In this paper the extended classification of the attacks on the protocols and practically realized systems of quantum cryptography with taking into account the kinds of attacks, which are known at present time, is proposed. This classification subdivides attacks on three classes: the passive attacks, which are possible when the honest participants use single-photon sources, passive and active attacks, which are due to imperfection of the equipment of the quantum communication systems (quantum hacking), passive and active attacks, which are due to the own protocols imperfection. The existence of such classification lets to realize the necessary security estimation of quantum cryptography protocols and to make a decision concerning choice commercially available quantum cryptosystems by criterion of their ability to resist against present and perspective methods of quantum cryptanalysis. The Trojan-horse attack and attack of the remote control of the single-photon detectors with using of the tailored bright illumination in detail are described. In the frame of describing of the detectors control attack the principle of using of the faked states is stated. In addition, the varieties of such attack, which are depended from type of avalanche photodiodes: with passive and active method of avalanche quenching, gated photodiodes, are considered.
In this paper the extended classification of the attacks on the protocols and practically realized systems of quantum cryptography with taking into account the kinds of attacks, which are known at present time, is proposed. This classification subdivides attacks on three classes: the passive attacks, which are possible when the honest participants use single-photon sources, passive and active attacks, which are due to imperfection of the equipment of the quantum communication systems (quantum hacking), passive and active attacks, which are due to the own protocols imperfection. The existence of such classification lets to realize the necessary security estimation of quantum cryptography protocols and to make a decision concerning choice commercially available quantum cryptosystems by criterion of their ability to resist against present and perspective methods of quantum cryptanalysis. The Trojan-horse attack and attack of the remote control of the single-photon detectors with using of the tailored bright illumination in detail are described. In the frame of describing of the detectors control attack the principle of using of the faked states is stated. In addition, the varieties of such attack, which are depended from type of avalanche photodiodes: with passive and active method of avalanche quenching, gated photodiodes, are considered.
Abstract Early proofs of key secrecy in quantum cryptography systems were based on the assumption that the transmitting and receiving stations are completely isolated from the outside world—the eavesdropper. However, this condition cannot be implemented in practice since quantum cryptography systems are open systems in the sense that the eavesdropper may have indirect access, for example, through a fiber communication channel, to the critical elements of the equipment (phase modulators, intensity modulators, etc.) using active probing of the state of these elements. The state of the elements carries information about the transmitted key. In addition, the eavesdropper can use passive detection of side radiation from the receiving and transmitting equipment. Signals in side channels of information leakage may have extremely low intensity and are actually quantum signals. The eavesdropper may use the joint measurement of quantum information states in the communication channel and of states in various side channels of information leakage. The paper considers both passive attacks with measurement of side radiation and active attacks involving the probing of the states of the phase modulator and the intensity modulator, as well as backscattering radiation of single-photon avalanche detectors, which occurs during detecting information states on the receiver side. Combined attacks are also considered. The decoy state method is generalized with regard to active probing attacks, and boundaries for state parameters in side communication channels are obtained that guarantee secret key distribution for a given length of the communication channel.
A new type of attack on quantum cryptography systems is proposed. In this attack, Eve utilizes various optical imperfections in Bob's scheme and constructs light pulses so that Bob does not distinguish his detection results from normal, whereas they give Bob the basis and bit value chosen at Eve's discretion. Applying this attack to systems with passive basis choice on Bob's side is considered. Also, a general workflow of breaking into a running quantum cryptolink using this or Trojan horse attack is discussed.
Abstract Early security proofs of the keys in quantum cryptography systems were based on the assumption that the transmitting and receiving stations were completely isolated from the outside world—the eavesdropper. However, this condition cannot be implemented in practice, since quantum cryptography systems are open systems, in the sense that an eavesdropper can have indirect access, for example, through a fiber communication channel to critical equipment elements (phase modulators, intensity modulators, etc) using active sensing of the state of these elements—Trojan-horse attacks. A new Trojan-horse attack based on joint unambiguous measurements of reflected probing states from an intensity modulator and information states in a quantum communication channel is proposed. Estimates of attack parameters for a number of quantum key distribution protocols are given, when an attack leads to compromise of keys.
Abstract Various Trojan-horse attacks on quantum cryptography systems are systematically considered: an attack with passive detection of side radiation, an attack with active sensing, as well as joint attacks on states in the quantum channel, side and reflected radiation. It is shown that the most effective attack is an attack with the measurement of the number of photons in the reflected states and further joint measurement of information and reflected quantum states. Explicit estimates are obtained for the intensity of the reflected quantum states at which secret keys can be transmitted to a given length.
The peculiar properties of quantum mechanics enable possibilities not allowed by classical physics. In particular, two parties can generate a random, secret key at a distance, even though an eavesdropper can do anything permitted by the laws of physics. Measuring the quantum properties of the signals generating the key, would ultimately change them, and thus reveal the eavesdropper’s presence. This exchange of a random, secret key is known as quantum cryptography.\n\nQuantum cryptography can be, and has been proven unconditionally secure using perfect devices. However, when quantum cryptography is implemented, one must use components available with current technology. These are usually imperfect. Although the security of quantum cryptography has been proven for components with certain imperfections, the question remains: can quantum cryptography be implemented in a provable, unconditionally secure way, using components available with current technology? This thesis contains both a theoretical, and an experimental contribution to the answer of this question. On the experimental side, components used in, and complete quantum cryptography systems have been carefully examined for security loopholes. In particular, it turned out that two commercial quantum cryptography systems contained loopholes, which would allow an eavesdropper to capture the full secret key, without exposing her presence. Furthermore, this detector control attack could be implemented with current technology. The attack is applicable against a variety of quantum cryptography implementations and protocols.\n\nThe theoretical contribution consists of security proofs for quantum cryptography in a very general setting. Precisely, the security is proven with arbitrary individual imperfections in the source and detectors. These proofs should make it possible to use a wide array of imperfect devices in implementations of quantum cryptography.\n\nFinally, a secure detection scheme is proposed, immune to the detector control attack and compatible with those security proofs. Therefore, if this scheme is implemented correctly, it offers provable security.
The fundamental quantum mechanics prohibitions on the measurability of quantum states allow secure key distribution between spatially remote users to be performed. Experimental and commercial implementations of quantum cryptography systems, however, use components that exist at the current technology level, in particular, one-photon avalanche photodetectors. These detectors are subject to the blinding effect. It was shown that all the known basic quantum key distribution protocols and systems based on them are vulnerable to attacks with blinding of photodetectors. In such attacks, an eavesdropper knows all the key transferred, does not produce errors at the reception side, and remains undetected. Three protocols of quantum key distribution stable toward such attacks are suggested. The security of keys and detection of eavesdropping attempts are guaranteed by the internal structure of protocols themselves rather than additional technical improvements.