Crypto: Swift wrapper for the Curve25519 C code

Signed-off-by: Roopesh Chander <roop@roopc.net>

WireGuard/WireGuard/Crypto/Curve25519.swift

@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2018 WireGuard LLC. All rights reserved.
+
+import UIKit
+
+struct Curve25519 {
+    static func generatePrivateKey() -> Data {
+        var privateKey = Data(repeating: 0, count: 32)
+        privateKey.withUnsafeMutableBytes { (bytes: UnsafeMutablePointer<UInt8>) in
+            curve25519_generate_private_key(bytes)
+        }
+        assert(privateKey.count == 32)
+        return privateKey
+    }
+
+    static func generatePublicKey(fromPrivateKey privateKey: Data) -> Data {
+        assert(privateKey.count == 32)
+        var publicKey = Data(repeating: 0, count: 32)
+        privateKey.withUnsafeBytes { (privateKeyBytes: UnsafePointer<UInt8>) in
+            publicKey.withUnsafeMutableBytes { (bytes: UnsafeMutablePointer<UInt8>) in
+                curve25519_derive_public_key(bytes, privateKeyBytes)
+            }
+        }
+        assert(publicKey.count == 32)
+        return publicKey
+    }
+}