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How can I check if a file uploaded through an input field has a signature? After converting it to Base64, what is the process to verify if it contains any signature?

2

Answers


  1. Could you please clarify if the uploaded file should have a specific signature that matches a known signature, or if it can have any signature that is not known or controlled by you?

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  2. After conversion of anything (PDF or not) to base 64 you will require at least 6 times the effort. So to detect one single word here are some of its fingerprints.

    • L1NpZ
    • IC9TaWc
    • ZS9TaWcK
    • cGUvU2ln

    and you can see a pattern but how could you tell this is a match too.

    • U0lHTkFUVVJF

    Thus the only reliable method is permutate manifold the endless possibilities or reverse to Plain Text.

    The secondary issue is that a PDF signature could be encoded or encrypted or both or neither or perhaps compressed, so the permutations become ad infinitum.

    So you need to use a plain text string as a signature and then its only one of three to detect. This file was signed and is now not signed but still has the fingerprint of a signature.

    enter image description here

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