We investigate the possibility of using multiple-scattering optical media, as resources of randomness in cryptographic tasks pertaining to commitments and auctions. The proposed commitment protocol exploits standard wavefront-shaping and heterodyne-detection techniques, and can be implemented with current technology. Its security is discussed in the framework of a tamper-resistant trusted setup.
We investigate the possibility of using multiple-scattering optical media, as resources of randomness in cryptographic tasks pertaining to commitments and auctions. The proposed commitment protocol exploits standard wavefront-shaping and heterodyne-detection techniques, and can be implemented with current technology. Its security is discussed in the framework of a tamper-resistant trusted setup.
We propose a scheme for authentication of physical keys that are materialized by optical multiple-scattering media. The authentication relies on the optical response of the key when probed by randomly selected coherent states of light, and the use of standard wavefront-shaping techniques that direct the scattered photons coherently to a specific target mode at the output. The quadratures of the electromagnetic field of the scattered light at the target mode are analysed using a homodyne detection scheme, and the acceptance or rejection of the key is decided upon the outcomes of the measurements. The proposed scheme can be implemented with current technology and offers collision resistance and robustness against key cloning.
Abstract Secure communication is of paramount importance in modern society. Asymmetric cryptography methods such as the widely used RSA cryptosystem allow secure exchange of information between parties who have never previously shared keys. However, the existing asymmetric cryptographic schemes rely on unproven mathematical assumptions for security. Further, the digital keys used in their implementation are susceptible to copying that might remain unnoticed. Here, we introduce a secure communication method based on Physical Unclonable Keys (PUKs), which we call PUK-Enabled Asymmetric Communication (PEAC). PEAC uses physical keys and thus overcomes the problem of unnoticed copying. As all the information about the PUK is allowed to be public, PEAC does not require the safekeeping of any digital information. Using optical PUKs realized in opaque scattering materials, we transmit messages in an error-corrected way employing off-the-shelf equipment. Information is transmitted as patterned wavefronts of few-photon wavepackets which can be successfully decrypted only with the receiver’s PUK. The security of PEAC assumes technological constraints in distinguishing between different few-photon wavefronts. A heuristic argument for the security of PEAC is outlined focusing on a specific attack, namely state estimation. We demonstrate secure transmission of messages over a 2 m free-space line-of-sight quantum channel. PEAC enables new directions for physical key based cryptography.
We report a novel optical encryption strategy that utilizes highly scattered wavefront of light field to encrypt the plaintext and exploits a scattering medium as the unique physical key. For information decryption, an imaging technique based on the speckle-correlation scattering matrix is adopted to directly extract the wavefront information from speckles, i.e., the ciphertext. The decryption relies on the transmission matrix of the scattering medium which serves as the unique key. In particular, different parts of a scattering medium have absolutely different TMs. Thus, even if attackers get the cryptosystem and repeat the measurement process, they cannot recover the key without knowing the exact part of the medium we used. The security of this scheme is further guaranteed by the advantage that data cannot be leaked without a large percentage (>60%) of the key eavesdropped. In addition, its feasibility and advantage are demonstrated experimentally.
In this paper, we discuss the question how physical statements can be proven remotely over digital communication channels without using classical secret keys, and without assuming tamper-resistant and trusted measurement hardware in the location of the prover. Examples for the considered physical statements are: (i) “the temperature of a certain object is X◦C”, (ii) “two certain objects are positioned at distance X”, or (iii) “a certain object has been irreversibly altered or destroyed”. In lack of an established name, we would like to call the corresponding security protocols ”virtual proofs of reality” (VPs). While a host of variants seems conceivable, this paper focuses on VPs in which the verifier has handed over one or more specific physical objects Oi to the prover at some point prior to the VP. These “witness objects” assist the prover during the proof, but shall not contain classical digital keys nor be assumed tamper-resistant in the classical sense. The prover is allowed to open, inspect and alter these objects in our adversarial model, only being limited by current technology, while he shall still be unable to prove false claims to the verifier. In order to illustrate our concept, we give example protocols built on temperature sensitive integrated circuits, disordered optical scattering media, and quantum systems. These protocols prove the temperature, destruction/modification, or relative position of witness objects in the prover’s location. Full experimental realizations of these schemes are beyond the scope of this paper. But the protocols utilize established technologies from the areas of physical unclonable functions and quantum cryptography, and hence appear plausible also without such proof. Finally, we also discuss potential advancements of our method in theory, for example “public virtual proofs” that function without exchanging witness objects Oi between the verifier and the prover. Our work touches upon and partly extends several established cryptographic and security concepts, including physical unclonable functions, quantum cryptography, and interactive proof systems. Keywords-Virtual Proofs of Reality (VPs), Physical Unclonable Functions (PUFs), Interactive Proof Systems, Quantum Cryptography, Physical Cryptography
This thesis proposes several protocols for achieving secure com- putation under concurrent and physical attacks. Secure computation allows many parties to compute a joint function of their inputs, while keeping the privacy of their input preserved. It is required that the pri- vacy one party's input is preserved even if other parties participating in the protocol collude or deviate from the protocol. In this thesis we focus on concurrent and physical attacks, where adversarial parties try to break the privacy of honest parties by ex- ploiting the network connection or physical weaknesses of the honest parties' machine. In the rst part of the thesis we discuss how to construct proto- cols that are Universally Composable (UC for short) based on physical setup assumptions. We explore the use of Physically Uncloneable Func- tions (PUFs) as setup assumption for achieving UC-secure computa- tions. PUF are physical noisy source of randomness. The use of PUFs in the UC-framework has been proposed already in [14]. However, this work assumes that all PUFs in the system are trusted. This means that, each party has to trust the PUFs generated by the other parties. In this thesis we focus on reducing the trust involved in the use of such PUFs and we introduce the Malicious PUFs model in which only PUFs generated by honest parties are assumed to be trusted. Thus the secu- rity of each party relies on its own PUF only and holds regardless of the goodness of the PUFs generated/used by the adversary. We are able to show that, under this more realistic assumption, one can achieve UC- secure computation, under computational assumptions. Moreover, we show how to achieve unconditional UC-secure commitments with (ma- licious) PUFs and with stateless tamper-proof hardware tokens. We discuss our contribution on this matter in Part I. These results are contained in papers [80] and [28]. In the second part of the thesis we focus on the concurrent setting, and we investigate on protocols achieving round optimality and black- box access to a cryptographic primitive. We study two fundamental functionalities: commitment scheme and zero knowledge, and we focus on some of the round-optimal constructions and lower bounds con- cerning both functionalities. We nd that such constructions present subtle issues. Hence, we provide new protocols that actually achieve the security guarantee promised by previous results. Concerning physical attacks, we consider adversaries able to re- set the machine of the honest party. In a reset attack a machine is forced to run a protocol several times using the same randomness. In this thesis we provide the rst construction of a witness indistinguish- able argument system that is simultaneous resettable and argument of knowledge. We discuss about this contribution in Part III, which is the content of the paper. [edited by Author]