable assumption about the hardness of a search problem on graded 
encodings (a milder cryptographic assumption). This result builds on the 
interactive proof of Goldwasser, Kalai and Rothblum (STOC 2008), using 
graded encodings to construct a non-interactive version of their protocol.

Joint work with Guy Rothblum.

*Speaker: Elaine Shi* 
*Title: Programs to Circuits: Towards a Programming Language for 
Cryptography*

Modern cryptography (e.g., secure multi-party computation, 
fully-homomorphic encryption, program obfuscation) commonly models 
computation as “circuits”. To make modern cryptography work for real-world 
programs, it is necessary to compile “programs” into compact “circuits”. 
The key difficulty is that programs make dynamic memory accesses, whereas 
circuits have static wiring. To address this challenge, we need efficient 
Oblivious RAM and oblivious algorithms.

In this talk, I will first describe Circuit ORAM, a new ORAM scheme that 
yields very small circuit size. Circuit ORAM shows the tightness of certain 
stronger interpretations of the well-known Goldreich-Ostrovsky lower bound.

Next, I will describe ObliVM, a programming framework that compiles 
real-life programs into compact circuits, while offering formal security 
guarantees.

*Speaker: Sergey Gorbunov* 

*Title: Leveled Fully Homomorphic Signatures from Standard Lattices*

In a homomorphic signature scheme, a user Alice signs some large dataset *x* using 
her secret signing key and uploads the signed data to an untrusted remote 
server. The server can then run some computation y=f(x) over the signed 
data and homomorphically derive a short signature \sigma_{f,y} certifying 
that y is the correct output of the computation f. Anybody can verify the 
tuple (f, y, \sigma_{f,y}) using Alice’s public verification key and become 
convinced of this fact without having to retrieve the entire underlying 
data.

In this work, we construct the first (leveled) fully homomorphic signature 
schemes that can evaluate arbitrary circuits over signed data. Only the 
maximal depth d of the circuits needs to be fixed a-priori at setup, and 
the size of the evaluated signature grows polynomially in d, but is 
otherwise independent of the circuit size or the data size. Our solution is 
based on the (sub-exponential) hardness of the small integer solution (SIS) 
problem in standard lattices. In the standard model, we get a scheme with 
large public parameters whose size exceeds the total size of a dataset. In 
the random-oracle model, we get a scheme with short public parameters. In 
both cases, the schemes can be used to sign many different datasets. The 
complexity of verifying a signature for a computation f is at least as 
large as that of computing f, but can be amortized when verifying the same 
computation over many different datasets. Furthermore, the signatures can 
be made context-hiding so as not to reveal anything about the data beyond 
the outcome of the computation.

These results offer a significant improvement in capabilities and 
assumptions over the best prior homomorphic signature schemes, which were 
limited to evaluating polynomials of constant degree.

As a building block of independent interest, we introduce and construct a 
new object called homomorphic trapdoor functions (HTDF) which conceptually 
unites homomorphic encryption and signatures.

Joint work with Vinod Vaikuntanathan (MIT) and Daniel Wichs (Northeastern).

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