Trusted Timestamping

The core mechanism that creates a tamper-evident seal between the data and the timestamp. The process involves generating a cryptographic hash of the data client-side, sending only this hash to the Time Stamping Authority (TSA), and receiving a signed token that binds the hash to a trusted time source.

• Hash Function: Typically SHA-256 or SHA-3, ensuring any data alteration invalidates the timestamp.
• Digital Signature: The TSA signs the binding using a private key, verifiable via a public key infrastructure (PKI).
• Data Privacy: The TSA never sees the original data, only its hash.

The legal and technical validity of a timestamp relies on the impartiality and auditability of the Time Stamping Authority (TSA). The TSA acts as a neutral witness, eliminating the possibility of backdating or collusion.

• RFC 3161 Standard: Defines the protocol for requesting and issuing timestamps.
• Audit Trails: TSAs maintain secure logs of all issued timestamps for independent verification.
• Accreditation: Trusted TSAs often operate under strict regulatory frameworks like eIDAS (EU) or NIST (US) guidelines.

A mechanism to ensure a timestamp remains verifiable for years or decades, even after the original cryptographic algorithms are deprecated or certificates expire. This is critical for archival integrity.

• Periodic Re-Timestamping: Applying a fresh timestamp to the original token and its chain of trust before the old algorithms become vulnerable.
• Evidence Record Syntax (ERS): A standard (RFC 6283) for packaging the complete renewal history into a single, self-contained proof.
• Hash Tree Storage: Using Merkle trees to efficiently aggregate and verify multiple timestamps over long periods.

A modern evolution that augments or replaces a centralized TSA by anchoring a hash of the data into a public, immutable blockchain. This provides censorship-resistant, globally verifiable proof of existence without relying on a single entity's continued operation.

• Proof of Existence: Embedding a hash into a blockchain transaction (e.g., using OP_RETURN in Bitcoin).
• Decentralized Trust: Eliminates the single point of failure and trust inherent in a traditional TSA.
• OpenTimestamps: A popular open-source protocol for creating and verifying blockchain-based timestamps.

The legal weight of a timestamp depends on its traceability to a recognized, authoritative time source. TSAs must synchronize their clocks to Coordinated Universal Time (UTC) through a documented chain of calibration.

• Stratum 1 Time Sources: Directly connected to atomic clocks or GPS signals.
• Network Time Protocol (NTP): Used for distribution, but the TSA must prove its accuracy and prevent drift.
• Legal Traceability: The exact moment recorded must be defensible in court, requiring a clear audit trail back to a national metrology institute.

The ultimate goal of trusted timestamping: providing irrefutable proof that a specific party possessed certain data at a specific time, preventing them from later denying its existence or authenticity.

• Digital Signature Integration: Combining a user's digital signature with a trusted timestamp proves both authorship and time of signing.
• Regulatory Compliance: Essential for meeting requirements in financial regulations (e.g., MiFID II), intellectual property protection, and electronic invoicing.
• Legal Admissibility: Establishes a verifiable chain of evidence that holds up under legal scrutiny.