# Verifying signature owner (without verifying the actual document)

Programming in Java.

I have an RSA key-pair, a document, and a signature created with the Java Signature class, using SHA512WithRSA. In order to verify the signature, of course, I need to provide the

• public key,
• signature,
• document.

Is it possible to verify the owner of the signature, using only:

• public key
• signature

An RSA signature is just a single number, encoded in a certain way. The number represents $x^d$, where $x$ is a padded hash of the document and $d$ the private exponent. If you know a public key $(m,e)$, you can calculate $x = (x^d)^e \mod m$, but without a document (or at least its hash) there is nothing to compare it with to verify anything.