Keychain is a shell script which acts as a user-friendly front-end to
ssh-agent(1), allowing you to have one long-running ssh-agent process per
system rather than per login session.

Please study the documentation on the keychain website carefully since
incorrect usage of this script may have certain security implications.

Author: Daniel Robbins <drobbins@funtoo.org>
WWW:    http://www.funtoo.org/en/security/keychain/intro/