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Plaintext-aware encryption
Plaintext-awareness is a notion of security for public-key encryption. A cryptosystem is plaintext-aware if it is difficult for any efficient algorithm to come up with a valid ciphertext without being aware of the corresponding plaintext.
From a lay point of view, this is a strange property. Normally, a ciphertext is computed by encrypting a plaintext. If a ciphertext is created this way, its creator would be aware, in some sense, of the plaintext. However, many cryptosystems are ''not'' plaintext-aware. As an example, consider the RSA cryptosystem without padding. In the RSA cryptosystem, plaintexts and ciphertexts are both values modulo N (the modulus). Therefore, RSA is not plaintext aware: one way of generating a ciphertext without knowing the plaintext is to simply choose a random number modulo N.
In fact, plaintext-awareness is a very strong property. Any cryptosystem that is semantically secure and is plaintext-aware is actually secure against a chosen-ciphertext attack, since any adversary that chooses ciphertexts would already know the plaintexts associated with them.
==History==
The concept of plaintext-aware encryption was developed by Mihir Bellare and Phillip Rogaway in their paper on optimal asymmetric encryption,〔M. Bellare and P. Rogaway. ''Optimal Asymmetric Encryption -- How to encrypt with RSA''. Extended abstract in Advances in Cryptology - Eurocrypt '94 Proceedings, Lecture Notes in Computer Science Vol. 950, A. De Santis ed, Springer-Verlag, 1995. (full version (pdf) )〕 as a method to prove that a cryptosystem is chosen-ciphertext secure.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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