A client application sends an hash of the data it wants to time-stamp to a Time-Stamp authority server.
The Time-Stamp authority server retrieves the current date, concatenates it with the hash and uses its private key to create the time-stamp (kind of like a signature).
The Time-Stamp authority server returns the generated time-stamp to the client application.

Then a client can verify the piece of data with the time-stamp using the Certificate Authority of the time-stamp key pair (X509 certificates).

It gives a cryptographic proof of a piece of data content, for example a file, at a given time.

Some use cases:

time-stamp log files at rotation time.
time-stamp file at upload to prove it was delivered in due time or not.

Quick (and dirty) Testing

Here a few steps to quickly try out uts-server, for production setup, please compile civetweb externally and create proper CA and certificates:

# Building with civetweb embedded (will recover civetweb from github).
# Note: the BUNDLE_CIVETWEB option is only here for fast testing purpose
# The recommended way to deploy uts-server in production is to build civetweb
# separatly and to link against it.
$ cmake . -DBUNDLE_CIVETWEB=ON
$ make

# Create some test certificates.
$ ./tests/cfg/pki/create_tsa_certs

# Launching the time-stamp server with test configuration in debug mode.
$ ./uts-server -c tests/cfg/uts-server.cnf -D

# In another shell, launching a time-stamp script on the README.md file.
$ ./goodies/timestamp-file.sh -i README.rst -u http://localhost:2020 -r -O "-cert";

# Verify the time-stamp.
$ openssl ts -verify -in README.rst.tsr -data README.rst -CAfile ./tests/cfg/pki/tsaca.pem

# Display the time-stamp content.
$ openssl ts -reply -in README.rst.tsr -text

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