feat: link_file_types

Initial support for extending the link_file interfaces. This change
attempts to follow pre-existing dev patterns.

Extracted from fork https://github.com/henrybear327/go-proton-api

link_file_types.go

@@ -1,5 +1,40 @@
 package proton
 
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+
+	"github.com/ProtonMail/gopenpgp/v2/crypto"
+)
+
+/* Helper function */
+func getEncryptedName(name string, addrKR, nodeKR *crypto.KeyRing) (string, error) {
+	clearTextName := crypto.NewPlainMessageFromString(name)
+
+	encName, err := nodeKR.Encrypt(clearTextName, addrKR)
+	if err != nil {
+		return "", err
+	}
+
+	encNameString, err := encName.GetArmored()
+	if err != nil {
+		return "", err
+	}
+
+	return encNameString, nil
+}
+
+func GetNameHash(name string, hashKey []byte) (string, error) {
+	mac := hmac.New(sha256.New, hashKey)
+	_, err := mac.Write([]byte(name))
+	if err != nil {
+		return "", err
+	}
+
+	return hex.EncodeToString(mac.Sum(nil)), nil
+}
+
 type CreateFileReq struct {
 	ParentLinkID string