Which factors influence the quality of an attribute?

The lifetime of the attribute value (rarely changing vs. needing regular re-checks), the data provenance (source and how the value was determined), the transmission form (signature, encryption, front or back channel) and the quality of the authentication of the subject it belongs to.

• Lifetime of the value (two categories):
  • Values that rarely change: surname, first name, date of birth.
  • Values that must be checked regularly: derived attributes such as the subject's age (changes every birthday), address, canton of residence.
• Data provenance (Datenherkunft): how the RP uses the attribute affects what it needs to know about it. If an attribute drives access decisions (e.g. "employee of hospital X" grants access to patient records), the RP may need to know the source of the attribute and the process by which its value was determined.
• Transmission form: is the attribute signed, encrypted, sent via front or back channel? These are the same protections as for the authentication confirmation.
• Quality of the authentication: an attribute is only as reliable as the binding to the person who logs in.
• (The list is open; other factors can be added.)

A useful habit: for each attribute, ask "who said so, how did they know, and when?".

Go deeper:

• NIST IR 8112: Attribute Metadata — metadata fields such as origin, verification method and last update.