timestamping

Timestamping is the process of recording a precise point in time for a data item or event, with the goal of establishing a verifiable chronology. Timestamps are used to prove when a document was created or modified, when an event occurred, or when data was received, making them important for legal, administrative, and archival purposes. In computing, timestamps typically reflect a moment in Coordinated Universal Time (UTC) and are expressed in standards such as ISO 8601 or as epoch seconds.

There are two broad approaches to timestamping. Non-cryptographic timestamping relies on the local system clock or network time services to provide a time value, but its trust depends on clock accuracy and cannot prove data integrity. Cryptographic timestamping uses a trusted time-stamp authority (TSA). In this model, a client computes a cryptographic hash of the data and sends it to the TSA, which signs the hash together with the current time to produce a time-stamp token. This token can be independently verified against the TSA’s public key, establishing both the time and the data’s existence at that time. The process is often described by standards such as RFC 3161.

Representations of timestamps emphasize standardized formats and clock synchronization. ISO 8601 and RFC 3339 are common textual representations, typically in UTC. Precision can vary from seconds to fractions of a second, and considerations such as leap seconds and clock drift affect accuracy.

Applications span digital documents, software distribution, legal and regulatory compliance, audit logs, medical records, and blockchain or distributed ledger systems, where verifiable timing supports integrity, trust, and traceability.