We have seen that public-key encryption is slow compared to symmetric-key encryption and that public-key encryption is useful for distributing a key between two parties which can then be used for symmetric encryption.

The exact workings for this are as follows:

- Each side generates half of the key
- They encrypt the half they generated with the other persons public key
- Each side then sends their half to the other
- As they receive the other half they decrypt with their private key so both parties now have both parts of the key and can now use symmetric-key encryption

While it would be possible for one side to generate the whole key this doubles the security as even if someone knew one parties private key they would only have half the key.