Add DeriveKey func

encryption/derive_key.go

@@ -1 +1,36 @@
 package encryption
+
+import (
+	"crypto/sha512"
+	"golang.org/x/crypto/hkdf"
+	"io"
+)
+
+func DeriveKey(k []byte, nonce []byte) ([32]byte, error) {
+	var key [32]byte
+
+	// TODO: remove experiment
+	//d := sha3.NewShake256()
+	//_, err := d.Write(k)
+	//if err != nil {
+	//	return [64]byte{}, err
+	//}
+	//_, err = d.Write(nonce)
+	//if err != nil {
+	//	return [64]byte{}, err
+	//}
+	//
+	//_, err = d.Read(key[:])
+	//if err != nil {
+	//	return [64]byte{}, err
+	//}
+
+	// SHA2-512 related code
+	kdf := hkdf.New(sha512.New, k, nonce, nil)
+	_, err := io.ReadFull(kdf, key[:])
+	if err != nil {
+		return [32]byte{}, err
+	}
+
+	return key, nil
+}