Cryptosystems

All public key/private key cryptosystems have the same problem, even if in slightly different guises, and no fully satisfactory solution is known.

Cryptography Cryptosystems often compress data (the "plaintext") before encryption for added security.

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.

RSA and DSA are two popular public-key cryptosystems; DSA keys can only be used for signing and verifying, not for encryption.

The historian David Kahn notes: Many are the cryptosystems offered by the hundreds of commercial vendors today that cannot be broken by any known methods of cryptanalysis.

Thus, cryptosystems must utilize compression algorithms whose output does not contain these predictable patterns.