Acrobat Pro 9 Digital Signature Error

Question

I have been digitally signing documents for quite some time. I am suddenly unable to sign. It does not matter the document. Documents sent to me, documents that I create, it does not matter. I have changed nothing on my system.

I tried repairing, but that is not working.

Error message:

Signature contains incorrect, unrecognized, corrupted or suspicious data.

Unsupported algorithm

Any help would be greatly appreciated!!!!

MikelKlink · Answer

You mention Acrobat 9. That product has stopped being supported in June 2013, more than 10 years ago.

In the meantime quite some changes occurred in the cryptography used in signatures. A number of algorithms (or at least algorithm parameterizations) have become obsolete while other, newer algorithms became state of the art.

I assume your own key pair, some key pair of your OS, or some underlying key pair of your provider changed to make use of an algorithm Acrobat 9 doesn't know and, therefore, informs you about an "Unsupported algorithm".

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