12
votes
How can you prove that a certain file was downloaded from a certain website?
Daniel S explains what is needed to provide repudiation for file downloads, so I'll explain why you cannot prove a file was downloaded in the typical situation when using regular TLS.
When a server ...
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12
votes
How can you prove that a certain file was downloaded from a certain website?
This is possible, but only with the co-operation of the website. Whatever the downloaded file is, along with the associate metadata such as time and server identity, can be cryptographically hashed to ...
- 26.4k
11
votes
Accepted
What advantage is there for using a nonce and a timestamp?
However, if a nonce can provide all the protection a timestamp does, why would they ever be used together?
If you use a timestamp in combination with a nonce, it can help mitigate the risk of nonce ...
- 14.7k
9
votes
Accepted
Is there a way to get time from signature? Or is it possible to ensure the message was signed at the time that it says it was signed?
There is no way to get time of signature from a standard ECDSA signature: it does not embed recoverable information†.
And under the conditions in this related question or messages with structure ...
- 146k
5
votes
Can timestamping provide evidence of absence before a certain time?
One application for a randomness beacon is to get this assurance. A randomness beacon (NIST runs a prototype one) generates a sequence of public, signed, timestamped random numbers on a fixed ...
- 219
4
votes
Why do key exchange protocols need secure clock synchronization?
Kerberos requires synchronised clocks mainly to ensure the messages are fresh and to thwart replay attacks. The messages include timestamps so that those with outdated timestamps (e.g. more than 5 ...
- 4,198
4
votes
Accepted
Can timestamping provide evidence of absence before a certain time?
Your problem is a tricky one to solve that has been discussed over a period of decades. Tierion (disclosure, where I am VP Engineering), provides a solution for at least part of your problem with our ...
- 194
4
votes
Is there a way to get time from signature? Or is it possible to ensure the message was signed at the time that it says it was signed?
There needs to be a timestamping authority (TSA), but your need deviates slightly from what it achieves.
A signature from a TSA only guarantees the data existed before the said timestamp, where as you ...
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4
votes
How can you prove that a certain file was downloaded from a certain website?
You can have witnesses watch you download the file to attest to the fact. I'm not sure how many witnesses you would need, but I'm sure the more the merrier.
On the day that you download the file, ...
- 151
3
votes
How can you prove that a certain file was downloaded from a certain website?
Two variants of an idea. First, submit a request to Internet Archive/Wayback Machine to have them mirror the page in question. Note, however, that a particular site might not allow them to mirror it ...
- 131
3
votes
Timestamps, sequence numbers, and nonces for replay attack
AEAD constructions encrypt messages and append an authentication tag. That authentication tag is computed using the following data:
The secret key
The nonce
The message, before or after encryption
...
- 3,053
3
votes
Clarification questions about timestamp servers
In 1991, Stuart Haber and Scott Stornetta proposed a method for time stamping a digital document. In their method, when someone (Alice) wants to timestamp a document, she send the hash of her document ...
- 375
3
votes
How useful is NIST's Randomness Beacon for cryptographic use?
The previous poster got voted down for pointing out that the service freezes, but I think that's unfair: the original question asked if the NIST beacon is useful; prototype or not, it does in fact ...
- 131
3
votes
Is there a digital time-stamping scheme that does not rely on a time-stamping authority?
If being decentralized with no trusted timestamping authority that could backdate things is a must, then the solution is Bitcoin's blockchain (or a similar cryptocurrency's blockchain). OpenTimestamps ...
- 528
2
votes
Can timestamping provide evidence of absence before a certain time?
I think this is a hard question to answer. However, I believe since you are utilizing a trusted third party, then one way to do this is to use trusted platform module (TPM) [read more about it on ...
- 452
2
votes
Is it possible to have a PAdES signature with only a timestamp?
Short answer: No. If you look at the PAdES specification, it is clear that each profile relies on at least one normal signature.
Longer answer: A timestamp and a signature serve different purposes. ...
- 2,548
2
votes
Using a block cipher with timestamp instead of counter
Firstly, if your plaintext is bigger than the block size of your symmetric cipher, then you can use a mode of operation which is compatible with your purpose.
If you wish to simply have the timestamp ...
- 7,789
2
votes
Using a block cipher with timestamp instead of counter
A timestamp in the message won't fix the problem with ECB mode. ECB mode uses the same key for each block, so you will leak the fact that blocks are the same within the same message, and if you use ...
- 51
2
votes
Remotely Verify File Timestamp
This is exactly the scenario that the Timestamp Protocol has been created for.
You need to provide your students with access to a trusted timestamping authority (TSA). This could be you yourself or ...
- 2,548
2
votes
Accepted
Commitment for bid
Let me restate your game to be sure I understood you correctly:
There's $n$ players
Casino presents number $R$
Each player sends commitment to some number $0$ and $R$
After that casino sends "betting ...
2
votes
Accepted
Revoke key without communication between the party who revoked it and the party who is validating
We need not trust the messenger to allow revocation. A public broadcast is usually sufficient. Obviously some communication is necessary between the revoker and the verifier but it need not be over a ...
- 12k
2
votes
What is a clearsigned message?
From dictionary.university with search clearsigned definition
Dictionary of Internet Terms A digitally signed S/MIME or PGP message in which the content of the message is readable even if the ...
- 49.5k
2
votes
Clarification questions about timestamp servers
Section 4 of the linked paper answers some of your questions:
To implement a distributed timestamp server on a peer-to-peer basis, we will need to use a proof-of-work system similar to Adam Back's ...
- 1,463
2
votes
Why Nonces and timestamps are used in Public key authority?
To understand how nonces and timestamps are used to prevent a replay attack, you must understand generally what a replay attack is. A replay attack is a network attack in which a data transmission (...
2
votes
Accepted
What is an "anonymous admissible timestamp"?
What he meant is quite unclear. It could be that he's referring to a Timestamping Authority (TA) (See related RFC like 3161). What they do is basically sign a document/hash with the current time and ...
- 376
1
vote
How can you prove that a certain file was downloaded from a certain website?
Since you asked this on Cryptography, not Law, the answer is simple: you cannot. The TLS protocol (arguably very intentionally at this point, although originally it may have been unintentional) does ...
1
vote
How truncated timestamps are used?
how this is done in practice
You always can change "starting point" for timestamp.
This site says that current timestamp is ...
- 285
1
vote
Is there a digital time-stamping scheme that does not rely on a time-stamping authority?
Technically no. But practically, possibly, yes.
Time is an absolute measurement using an agreed standard (UTC, hours, minutes, seconds, etc...). It's a human construct to log a progression of local (...
- 147
1
vote
Guaranteed decryption time schedule
Are there known any protocols or algorithms with precisely narrowed time estimate above?
Of course not, because it would depend on the details of the system performing the brute forcing / dictionary ...
- 94.5k
1
vote
Can timestamping provide evidence of absence before a certain time?
No, it can not. If you have an image and you add a timestamp to it you can only attest that the image already existed at the moment that you submitted it to your timestamping service or similar.
...
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