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7

I would characterize the service as similar to a trusted time-stamping service. Except they do not do the time-stamping, but just provide the "key". This allows a user to decide what do to with it, such as using it as a private key to sign something, or an HMAC key, proving the signature is "not older" than the timestamp. If the signature is published to a ...


6

If you search on "timestamp", "timestamping", and "notary" on Crypto.SE and Security.SE, you'll find lots of references. I've collected a number of timestamping services that were mentioned in one of those places; this should provide a number of companies and online services you can check out: http://www.proofofexistence.com/ https://www.btproof.com/ ...


3

Several certificate authorities operate RFC-3161-compliant time-stamp servers that can be used free-of-charge. OpenSSL can create RFC 3161 time-stamp requests and verify the responses. Here is a simple Bash script that time-stamps a file using the time-stamp server operated by StartSSL: in_file='[path to file]' # name of file to be hashed and time-stamped ...


3

Updated answer: No, this is not possible with cryptography. You have the ciphertext and you have the key. For all anyone knows, you could have made a copy of those to some other computer and decrypted the ciphertext without telling anyone. There's no way (with cryptography) to prove you haven't done that. One approach would be to implement a secure service ...


2

I wonder why anyone would choose to rely on a source of true random numbers fraught with questions that will ultimately have no provable - or perhaps even satisfactory - answer. There are at least a couple of companies that sell generators that provide high quality true random numbers. Having a generator on-site and available real-time allows the necessary ...


2

I don't think there is a pure-cryptography solution to this. Suppose you built a chip, and it time-stamped whatever message you wanted, using an internal atomic clock. For the sake of argument, let's say that it's unhackable, and totally tamper-proof. Well, there's still a loophole. Put the chip on a spacecraft and speed it up to 99% the speed of light for ...


2

Actually, I guess that you are talking about digital signatures and not about public key encryption (since you want to have message authenticity and not confidentiality). Whether using time-stamps or not makes sense depends on your application. Basically, the idea is that the verifier can determine when the signature has been issued and in particular that ...


1

You can guess it's the correct timestamp if it's within a few seconds (or minutes) from the current timestamp. At the very least you can assume that the timestamp of the message that just came in must be greater than the timestamp of the last one. Similarly, if the timestamp points to the future by any reasonable margin (a few seconds) you know the other ...


1

Timestamps allow the recipients to know the order in which messages from an honest party were sent. This is sometimes important in cryptographic protocols. Timestamps sometimes allow the recipient to know that a message from an honest party has been replayed. This is important in cryptographic protocols. These properties sometimes allow protocols using ...


1

It is possible for Bob and Alice to store many files on some host file server using a host-proof protocol -- i.e., in such a way that even the sysadmins of that server cannot decrypt and read the plaintext of those files. You may be interested in browsing the questions with the host-proof tag. As far as I know, there is only one way to prove that those ...



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