A cryptosystem (or cipher system) is a system consisting of an encryption algorithm, a decryption algorithm, and a well-defined triple of text spaces: plaintexts, ciphertexts, and keytexts. For a given keytext the encryption algorithm will map a plaintext to a (usually uniquely determined) ciphertext. For the corresponding keytext, the decryption algorithm will map the ciphertext to the {(usually uniquely determined) plaintext. The cryptosystem may be performed by hand methods (“hand cipher”), by machine methods (“machine cipher”), or by software (see also Shannon's model).
Plaintext: text in an open language that is commonly understood among a larger group of people.
Ciphertext: text (“cryptogram”) in a secret language that is understood only by few, authorized people, usually after decryption by hand or machine.
We mention two special properties: an endomorphic cryptosystem is a cryptosystem with identical plaintext and ciphertext space. Example: \(\{{\rm a,b,c,\ldots, z}\}...
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References
Bauer, F.L. (1997). “Decrypted secrets.” Methods and Maxims of Cryptology. Springer-Verlag, Berlin.
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© 2005 International Federation for Information Processing
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Bauer, F.L. (2005). Cryptosystem. In: van Tilborg, H.C.A. (eds) Encyclopedia of Cryptography and Security. Springer, Boston, MA . https://doi.org/10.1007/0-387-23483-7_90
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