Editing Quantum key distribution (section)

=== Man-in-the-middle attack ===
Quantum key distribution is vulnerable to a [[man-in-the-middle attack]] when used without authentication to the same extent as any classical protocol, since no known principle of quantum mechanics can distinguish friend from foe. As in the classical case, Alice and Bob cannot authenticate each other and establish a secure connection without some means of verifying each other's identities (such as an initial shared secret). If Alice and Bob have an initial shared secret then they can use an unconditionally secure authentication scheme (such as [[Carter-Wegman MAC|Carter-Wegman]],<ref>{{cite journal | last1=Wegman | first1=Mark N. | last2=Carter | first2=J.Lawrence | title=New hash functions and their use in authentication and set equality | journal=Journal of Computer and System Sciences | publisher=Elsevier BV | volume=22 | issue=3 | year=1981 | issn=0022-0000 | doi=10.1016/0022-0000(81)90033-7 | pages=265–279| doi-access=free }}</ref>) along with quantum key distribution to exponentially expand this key, using a small amount of the new key to authenticate the next session.<ref>{{Cite arXiv |eprint = quant-ph/0701168|last1 = Nguyen|first1 = Kim-Chi|title = Using quantum key distribution for cryptographic purposes: A survey|author2 = Gilles Van Assche|last3 = Cerf|first3 = Nicolas J.|year = 2007}}</ref> Several methods to create this initial shared secret have been proposed, for example using a 3rd party<ref>{{cite journal | last1 = Zhang | first1 = Z. | last2 = Liu | first2 = J. | last3 = Wang | first3 = D. | last4 = Shi | first4 = S. | year = 2007 | title = Quantum direct communication with authentication | journal = Phys. Rev. A | volume = 75 | issue = 2| page = 026301 | doi=10.1103/physreva.75.026301| arxiv = quant-ph/0604125 | bibcode = 2007PhRvA..75b6301Z | s2cid = 5529511 }}</ref> or chaos theory.<ref>D. Huang, Z. Chen, Y. Guo and M. Lee "Quantum Secure Direct Communication Based on Chaos with Authentication", Journal of the Physical Society of Japan Vol. 76 No. 12, 124001 (2007) ({{cite web |url=https://journals.jps.jp/doi/10.1143/JPSJ.76.124001 |title=124001 |doi=10.1143/JPSJ.76.124001 |access-date=2 May 2024}})</ref> Nevertheless, only "almost strongly universal" family of hash functions can be used for unconditionally secure authentication.<ref>{{cite web|url=http://www.lysator.liu.se/~jc/mthesis/5_Unconditionally_secure_au.html|title=5. Unconditionally secure authentication|access-date=18 August 2016}}</ref>