The Horodocs system allows files to be timestamped, in particular to strengthen the chain of custody in forensic science The user receives a PDF receipt containing a QR code. By scanning this QR code, a verifier can check that the file hash values were indeed timestamped at the time specified in the receipt.

The user can use the web interface to timestamp a file via its hash values. The file’s hash values are not stored, but are used to calculate intermediate and final values used in the timestamping process.The Horodocs timestamping server generates and sends the PDF receipt which includes:

• the QR code, which can be scanned to verify the timestamping of the file’s hash values;
• the QR code content to use the link directly from the PDF receipt
• a case identifier (freely chosen by the user);
• a file identifier (freely chosen by the user);
• an investigator identifier (freely chosen by the user);
• a free-form text (freely chosen by the user);
• the date and time at which the file’s hash values were submitted (to the timestamping system);
• the hash values of the timestamped file (MD5 and SHA256);
• the control value (16 hexadecimal characters) stored in the blockchain.

As well as more technical information:

• the salt value;
• forward and backward branches of the tree needed to find its root from the leaf corresponding to the timestamped file.