Context

An enterprise Contract Management System (CMS) handles legally binding agreements between multiple parties. To prevent legal disputes, the system must provide irrefutable proof of who signed what and when, ensuring that even system administrators cannot forge or alter signatures after the fact.

Trigger

A user (Signer) completes the signing workflow for a digital contract.

Acceptance Criteria

• Every signature is cryptographically bound to the document content such that any modification — however small — causes verification to fail; this is confirmed by automated tests that alter a single byte and assert rejection
• Each signature is bound to an independent, trusted timestamp (sourced outside the CMS) accurate to ≤ 1 second; the timestamp remains verifiable even if the CMS is unavailable
• For every signed contract, the system produces a portable evidence package that an external auditor or court can verify with standard, publicly available tooling at p95 <= 5 seconds for documents up to 10 MB and evidence packages up to 50 MB on a reference verifier environment (at least 4 vCPU, 8 GB RAM), without accessing CMS databases or internal services
• The signing event is only completed after multi-factor authentication; the audit trail permanently links each signature to the authentication session, originating IP address, and device identifier — these fields are immutable after signing
• Signatures and their evidence packages remain independently verifiable for >= 10 years after signing, even if the issuing certificate authority is decommissioned or unreachable; the evidence package contains all required verification material (certificate chain, trusted timestamp token, and revocation evidence such as OCSP/CRL artifacts or equivalent)
• Cryptographic proofs and audit records are retained for ≥ 10 years; automated integrity checks run at least quarterly on a statistically representative sample (≥ 5% of stored contracts, randomly selected) and alert within 24 hours if corruption is detected

one reviewer remarked: The MFA requirement is intentionally strict for high-assurance signing contexts. In environments with different legal or privacy constraints, an equivalent policy-defined signer-assurance mechanism may be used.