5 research outputs found
Everlasting Multi-Party Computation
A protocol has everlasting security if it is secure against
adversaries that are computationally unlimited after the
protocol execution. This models the fact that we cannot predict which
cryptographic schemes will be broken, say, several decades after the
protocol execution. In classical cryptography, everlasting security is
difficult to achieve: even using trusted setup like common reference
strings or signature cards, many tasks such as secure communication
and oblivious transfer cannot be achieved with everlasting security.
An analogous result in the quantum setting excludes protocols based on
common reference strings, but not protocols using a signature card. We
define a variant of the Universal Composability framework, everlasting
quantum-UC, and show that in this model, we can implement secure
communication and general multi-party computation using signature
cards as trusted setup
Ideal quantum protocols in the non-ideal physical world
The development of quantum protocols from conception to experimental realizations is one of
the main sources of the stimulating exchange between fundamental and experimental research
characteristic to quantum information processing. In this thesis we contribute to the development
of two recent quantum protocols, Universal Blind Quantum Computation (UBQC) and Quantum
Digital Signatures (QDS). UBQC allows a client to delegate a quantum computation to a more
powerful quantum server while keeping the input and computation private. We analyse the resilience
of the privacy of UBQC under imperfections. Then, we introduce approximate blindness
quantifying any compromise to privacy, and propose a protocol which enables arbitrary levels of
security despite imperfections. Subsequently, we investigate the adaptability of UBQC to alternative
implementations with practical advantages. QDS allow a party to send a message to other
parties which cannot be forged, modified or repudiated. We analyse the security properties of a
first proof-of-principle experiment of QDS, implemented in an optical system. We estimate the
security failure probabilities of our system as a function of protocol parameters, under all but the
most general types of attacks. Additionally, we develop new techniques for analysing transformations
between symmetric sets of states, utilized not only in the security proofs of QDS but in
other applications as well