[Yum] V3 DSA signature

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Hi,

I am trying to install tomcat5 via YUM. But i keep getting this error and 
quit. How can I install tomcat?

Downloading Packages:
warning: rpmts_HdrFromFdno: V3 DSA signature: NOKEY, key ID c431416d
public key not available for mx4j-3.0.1-1jpp.noarch.rpm

thanks