Xml digital Signature

Hi, I've a question about the xml digital signature procedure.

I got a code written in C# that sign and verify an xml document and it works
well, but the question is:

How can I know that the signature come from a certain user?

I know that is possible add the tags:



<KeyInfo>

<X509Data>

<X509IssuerSerial>



<X509IssuerName>CN=TAMURA Kent, OU=TRL, O=IBM,

L=Yamato-shi, ST=Kanagawa, C=JP

</X509IssuerName>



<X509SerialNumber>12345678</X509SerialNumber>



</X509IssuerSerial>

<X509SKI>31d97bd7</X509SKI>

</X509Data>

</KeyInfo

But those tags aren't hashed and I can change the CN= TAMURA Kent with
CN=ROSS Bill and the verify procedure still works.

Is it correct?

How can I do?

Thanks!

Marco Moioli