NotBeforetijdstip

NotBeforetijdstip is a term used in digital security to designate the earliest moment at which a data object becomes valid. It defines the lower bound of the object's validity window, often paired with a notAftertijdstip that marks when the object expires. In Dutch discussions, notBeforetijdstip helps describe when a certificate, token, signature, or other credential may legally be used.

In the context of X.509 digital certificates, the notBefore tijdstip is a field in the certificate that specifies the start of the certificate’s validity period. The certificate cannot be trusted or used before this time, provided the current time is also before the notAfter time. NotBefore and NotAfter are typically represented in Coordinated Universal Time (UTC) and follow standard time formats such as GeneralizedTime.

In JSON Web Tokens (JWT) and related token schemes, a similar concept appears as the not-before claim, often abbreviated as nbf. This is a numeric date (Unix timestamp) indicating the token should not be accepted before that time. Validity then depends on both the nbf value and any other temporal checks (such as exp, the expiry).

Common considerations include clock synchronization between systems, time zone handling, and how to treat small clock skews. It is also important to distinguish notBeforetijdstip from related concepts like iat (issued at) and exp (expiry). Accurate handling of notBeforetijdstip helps ensure that credentials are used only within their intended security window.