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Is there a cryptographic mechanism by which it is possible to sign a document with a date, such that it is not possible to forge that same signature at a later date? Maybe some sort of server that publishes daily cryptographic keys (but how can you trust them? ;-).
For the inevitable prodding pragmatists, I'm not trying to accomplish some task. I'm just curious what the solution space is like.
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The encryption time is used to calculate the throughput of any process of encryption, which is calculated as the total encrypted plaintext (in bytes) divided by the encryption time (in ms). The LabVIEW 2016 simulation design results are shown in table 1 and figure 4.
Cryptography is the study of secure communications techniques that allow only the sender and intended recipient of a message to view its contents. The term is derived from the Greek word kryptos, which means hidden.
Modern cryptography uses sophisticated mathematical equations (algorithms) and secret keys to encrypt and decrypt data. Today, cryptography is used to provide secrecy and integrity to our data, and both authentication and anonymity to our communications.
A cryptoperiod is the time span during which a specific cryptographic key is authorized for use. Common government guidelines range from 1 to 3 years for asymmetric cryptography, and 1 day to 7 days for symmetric cipher traffic keys.
This is called Timestamping (TSP protocol, RFC 3161). Different digital signature standards (PDF and XML signatures, CAdES, PAdES, XAdES) include support for advanced timestamping based on TSP.
MS Authenticode also includes timestamping, but uses different (incompatible and less secure) mechanism for it.
TSP alone (without signature protocols) is not used a lot, but in conjunction with signature standards it becomes very handy.
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GuardTime has an interesting service, where the timestamp does not depend on a trusted third party ("signed time") but can be independently verified by any interested party. It works somewhat similarly as Bitcoins, based on hash trees.
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