[arch-general] How long do you make the passphrase for the private key?

Hello, I want to publish a package repository with some packages that I need and only want to build once for all my systems. I want to make the packages available for general use. I have server space for that so I only have to rsync my final repo to my server after compiling my packages. I have my autobuild set up and signing seems to work, too. For convenience, I decided to make the passphrase not too long. I have 10 characters with both, alphanumeric and "special characters". I think if the passphrase is meant to be uncrackable alone, then we wouldn't need the big private key file, right? Is my passphrase long enough? What do the trusted users think about this topic? Thanks in advance Manuel