We consider communication networks in which it is not possible to identify the source of a message which is broadcastes through the network. A natural question is whether it is possible for two users to identify each other concurrently, through a secure two-party protocol. We show that more than the existence of a secure Public Key Cryptosystem should be assumed in order to present a secure protocol for concurrent identification. We present two concurrent identification protocols: The first one relies on the existence of a center who has distributed "identification tags" two the users; while the second protocol relies on the distribution of "experimental sequences" by instances of a pre-protocol which have taken place between every two users.
We consider communication networks in which it is not possible to identify the source of a message which is broadcastes through the network. A natural question is whether it is possible for two users to identify each other concurrently, through a secure two-party protocol. We show that more than the existence of a secure Public Key Cryptosystem should be assumed in order to present a secure protocol for concurrent identification. We present two concurrent identification protocols: The first one relies on the existence of a center who has distributed "identification tags" two the users; while the second protocol relies on the distribution of "experimental sequences" by instances of a pre-protocol which have taken place between every two users.
A secure quantum identification system combining a classical identification procedure and quantum key distribution is proposed. Each identification sequence is always used just once and sequences are ``refueled'' from a shared provably secret key transferred through the quantum channel. Two identification protocols are devised. The first protocol can be applied when legitimate users have an unjammable public channel at their disposal. The deception probability is derived for the case of a noisy quantum channel. The second protocol employs unconditionally secure authentication of information sent over the public channel, and thus can be applied even in the case when an adversary is allowed to modify public communications. An experimental realization of a quantum identification system is described.
For a secure communication through the public network, cryptographic encryption must be applied. The key establishment issue is the most important part in cryptographic encryption. Only the legitimate principals who have the key can encrypt messages and decrypt cryptograms. A secure multi-party communication held through the public network can only take place after a multi-party key establishment protocol has been executed. The multi-party key establishment protocol is designed so that the principals can receive a common key and use it to securely exchange the messages.\nIn this thesis, the secure multi-party key establishment protocols are discussed. W e start from investigating properties of two-party key establishment protocols such as motivation of using session key, adversaries in the protocols, attacks of the protocol and security analysis of the protocol. Then we give the requirements of a multi-party key establishment protocol and summarize about what should be considered in designing a multi-party key establishment protocol. After that we review some of the previous proposed multi-party key establishment protocol. The existing multi-party key establishment protocols are either impractical ( not efficient enough) or missing some important security goals such as authentication of principals. Three new protocols are proposed in this thesis. The first protocol addresses how to hold a conference for members of two hierarchical groups in an efficient way. The message broadcasting is used to reduce the cost of secure message transport.\nThe second and the third protocols manage the authentication problem by using a secret sharing scheme. We replace the principal authentication with the group authentication so that the computational overhead and communication overhead will be reduced especially in reuse of the protocol for new communication. Again, message broadcasting is used for replacing the expansive secure communication channel.\nPart of this thesis appeared in ACSC'99(Australian Computer Science Conference) and ACISP'99(Australian Conference of Information Security and Privacy).
We consider the problem of designing an efficient oblivious transfer (OT) protocol that is provably secure in a concurrent setting, i.e., where many OT sessions may be running concurrently with their messages interleaved arbitrarily. Known OT protocols use zero-knowledge proofs, and no concurrent zero-knowledge proofs are known that use less than a poly-logarithmic number of rounds (at least without requiring a pre-processing phase, a public random string, an auxiliary string, timing constraints, or pre-distributed public keys). We introduce a model for proving security of concurrent OT protocols, and present a protocol that is proven secure in this model based on the decisional Diffie-Hellman problem. The protocol is efficient, requiring only a slightly non-constant number of rounds.
Oblivious transfer is a powerful cryptographic primitive that is complete for secure multi-party computation. In oblivious transfer protocols a user sends one or more messages to a receiver, while the sender remains oblivious as to which messages have been received. Protocols for oblivious transfer cannot exist in a classical or fully-quantum world, but can be implemented by restricting the users' power. The isolated qubits model is a cryptographic model in which users are restricted to single-qubit operations and are not allowed to use entangling operations. Furthermore, all parties are allowed to store qubits for a long time before measuring them. In this model, a secure single-bit one-out-of-two randomised oblivious transfer protocol was recently presented by Liu. Motivated by this result, we construct a protocol for secure string one-out-of-two randomised oblivious transfer by simplifying and generalising the existing proof. We then study for the first time interactive protocols for more complex two-party functionalities in this model based on the security of our construction. In order to guarantee the composability of our construction, users are restricted to measurement at the end of each sub-protocol. It is then possible to construct secure one-out-of-two and one-out-of-k oblivious transfer protocols in the isolated qubits model. Moreover, we study secure password-based identification, where a user identifies himself to another user by evaluating the equality function on their inputs, or passwords. We use the oblivious transfer constructions mentioned above as sub-protocols to construct a secure identification protocol. Finally, we prove that constructing a secure identification protocol non-interactively is impossible, even using oblivious transfer.
In this paper, we propose a new zero-knowledge identification protocol. While the protocol consists of only two message flows, it does not rely on any underlying signature or encryption scheme. Its zero-knowledge property is preserved under concurrent composition and reset settings. It is secure under the strongest attack model which incorporates concurrent attacks, active-intruder attacks and reset attacks. Meanwhile its performance in computation and communication is close to that of the most efficient identification protocols not based on signature or encryption systems, most of which are insecure in this strong attack model.
Until recently, most research on the topic of secure computation focused on the stand-alone model, where a single protocol execution takes place. In this paper, we construct protocols for the setting of bounded-concurrent self composition, where a (single) secure protocol is run many times concurrently, and there is a predetermined bound on the number of concurrent executions. In short, we show that any two-party functionality can be securely computed under boundedconcurrent self composition, in the plain model (where the only setup assumption made is that the parties communicate via authenticated channels). Our protocol provides the first feasibility result for general two-party computation in the plain model, for any model of concurrency. All previous protocols assumed a trusted setup phase in order to obtain a common reference string. On the downside, the number of rounds of communication in our protocol is super-linear in the bound on the number of concurrent executions. However, we believe that our constructions will lead to more efficient protocols for this task.