How to Check if the uploaded file has signature

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?

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.

Answer

From a programmers perspective

So if it is 3 times or more (x9 x27 x87) to do a quick test then it will be faster to compress the base64 back to binary and do a single test there.

And for that there are several answers but this one is not a recommendation for any.

I would simply filter 1st based on "/Sig" then try to verify that signature.