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Questions tagged [timestamping]

Generally, a timestamp is the current time of an event that is recorded by a computer. You can use digital timestamps via a trusted authority to certify and protect your intellectual property or your records integrity.

Generally, a timestamp is the current time of an event that is recorded by a computer. You can use digital timestamps via a trusted authority to certify and protect your intellectual property or your records integrity.

A special form of timestamping is called "trusted timestamping", which is described in RFC 3161. 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 without the possibility that the owner can backdate the timestamps.

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How useful is NIST's Randomness Beacon for cryptographic use?

NIST have just launched a new service called the NSANIST Randomness Beacon. It has been met with some initial skepticism. Perhaps the cryptography community would have used it before June 2013 when NIST had a trusted reputation. At first I thought…
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A timestamping authority (digital notary)

Does there currently exist a free online service that accepts a file, hashes it, takes an authoritatively chosen timestamp (from one or more time services), signs these and sends this signed message back? E.g. a digital notary, but only with regards…
sshine
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Is SHA-256 irreversible for each input?

There are more inputs to the SHA-256 function than outputs, so it must be a many-to-one function by the Pigeonhole Principle. However, that doesn't automatically imply that it send more than one input to each of its outputs. For instance, Squaring…
Tristan Laguz
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How are timestamps verified?

You put an input and the hash value comes as an output then when someone puts the input the hash function it is applied to see if it is the same hash original value is stored in some database , that is how it works if I remember it…
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Is there an algorithm or hardware that can sign/verify natural time?

PGP/GPG can used to sign text, others use public key to verify them. So one could say, that these cryptographic algorithms deal with space. Are there any algorithms that can deal with time? E.g. I sign a document at 2011-12-31 23:59:59, others can…
est
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Can timestamping provide evidence of absence before a certain time?

Normally trusted timestamping proves that certain information existed at or before a certain time. However, sometimes there is a need to prove the opposite; that something did not exist before a certain time. Consider that I want to prove by…
Tobias Bengtsson
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Is there a digital time-stamping scheme that does not rely on a time-stamping authority?

Given a bit string, is it possible to assign it an immutable time stamp that is verifiable as correct without assuming a (one or more) trusted time-stamping authority? A time-stamp is correct if it is within delta milliseconds of the creation of the…
Swapnil Bhatia
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How can you prove that a certain file was downloaded from a certain website?

Let's say you downloaded a file from a certain website, and later the website claims that it didn't made that file available, is there any way to prove that the website is lying? Example 1: You download a youtube video and the channel later delete…
TimestampQuestion
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Which organization is responsible for certifying a TSA?

I see there a number of free TSA services according to this page (not all are still in service). In other sources I see references to the requirement of audits for the TSA to be 'rfc3161 compliant'. Given the number of free services, not to mention…
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Why do key exchange protocols need secure clock synchronization?

I'm studying Kerberos and other Key Exchange Protocols. They always (or very often) require that the clocks are synchronized. To this purpose they periodically probe a time-server. This is said to be a critical operation because new kind of attacks…
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What advantage is there for using a nonce and a timestamp?

I know both nonces and timestamps are used to prevent replay attacks, and nonces may offer increased security in the situation a message could be replayed with the timestamp in the allowable window. However, if a nonce can provide all the protection…
tpm900
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Why use a timestamp and how can someone know it's the correct one?

Let's say A wants to send a message, so everyone who gets the message, can be assured that it's from A. A then sends a message message|timestamp|E(A_private_key, Hash(message|timestamp)) What are the benefits of timestamp? How can a person who gets…
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Signature and Timestamp for Long Term Document Archival Question

I have a PDF document intended for long-term (many years, maybe decades) archival which I would like to digitally sign with my personal certificate to ensure its integrity. As far as I understand, I need to timestamp the signature in order to ensure…
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How can I know when a file was signed?

I have been thinking about digitally signed documents (Word files and PDF files) and can not get over the fact about - how can I securely know when the file was signed? Scenario: If the date of the signature is saved in the file that I am signing.…
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Timestamps, sequence numbers, and nonces for replay attack

What are the best practices or standardized methods to prevent replay attacks in a simple server client setup (preferably where the server is stateless) ? When should timestamps, sequence numbers, and nonces be used, and what is the main…
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