1.5.3 Timestamp a PDF Document in Adobe Reader - encryption simply explained

Hi, this is Mike from Mimaception Academy and in this video I want to show you how to time stamp your PDF documents. How can you actually prove that your documents existed at a certain point in time? Let's take a look at this now. Let's consider the following situation: You have the task to finish a document by a certain date. Now you have your PDF document ready, but how can you prove that it was created at the current time? As an example I take this document and for each file Windows additionally stores when it was created. I open the properties of the document to have a look at this time. Here in the "General" tab, several times are displayed to me. But can we really trust them? No, because these times depend on what time is set in your PC. Here in the properties we see a time, far in the future. This is because I have set the time in Windows to this year. So we cannot trust the time of our PC. But how can we prove that this document existed at a certain time? The solution is: time stamps. An electronic time stamp assigns the hash value of a document to a specific point in time, and this time stamp is then digitally signed. So here, the digital signature plays also a very important role. A timestamp must be managed by a trusted service that ensures that the correct time is always generated. Since the hash value of a document is always unique and the timestamp service is trusted, your document with a timestamp can serve as proof that the document existed at a certain point in time. In Acrobat Reader, you can have documents signed with a timestamp. First open your PDF document with Acrobat Reader. First you need to set which timestamp server you want to use. Click with your mouse on "Edit" and then on "Preferences". A dialog opens where you can set all preferences for the reader. On the left side of the list you can click on "Signatures". An electronic timestamp is digitally signed, so this setting is here. And on the right side you can see the settings for "Document Timestamping" at the bottom. Click on the button "More". In this dialog you can configure one or more servers for the timestamp. For this exercise, I have stored several servers and their urls. Click here on the button "Plus". First you should enter the name of the server. I usually enter the name of the company here. Below that the url of the server where the timestamp will be created. Then click on "OK". Here in the list you can see the configured timestamp service. You can also configure several such services here. Just have a look at the information of this tutorial, there I have specified several servers. Next you have to set a "Default". I select this server and go to the button "Set Default". Here click on "Ok". Here in the list there is now a star at this entry. Ok, with this the configuration is finished. Next, we will now have a timestamp created for this PDF document. Click with your mouse on the "Tools" tab. And down here you click on "Open" at "Certificate". Now you can see the toolbar for creating digital signatures. And here you click on the button "Time Stamp". Now you have to enter a new file name where your PDF document with time stamp should be saved. Why is a new PDF document created now? Once the document is signed, it cannot be edited in Adobe Acrobat. So that you can continue working with the original, a copy with timestamp is saved separately here. I extend the file name with "ts" for timestamp. Ok, the timestamp has been created and embedded in the PDF document. Adobe Reader now opens a panel up here where the status of the signature from the timestamp is displayed. Here on the top right is the button to open the signature panel. If you don't see it, you can also open the signature panel as follows. Go to "View", then to "Show/Hide", then to "Navigation Panes" and here you click on "Signatures". And here you can see our signature from the timestamp. Ok, what happened now? Adobe has calculated a hash value from the PDF document and sent it to the timestamp server. The server signed the hash value and Adobe embedded this signature into the PDF document. And now here on the left in the signature panel, it shows us the information about the signature. First it shows us that the signature is valid. That means the document has not been modified since the time stamp. Below it says "Signer identity is valid". This means the company of the timestamp service is trusted. Adobe Reader knows because its certificate is valid. Below it says: "Signature is a document timestamp signature". This means that this type of signature only confirms that the content was present at a certain point in time and that it has not changed since then. This signature says nothing about the owner of the document. It is my document, but the signature has been created by the company DigiCert. Let me open the details of the certificate. DigiCert has created this signature, but does not know what the content of the document is and does not take responsibility for it. This means that a timestamp can only confirm that a document existed at a certain time. A timestamp cannot provide any information about the owner of the document. There are other types of signatures, such as the advanced and the qualified digital signature. With these you can sign your document with your own name. How this works, I have created the course "Digital Signature" for you. If you right click here at "Revision 1", you can explicitly start the signature check. First a small dialog opens. Here only the most important information is shown, the document was not changed and the signer is valid. and the signer is valid. If you click on the button "Signature Properties", more information will be displayed. Here in the middle is the "timestamp", which is the time when a timestamp was created for this document on the server. This time comes from the server and is independent of the time that is set on my PC. At this real time this document must have existed. Ok, I have now opened this document with Adobe Acrobat and here on the left you can see again the timestamp details and their signature. Now what happens if I modify the document? For this I open the toolbar "Edit PDF" in Acrobat. Up here you see the elements for editing the document. I will add some more text. You see, an error message appears. Acrobat does not allow editing the document because it is signed. This is also the reason why the Reader saved the document with a timestamp under a different name. Ok, with this I have shown you how to add a timestamp to a PDF document in Adobe Reader. This way you have the possibility to prove that your PDF document existed from that point in time. Of course, this only works if the server is trusted.

Channel: Encryption for Beginners

Views: 4,613

Keywords: Encryption beginners, Encryption explained, mike kurtze, mimaception academy, RSA, aes encryption, algorithm, asymmetric, asymmetric encryption, basics, comprehension, cryptography, educate, education, encryption, encryption and decryption, encryption explained, introduction, key, knowledge, learning, lesson, privacy, private key, public key, public key encryption, school, secure, security, symmetric, symmetric encryption, understand, what is encryption, encryption beginners, encryption tutorial

Id: WNS4scgdjmE

Length: 9min 56sec (596 seconds)

Published: Tue Oct 11 2022