You'll need to generate a Secure Shell Protocol (SSH) key if you use the Git source code management system. Mercurial repositories are also available though SSH as a more secure and reliable alternative to the HTTPS access mechanism. SSH provides higher performance and authentication via public key cryptography rather than with a password.
To access your repositories via SSH, first ensure that you have an SSH client available on your local system, as described below. You use that client to generate a pair of cryptographic keys, which you use in place of a password when you authenticate to our servers.
The type of key to generate is an SSH2 key. You can generate either an RSA or a DSA key. Both will work on Kenai.com. After you use your SSH client on your system to generate an SSH key pair, you copy the public key to the SSH Keys tab in your personal profile. Subsequently, you need to use the SSH client to access the repository.
Most UNIX, Linux, and Mac systems come with a built-in SSH client, OpenSSH.
If you have a Microsoft Windows system, there are a number of SSH clients you can run.
If you're new to the whole SSH thing, this blog might help you: http://jimmyg.org/blog/2008/beginners-guide-to-ssh-keys-with-ssh2.html.