Digital signing is working correctly but after sending the signed file over internet the signature has become invalid

In this case the fault is usually in antivirus or firewall software that open the digitally signed files to check if they contain viruses. Closing the file is not done exactly the same and thus the digitally signed file has been altered and signature is displayed as invalid or altered. Problem can be solved by simply compressing the Digidoc format (ddoc) files either using Zip or Rar before sending them over internet.

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