Cryptosystem

Academic attacks are often against weakened versions of a cryptosystem, such as a block cipher or hash function with some rounds removed.

A cryptosystem is called semantically secure if an attacker cannot distinguish two encryptions from each other even if the attacker knows (or has chosen) the corresponding plaintexts.

Furthermore, it might only reveal a small amount of information, enough to prove the cryptosystem imperfect but too little to be useful to real-world attackers.

In 1979, Michael O. Rabin published a related cryptosystem that is probably secure as long as the factorization of the public key remains difficult – it remains an assumption that RSA also enjoys this security.

In WWII, for example, the Japanese Navy, by poor practice, identified a key person's movement over a low-security cryptosystem.

Key escrow (also known as a “fair” cryptosystem) is an arrangement in which the keys needed to decrypt encrypted data are held in escrow so that, under certain circumstances, an authorized third party may gain access to those keys.

Most are used in hybrid cryptosystems for reasons of efficiency – in such a cryptosystem, a shared secret key (" session key ") is generated by one party, and this much briefer session key is then encrypted by each recipient's public key.

Some well-known asymmetric encryption algorithms are based on the RSA cryptosystem.

The result was a potentially excellent cryptosystem.

The time-shift attack has even been demonstrated on a commercial quantum cryptosystem.