| Revision as of 23:17, 5 September 2026 by OpenWiki (Imported from the OpenWiki starter corpus) | Revision as of 00:19, 6 September 2026 by OpenWiki (Updated from the starter corpus) | ||
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| == Machine ciphers == | == Machine ciphers == | ||
| − | Electromechanical rotor machines mechanised polyalphabetic substitution. The German '''Enigma''' passed each keystroke through a set of rotating wired discs, which advanced after every letter, so the same plaintext letter almost never encrypted the same way twice. Polish mathematicians at the Cipher Bureau, led by Marian Rejewski, reconstructed the machine's wiring in the early 1930s. At Bletchley Park, [[Alan Turing]] and Gordon Welchman built on that work with the Bombe, exploiting a structural weakness | + | Electromechanical rotor machines mechanised polyalphabetic substitution. The German '''Enigma''' passed each keystroke through a set of rotating wired discs, which advanced after every letter, so the same plaintext letter almost never encrypted the same way twice. Polish mathematicians at the Cipher Bureau, led by Marian Rejewski, reconstructed the machine's wiring in the early 1930s. At Bletchley Park, [[Alan Turing]] and Gordon Welchman built on that work with the Bombe, exploiting a structural weakness (Enigma never encrypted a letter as itself) and the predictability of German message formats. |
| == Modern cryptography == | == Modern cryptography == | ||
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| ; Kerckhoffs's principle : A system's security must depend only on the secrecy of the key, never on the secrecy of its design. Algorithms are published and attacked publicly; those that survive are used. | ; Kerckhoffs's principle : A system's security must depend only on the secrecy of the key, never on the secrecy of its design. Algorithms are published and attacked publicly; those that survive are used. | ||
| − | ; Public-key cryptography : Proposed by Whitfield Diffie and Martin Hellman in 1976, and realised by Rivest, Shamir and Adleman in 1977, this splits the key in two. A public key encrypts; only the matching private key decrypts. Two parties who have never met can therefore establish a shared secret over a channel an adversary is | + | ; Public-key cryptography : Proposed by Whitfield Diffie and Martin Hellman in 1976, and realised by Rivest, Shamir and Adleman in 1977, this splits the key in two. A public key encrypts; only the matching private key decrypts. Two parties who have never met can therefore establish a shared secret over a channel an adversary is watching. Before this, secure communication was limited to those who could exchange keys in advance. |
| Public-key cryptography is what makes commerce on the [[Internet]] possible. Symmetric ciphers such as AES do the bulk encryption because they are fast; public-key methods are used to agree the symmetric key and to sign messages. | Public-key cryptography is what makes commerce on the [[Internet]] possible. Symmetric ciphers such as AES do the bulk encryption because they are fast; public-key methods are used to agree the symmetric key and to sign messages. | ||
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| == Hash functions == | == Hash functions == | ||
| − | A cryptographic hash maps data of any size to a fixed-size value such that finding two inputs with the same output is infeasible. Hashes underpin digital signatures, password storage and content | + | A cryptographic hash maps data of any size to a fixed-size value such that finding two inputs with the same output is infeasible. Hashes underpin digital signatures, password storage and content addressing, including the way this wiki stores each revision under the hash of its text, so that identical revisions are stored once. |
| == See also == | == See also == | ||
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