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The two tables on this page are used to explain our selection of acceptable multi-factor authentication technology for use in assurance profiles.  Table 1 describes commonly used authentication factors and summarizes their resistance to common threats.  Table 2 summarizes Authentication Types or Groups of Types which meet the needs of authentication profiles. 

Table 1 - Authentication Factors and Threat Resistance

AuthN Type NumberAuthentication FactorResistance to Threat
  (Phishing, etc.)
Theft via Dynamic MITM  PhishingGuessing / Offline CrackingMFA Device
User Workstation Compromise
2Phone call see Voice Restrictions, note 1LowLowHighLowHigh
3Phone call (VoIP) see Additional
VoIP Restrictions, note 2
5SMS (VoIP) see Additional
VoIP restrictions, note 2
6HOTP cell phone software see notes 1 and 3MediumLowHighMediumHigh
7TOTP cell phone software see notes 1 and 3MediumLowHighMediumHigh
8HOTP tokenMediumLowHighHighHigh
9TOTP tokenMediumLowHighHighHigh
10HOTP written (back up codes)LowLowHighHighLow
11DUO Push see note 3HighLowHighMediumHigh
12FIDO U2F token with passwordHighHighHighHighHigh
13PKI device certificate with
  device password
14PKI token certificate with token


  1. Voice Restrictions: Institutions deploying a phone call based solution for one of their authentication factors must incorporate multi-factor authentication concepts into their security awareness training.  Specifically, a prohibition on configuring voicemail greetings to respond to MFA prompts must be in-place and discussed in training.  Training should also include the prohibition against using Enterprise passwords on personal devices.
  2. Additional VoIP Restrictions: The use of VoIP systems (or traditional PBX solutions) that use the Enterprise password for call control or call redirection may not be used.  The creators of this document note that accessibility needs can often be addressed using a hardware token instead of a voice-based solution.

  3. Campus deployers should pay careful attention to cell phone security.  Some data sources report that the majority of Android devices are not updated and are thus highly vulnerable.  Some vendors have the ability to restrict MFA use to fully patched cell phones.  This table assumes that cell phones used for MFA are receiving software updates.


Table 2 - Authentication Types and Combinations of Authentication Types that meet profile requirements.

The Standard MFA Profile that we are developing now focuses on simple passwords no longer being sufficient in a modern world full of phishing threats.  The Stronger MFA profile column would be for some future work to support an overall higher LoA, likely coupled with corresponding Identity Proofing requirements.  It's helpful to see how the two might differ in their technology requirements.

ItemMFA Type Number(s)
from Table 1
Standard MFA Profile (anti-phish - replace
Stronger MFA Profile (could
  support a stronger LoA)
11 plus any one of 2-14Yesn/a - see below
51 plus any one of 12-14YesYes
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  1. I'm not clear what the distinction is in the first two rows (much later errata: this column was actually referring to columns). I think of the distinction as "phishing for later use" ("static") vs "phishing for immediate use" ("dynamic"). MITM is an attack vector that could be used to support either "static" or "dynamic" scenarios (and other methods could be used for either). With those definition, I'd raise the resistance level of some of the telephony and OTP (or at least TOTP) approaches in the "static phishing" (for later use) column.

  2. What does 'HOTP written' mean and why is its resistance to user workstation compromise low?

    1. This was referring to "back-up login codes" a la Google's "here are ten codes to keep in your wallet".

      1. OK, makes sense.  Maybe easier to interpret if it was listed as "HOTP back-up codes" or something.

  3. In conversations after the workgroup submitted its report, a point came up that might require clarification or re-working:

    We don't explicitly allow for an IdP to separately (a) verify your device's access to a (non-password secured) locally installed private key and (b) authenticates the user via forms (username/password). It seems like this would be okay, however, we don't clearly identify it as acceptable because all of the explicitly listed PKI-challenge based solutions in Table 1 (#11-14) indicate that password protection exists at the cert/device level. (Non-password protected H/TOTP tokens are listed, but not PKI challenge based ones).

    A future, updated version of this page should probably include enough information to clarify that this approach (IdP performs separate key and password challenges) is acceptable.