CONFIG_CRYPTO_LIB_CURVE25519 (not configurable)

modulename: libcurve25519.ko

configname: CONFIG_CRYPTO_LIB_CURVE25519

Linux Kernel Configuration
└─>Library routines
└─>Crypto library routines
└─>CRYPTO_LIB_CURVE25519
In linux kernel since version 4.14.326 (release Date: 2023-09-23)  
The Curve25519 library functions. Select this if your module uses any
of the functions from <crypto/curve25519.h>.

source code:
lib/crypto//