Several simple yet secure protocols to authenticate the quantum channel of various QKD schemes, by coupling the photon sender's knowledge of a shared secret and the QBER Bob observes, are presented. It is shown that Alice can encrypt certain portions of the information needed for the QKD protocols, using a sequence whose security is based on computational-complexity, without compromising all of the sequence's entropy. It is then shown that after a Man-in-the-Middle attack on the quantum and classical channels, there is still enough entropy left in the sequence for Bob to detect the presence of Eve by monitoring the QBER. Finally, it is shown that the principles presented can be implemented to authenticate the quantum channel associated with any type of QKD scheme, and they can also be used for Alice to authenticate Bob.
Several simple yet secure protocols to authenticate the quantum channel of various QKD schemes, by coupling the photon sender's knowledge of a shared secret and the QBER Bob observes, are presented. It is shown that Alice can encrypt certain portions of the information needed for the QKD protocols, using a sequence whose security is based on computational-complexity, without compromising all of the sequence's entropy. It is then shown that after a Man-in-the-Middle attack on the quantum and classical channels, there is still enough entropy left in the sequence for Bob to detect the presence of Eve by monitoring the QBER. Finally, it is shown that the principles presented can be implemented to authenticate the quantum channel associated with any type of QKD scheme, and they can also be used for Alice to authenticate Bob.
Quantum key distribution (QKD) is intended to produce cryptographic secret keys between two remote parties, usually called Alice and Bob. Even though QKD has been proven to be unconditionally secure against the eavesdropper, commonly called Eve, practical implementations of QKD may contain vulnerabilities that may lead to the generated secret keys being compromised. In order to detect the presence of the eavesdropper in the channel, in our proposal Alice introduces an interleaved sequence of decoy states which produce a characteristic distribution at Bob's station. Thus, in analyzing such distribution in presence and absence of the eavesdropper Eve, her activity in the channel is detected. This protocol doesn’t require changes at the quantum physical level, but it can be incorporated at the high software level.
Privacy and authenticity are two main tasks for secure communication. In this paper, a quantum authenticated encryption scheme is proposed. This scheme is devised to encrypt and authenticate classical information using quantum states. We assume that Alice and Bob share a classical bits string y as their private key. Alice generates quantum cipher text and authentication tag using her secret key. Bob can decrypt and verify the authenticity of the received message. Security analysis shows that the proposed protocol is a computationally secure encryption and statistically secure authentication scheme.
Quantum Key Distribution (QKD) is a secret key agreement technique that consists of two parts: quantum transmission and measurement on a quantum channel, and classical post-processing on a public communication channel. It enjoys provable unconditional security provided that the public communication channel is immutable. Otherwise, QKD is vulnerable to a man-in-the-middle attack. Immutable public communication channels, however, do not exist in practice. So we need to use authentication that implements the properties of an immutable channel as well as possible. One scheme that serves this purpose well is the Wegman-Carter authentication (WCA), which is built upon Almost Strongly Universal2 (ASU2) hashing. This scheme uses a new key in each authentication attempt to select a hash function from an ASU2 family, which is then used to generate the authentication tag for a message. The main focus of this dissertation is on authentication in the context of QKD. We study ASU2 hash functions, security of QKD that employs a computationally secure authentication, and also security of authentication with a partially known key. Specifically, we study the following. First, Universal hash functions and their constructions are reviewed, and as well as a new construction of ASU2 hash functions is presented. Second, security of QKD that employs a specific computationally secure authentication is studied. We present detailed attacks on various practical implementations of QKD that employs this authentication. We also provide countermeasures and prove necessary and sufficient conditions for upgrading the security of the authentication to the level of unconditional security. Third, Universal hash function based multiple authentication is studied. This uses a fixed ASU2 hash function followed by one-time pad encryption, to keep the hash function secret. We show that the one-time pad is necessary in every round for the authentication to be unconditionally secure. Lastly, we study security of the WCA scheme, in the case of a partially known authentication key. Here we prove tight information-theoretic security bounds and also analyse security using witness indistinguishability as used in the Universal Composability framework.
Quantum key distribution (QKD) is a method using some properties of quantum mechanics to create a secret shared cryptographic key even if an eavesdropper has access to unlimited computational power. All QKD protocols require that the parties have access to an authentic channel. Otherwise, QKD is vulnerable to man-in-the-middle attacks. This paper studies QKD from this point of view, emphasizing the necessity and sufficiency of using unconditionally secure authentication in QKD. In this work, a new technique of using unconditionally secure authentication is proposed for quantum cryptosystems. This technique is based on a hybrid of normal application of authentication codes and the so-called “counter-based” authentication method such that to achieve a better trade-off between security and efficiency (in terms of the required size of initially shared secret data). Based on this strategy, an authenticated version of a typical QKD protocol (the well-known BB84 protocol) is described. Some advantages of our protocol in comparison to other proposals are also highlighted.
The paper addresses entity authentication in quantum key distribution (QKD) systems as a decisive condition of their practical security. It is shown that the information-theoretic security of quantum key agreement does not eliminate the need to authenticate the communicating parties: an unauthenticated classical channel leaves the system exposed to the man-in-the-middle attack, since the eavesdropper can run independent QKD instances with each party and reconcile two keys under full control. Existing authentication methods are analysed and classified by the underlying cryptographic primitive: symmetric schemes based on Wegman–Carter universal hashing, pre-shared and fixed keys, public-key infrastructure, two-way authentication, quantum entity/identity authentication, and zero-knowledge proofs. For each class the operating principle, advantages and limitations are determined, with emphasis on key management, scalability and trust distribution. It is established that symmetric and quantum-layer methods rely on pre-shared secrets with a quadratic growth of key material, public-key infrastructure introduces a single trust bottleneck and quantum-vulnerable primitives, while existing zero-knowledge authentication schemes are quantum and bound to the physical layer or solve network properties other than identity. A comparative analysis reveals an unresolved scientific gap: the absence of a scalable entity-authentication method that simultaneously provides non-disclosure of the secret, quantum resistance, sub-quadratic scalability and minimisation of trust assumptions. On this basis, a prospective research direction is substantiated – the construction of entity-authentication methods based on post-quantum zero-knowledge proofs operating over the classical control plane of scalable QKD networks. The requirements for such a method are formulated, and its compatibility with formal QKD security proofs is discussed.