Content classifier for Private Key files

Hi Websense, 

We're looking at setting up some connections with external partners using SFTP authenticated using a public / private key pair. 

To protect from misuse, we'd like to make sure that no one could send the private key files used for these connections out of the network. Are there any available content classifiers that could be used for identifying private key files? 

You can generate a keyfile pair using Puttygen (part of Putty). I've already tested using the built in encryption content classifiers (including Encrypted files (unknown format)) but none seem to detect the private key file. 

Please could a content classifier for public and private key files be added to an upcoming release of DSS?

Thanks, 

Phil.