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Debra Garls

Business Development Manager

+1 774-200-0933

Digital Signature of Files

Providing verification of the author and the integrity of the document with a signature

Digital Signature of Files

Digital Signature – What is it?

With a digital signature, a person sending a message or a person signing a document can prove their identity. And, therefore, can make it possible to prove that a document that was sent (or a message) has not been changed and only has the original content. The digital signature of the user, their certificate, is inseparably linked with a unique fingerprint of the document and, in the case of modern formats like PDF, the file itself. This means that you always have everything you need to check the authenticity of the document and the author.


Digital-Signature-1200-en Digital SignatureSEAL Systems helps you…

  • Configure the digital approval process of your documents on a consistent and clear basis – by adding the digital signature of the approving editor on the document.
  • Add a clear sender to externally distributed documents with the digital signature that contains the private key of the sender – which can be checked online everywhere and at all times

Typical Questions

The application of digital signatures to documents, and a qualified digital signature (where appropriate) is often subject to legal stipulations.

SEAL Systems make it possible to integrate signature workflows into your tried and trusted document distribution processes, so you can fulfill these stipulations.


These may include:

  • The qualified digital signature when sending invoices
  • The digital signatures in an approval workflow
  • The certificates when sending documents to your suppliers

schluessel-136x300 Digital SignatureThe encryption and decryption can also be carried out with different keys – i.e., asymmetrical key pairs.


In this case, it is imperative that the keys of a pair belong together and are irreplaceable. These keys are known as a private key and a public key. With the assumption that the sender of a piece of information is only interested in the correct recipient receiving a certain piece of information, the sender starts the process by requesting the recipient to send their public key to them. The actual information is then encrypted with the public key that belongs to the recipient -and is then sent. Decryption is only possible with the recipient’s private key.

signatur-300x239 Digital SignatureYes! Modern asymmetrical key technology also enables the clear identification of authors. Certificates can be used to answer the question of whether the person who sends the key for an asymmetrical system is really the person you suspect to hold it. The ownership of a public key by a certain person can be verified and certified by certification authorities (organizations, government agencies). There are also agencies (TrustStores) that can affirm the validity of a certificate online. The components of a certificate are: Information on the owner, information on the issuer, the validity period, the public key, information on the scope and coverage of the key and the certificate. The certificate, is then protected with a signature once more.

sicherheit-300x210 Digital SignatureA digital signature does not necessarily mean that the signed content is encrypted. The signature only serves to securely determine the author or the organization that has issued the document. In this case, the private key and the public key are used in the opposite way as compared with the data encryption: A checksum that has been generated from the document which describes the document is encoded with the private key of the signing party. The public key is attached to the certificate. If the decryption with the attached public key is successful, then it is proof that the certificate is true – and is the one that received the checksum. If the checksum correlates with the file, then the signature is valid.


You can also have the issuer of the certificate verified by an independent agency. If the independent audit confirms the entire process of signature application, and the use of trust centers for key distribution and administration – then the signature also fulfills the requirements of a qualified digital signature.


The use of encryption methods and certificates is regulated by numerous standards and laws. In this context, an electronic signature is frequently mentioned, which places emphasis on the legal aspects rather than the technical ones. Here, the simple electronic signature which uses digitally processed manual signatures (writing scanned in) is included as the simplest form.

In contrast to many other data formats, PDF has an advantage because it offers space for an integrated signature instead of a detached signature. This makes transporting the signature (with the signed file) easier and safer.


With PDF, the distinct correlation of the signature and file is verified by an encrypted checksum. This means that ex-post changes are no longer signed and can only be added to the file using incremental changes. However, it is still possible to sign these changes later using multiple signatures.

APDF-A-265x300 Digital Signatures PDF/A stipulates that a standard-compliant file may not be encrypted or protected against access in any other way. This can be concerning if, as a proprietor of a PDF/A file, you want to protect the information that the PDF/A contains.


In such cases, digital signatures can do a good job. Signatures that have been verified as valid prove that the pertinent file has not been changed since it was signed. PDF/A – 2 has also improved another important function: it is now possible to update a certificate after it has expired without having to change the PDF/A file itself. The inclusion of the latest signature technology in the standard has made this possible.


Signatures use encryption technology. The actual content of a PDF/A file, however, remains unchanged.


Therefore, this technology is permissible for PDF/A and widely standardized. But, an encryption of all the data is not allowed for PDF/A. So, when a file is sent via unsecured channels, it may be sent using encrypted methods: Via secure email based methods or packaged in a PDF container – which is also encrypted.

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