An RSA digital signature is superior to a handwritten signature in that it
attests to the contents of a message as well as to the identity of the
signer. As long as a secure hash function (see Question 3.8.2) is
used, there is no way to take someone's signature from one document and
attach it to another, or to alter the signed message in any way. The
slightest change in a signed document will cause the digital signature
verification process to fail. Thus, RSA authentication allows people to
check the integrity of signed documents. Of course, if a signature
verification fails, it may be unclear whether there was an attempted
forgery or simply a transmission error.