xWarden: Physical Evidence Custody Chain

The Problem

Physical evidence chain of custody relies on paper logs and institutional trust. Tampered logs can undermine forensic integrity. There is no cryptographic proof that evidence was not altered between custody transfers.

From the crime scene to the courtroom, physical evidence passes through multiple custodians: investigators, transport officers, lab technicians, evidence room clerks, and attorneys. Each transfer is recorded in a paper log or basic database that can be altered without detection.

A single compromised custodian can alter the log to cover evidence tampering. Defense attorneys routinely challenge chain of custody — and win — because paper logs provide no cryptographic guarantee that the evidence presented in court is identical to what was collected at the scene. The integrity of the entire justice system depends on trust in a paper trail.

The Old Way

The PRIVATE.ME Solution

Each evidence item is XorIDA-split into QR shares distributed to custodians. Every custody transfer generates an Ed25519-signed, HMAC-chained audit entry. The append-only chain is cryptographic proof of unbroken custody.

When evidence is collected, its digital fingerprint (hash + metadata) is XorIDA-split into QR shares distributed to independent custodians. The evidence item carries a QR tag linking it to its custody chain. Every transfer between custodians generates a log entry signed with the outgoing custodian's Ed25519 key and countersigned by the incoming custodian.

Each log entry includes the HMAC of the previous entry, creating an append-only chain. Altering any entry breaks the chain from that point forward. In court, the HMAC chain provides mathematical proof that the evidence custody record has not been tampered with — replacing "trust us" with "verify the math."

The New Way

How It Works

A four-stage pipeline: evidence registration with digital fingerprint, QR share distribution to custodians, Ed25519-signed transfer logging, and HMAC-chained custody verification.

Use Cases

Integration

import { registerEvidence, transferCustody } from '@private.me/physicalcustody';

// Register evidence with custodian list
const chain = await registerEvidence(
  { id: 'EV-2026-0042', hash: evidenceHash, type: 'physical' },
  ['officer-badge-1234', 'lab-tech-5678', 'clerk-9012']
);

// Transfer custody (both parties sign)
const result = await transferCustody(chain, {
  from: 'officer-badge-1234',
  to: 'lab-tech-5678',
  condition: 'sealed, intact'
});
// result.auditLog contains HMAC-chained entries

Security Properties

Verifiable Data Protection

Every operation in this ACI produces a verifiable audit trail via xProve. HMAC-chained integrity proofs let auditors confirm that data was split, stored, and reconstructed correctly — without accessing the data itself.

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Ship Proofs, Not Source

xWarden generates cryptographic proofs of correct execution without exposing proprietary algorithms. Verify integrity using zero-knowledge proofs — no source code required.

Use Cases