{"id":7405,"date":"2025-08-19T16:54:01","date_gmt":"2025-08-19T14:54:01","guid":{"rendered":"https:\/\/podpisano-new.local\/?p=7405"},"modified":"2026-08-18T21:42:06","modified_gmt":"2026-08-18T19:42:06","slug":"podpis-wewnetrzny-a-zewnetrzny-czym-sie-roznia-i-kiedy-je-stosowac","status":"publish","type":"post","link":"https:\/\/podpisano.pl\/en\/podpis-wewnetrzny-a-zewnetrzny-czym-sie-roznia-i-kiedy-je-stosowac\/","title":{"rendered":"Internal versus external signature - differences, formats and applications (Part 1)"},"content":{"rendered":"
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We <\/span>earlier post<\/span><\/a> we discussed the two basic electronic signature formats - XAdES and PAdES - most commonly used for qualified e-signatures. Continuing with this topic, we will address another important issue: internal and external signatures.<\/span><\/p>

Whether an electronic signature is embedded in a file or saved as a separate file is of great practical importance - especially when signing a large<\/a> files or working with complex data communications systems.<\/span><\/p>

In this article, we explain what qualified internal and external signatures are and what they mean in the context of different formats (PAdES, XAdES, CAdES). We outline their main pros and cons, and suggest when it's a good idea to use each of these solutions.<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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What is an internal signature and what is an external signature?\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Internal signature<\/strong> is one that is incorporated directly into the document being signed. To put it simply: when you sign a file with an internal signature, you get a single file containing both the content of the document and the signature information (certificate, timestamp, etc.). The internal signature type is available in standards, among others PAdES and XAdES<\/a> - both allow you to embed the e-signature inside the file being signed. For example, the PAdES signature always saves the signature together with the PDF in a single file, while XAdES can embed the signature as an element in the XML structure of the original document.<\/span><\/p>

External signature<\/strong> while it is a separate file - after signing the document, you get two (or more) files: the original document and a separate file with the digital signature. This external file (e.g., with an extension of .xades or .sig) contains cryptographic data confirming the signature, but does not contain the contents of the original document. Such qualified external signatures can be created in XAdES or CAdES formats. In practice, this means that to verify the signature and content, the recipient must have both parts - the document and the signature file. The absence of either will make it impossible to verify the authenticity of the signature and the contents of the document.<\/span><\/p>

Difference between internal and external signatures<\/strong> boils down to how the signature is placed - either inside the signed file or as a separate companion file.<\/span><\/p>

However, it is important to emphasize that In legal terms, both types are equivalent.<\/strong> Both qualified internal and external signatures meet the requirements of the eIDAS regulation and are considered legally binding. Thus, the choice of signature type mainly affects technical and usability issues - e.g., ease of storing, verifying or transmitting documents - rather than the legal force of the e-signature itself.<\/span><\/p>

Both types of signatures support add-ons like timestamps<\/a>, signature policy, etc., increasing long-term security<\/a>.<\/span>
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PAdES format - signature in PDF file (internal signature)<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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PAdES<\/strong> (PDF Advanced Electronic Signature) is a qualified signature format designed for for PDF files only<\/strong>. In this standard, the electronic signature (and the signer's certificate) becomes embedded<\/strong> into a PDF structure - it becomes an integral part of the document. This puts everything needed for verification in a single file that can be opened in popular programs like Adobe Reader. What's more, PAdES makes it possible to add a visual representation of the signature on the document page (e.g., a graphic seal or signature information), which increases readability and makes the e-signature more similar to a handwritten signature on paper.<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Advantages of the PAdES format<\/h4>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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