feat(crypto): ✨ add mlock and munlock in sodium

Author: jasonboukheir

Runtime/Algorand.Unity.Crypto/Interop/sodium.cs

@@ -19,5 +19,11 @@ internal static unsafe partial class sodium
 
         [DllImport(Library, CallingConvention = CallingConvention.Cdecl)]
         internal static extern void sodium_free(IntPtr handle);
+
+        [DllImport(Library, CallingConvention = CallingConvention.Cdecl)]
+        internal static extern void sodium_mlock(IntPtr handle, UIntPtr size);
+
+        [DllImport(Library, CallingConvention = CallingConvention.Cdecl)]
+        internal static extern void sodium_munlock(IntPtr handle, UIntPtr size);
     }
 }

Runtime/Algorand.Unity.Crypto/SecureString.cs

@@ -27,18 +27,21 @@ public struct SecureString : INativeDisposable
         public SecureString(ReadOnlySpan<char> source)
         {
             totalCapacity = source.Length * 2;
-            handle = SecureMemoryHandle.Create((UIntPtr)totalCapacity);
+            var totalCapacityNUint = (UIntPtr)totalCapacity;
+            handle = SecureMemoryHandle.Create(totalCapacityNUint);
             unsafe
             {
                 fixed (char* sourceptr = source)
                 {
+                    sodium.sodium_mlock((IntPtr)sourceptr, totalCapacityNUint);
                     var error = UTF8ArrayUnsafeUtility.Copy(
                         handle.GetUnsafePtr(),
                         out length,
                         totalCapacity - 1,
                         sourceptr,
                         source.Length
                     );
+                    sodium.sodium_munlock((IntPtr)sourceptr, totalCapacityNUint);
                     if (error != CopyError.None)
                     {
                         if (handle.IsCreated) handle.Dispose();