What is used to bind a document to its creation at a particular time?

A.
Network Time Protocol (NTP)

B.
Digital Signature

C.
Digital Timestamp

D.
Certification Authority (CA)

Explanation:
While a digital signature binds a document to the possessor of a particular key, a digital timestamp binds a
document to its creation at a particular time. Trusted timestamping is the process of securely keeping track of
the creation and modification time of a document.
Security here means that no one — not even the owner of the document — should be able to change it once it
has been recorded provided that the timestamper’s integrity is never compromised. The administrative aspect
involves setting up a publicly available, trusted timestamp management infrastructure to collect, process and
renew timestamps or to make use of a commercially available time stamping service. A modern example of
using a Digital Timestamp is the case of an industrial research organization that may later need to prove, for
patent purposes, that they made a particular discovery on a particular date; since magnetic media can be
altered easily; this may be a nontrivial issue. One possible solution is for a researcher to compute and record in
a hardcopy laboratory notebook a cryptographic hash of the relevant data file. In the future, should there be a
need to prove the version of this file retrieved from a backup tape has not been altered, the hash function could
be recomputed and compared with the hash value recorded in that paper notebook. According to the RFC 3161
standard, a trusted timestamp is a timestamp issued by a trusted third party (TTP) acting as a Time Stamping
Authority (TSA). It is used to prove the existence of certain data before a certain point (e.g. contracts, research
data, medical records…) without the possibility that the owner can backdate the timestamps.
Multiple TSAs can be used to increase reliability and reduce vulnerability. The newer ANSI ASC X9.95
Standard for trusted timestamps augments the RFC 3161 standard with data-level security requirements to
ensure data integrity against a reliable time source that is provable to any third party. This standard has been
applied to authenticating digitally signed data for regulatory compliance, financial transactions, and legal
evidence. Digital TimeStamp The following are incorrect answers: Network Time Protocol (NTP) is used to
achieve high accuracy time synchronization for computers across a network. A Certification Authority (CA) is
the entity responsible for the issuance of digital certificates. A Digital Signature provides integrity and
authentication but does not bind a document to a specific time it was created.

http://en.m.wikipedia.org/wiki/File:Trusted_timestamping.gif
http://en.wikipedia.org/wiki/Trusted_timestamping