Add KeyDerivation implementation in swift

ios/Classes/KeyGeneration.swift

@@ -0,0 +1,25 @@
+//
+//  KeyGeneration.swift
+//
+//  NativeCryptoPlugin
+//
+//  Copyright (c) 2020
+//  Author: Hugo Pointcheval
+//
+import Foundation
+
+class KeyGeneration {
+    func keygen(size : NSNumber) -> Data? {
+        var bytes = [Int8](repeating: 0, count: size.intValue / 8)
+        let status = SecRandomCopyBytes(kSecRandomDefault, bytes.count, &bytes)
+
+        if status == errSecSuccess {
+            let keyBytes = bytes.withUnsafeBytes {
+                return Data(Array($0))
+                
+            }
+            return keyBytes
+        }
+        return nil
+    }
+}