alidity of the keying.
In general a cryptosystem can never be shown to be completely secure in practice, in the sense that without knowledge of the decryption key it is impossible to recover the plaintext with real-world computing power in less than, say, a thousand years. There is always something that could go wrong, and future advances in computing power (sufficient to render a cryptanalyst's task easy) cannot be known in advance.
The table below shows the main encryption systems in use today.
56-bit private key encryption algorithm
Diffie-Hellman/Digital Signature Standard
Popular encryption standard developed
...