Computer implemented method for automatically certifying documents with integrity and authenticity guarantees and computer programs thereof

A computer implemented method comprising:

• receiving, by a second computer system from a first computer system, an original document to be certified, and performing the followings:
• calculating, by the second computer system, a cryptographic function of the received original document;
• transmitting, by the second computer system, the calculated cryptographic function of the original document to a third computer system;
• storing, by the third computer system, the cryptographic function in at least one memory of a distributed ledger such that the calculated cryptographic function of the original document is unalterable in the distributed ledger;
• receiving, by the second computer system from the third computer system, a first message digest corresponding to a first identifier identifying the cryptographic function of the original document stored in the distributed ledger, and performing:
• (i) creating, by the second computer system, a key by combining the received first message digest, an identifier of the first computer system, and a timestamp, wherein metadata of the original document includes the identifier of the first computer system and the timestamp, (ii) creating, by the second computer system, a watermark by using the key, (iii) creating, by the second computer system, a modified document by applying the created watermark to the original document, (iv) transmitting, by the second computer system, the modified document to the first computer system, (v) calculating, by the second computer system, a cryptographic function of the modified document, (vi) transmitting, by the second computer system, the calculated cryptographic function of the modified document and the modified document to the third computer system, and (vii) holding, by the third computer system, the cryptographic function of the modified document and the modified document within the distributed ledger by storing the cryptographic function of the modified document and the modified document in the distributed ledger such that the cryptographic function of the modified document and the modified document are unalterable in the distributed ledger;
• and
• receiving, by the second computer system from the third computer system, a second message digest corresponding to a second identifier identifying the cryptographic function of the modified document and the modified document stored in the distributed ledger, and storing the second message digest locally in the second computer system;
• receiving, by the second computer system, a new document that is a digital document to be authenticated from a user terminal, and performing:
• (i) extracting a first watermark from the received digital document, (ii) decoding, from the first extracted watermark, a key, (iii) transmitting, to the third computer system, the locally stored second message digest corresponding to the decoded key and receiving the cryptographic function of the modified document, from the third computer system, (iv) calculating a cryptographic function of the digital document, (v) comparing the cryptographic function of the digital document with the cryptographic function that has been received from the third computer system, and (vi) transmitting, to the user terminal, information of a result of the comparing;
• and
• receiving, by the second computer system, a new document that is a digitized or a digitalized document to be authenticated from the user terminal, and performing:
• (i) extracting a second watermark from the received digitized or digitalized document, (ii) decoding, from metadata of the second extracted watermark, a key, (iii) extracting metadata of the received digitalized or digitalized document to be authenticated, and the first message digest from the key, (iv) transmitting, to the third computer system, the first message digest corresponding to the decoded key to recover the cryptographic function of the original document from the third computer system to check existence and registration of the received digitized or digitalized document, (v) receiving a digitized or digitalized document stored in the distributed ledger in response to transmitting the first message digest, and performing the following:
• extracting a third watermark from the digitized or digitalized document from the distributed ledger, decoding, from the third extracted watermark, the key, using the second message digest to recover the modified document from the third computer system, extracting, by the second computer system, the metadata including the identifier of the first computer system and the timestamp from the key, and transmitting, by the second computer system to the user terminal, the extracted metadata and the recovered modified document;
• wherein the digitized document is a document previously printed and converted into a digital form, and the digitalized document is a digital document previously converted into a different digital form.