Editing Quantum key distribution (section)

== Quantum hacking ==
Hacking attacks target vulnerabilities in the operation of a QKD protocol or deficiencies in the components of the physical devices used in construction of the QKD system. If the equipment used in quantum key distribution can be tampered with, it could be made to generate keys that were not secure using a [[random number generator attack]]. Another common class of attacks is the [[Trojan horse]] attack<ref>{{cite journal | last1=Vakhitov | first1=Artem | last2=Makarov | first2=Vadim | last3=Hjelme | first3=Dag R. | title=Large pulse attack as a method of conventional optical eavesdropping in quantum cryptography | journal=Journal of Modern Optics | publisher=Informa UK Limited | volume=48 | issue=13 | year=2001 | issn=0950-0340 | doi=10.1080/09500340108240904 | pages=2023–2038| bibcode=2001JMOp...48.2023V | s2cid=16173055 }}</ref> which does not require physical access to the endpoints: rather than attempt to read Alice and Bob's single photons, Eve sends a large pulse of light back to Alice in between transmitted photons. Alice's equipment reflects some of Eve's light, revealing the state of Alice's basis (e.g., a polarizer). This attack can be detected, e.g. by using a classical detector to check the non-legitimate signals (i.e. light from Eve) entering Alice's system. It is also conjectured{{by whom|date=February 2018}} that most hacking attacks can similarly be defeated by modifying the implementation, though there is no formal proof.

Several other attacks including faked-state attacks,<ref>{{cite journal | last1=Makarov * | first1=Vadim | last2=Hjelme | first2=Dag R. | title=Faked states attack on quantum cryptosystems | journal=Journal of Modern Optics | publisher=Informa UK Limited | volume=52 | issue=5 | date=2005-03-20 | issn=0950-0340 | doi=10.1080/09500340410001730986 | pages=691–705| bibcode=2005JMOp...52..691M | s2cid=17478135 }}</ref> phase remapping attacks,<ref>{{cite journal | last1=Fung | first1=Chi-Hang Fred | last2=Qi | first2=Bing | last3=Tamaki | first3=Kiyoshi | last4=Lo | first4=Hoi-Kwong | title=Phase-remapping attack in practical quantum-key-distribution systems | journal=Physical Review A | volume=75 | issue=3 | date=2007-03-12 | issn=1050-2947 | doi=10.1103/physreva.75.032314 | page=032314| arxiv=quant-ph/0601115 | bibcode=2007PhRvA..75c2314F | s2cid=15024401 }}</ref> and time-shift attacks<ref>B. Qi, C.-H. F. Fung, H.-K. Lo, and X. Ma, Quant. Info. Compu. 7, 43 (2007)</ref> are now known. The time-shift attack has even been demonstrated on a commercial quantum cryptosystem.<ref>{{cite journal | last1=Zhao | first1=Yi | last2=Fung | first2=Chi-Hang Fred | last3=Qi | first3=Bing | last4=Chen | first4=Christine | last5=Lo | first5=Hoi-Kwong | title=Quantum hacking: Experimental demonstration of time-shift attack against practical quantum-key-distribution systems | journal=Physical Review A | volume=78 | issue=4 | date=2008-10-28 | issn=1050-2947 | doi=10.1103/physreva.78.042333 | page=042333| arxiv=0704.3253 | bibcode=2008PhRvA..78d2333Z | s2cid=117595905 }}</ref> This is the first demonstration of quantum hacking against a non-homemade quantum key distribution system. Later on, the phase-remapping attack was also demonstrated on a specially configured, research oriented open QKD system (made and provided by the Swiss company Id Quantique under their Quantum Hacking program).<ref>F. Xu, B. Qi, and H.-K. Lo, New J. Phys. 12, 113026 (2010)</ref> It is one of the first 'intercept-and-resend' attacks on top of a widely used QKD implementation in commercial QKD systems. This work has been widely reported in media.<ref>[https://www.theregister.co.uk/2010/05/18/quantum_crypto_attack/ Quantum crypto boffins in successful backdoor sniff – Erroneous error-handling undermines bulletproofness] retrieved 2010-05-26</ref><ref>{{cite journal|url=http://www.nature.com/news/2010/100520/full/news.2010.256.html|title=Quantum crack in cryptographic armour|first=Zeeya|last=Merali|date=20 May 2010|access-date=18 August 2016|via=www.nature.com|doi=10.1038/news.2010.256|journal=Nature}}</ref><ref>{{cite news| url=http://www.economist.com/node/16681905 | newspaper=The Economist | title=Light fantastic | date=26 July 2010}}</ref><ref>{{Cite web |url=http://physicsworld.com/cws/article/news/42667 |title=Quantum cryptography system hacked - physicsworld.com |access-date=26 July 2011 |archive-url=https://web.archive.org/web/20111108030705/http://physicsworld.com/cws/article/news/42667 |archive-date=8 November 2011 |url-status=dead}}</ref>

The first attack that claimed to be able to eavesdrop the whole key<ref>{{cite journal | last1=Lydersen | first1=Lars | last2=Wiechers | first2=Carlos | last3=Wittmann | first3=Christoffer | last4=Elser | first4=Dominique | last5=Skaar | first5=Johannes | last6=Makarov | first6=Vadim | title=Hacking commercial quantum cryptography systems by tailored bright illumination | journal=Nature Photonics | publisher=Springer Science and Business Media LLC | volume=4 | issue=10 | date=2010-08-29 | issn=1749-4885 | doi=10.1038/nphoton.2010.214 | pages=686–689| arxiv=1008.4593 | bibcode=2010NaPho...4..686L | s2cid=58897515 }}</ref> without leaving any trace was demonstrated in 2010. It was experimentally shown that the single-photon detectors in two commercial devices could be fully remote-controlled using specially tailored bright illumination. In a spree of publications<ref>{{cite journal | last1=Lydersen | first1=Lars | last2=Wiechers | first2=Carlos | last3=Wittmann | first3=Christoffer | last4=Elser | first4=Dominique | last5=Skaar | first5=Johannes | last6=Makarov | first6=Vadim | title=Thermal blinding of gated detectors in quantum cryptography | journal=Optics Express | volume=18 | issue=26 | pages=27938–27954 | date=2010-12-17 | issn=1094-4087 | doi=10.1364/oe.18.027938 | pmid=21197067 | arxiv=1009.2663 | bibcode=2010OExpr..1827938L | s2cid=13395490 }}</ref><ref>{{cite journal | last1=Wiechers | first1=C | last2=Lydersen | first2=L | last3=Wittmann | first3=C | last4=Elser | first4=D | last5=Skaar | first5=J | last6=Marquardt | first6=Ch | last7=Makarov | first7=V | last8=Leuchs | first8=G | title=After-gate attack on a quantum cryptosystem | journal=New Journal of Physics | volume=13 | issue=1 | date=2011-01-26 | issn=1367-2630 | doi=10.1088/1367-2630/13/1/013043 | page=013043|doi-access=free| bibcode=2011NJPh...13a3043W | arxiv=1009.2683 }}</ref><ref>{{cite journal | last1=Jain | first1=Nitin | last2=Wittmann | first2=Christoffer | last3=Lydersen | first3=Lars | last4=Wiechers | first4=Carlos | last5=Elser | first5=Dominique | last6=Marquardt | first6=Christoph | last7=Makarov | first7=Vadim | last8=Leuchs | first8=Gerd | title=Device Calibration Impacts Security of Quantum Key Distribution | journal=Physical Review Letters | volume=107 | issue=11 | date=2011-09-09 | issn=0031-9007 | doi=10.1103/physrevlett.107.110501 | pmid=22026652 | page=110501| arxiv=1103.2327 | bibcode=2011PhRvL.107k0501J | s2cid=6778097 }}</ref> thereafter, the collaboration between the [[Norwegian University of Science and Technology]] in Norway and [[Max Planck Institute for the Science of Light]] in Germany, has now demonstrated several methods to successfully eavesdrop on commercial QKD systems based on weaknesses of [[avalanche photodiodes]] (APDs) operating in gated mode. This has sparked research on new approaches to securing communications networks.<ref>{{cite journal|author= Richard Hughes and [[Beth Nordholt|Jane Nordholt]] |title= Refining Quantum Cryptography |journal=Science|pages= 1584–6 |volume= 333 |date= 16 September 2011|doi= 10.1126/science.1208527|pmid= 21921186|issue= 6049|bibcode = 2011Sci...333.1584H |s2cid= 206535295 |url= https://zenodo.org/record/1230916 }}</ref>