If you are ever in a situation that you need to generate a large (or small) random string or an authentication key you can combine some of the command line tools available on Linux to realize that goal. For example:
The following command will pull 4096 bytes from the pseudo-random number generator on Linux after which it will produce a sha1 hashed value:
$ dd if=/dev/urandom bs=2 count=2048 | openssl sha1 (stdin)= de07d8a695984fc3556f4f91a244dba5e8e03d8b
The following command will pull 256 bytes from the pseudo-random number generator and it will encode them as base64 string.
This is quite helpful if you need to generate unique phrases for a Wordpress installation.
$ dd if=/dev/urandom bs=16 count=16 | openssl base64 | tr -d '\n'