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arXiv:1410.8019

Bounding the seed length of Miller and Shi's unbounded randomness expansion protocol

Renan Gross, Scott Aaronson

Published Oct 29, 2014• 1 citation
arXivHTMLPDF

Abstract

Recent randomness expansion protocols have been proposed which are able to generate an unbounded amount of randomness from a finite amount of truly random initial seed. One such protocol, given by Miller and Shi, uses a pair of non-signaling untrusted quantum mechanical devices. These play XOR games with inputs given by the user in order to generate an output. Here we present an analysis of the required seed size, giving explicit upper bounds for the number of initial random bits needed to jump-start the protocol. The bits output from such a protocol are $\varepsilon$-close to uniform even against quantum adversaries. Our analysis yields that for a statistical distance of $\varepsilon=10^{-1}$ and $\varepsilon=10^{-6}$ from uniformity, the number of required bits is smaller than 225,000 and 715,000, respectively; in general it grows as $O(\log\frac{1}{\varepsilon})$.

DOI
10.48550/arxiv.1410.8019

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Recent randomness expansion protocols have been proposed which are able to generate an unbounded amount of randomness from a finite amount of truly random initial seed. One such protocol, given by Miller and Shi, uses a pair of non-signaling untrusted quantum mechanical devices. These play XOR games with inputs given by the user in order to generate an output. Here we present an analysis of the required seed size, giving explicit upper bounds for the number of initial random bits needed to jump-start the protocol. The bits output from such a protocol are ε\varepsilonε-close to uniform even against quantum adversaries. Our analysis yields that for a statistical distance of ε=10−1\varepsilon=10^{-1}ε=10−1 and ε=10−6\varepsilon=10^{-6}ε=10−6 from uniformity, the number of required bits is smaller than 225,000 and 715,000, respectively; in general it grows as O(log⁡1ε)O(\log\frac{1}{\varepsilon})O(logε1​).
We present a device-independent randomness expansion protocol, involving only a constant number of non-signaling quantum devices, that achieves infinite expansion: starting with m bits of uniform private randomness, the protocol can produce an unbounded amount of certified randomness that is exp(--Ω(m1/3))-close to uniform and secure against a quantum adversary. The only parameters which depend on the size of the input are the soundness of the protocol and the security of the output (both are inverse exponential in m). This settles a long-standing open problem in the area of randomness expansion and device-independence.
We present a device-independent randomness expansion protocol, involving only a constant number of non-signaling quantum devices, that achieves \emph{infinite expansion}: starting with mmm bits of uniform private randomness, the protocol can produce an unbounded amount of certified randomness that is exp⁡(−Ω(m1/3))\exp(-Ω(m^{1/3}))exp(−Ω(m1/3))-close to uniform and secure against a quantum adversary. The only parameters which depend on the size of the input are the soundness of the protocol and the security of the output (both are inverse exponential in mmm). This settles a long-standing open problem in the area of randomness expansion and device-independence. The analysis of our protocols involves overcoming fundamental challenges in the study of \emph{adaptive} device-independent protocols. Our primary technical contribution is the design and analysis of device-independent protocols which are \emph{Input Secure}; that is, their output is guaranteed to be secure against a quantum eavesdropper, \emph{even if the input randomness was generated by that same eavesdropper}! The notion of Input Security may be of independent interest to other areas such as device-independent quantum key distribution.
Randomness is a vital resource for modern day information processing, especially for cryptography. A wide range of applications critically rely on abundant, high quality random numbers generated securely. Here we show how to expand a random seed at an exponential rate without trusting the underlying quantum devices. Our approach is secure against the most general adversaries, and has the following new features: tolerating a constant level of implementation imprecision, requiring only a unit size quantum memory per device component for the honest implementation, and allowing a large natural class of constructions. In conjunct with a recent work by Chung, Shi and Wu (QIP 2014), it leads to robust unbounded expansion using just 2 multi-part devices. It can also be adapted for distributing cryptographic keys securely. The proof begins with a known protocol and proceeds by showing that the Renyi divergence of the outputs of the protocol (for a specific bounding operator) decreases linearly as the protocol iterates. At the heart of the proof are a new uncertainty principle on quantum measurements, and a method for simulating trusted measurements with untrusted devices. A full version of this paper containing additional results developed after the conference submission is available as arXiv:1402.0489.
We introduce a protocol through which a pair of quantum mechanical devices may be used to generate n bits of true randomness from a seed of O(log n) uniform bits. The bits generated are certifiably random based only on a simple statistical test that can be performed by the user, and on the assumption that the devices obey the no-signaling principle. No other assumptions are placed on the devices' inner workings. A modified protocol uses a seed of O(log^3 n) uniformly random bits to generate nnn bits of true randomness even conditioned on the state of a quantum adversary who may have had prior access to the devices, and may be entangled with them.
A device-independent randomness expansion protocol aims to take an initial random seed and generate a longer one without relying on details of how the devices operate for security. A large amount of work to date has focussed on a particular protocol based on spot-checking devices using the CHSH inequality. Here we show how to derive randomness expansion rates for a wide range of protocols, with security against a quantum adversary. Our technique uses semidefinite programming and a recent improvement of the entropy accumulation theorem. To support the work and facilitate its use, we provide code that can generate lower bounds on the amount of randomness that can be output based on the measured quantities in the protocol. As an application, we give a protocol that robustly generates up to two bits of randomness per entangled qubit pair, which is twice that established in existing analyses of the spot-checking CHSH protocol in the low noise regime.
A device-independent randomness expansion protocol aims to take an initial random seed and generate a longer one without relying on details of how the devices operate for security.A large amount of work to date has focussed on a particular protocol based on spot-checking devices using the CHSH inequality.Here we show how to derive randomness expansion rates for a wide range of protocols, with security against a quantum adversary.Our technique uses semidefinite programming and a recent improvement of the entropy accumulation theorem.To support the work and facilitate its use, we provide code that can generate lower bounds on the amount of randomness that can be output based on the measured quantities in the protocol.As an application, we give a protocol that robustly generates up to two bits of randomness per entangled qubit pair, which is twice that established in existing analyses of the spot-checking CHSH protocol in the low noise regime.