Validating a signed PDF with PSPDFKit using a set of trusted certificates is easy. How to Validate a Digitally Signed Document with PSPDFKit This whole process is automatically supported by PSPDFKit, so you don’t need to perform these steps manually. If both hashes match, then the document has not been modified and was created by you. When the person you send a signed document to receives it, they can decrypt the encrypted hash and compute a hash of the same parts of the document they’ve received. To be efficient without compromising security, PSPDFKit does not encrypt the entire PDF document rather, only a hash of it is encrypted. If these things are true, then both parties can be sure that the message was created by the sender and not somebody else. Second, nobody should have access to the private key except the sender. First, the receiver must be able to decrypt the message using that public key. The sender encrypts the message using a key that is meant to be private (the “private key”) and shares the other key (the “public key”) with the receiver. But this requires that both parties are able to securely and secretly communicate the encryption key they are going to use beforehand.Īlternatively, you can use asymmetric encryption, which means that the sender and the receiver use different keys. If you want to send a message to another person and you don’t want it to fall into the wrong hands, you could use an algorithm to encrypt it and tell the other person to use the same algorithm to decrypt it. What if a malicious person guesses the hash function that was used, modifies the PDF document, and then stores the new hash in it? To solve this second problem, we need asymmetric encryption. However, this does not completely solve the problem of document integrity. When you sign a PDF document, this hash function is applied to almost all of the document’s contents and then stored inside it. The result of this hash function is always identical provided that the block of data has not been modified. A hash is a mathematical function that converts an arbitrary block of data into a fixed-size string. Digital signatures in PDF documents use the concept of hashing to prevent such a scenario. Imagine that somebody intercepts a PDF document with some important contractual agreement and tries to modify it to show different terms. How the Integrity of a PDF Document Is Checked That the person who claims to have authored the document is really the person who created it. That the document has not been modified by an unknown person. This piece of information is placed inside a document, and it lets PSPDFKit and other PDF readers check two important things: OverviewĪ digital signature in a PDF is the equivalent of an ink signature on a paper document, but it’s much more secure. In order to ensure that a document has not been modified by someone other than its author, and to verify that the author is who we expect and not somebody else, digital signatures are necessary. PDF documents are used to share all kinds of information, including that of a confidential nature or with a legal value, like a contract.
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