Abstract Previous research on information security has focused on the protection of the contents of messages. But in many cases it is equally important to protect the identities of the sender and receiver and also the time of message transmission. This paper proposes communication protocols which make it impossible both for the entities other than the right receiver to decipher the message and for any third party to identify the communicating entities. Since it is impossible in these protocols for any third party to identify the communicators, the protocols are classified into four groups according to whether or not the communicating pair can identify each other. In addition, the security, the implementability, and the mutual relationship of these four kinds of communication protocols are studied.
Abstract Previous research on information security has focused on the protection of the contents of messages. But in many cases it is equally important to protect the identities of the sender and receiver and also the time of message transmission. This paper proposes communication protocols which make it impossible both for the entities other than the right receiver to decipher the message and for any third party to identify the communicating entities. Since it is impossible in these protocols for any third party to identify the communicators, the protocols are classified into four groups according to whether or not the communicating pair can identify each other. In addition, the security, the implementability, and the mutual relationship of these four kinds of communication protocols are studied.
In this thesis we focus on various aspects of secure message transmission protocols. Such protocols achieve the secure transmission of a message from a sender to a receiver - where the term “secure” encapsulates the notion of privacy and reliability of message transmission. These two parties are connected using an underlying network in which a static computationally unlimited active adversary able to corrupt up to t network nodes is assumed to be present. Such protocols are important to study as they are used extensively in various cryptographic protocols and are of interest to other research areas such as ad-hoc networks, military networks amongst others. Optimal bounds for the number of phases (communication from sender to receiver or vice versa), connectivity requirements (number of node disjoint network paths connecting sender and receiver - denoted by n), communication complexity (complexity of the number of field elements sent - where F is the finite field used and jFj = q) and transmission complexity (proportion of communication complexity to complexity of secrets transmitted) for secure message transmission protocols have been proven in previous work. In the one-phase model it has been shown that n 3t+1 node disjoint paths are required to achieve perfect communication. In the two phase model only n 2t + 1 node disjoint paths are necessary. This connectivity is also the required bound for almost perfectly secure one-phase protocols - protocols which achieve perfect privacy but with a negligible probability may fail to achieve reliability. In such cases the receiver accepts a different message to that transmitted by the sender or does not accept any message. The main focus of recent research in secure message transmission protocols has been to present new protocols which achieve optimal transmission complexity. This has been achieved through the transmission of multiple messages. If a protocol has a communication complexity of O(n3) field elements, to achieve optimal transmission complexity O(n2) secrets will have to be communicated. This has somewhat ignored the simplification and improvement of protocols which securely transmit a single secret. Such improvements include constructing more efficient protocols with regards to communication complexity, computational complexity and the number of field elements sent throughout the whole protocol. In the thesis we first consider one-phase almost perfectly secure message transmission and present two new protocols which improve on previous work. We present a polynomial time protocol of O(n2) communication complexity which at the time of writing this thesis, is computationally more efficient than any other protocol of similar communication complexity for the almost perfectly secure transmission of a single message. Even though our first almost perfectly secure transmission protocol is of polynomial time, it is important to study other protocols also and improve previous work presented by other researchers. This is the idea behind the second one-phase almost perfectly secure message transmission protocol we present which requires an exponential complexity of field operations but lower (O(n)) communication complexity. This protocol also improves on previous protocols of similar communication complexity, requiring in the order of O(log q) less computation to complete - where q denotes the size of the finite field used. Even though this protocol is of exponential time, for small values of n (e.g. when t = 1, t = 2 or t = 3) it may be beneficial to use this protocol for almost perfectly secure communication as opposed to using the polynomial time protocol. This is because less field elements need to be transmitted over the whole network which connects a sender and a receiver. Furthermore, an optimal almost perfectly secure transmission protocol will be one with O(n) communication complexity and with polynomial computational complexity. We hope that in the future, other researchers will be inspired by our proposed protocol, improve on our work and ideally achieve these optimal results. We also consider multi-phase protocols. By combining various cryptographic schemes, we present a new two-phase perfectly secure single message transmission protocol. At the time of writing this thesis, the protocol is the most efficient protocol when considering communication complexity. Our protocol has a communication complexity of O(n2) compared to O(n3) of previous work thus improving on the communication complexity by an order of O(n) for the perfectly secure message transmission of a single message. This protocol is then extended to a three phase protocol where a multi-recipient broadcast end channel network setting is considered. As opposed to point to point networks where a path from a sender reaches a single receiver, this network model is new in the field of message transmission protocols. In this model each path from a sender reaches multiple receivers, with all receivers receiving the same information from their common network communication channel. We show how the use of this protocol upon such a network can lead to great savings in the transmission and computation carried out by a single sender. We also discuss the importance and relevance of such a multi-recipient setting to practical applications. The first protocols in the field of perfectly secure message transmission with a human receiver are also presented. This is a topic proposed by my supervisor Professor Yvo Desmedt for which I constructed solutions. In such protocols, one of the communicating parties is considered to be a human who does not have access to a computational device. Because of this, solutions for such protocols need to be computationally efficient and computationally simple so that they can be executed by the human party. Experiments with human participants were carried out to assess how easily and accurately human parties used the proposed protocols. The experimental results are presented and these identify how well human participants used the protocols. In addition to the security of messages, we also consider how one can achieve anonymity of message transmission protocols. For such protocols, considering a single-receiver multi-sender scenario, the presence of a t-threshold bounded adversary and the transmission of multiple secrets (as many as the number of sender), once the protocols ends one should not be able to identify the sender of a received message. Considering a passive and active adversary new protocols are presented which achieve the secure and anonymous transmission of messages in the information-theoretic security model. Our proposed solutions can also be applied (with minor alterations) to the dual problem when a single-sender multi-recipient communication setting is considered. The contributions of the thesis are primarily theoretical - thus no implementation of the proposed protocols was carried out. Despite this, we reflect on practical aspects of secure message transmission protocols. We review the feasibility of implementing secure message transmission protocols in general upon various networks - focusing on the Internet which can be considered as the most important communication network at this time. We also describe in theory how concepts of secure message transmission protocols could possibly be used in practical implementations for secure communication on various existing communication networks. Open problems that remain unsolved in the research area of the proposed protocols are also discussed and we hope that these inspire research and future solutions for the design (and implementation) of better and more efficient secure message transmission protocols.
In data communications, digital signature schemes have been used to ensure non repudiation of sending data and the integrality of data, and non repudiation of receiving data is also very important in the secure communication. In the past years, this kind of cryptographic protocols was mainly implemented by the intervention of the trusted third party in transmission and encryption of data, thus the dependability and security of the trusted third party was a bottleneck in these secure systems. To solve this problem, an undeniable cryptographic protocol for both sender and receiver is proposed. It is more efficient. Finally, its applications in electric mail are discussed.
We present the first quantum secure communication protocol for an anonymous receiver without the assistance of anonymous entanglement. In previous works, if a public sender wants to send quantum messages to a chosen receiver while protecting the identity of the receiver from others, all participants should cooperate first to construct the entanglement between the sender and the anonymous receiver. This is the most important process in anonymous quantum communications. With anonymous entanglement, the sender can communicate quantum messages to the anonymous receiver by applying teleportation protocols. In contrast, our protocol is novel and achieves communication of quantum messages directly from the public sender to the anonymous receiver based on the quantum one-time pad and current achievements. Notably, the anonymity of the receiver, as well as the privacy of the quantum messages, is perfectly protected with the exception of an exponentially small probability in our protocol.
T wo non-interactive three parties k out of n oblivious transfer protocols from bilinear pairings are proposed i n this paper. In these protocols , a sender can obliviously transfer n messages to a receiver without communication with him/her. The public keys that a sender used to encrypt his/her messages are made by a third party. The receiver can extract k out of n messages at his/her choices by using the corresponding secret keys. The choices of the receiver are unconditionally secure. The sender's secrecy is guaranteed if the receiver is semi-honest in the standard model since the decision bilinear Diffie-Hellman problem (DBDH) is hard and the sender's secrecy is achieved when the receiver is a malicious party in the random oracle model since the bilinear Diffie-Hellman problem assumption (BDHA) holds. When a sender is a cheating party, the receiver will detect him/her and halt the protocol. A precise proof of the security of the protocols is presented.
An authentication protocol is a procedure by which a sender tries to convey n bits of information, which we call an input message, to a receiver. An adversary controls the network over which the sender and the receiver talk and may change any message before it reaches its destination. This paper deals with the simple scenario where two parties, Alice and Bob, communicate and want to assure that the message received by Bob is the one sent by Alice. Unconditional cryptographic security cannot be generated simply from scratch, but must be based on some given primitive to start with. In this paper, we introduce a message authentication protocol with unconditional cryptographic security. More precisely, we give protocols using a weakly secret key allowing for the exchange of authenticated messages.
The notion of deniable authentication protocol was introduced in 1998 by Dwork et al. [11] and Aumann and Rabin [1, 2] independently. As a new cryptographic authentication protocol, a deniable authentication protocol enables an intended receiver to identify the source of a given message without being able to prove the identity of the sender to a third party. Over the past years, many deniable authentication protocols have been proposed. In this paper, we would like to present a universal encrypted deniable authentication protocol from any public key encryption scheme. Provided that the public key encryption scheme is secure, a secure deniable authentication protocol can be directly derived.