Asymmetric (public-key cryptographic) key type

modulename: asymmetric_keys.ko

and/or

keyctl_pkey.ko

configname: CONFIG_ASYMMETRIC_KEY_TYPE

Linux Kernel Configuration
└─>Cryptographic API
└─>Asymmetric (public-key cryptographic) key type
In linux kernel since version 3.1 (release Date: 2011-10-24)  
This option provides support for a key type that holds the data for
the asymmetric keys used for public key cryptographic operations such
as encryption, decryption, signature generation and signature
verification.

source code:
crypto/asymmetric_keys/