CONFIG_SIGNATURE (not configurable)

modulename: digsig.ko

configname: CONFIG_SIGNATURE

Linux Kernel Configuration
└─>Library routines
└─>SIGNATURE
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Digital signature verification. Currently only RSA is supported.
Implementation is done using GnuPG MPI library

source code:
lib/digsig.c