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This paper introduces a novel framework for action mediation that separates the disclosure of action parameters from their authorization, addressing the challenge of balancing auditability and privacy in append-only ledgers. By classifying parameters into three distinct tiers based on their relevance to policy and their potential for identification, the authors demonstrate that it is possible to minimize the information disclosed without compromising the integrity of the audit trail. The key finding is that the ledger's commitment can remain intact even when the classification of fields changes, allowing for flexible reclassification without affecting historical entries or verification processes.
Reclassifying action parameters can enhance privacy without sacrificing audit integrity, revealing a new dimension in ledger design.
A system that authorizes an action must see enough of it to decide, and a system that attests to its decision must record enough to be audited. Both pressures push raw action parameters -- recipients, payment memos, record identifiers -- into an append-only ledger that cannot delete them. We show the two are separable. We classify each parameter field, not each action class, into three tiers: fields a policy may legitimately match on, which cross raw; fields that are policy-relevant but identifying, which cross only as projections such as an email domain or a templated route shape; and fields with no legitimate policy use, which never leave the workload. The central property is that the ledger's commitment is a canonical digest of the full, unminimized parameters, computed before minimization runs. The commitment is therefore independent of the tier table: reclassifying a field changes what is disclosed without invalidating a historical entry, reopening a hash, or altering what an offline verifier checks. Tier table, policy schema and wire schema are generated from one per-action declaration, so the deciding and recording parties cannot hold different rules. We then address a question the architecture forces: which party should compute each attested fact? We argue it is settled by which party could lie about it undetectably, and derive three answers within one request -- the client computes the parameter digest, being the only party holding the data; it is structurally prevented from naming the definition that governed it, since that would write a false statement into a signed ledger; and it attests which tier table it applied, so divergence is detectable. We give a leakage analysis of each projection, report an incident in which a first-cut projection preserved the identifier it was written to remove, and state the residual trust the design does not eliminate.
