Digital signature schemes are often used in interconnected computer networks to verify the origin and authenticity of messages. Current classical digital signature schemes based on so-called “one-way functions” rely on computational complexity to provide security over sufficiently long timescales. However, there are currently no mathematical proofs that such functions will always be computationally complex. Quantum digital signatures offers a means of confirming both origin and authenticity of a message with security verified by information theoretical limits. The message cannot be forged or repudiated. We have constructed, tested and analyzed the security of what is, to the best of our knowledge, the first example of an experimental quantum digital signature system.
Digital signature schemes are often used in interconnected computer networks to verify the origin and authenticity of messages. Current classical digital signature schemes based on so-called “one-way functions” rely on computational complexity to provide security over sufficiently long timescales. However, there are currently no mathematical proofs that such functions will always be computationally complex. Quantum digital signatures offers a means of confirming both origin and authenticity of a message with security verified by information theoretical limits. The message cannot be forged or repudiated. We have constructed, tested and analyzed the security of what is, to the best of our knowledge, the first example of an experimental quantum digital signature system.
As society becomes more reliant on electronic communication and transactions, ensuring the security of these interactions becomes more important. Digital signatures are a widely used form of cryptography which allows parties to certify the origins of their communications, meaning that one party, a sender, can send information to other parties in such a way that messages cannot be forged. In addition, messages are transferrable, meaning that a recipient who accepts a message as genuine can be sure that if it is forwarded to another recipient, it will again be accepted as genuine. The classical digital signature schemes currently employed typically rely on computational complexity for security. Quantum digital signatures offer the potential for increased security. In our system, quantum signature states are passed through a network of polarization maintaining fiber interferometers (a multiport) to ensure that recipients will not disagree on the validity of a message. These signatures are encoded in the phase of photonic coherent states and the choice of photon number, signature length and number of possible phase states affects the level of security possible by this approach. We will give a brief introduction into quantum digital signatures and present results from our experimental demonstration system.
Digital signatures are frequently used in data transfer to prevent impersonation, repudiation and message tampering. Currently used classical digital signature schemes rely on public key encryption techniques, where the complexity of so-called ‘one-way’ mathematical functions is used to provide security over sufficiently long timescales. No mathematical proofs are known for the long-term security of such techniques. Quantum digital signatures offer a means of sending a message, which cannot be forged or repudiated, with security verified by information-theoretical limits and quantum mechanics. Here we demonstrate an experimental system, which distributes quantum signatures from one sender to two receivers and enables message sending ensured against forging and repudiation. Additionally, we analyse the security of the system in some typical scenarios. Our system is based on the interference of phase-encoded coherent states of light and our implementation utilizes polarization-maintaining optical fibre and photons with a wavelength of 850 nm. Quantum digital signatures exploit quantum mechanics to provide verification of messages at the limits of information theory. Clarkeet al.demonstrate a photonic system that provides quantum digital signatures for messages sent to two receivers and is secure against forgery and repudiation.
Classical digital signatures are commonly used in e-mail, electronic financial transactions and other forms of electronic communications to ensure that messages have not been tampered with in transit, and that messages are transferrable. The security of commonly used classical digital signature schemes relies on the computational difficulty of inverting certain mathematical functions. However, at present, there are no such one-way functions which have been proven to be hard to invert. With enough computational resources certain implementations of classical public key cryptosystems can be, and have been, broken with current technology. It is nevertheless possible to construct information-theoretically secure signature schemes, including quantum digital signature schemes. Quantum signature schemes can be made information theoretically secure based on the laws of quantum mechanics, while classical comparable protocols require additional resources such as secret communication and a trusted authority. Early demonstrations of quantum digital signatures required quantum memory, rendering them impractical at present. Our present implementation is based on a protocol that does not require quantum memory. It also uses the new technique of unambiguous quantum state elimination, Here we report experimental results for a test-bed system, recorded with a variety of different operating parameters, along with a discussion of aspects of the system security.
Digital signatures guarantee the authenticity and transferability of messages and are widely used in modern communication. The security of currently used classical digital signature schemes, however, relies on computational assumptions. In contrast, quantum digital signature (QDS) schemes offer information-theoretic security guaranteed by the laws of quantum mechanics. We present two QDS protocols which have the same experimental requirements as quantum key distribution, which is already commercially available. We also give a security proof for the presented QDS schemes against coherent forging attacks.
Quantum digital signatures can be used to authenticate classical messages in an information-theoretically secure way. Previously, a novel quantum digital signature for classical messages has been proposed and gave an experimental demonstration of distributing quantum digital signatures from one sender to two receivers. Some improvement versions were subsequently presented, which made it more feasible with present technology. These proposals for quantum digital signatures are basic building blocks which only deal with the problem of sending single bit messages while no-forging and non-repudiation are guaranteed. For a multi-bit message, it is only mentioned that the basic building blocks must be iterated, but the iteration of the basic building block still does not suffice to define the entire protocol. In this paper, we show that it is necessary to define the entire protocol because some attacks will arise if these building blocks are used in a naive way of iteration. Therefore, we give a way of defining an entire protocol to deal with the problem of sending multi-bit messages based on the basic building blocks and analyse its security.
Modern cryptography encompasses much more than encryption of secret messages. Signature schemes are widely used to guarantee that messages cannot be forged or tampered with, for example in e-mail, software updates and electronic commerce. Messages are also transferrable, which distinguishes digital signatures from message authentication. Transferability means that messages can be forwarded; in other words, that a sender is unlikely to be able to make one recipient accept a message which is subsequently rejected by another recipient if the message is forwarded. Similar to public-key encryption, the security of commonly used signature schemes relies on the assumed computational difficulty of problems such as finding discrete logarithms or factoring large primes. With quantum computers, such assumptions would no longer be valid. Partly for this reason, it is desirable to develop signature schemes with unconditional or information-theoretic security. Quantum signature schemes are one possible solution. Similar to quantum key distribution (QKD), their unconditional security relies only on the laws of quantum mechanics. Quantum signatures can be realized with the same system components as QKD, but are so far less investigated. This talk aims to provide an introduction to quantum signatures and to review theoretical and experimental progress so far.