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'''Quantum cryptography''' is the science of exploiting [[Quantum mechanics|quantum mechanical]] properties such as quantum entanglement, measurement distrubancedisturbance, no-cloning theorem, and the principle of superposition to perform various [[cryptographic]] tasks.<ref>{{Cite journal|last1=Gisin|first1=Nicolas|last2=Ribordy|first2=Grégoire|last3=Tittel|first3=Wolfgang|last4=Zbinden|first4=Hugo|display-authors=|year=2002|title=Quantum cryptography|url=https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.74.145|journal=Reviews of Modern Physics|volume=74|issue=1|pages=145–195|doi=10.1103/RevModPhys.74.145|arxiv=quant-ph/0101098|bibcode=2002RvMP...74..145G|s2cid=6979295}}</ref><ref name=":4">{{Cite journal|last1=Pirandola|first1=S.|last2=Andersen|first2=U. L.|last3=Banchi|first3=L.|last4=Berta|first4=M.|last5=Bunandar|first5=D.|last6=Colbeck|first6=R.|last7=Englund|first7=D.|last8=Gehring|first8=T.|last9=Lupo|first9=C.|last10=Ottaviani|first10=C.|last11=Pereira|first11=J. L.|display-authors=et al.|year=2020|title=Advances in quantum cryptography|url=https://www.osapublishing.org/aop/abstract.cfm?uri=aop-12-4-1012|journal=Advances in Optics and Photonics|volume=12|issue=4|pages=1012–1236|arxiv=1906.01645|doi=10.1364/AOP.361502|bibcode=2020AdOP...12.1012P|s2cid=174799187}}</ref><ref>{{Cite journal |last=Renner |first=Renato |last2=Wolf |first2=Ramona |date=2023 |title=Quantum Advantage in Cryptography |url=https://doi.org/10.2514/1.J062267 |journal=AIAA Journal |volume=61 |issue=5 |pages=1895–1910 |doi=10.2514/1.J062267 |issn=0001-1452}}</ref> Historically defined as the practice of encoding messages, a concept now referred to as encryption, cryptography plays a crucial role in the secure processing, storage, and transmission of information across various domains. One aspect of quantum cryptography is [[quantum key distribution]] (QKD), which offers an [[Information-theoretic security|information-theoretically secure]] solution to the [[key exchange]] problem. The advantage of quantum cryptography lies in the fact that it allows the completion of various cryptographic tasks that are proven or conjectured to be impossible using only classical (i.e. non-quantum) communication. Furthermore, quantum cryptography affords the authentication of messages, which allows the legitimates parties to prove that the messages wre not wiretaped during transmission.<ref>{{Cite journal |last=Gisin |first=Nicolas |last2=Ribordy |first2=Grégoire |last3=Tittel |first3=Wolfgang |last4=Zbinden |first4=Hugo |date=2002-03-08 |title=Quantum cryptography |url=https://link.aps.org/doi/10.1103/RevModPhys.74.145 |journal=Reviews of Modern Physics |volume=74 |issue=1 |pages=145–195 |doi=10.1103/RevModPhys.74.145}}</ref> For example, in a cryptographic set-up, it is [[No-cloning theorem|impossible to copy]] with perfect fidelity, the data encoded in a [[quantum state]]. If one attempts to read the encoded data, the quantum state will be changed due to [[wave function collapse]] ([[no-cloning theorem]]). This could be used to detect eavesdropping in QKD schemes, or in quantum communication links and networks. These advantages have significantly influenced the evolution of quantum cryptography, making it practical in today's digital age, where devices are increasingly interconnected and cyberattacks have become more sophisticated. As such quantum cryptography is a critical component in the advancement of a quantum internet, as it establishes robust mechanisms to ensure the long-term privacy and integrity of digital communications and systems.<ref>{{Cite journal |last=Mitra |first=Saptarshi |last2=Jana |first2=Bappaditya |last3=Bhattacharya |first3=Supratim |last4=Pal |first4=Prashnatita |last5=Poray |first5=Jayanta |date=November 2017 |title=Quantum cryptography: Overview, security issues and future challenges |url=https://ieeexplore.ieee.org/abstract/document/8350006 |journal=2017 4th International Conference on Opto-Electronics and Applied Optics (Optronix) |pages=1–7 |doi=10.1109/OPTRONIX.2017.8350006}}</ref>
