TSA Timestamp (Timestamp Authority)
Definition
A cryptographically protected record of the time at which a signature was created, issued by a Timestamp Authority (TSA) whose own certificate is on a trusted list. The TSA signs a hash of the signature value together with the current time, providing non-repudiable evidence of the signing time.
- Issuer
- Timestamp Authority (TSA)
- What is signed
- Hash of the signature value plus current time
- Trust basis
- TSA certificate must be on a trusted list
- Purpose
- Non-repudiable evidence of signing time
- Context
- E-signature frameworks such as Aadhaar e-Sign, eIDAS, ESIGN/UETA
Common questions
Why does a signature need a timestamp separate from the signer's own device clock?+
A device clock can be altered by the signer, so it offers no independent proof of when signing occurred. A TSA is a trusted third party whose signed timestamp cannot be backdated by either party to the transaction, which supports later legal challenges over signing date.
What happens to the evidentiary value of a signature if the TSA's own certificate later expires or is revoked?+
A properly applied timestamp remains valid evidence of the time it was created, since the timestamp itself is verified against the TSA certificate's validity at the moment of signing, not at the time the signature is later checked.
Related terms
- Aadhaar E-Sign
- India's authentication-linked electronic signature service in which the user's Aadhaar biometric or OTP authentication triggers the generation of a short-validity signing certificate...
- ESIGN Act (Electronic Signatures in Global and National Commerce Act)
- US federal legislation (2000) providing that no electronic signature may be denied legal effect solely because it is in electronic form. Technology-neutral:...
- EU Trusted List (EUTL)
- The authoritative list maintained by the European Commission listing all Trust Service Providers per EU member state that are supervised to issue...
- Long-Term Validation (LTV)
- A PDF signature profile (PAdES-LTV, ETSI EN 319 102-1) in which the OCSP responses, CRL data, and TSA certificate chain information are...
- OCSP (Online Certificate Status Protocol)
- A real-time certificate revocation protocol in which the verifier queries the CA's OCSP responder with the certificate's serial number and receives a...
- Public Key Infrastructure (PKI)
- The system of hardware, software, policies, and standards that manage digital certificates and public-key encryption. Provides the trust architecture underpinning all cryptographic...
- QSCD (Qualified Signature Creation Device)
- A hardware or remote HSM-based device that stores the signer's private key such that it cannot be extracted, ensuring sole control under...
- Qualified Electronic Signature (QES)
- The highest tier of electronic signature under EU eIDAS Regulation 910/2014. Created by a Qualified Signature Creation Device (QSCD), backed by a...
- X.509 Certificate
- A digitally signed data structure that binds a public key to a named identity (subject) and is issued by a Certificate Authority....