Document signing

A signed document — a contract, a regulatory filing, a clinical trial report — typically requires multiple stakeholders to approve. Today this is done by having one party collect signatures serially, or by trusting a single signing service. Confium replaces both with threshold signing: T-of-N authorized signers must co-sign; the output is a single standard signature any verifier accepts.

When to choose this use case

  • You sign contracts that require sign-off from multiple parties (legal, finance, operations).
  • You sign regulated documents where the signing authority itself should be multi-stakeholder (e.g. FDA drug approvals, SEC filings).
  • You want a single verifiable signature on the final document rather than N separate signature blocks.
  • You need long-term verifiability (decades) and want post-quantum readiness from day one.

How Confium solves it

Each signing party runs a Confium signer process. The document hash is submitted to the coordinator; the coordinator collects partial signatures from the participating parties; the final signature is published alongside the document. The signing key never exists on any single machine.

The output signature is a standard CMS / PAdES / XAdES signature. Existing PDF readers, Office applications, and signature verifiers accept it without modification.

Composite signature: three algorithms verified as one. Break any single algorithm and the composite still holds. MESSAGE ED25519 classical sig[0] = 64 bytes ✓ verifies since 2015 ECDSA-P256 classical sig[1] = DER bytes ✓ verifies TLS standard ML-DSA-65 post-quantum sig[2] = ~3.3 KB ✓ verifies FIPS 204 ∧ all must verify COMPOSITE VALID break any one → composite still holds

For long-lived documents (regulatory filings, contracts in force for decades), the composite signature includes both classical (Ed25519, ECDSA-P256) and post-quantum (ML-DSA-65) components. Today both verify; tomorrow, when classical algorithms fall to quantum attack, the PQ component still holds.

Architecture

[ Document authoring tool ]
            |
            | submit document hash
            v
[ Confium coordinator ] --------------------+
   |             |             |             |
   v             v             v             v
[Legal]      [Finance]     [Operations]   [Compliance]
   |             |             |             |
   +------ T-of-N signers -------------------+
            |
            v
   [ Composite signature + inclusion proof ]
            |
            v
   [ Transparency log anchors the event ]

Code sketch

Submit a document for threshold signing:

doc_hash = Confium::Transparency.compute_artifact_hash(
  artifact_type: :document,
  content: File.read("contract.pdf"),
)

session = Confium::TC::Session.start(
  coordinator: "docs.internal:7443",
  message: doc_hash,
  algorithm: "ECDSA-P256",
  quorum: { t: 3, n: 5 },
)

# Authorized signers join asynchronously and submit partial sigs.
# Coordinator combines when quorum reached.

final_sig = session.wait_for_completion
puts "signature: #{final_sig[:der].size} bytes (DER)"

The resulting signature embeds into the PDF via standard PAdES, into Office docs via XAdES, or attaches as a detached CMS SignedData.

Compliance hooks

  • eIDAS (EU): Qualified Electronic Signatures require P-384+; Confium’s jurisdictional policy enforces this at the engine level.
  • 21 CFR Part 11 (FDA, pharma): Audit trail with signer identity
    • attributes; transparency log anchors each signing event.
  • HIPAA: Audit trail of every signing operation (§164.312(b)).
  • ESIGN Act (US): Electronic signature validity; Confium’s signatures meet the technical requirements.

See also