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Granularity of Progressive Authentication Stages

The Question

IFP-5 defines four authentication levels as discrete stages in a progressive trust model. Each level represents a distinct verification mechanism:

Level	Mechanism	Jump from Previous
0	Shared secret (introduction token)	—
1	Public-key signature	Symmetric → asymmetric crypto
2	Key verified via identity document	Self-asserted → externally resolvable
3	Key bound to DID	Domain-specific → decentralized identity

The jumps between levels are large. Are there trust-relevant distinctions being collapsed? Are four stages the right granularity?

What Makes This Worth Investigating

The Level 0 → 1 jump is the largest. Moving from a shared secret to public-key signatures changes the entire trust model — from “someone we both know introduced us” to “I can verify your signature independently.” This single jump may be doing too much work.

Level 3 depends on DID infrastructure that does not yet exist at scale. If Level 3 is aspirational rather than practical, IFP effectively has three usable levels. Is that enough?

Christopher Allen’s progressive trust framework describes a richer spectrum than four discrete stages. The question is whether IFP’s four-level discretization loses important trust distinctions that the continuous model preserves.

The minimum viable architecture question applies. Are four levels a load-bearing architectural decision (the right boundaries, worth committing to early) or a tactical choice (the specific boundaries could be refined without reshaping the protocol)?

Possible Directions

• The four levels may be correct — each represents a genuinely distinct trust mechanism
• An intermediate level between 0 and 1 (e.g., verified introduction — the introducer’s identity is confirmed) might smooth the largest jump
• The levels might be better expressed as a continuous score with threshold behaviors rather than discrete stages
• Different application platforms (IFP-11) might need different granularity — Sanctuary (healthcare) may need finer stages than Friend Zone (social)

Sources

• IFP-5: Identity and Message Signing, Section 2
• [[Allen (2024) Progressive Trust]] — the continuous model these levels discretize

Relations

• relates_to::[[Progressive Authentication as Trust Deepening]]
  • The model this inquiry questions.
• relates_to::[[Allen (2024) Progressive Trust]]
  • The progressive trust framework describes a richer spectrum than four discrete stages.
• relates_to::[[Allen (2023) Minimum Viable Architecture]]
  • Are four levels a load-bearing decision or a tactical one?
• relates_to::[[Disclosure Spectrum as Discrete Tiers or Continuous Range]]
  • The same granularity question applies to disclosure tiers — both discretize a continuous spectrum.

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