Comment on "Resilience of gated avalanche photodiodes against bright illumination attacks in quantum cryptography"

This is a comment on the publication by Yuan et al. [Appl. Phys. Lett. 98, 231104 (2011); arXiv:1106.2675v1 [quant-ph]].Comment: 2 page

Secure gated detection scheme for quantum cryptography

Several attacks have been proposed on quantum key distribution systems with gated single-photon detectors. The attacks involve triggering the detectors outside the center of the detector gate, and/or using bright illumination to exploit classical photodiode mode of the detectors. Hence a secure detection scheme requires two features: The detection events must take place in the middle of the gate, and the detector must be single-photon sensitive. Here we present a technique called bit-mapped gating, which is an elegant way to force the detections in the middle of the detector gate by coupling detection time and quantum bit error rate. We also discuss how to guarantee single-photon sensitivity by directly measuring detector parameters. Bit-mapped gating also provides a simple way to measure the detector blinding parameter in security proofs for quantum key distribution systems with detector efficiency mismatch, which up until now has remained a theoretical, unmeasurable quantity. Thus if single-photon sensitivity can be guaranteed within the gates, a detection scheme with bit-mapped gating satisfies the assumptions of the current security proofs.Comment: 7 pages, 3 figure

After-gate attack on a quantum cryptosystem

We present a method to control the detection events in quantum key distribution systems that use gated single-photon detectors. We employ bright pulses as faked states, timed to arrive at the avalanche photodiodes outside the activation time. The attack can remain unnoticed, since the faked states do not increase the error rate per se. This allows for an intercept-resend attack, where an eavesdropper transfers her detection events to the legitimate receiver without causing any errors. As a side effect, afterpulses, originating from accumulated charge carriers in the detectors, increase the error rate. We have experimentally tested detectors of the system id3110 (Clavis2) from ID Quantique. We identify the parameter regime in which the attack is feasible despite the side effect. Furthermore, we outline how simple modifications in the implementation can make the device immune to this attack.Comment: 14 pages, 8 figure

Controlling an actively-quenched single photon detector with bright light

We control using bright light an actively-quenched avalanche single-photon detector. Actively-quenched detectors are commonly used for quantum key distribution (QKD) in the visible and near-infrared range. This study shows that these detectors are controllable by the same attack used to hack passively-quenched and gated detectors. This demonstrates the generality of our attack and its possible applicability to eavsdropping the full secret key of all QKD systems using avalanche photodiodes (APDs). Moreover, the commercial detector model we tested (PerkinElmer SPCM-AQR) exhibits two new blinding mechanisms in addition to the previously observed thermal blinding of the APD, namely: malfunctioning of the bias voltage control circuit, and overload of the DC/DC converter biasing the APD. These two new technical loopholes found just in one detector model suggest that this problem must be solved in general, by incorporating generally imperfect detectors into the security proof for QKD.Comment: Expanded discussions, updated references, added a picture of decapsulated APD, reformatted to single-column style. Accepted to Opt. Express. 11 pages, 6 figure

Device calibration impacts security of quantum key distribution

Characterizing the physical channel and calibrating the cryptosystem hardware are prerequisites for establishing a quantum channel for quantum key distribution (QKD). Moreover, an inappropriately implemented calibration routine can open a fatal security loophole. We propose and experimentally demonstrate a method to induce a large temporal detector efficiency mismatch in a commercial QKD system by deceiving a channel length calibration routine. We then devise an optimal and realistic strategy using faked states to break the security of the cryptosystem. A fix for this loophole is also suggested.Comment: 4 pages + 1 page of supplementary information. Considerable modification of Eve's attack strategy and QBER minimization technique. All figures have also been improve

Perceived social support among adolescents in Residential Youth Care

Social support may be of particular importance for vulnerable adolescents' develop-ment and health and can help them to cope with stressful life events. However,knowledge of perceived social support among adolescents in Residential Youth Care(RYC) is sparse. The present study therefore aimed to investigate perceived socialsupport among adolescents in Norwegian RYC (N= 304, mean age 16.3 years, girls57.2%), using a short form of the Social Support Questionnaire. The results werecompared with adolescents in the general population. The findings revealed thatadolescents in RYC reported a lower number of support persons compared withthe general population. Both populations reported a decreasing number of supportpersons as they aged, except for girls in RYC. The adolescents in both populationswere satisfied with the support perceived, especially those with the highest numberof support persons. However, social support providers differed between the two pop-ulations; RYC adolescents reported their extended family, other sources of support,and the institutional staff more often and their parents less. The findings are impor-tant for adolescents living in RYC, as knowledge of their social support network couldinfluence the current practices and ensure contact with important support persons,affecting their development and health

Thermal blinding of gated detectors in quantum cryptography

It has previously been shown that the gated detectors of two commercially available quantum key distribution (QKD) systems are blindable and controllable by an eavesdropper using continuous-wave illumination and short bright trigger pulses, manipulating voltages in the circuit [L. Lydersen et al., Nat. Photonics DOI:10.1038/nphoton.2010.214]. This allows for an attack eavesdropping the full raw and secret key without increasing the quantum bit error rate (QBER). Here we show how thermal effects in detectors under bright illumination can lead to the same outcome. We demonstrate that the detectors in a commercial QKD system Clavis2 can be blinded by heating the avalanche photo diodes (APDs) using bright illumination, so-called thermal blinding. Further, the detectors can be triggered using short bright pulses once they are blind. For systems with pauses between packet transmission such as the plug-and-play systems, thermal inertia enables Eve to apply the bright blinding illumination before eavesdropping, making her more difficult to catch.Comment: 10 pages, 12 figure

Water chemistry, zooplankton and benthos in small lakes within the distribution area of the rare European pool frog Pelophylax lessonae (Camerano) in Norway

Summary In June 2018, water chemistry, benthos and zooplankton were investigated in 7 small lakes/ ponds within the key area of the European pool frog Pelophylax lessonae (Camerano) in Norway. The geographic distribution of the Norwegian population is minor, limited to a very few small lakes in the county of Agder in southernmost Norway. Since the species is thermophilic, reproduction success only occurs in warm summers. Accordingly, the pool frog is one of the most rare vertebrates in Norwegian fauna, classified as critically endangered in the Norwegian red list. A breeding program is today established in order to rescue this species.The article deals with potential biotope challenges most relevant for the recruitment success of the pool frog in Norway, primarily related to physical, chemical and biological conditions in surface water. In addition, terrestrial biotope challenges and potential effects of low genetic diversity in the very small Norwegian population are discussed. Sammendrag Vannkjemi, zooplankton og bunndyr i små innsjøer innenfor leveområdet til en av Norges mest truete vertebrater, Europeisk damfrosk Pelophylax lessonae (Camerano). I juni 2018, ble vannkjemi, bunndyr og zooplankton undersøkt i 7 små tjern i kjerneområdet for den damfrosken Pelophylax lessonae (Camerano) i Norge. Utbredelsen av arten er svært begrenset, og populasjonen svært liten. Arten er relativt termofil, noe som sannsynligvis er hovedårsaken til den marginale utbredelsen. Arten er trolig den mest sjeldne vertebrat i norsk fauna, klassifisert som kritisk truet på den norske rødlista. Derfor er det også etablert et avlsprogram for om mulig å kunne redde denne sjeldne vertebraten i norsk natur. I tillegg til artens klimatiske begrensninger i Norge, tar denne artikkelen opp ulike biotop- utfordringer, i første rekke i forhold til artens muligheter for reproduksjon i de akvatiske miljøene den er avhengig av. I tillegg, tas det opp enkelte terrestriske utfordringer for arten, samt effekter av lav genetisk diversitet i den svært marginale norske populasjonen.publishedVersio