Cryptography, or cryptology,[1] <en.wikipedia.org/wiki/Cryptography#cite_note-1> is the practice and study of techniques for secure communication <en.wikipedia.org/wiki/Secure_communication> in the presence of adversarial <en.wikipedia.org/wiki/Adversary_(cryptography)> behavior.[2] <en.wikipedia.org/wiki/Cryptography#cite_note-2> More generally, cryptography is about constructing and analyzing protocols <en.wikipedia.org/wiki/Communication_protocol> that prevent third parties or the public from reading private messages.[3] <en.wikipedia.org/wiki/Cryptography#cite_note-3> Modern cryptography exists at the intersection of the disciplines of mathematics <en.wikipedia.org/wiki/Mathematics> , computer science <en.wikipedia.org/wiki/Computer_science> , information security <en.wikipedia.org/wiki/Information_security> , electrical engineering <en.wikipedia.org/wiki/Electrical_engineering> , digital signal processing <en.wikipedia.org/wiki/Digital_signal_processing> , physics <en.wikipedia.org/wiki/Physics> , and others.[4] <en.wikipedia.org/wiki/Cryptography#cite_note-4> Core concepts related to information security <en.wikipedia.org/wiki/Information_security> (data confidentiality <en.wikipedia.org/wiki/Confidentiality> , data integrity <en.wikipedia.org/wiki/Data_integrity> , authentication <en.wikipedia.org/wiki/Authentication> and non-repudiation <en.wikipedia.org/wiki/Non-repudiation> ) are also central to cryptography.[5] <en.wikipedia.org/wiki/Cryptography#cite_note-Menezes-1997-5> Practical applications of cryptography include electronic commerce <en.wikipedia.org/wiki/Electronic_commerce> , chip-based payment cards <en.wikipedia.org/wiki/Smart_card#EMV> , digital currencies <en.wikipedia.org/wiki/Digital_currencies> , computer passwords <en.wikipedia.org/wiki/Password> and military communications <en.wikipedia.org/wiki/Military_communications> .
Cryptography prior to the modern age was effectively synonymous with encryption <en.wikipedia.org/wiki/Encryption> , converting readable information (plaintext <en.wikipedia.org/wiki/Plaintext> ) to unintelligible nonsense <en.wikipedia.org/wiki/Nonsense> text (ciphertext <en.wikipedia.org/wiki/Ciphertext> ), which can only be read by reversing the process (decryption <en.wikipedia.org/wiki/Decryption> ). The sender of an encrypted (coded) message shares the decryption (decoding) technique only with the intended recipients to preclude access from adversaries. The cryptography literature often uses the names <en.wikipedia.org/wiki/Alice_and_Bob> “Alice” (or “A”) for the sender, “Bob” (or “B”) for the intended recipient, and “Eve” (or “E”) for the eavesdropping <en.wikipedia.org/wiki/Eavesdropping> adversary.[6] <en.wikipedia.org/wiki/Cryptography#cite_note-Biggs-2008-6> Since the development of rotor cipher machines <en.wikipedia.org/wiki/Rotor_machine> in World War <en.wikipedia.org/wiki/World_War_I> I and the advent of computers in World War <en.wikipedia.org/wiki/World_War_II> II, cryptography methods have become increasingly complex and their applications more varied.
Modern cryptography is heavily based on mathematical theory <en.wikipedia.org/wiki/Mathematical_theory> and computer science practice; cryptographic algorithms <en.wikipedia.org/wiki/Algorithm> are designed around computational hardness assumptions <en.wikipedia.org/wiki/Computational_hardness_assumption> , making such algorithms hard to break in actual practice by any adversary. While it is theoretically possible to break into a well-designed system, it is infeasible in actual practice to do so. Such schemes, if well designed, are therefore termed “computationally secure”. Theoretical advances (e.g., improvements in integer factorization <en.wikipedia.org/wiki/Integer_factorization> algorithms) and faster computing technology require these designs to be continually reevaluated and, if necessary, adapted. Information-theoretically secure <en.wikipedia.org/wiki/Information-theoretic_security> schemes that provably cannot be broken even with unlimited computing power, such as the one-time pad <en.wikipedia.org/wiki/One-time_pad> , are much more difficult to use in practice than the best theoretically breakable but computationally secure schemes.
The growth of cryptographic technology has raised a number of legal issues <en.wikipedia.org/wiki/Cryptography_law> in the Information Age <en.wikipedia.org/wiki/Information_Age> . Cryptography’s potential for use as a tool for espionage and sedition <en.wikipedia.org/wiki/Sedition> has led many governments to classify it as a weapon and to limit or even prohibit its use and export.[7] <en.wikipedia.org/wiki/Cryptography#cite_note-Crypto_Law_Survey-2013 -7> In some jurisdictions where the use of cryptography is legal, laws permit investigators to compel the disclosure <en.wikipedia.org/wiki/Key_disclosure_law> of encryption keys <en.wikipedia.org/wiki/Key_(cryptography)> for documents relevant to an investigation.[8] <en.wikipedia.org/wiki/Cryptography#cite_note-PC_World-2007-8> [9] <en.wikipedia.org/wiki/Cryptography#cite_note-Ranger-2015-9> Cryptography also plays a major role in digital rights management <en.wikipedia.org/wiki/Digital_rights_management> and copyright infringement <en.wikipedia.org/wiki/Copyright_infringement> disputes with regard to digital media <en.wikipedia.org/wiki/Digital_media> .[10] <en.wikipedia.org/wiki/Cryptography#cite_note-Doctorow-2007-10>
Cryptography prior to the modern age was effectively synonymous with encryption <en.wikipedia.org/wiki/Encryption> , converting readable information (plaintext <en.wikipedia.org/wiki/Plaintext> ) to unintelligible nonsense <en.wikipedia.org/wiki/Nonsense> text (ciphertext <en.wikipedia.org/wiki/Ciphertext> ), which can only be read by reversing the process (decryption <en.wikipedia.org/wiki/Decryption> ). The sender of an encrypted (coded) message shares the decryption (decoding) technique only with the intended recipients to preclude access from adversaries. The cryptography literature often uses the names <en.wikipedia.org/wiki/Alice_and_Bob> “Alice” (or “A”) for the sender, “Bob” (or “B”) for the intended recipient, and “Eve” (or “E”) for the eavesdropping <en.wikipedia.org/wiki/Eavesdropping> adversary.[6] <en.wikipedia.org/wiki/Cryptography#cite_note-Biggs-2008-6> Since the development of rotor cipher machines <en.wikipedia.org/wiki/Rotor_machine> in World War <en.wikipedia.org/wiki/World_War_I> I and the advent of computers in World War <en.wikipedia.org/wiki/World_War_II> II, cryptography methods have become increasingly complex and their applications more varied.
Modern cryptography is heavily based on mathematical theory <en.wikipedia.org/wiki/Mathematical_theory> and computer science practice; cryptographic algorithms <en.wikipedia.org/wiki/Algorithm> are designed around computational hardness assumptions <en.wikipedia.org/wiki/Computational_hardness_assumption> , making such algorithms hard to break in actual practice by any adversary. While it is theoretically possible to break into a well-designed system, it is infeasible in actual practice to do so. Such schemes, if well designed, are therefore termed “computationally secure”. Theoretical advances (e.g., improvements in integer factorization <en.wikipedia.org/wiki/Integer_factorization> algorithms) and faster computing technology require these designs to be continually reevaluated and, if necessary, adapted. Information-theoretically secure <en.wikipedia.org/wiki/Information-theoretic_security> schemes that provably cannot be broken even with unlimited computing power, such as the one-time pad <en.wikipedia.org/wiki/One-time_pad> , are much more difficult to use in practice than the best theoretically breakable but computationally secure schemes.
The growth of cryptographic technology has raised a number of legal issues <en.wikipedia.org/wiki/Cryptography_law> in the Information Age <en.wikipedia.org/wiki/Information_Age> . Cryptography’s potential for use as a tool for espionage and sedition <en.wikipedia.org/wiki/Sedition> has led many governments to classify it as a weapon and to limit or even prohibit its use and export.[7] <en.wikipedia.org/wiki/Cryptography#cite_note-Crypto_Law_Survey-2013 -7> In some jurisdictions where the use of cryptography is legal, laws permit investigators to compel the disclosure <en.wikipedia.org/wiki/Key_disclosure_law> of encryption keys <en.wikipedia.org/wiki/Key_(cryptography)> for documents relevant to an investigation.[8] <en.wikipedia.org/wiki/Cryptography#cite_note-PC_World-2007-8> [9] <en.wikipedia.org/wiki/Cryptography#cite_note-Ranger-2015-9> Cryptography also plays a major role in digital rights management <en.wikipedia.org/wiki/Digital_rights_management> and copyright infringement <en.wikipedia.org/wiki/Copyright_infringement> disputes with regard to digital media <en.wikipedia.org/wiki/Digital_media> .[10] <en.wikipedia.org/wiki/Cryptography#cite_note-Doctorow-2007-10>
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