Unlike the credentials for connecting to slaves, the password for ssh sites (stored in org.jvnet.hudson.plugins.SSHBuildWrapper.xml) are stored in plaintext.

<?xml version='1.0' encoding='UTF-8'?>
<org.jvnet.hudson.plugins.SSHBuildWrapper_-DescriptorImpl plugin="ssh@2.4">
<sites>
<org.jvnet.hudson.plugins.SSHSite>
<hostname>myhost</hostname>
<port>22</port>
<username>sgeorgio</username>
<password>plainpass</password>
<keyfile></keyfile>
<serverAliveInterval>0</serverAliveInterval>
<pty>false</pty>
</org.jvnet.hudson.plugins.SSHSite>
</sites>
</org.jvnet.hudson.plugins.SSHBuildWrapper_-DescriptorImpl>