static fun forSignatureSecretKey(secretKey: SecretKey!): SecretKey! (source)
Transforms the Ed25519 secret key to a Curve25519 secret key. See https://libsodium.gitbook.io/doc/advanced/ed25519-curve25519
secretKey - SecretKey!: the signature secret key
Return
SecretKey!: the secret key as a Curve25519 secret key