Back in December 2020, I dove into identity assurance levels (IALs) and digital identity, subsequently specifying the difference between identity assurance levels 2 and 3. These IALs are defined in section 4 of NIST Special Publication 800-63A, Digital Identity Guidelines, Enrollment and Identity Proofing Requirements.
It’s past time for me to move ahead to authenticator assurance levels (AALs).
Where are authenticator assurance levels defined?
Authenticator assurance levels are defined in section 4 of NIST Special Publication 800-63B, Digital Identity Guidelines, Authentication and Lifecycle Management. As with IALs, the AALs progress to higher levels of assurance.
- AAL1 (some confidence). AAL1, in the words of NIST, “provides some assurance.” Single-factor authentication is OK, but multi-factor authentication can be used also. All sorts of authentication methods, including knowledge-based authentication, satisfy the requirements of AAL1. In short, AAL1 isn’t exactly a “nothingburger” as I characterized IAL1, but AAL1 doesn’t provide a ton of assurance.
- AAL2 (high confidence). AAL2 increases the assurance by requiring “two distinct authentication factors,” not just one. There are specific requirements regarding the authentication factors you can use. And the security must conform to the “moderate” security level, such as the moderate security level in FedRAMP. So AAL2 is satisfactory for a lot of organizations…but not all of them.
- AAL3 (very high confidence). AAL3 is the highest authenticator assurance level. It “is based on proof of possession of a key through a cryptographic protocol.” Of course, two distinct authentication factors are required, including “a hardware-based authenticator and an authenticator that provides verifier impersonation resistance — the same device MAY fulfill both these requirements.”
This is of course a very high overview, and there are a lot of…um…minutiae that go into each of these definitions. If you’re interested in that further detail, please read section 4 of NIST Special Publication 800-63B for yourself.
Which authenticator assurance level should you use?
NIST has provided a handy dandy AAL decision flowchart in section 6.2 of NIST Special Publication 800-63-3, similar to the IAL decision flowchart in section 6.1 that I reproduced earlier. If you go through the flowchart, you can decide whether you need AAL1, AAL2, or the very high AAL3.
One of the key questions is the question flagged as 2, “Are you making personal data accessible?” The answer to this question in the flowchart moves you between AAL2 (if personal data is made accessible) and AAL1 (if it isn’t).
So what?
Do the different authenticator assurance levels provide any true benefits, or are they just items in a government agency’s technical check-off list?
Perhaps the better question to ask is this: what happens if the WRONG person obtains access to the data?
- Could the fraudster cause financial loss to a government agency?
- Threaten personal safety?
- Commit civil or criminal violations?
- Or, most frightening to agency heads who could be fired at any time, could the fraudster damage an agency’s reputation?
If some or all of these are true, then a high authenticator assurance level is VERY beneficial.
Bredemarket 