Credentials

Another PET is private credentials.
With regular digital certificates, it's like showing your passport (and all other personal info) just to prove any bit of info about yourself.
Private credentials store all your personal info, but when you show it to someone, you only reveal exactly what they need to know.
Very flexible!
"I am either over 65, or disabled."  (but you don't reveal which)
Also has protection against lending of certificates to others.
In order to use the certificate, you need to know all the personal info (even though it isn't revealed), so put some really personal info in there, like the passwords to your bank accounts.