Asymmetric Cyphers are so called because the key used for encryption is different from the key used for decryption. Until Diffie and Hellman proved otherwise, it was often accepted that key distribution was just a problem that had to be beared. The problem is clear - to communicate secretly, each person must have already secretly communicated the key to one another. This is how this catch-22 situation was resolved:
Asymmetric cyphers allow keys to be sent securely, and therefore allow the general public to be able to use cryptography without the expense of using couriers to deliver keys, as had been done before. This paved the way for the Internet to take full advantage of this to provide a secure way of communicating electronically.
Since the methods used for asymmetric ciphering is more complicated, and thus time-consuming, than symmetric methods, the asymmetric cyphers are not normally used to encode long messages. This is not a problem, as PGP shows.
| Cipher | Security | Speed | Key Length |
| Diffie-Hellman | Good | Slow | Varies - 1024 is safe |
| RSA | Good | Medium | Varies - 1024 is safe |