how to sign jar using maven

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>2.3</version>
    <executions>
        <execution>
            <goals>
                <goal>sign</goal>
           </goals>
        </execution>
    </executions>
    <configuration>
        <keystore>my.cer</keystore>
        <alias>my</alias>
        <storepass>secret</storepass>         <signedjar>${project.build.directory}/${project.build.finalName}.jar</signedjar>
        <verify>true</verify>
    </configuration>
</plugin>