Confidentiality is concerned with keeping information secret. It is a key information security objective.
A cipher can be used to achieve confidentiality.
As an example, if Alice wishes to communicate secretly with Bob, then they would choose a keypair
(e,d) which would give the encryption function
Ee and the decryption function
Dd. If Alice's plaintext is
then Alice sends the ciphertext
c=Ee(m) to Bob.
Bob can then compute the original plaintext as
A. Menzes, P. van Oorschot, and S. Vanstone, Handbook of Applied Cryptography. CRC Press, 1996.
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