ed25519Sk To Curve25519
The crypto_sign_ed25519_sk_to_curve25519() function converts an Ed25519 secret key ed25519_sk to an X25519 secret key and stores it into x25519_sk.
The crypto_sign_ed25519_sk_to_curve25519() function converts an Ed25519 secret key ed25519_sk to an X25519 secret key and stores it into x25519_sk.