[CentOS] A naive question respecting x.509 logins

I have been looking at replacing our current login systems with a single login solution. In the process I managed to get sidetracked into investigating pam_pkcs11. My question, which no doubt reveals the depth of my ignorance, is: Can a simple USB flash memory stick be configured to work with this or some similar module of which I as yet know nothing?

Everything I have managed to find about this method of loging on to CentOS implies that either a special smart-card and dedicated reader or a purpose-built usb smart-token is required. Is this in fact so? Is there no way to just use a standard usb flash memory 'key' to achieve the same effect?