$ sudo apt-get update
$ sudo apt-get install librpmsign1 

librpmsign1 is installed in your system.

Make ensure the librpmsign1 package were installed using the commands given below,

$ sudo dpkg-query -l | grep librpmsign1 *

You will get with librpmsign1 package name, version, architecture and description in a table

librpmsign1 package basic information: