1,721,008 research outputs found
Augmented ((t,n))-threshold Quantum Secret Sharing Schemes
No full textThreshold secret sharing schemes are procedures in which groups of a sufficient size can work together to recover a shared secret. In this thesis, we analyze quantum threshold schemes, which are threshold secret sharing schemes applied to quantum information. Many of the restrictions on quantum secret sharing schemes arise from the no-cloning theorem. We investigate the potential benefit of implementing quantum threshold schemes using two or more identical copies of a secret quantum state. This idea is motivated by the possibility that the availability of multiple copies of the secret can circumvent the restrictions imposed by the no-cloning theorem. Our approach takes advantage of the multiple copies by using the union of two or more access structures, one for each quantum state, in order to implement secret sharing schemes that would otherwise not be realizable. We find that we are indeed able to implement a wider range of access structures, but we show that we can only realize one new threshold scheme for every new copy of the share, given a fixed number of players
An Overview of Collision Resistance Against a Quantum Adversary
No full textQuantum computers are threatening to undermine cryptographic schemes that have been classically
proven to be secure. In this paper, we give an overview of the historical development of collision
and multi-collision finding quantum algorithms, analyzing their query and space complexity in the
Random Oracle Model
Augmented ((t,n))-threshold Quantum Secret Sharing Schemes
No full textThreshold secret sharing schemes are procedures in which groups of a sufficient size can work together to recover a shared secret. In this thesis, we analyze quantum threshold schemes, which are threshold secret sharing schemes applied to quantum information. Many of the restrictions on quantum secret sharing schemes arise from the no-cloning theorem. We investigate the potential benefit of implementing quantum threshold schemes using two or more identical copies of a secret quantum state. This idea is motivated by the possibility that the availability of multiple copies of the secret can circumvent the restrictions imposed by the no-cloning theorem. Our approach takes advantage of the multiple copies by using the union of two or more access structures, one for each quantum state, in order to implement secret sharing schemes that would otherwise not be realizable. We find that we are indeed able to implement a wider range of access structures, but we show that we can only realize one new threshold scheme for every new copy of the share, given a fixed number of players
Toward Secure Quantum Money
No full textThe no-cloning theorem of quantum physics may enable the creation of uncounterfeitable money. The design's central idea is to represent money as a quantum state. An arbitrary quantum state, whose superposition we know nothing about, is impossible to clone, and measuring the state will collapse the superposition. A quantum money scheme could be implemented to represent money if qubit coherence times improve enough to store a superposition over a period of weeks or longer.
Any quantum money scheme needs a verification algorithm, a method to distinguish valid and counterfeit money without destroying a valid state. In the first scheme proposed for quantum money, the mint that created the money state keeps a private description of the state and uses the description to verify a purported money state [Wie83]. This description, called the trapdoor, can also be used to produce duplicate states, so the mint must keep the trapdoor secret.
Recently, several schemes have been proposed for public key quantum money, which anyone can verify using only public information (a public trapdoor). [Zha17]’s proposed scheme, called quantum lightning, is a stronger form of public key quantum money where even the mint cannot duplicate a valid state. However, none of the public key schemes have been proven secure. It is difficult to show that the public trapdoor cannot be used to produce counterfeit states.
In this work, we show that [Zha17]’s quantum lightning construction is not secure. The construction's purported security is based on the multi-collision resistance of a hash function. However, we show how to break this collision-resistance by constructing collisions in the span of the verification algorithm's trapdoor. We call this the trapdoor span attack.
We also give the first detailed description and analysis of [Zha17]'s attempted construction for quantum lightning based on the SIS problem. The trapdoor span attack is powerful, as it allows counterfeiting in this construction as well.
Finally, we propose and analyze two modified versions of the construction based on SIS. These modifications are designed to foil the trapdoor span attack. The first proposal, though unsuccessful, could be useful for future attempts. The second construction is promising, but much more work is needed to develop and analyze it. We hope that the second construction may lead to a secure construction of quantum money
An Overview of Collision Resistance Against a Quantum Adversary
No full textQuantum computers are threatening to undermine cryptographic schemes that have been classically
proven to be secure. In this paper, we give an overview of the historical development of collision
and multi-collision finding quantum algorithms, analyzing their query and space complexity in the
Random Oracle Model
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Augmented ((t,n))-threshold Quantum Secret Sharing Schemes
No full textThreshold secret sharing schemes are procedures in which groups of a sufficient size can work together to recover a shared secret. In this thesis, we analyze quantum threshold schemes, which are threshold secret sharing schemes applied to quantum information. Many of the restrictions on quantum secret sharing schemes arise from the no-cloning theorem. We investigate the potential benefit of implementing quantum threshold schemes using two or more identical copies of a secret quantum state. This idea is motivated by the possibility that the availability of multiple copies of the secret can circumvent the restrictions imposed by the no-cloning theorem. Our approach takes advantage of the multiple copies by using the union of two or more access structures, one for each quantum state, in order to implement secret sharing schemes that would otherwise not be realizable. We find that we are indeed able to implement a wider range of access structures, but we show that we can only realize one new threshold scheme for every new copy of the share, given a fixed number of players
Obfuscating Compute-and-Compare Programs under the LWE assumption: Analysis of the Wichs & Zirdelis Scheme
No full textIn this thesis we analyze cryptanalytic attacks on the compute-and-compare program
obfuscation scheme proposed by Wichs and Zirdelis [WZ17].
The work of Wichs and Zirdelis is the first to give a provable VBB obfuscation scheme for
a large sub-class of evasive functions, compute-and-compare programs, under the Learning
with Errors (LWE) assumption. If f : {0, 1}
lin → {0, 1}
lout, and y ∈ {0, 1}
lout, then the
compute-and-compare program CC[f, y](x) is 1 whenever f(x) = y, and 0 otherwise. The
scheme starts by obfuscating a branching program P of length L that computes f, and
reads the input x according to a specified input function.
This is provably secure when y is computationally indistinguishable given f. In this paper, we
consider the case when lout = 1, i.e. y is a single bit. We show that in this case, the scheme is
not even iO-secure. Moreover, we show that we given enough examples of the form (x, f(x))
from a given distribution, with high probability we can learn f over that distribution. The key
to proving these results is that the encoded version of the program allows us to evaluate the
branching program P on inputs other than those specified by the input function. That is, this
encoding scheme reveals too much information about the structure of the underlying program
An Overview of Collision Resistance Against a Quantum Adversary
No full textQuantum computers are threatening to undermine cryptographic schemes that have been classically
proven to be secure. In this paper, we give an overview of the historical development of collision
and multi-collision finding quantum algorithms, analyzing their query and space complexity in the
Random Oracle Model
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