key derivation service that pinvokes into CommonCrypto for PBKDF2 key

src/iOS/Services/KeyDerivationService.cs

@@ -0,0 +1,35 @@
+using Bit.App.Abstractions;
+using Foundation;
+using System;
+using System.Runtime.InteropServices;
+using System.Text;
+
+namespace Bit.iOS.Services
+{
+    public class KeyDerivationService : IKeyDerivationService
+    {
+        private const uint PBKDFAlgorithm = 2; // PBKDF2
+        private const uint PseudoRandomAlgorithm = 3; // SHA256
+        private const uint Rounds = 5000;
+
+        public byte[] DeriveKey(string password, string salt)
+        {
+            var passwordData = NSData.FromArray(Encoding.UTF8.GetBytes(password));
+            var saltData = NSData.FromArray(Encoding.UTF8.GetBytes(salt));
+
+            var keyData = new NSMutableData();
+            keyData.Length = 32;
+            var result = CCKeyCerivationPBKDF(PBKDFAlgorithm, passwordData.Bytes, passwordData.Length, saltData.Bytes, 
+                saltData.Length, PseudoRandomAlgorithm, Rounds, keyData.MutableBytes, keyData.Length);
+
+            byte[] keyBytes = new byte[keyData.Length];
+            Marshal.Copy(keyData.Bytes, keyBytes, 0, Convert.ToInt32(keyData.Length));
+            return keyBytes;
+        }
+
+        // ref: http://opensource.apple.com//source/CommonCrypto/CommonCrypto-55010/CommonCrypto/CommonKeyDerivation.h
+        [DllImport(ObjCRuntime.Constants.libSystemLibrary, EntryPoint = "CCKeyDerivationPBKDF")]
+        public extern static int CCKeyCerivationPBKDF(uint algorithm, IntPtr password, nuint passwordLen,
+            IntPtr salt, nuint saltLen, uint prf, nuint rounds, IntPtr derivedKey, nuint derivedKeyLength);
+    }
+}