In cryptography, a cryptosystem is semantically secure if any probabilistic, polynomial-time algorithm (PPTA) that is given the ciphertext of a certain message (taken from any distribution of messages), and the message's length, cannot determine any partial information on the message with probability non-negligibly higher than all other PPTA's that only have access to the message length (and not the ciphertext). In other words, knowledge of the ciphertext (and length) of some unknown message does not reveal any additional information on the message that can be feasibly extracted. This concept is the computational complexity analogue to Shannon's concept of perfect secrecy. Perfect secrecy means that the ciphertext reveals no information at all about the plaintext, whereas semantic security implies that any information revealed cannot be feasibly extracted.
Famous quotes containing the words semantic and/or security:
“Watts need of semantic succour was at times so great that he would set to trying names on things, and on himself, almost as a woman hats.”
—Samuel Beckett (19061989)
“The reins of government have been so long slackened, that I fear the people will not quietly submit to those restraints which are necessary for the peace and security of the community.”
—Abigail Adams (17441818)