Implemented transport security to CLI connection.

It uses Diffie Hellman to come up with one-time session key, then have
the server sign this session key to allow the client to verify that
there's no man in the middle.

cli/src/test/java/hudson/cli/ConnectionTest.java

@@ -0,0 +1,70 @@
+package hudson.cli;
+
+import hudson.remoting.FastPipedInputStream;
+import hudson.remoting.FastPipedOutputStream;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import javax.crypto.SecretKey;
+import javax.crypto.spec.SecretKeySpec;
+import java.io.IOException;
+
+/**
+ * @author Kohsuke Kawaguchi
+ */
+public class ConnectionTest extends Assert {
+    Throwable e;
+    private Connection c1;
+    private Connection c2;
+
+    @Before
+    public void setUp() throws IOException {
+        FastPipedInputStream i = new FastPipedInputStream();
+        FastPipedInputStream j = new FastPipedInputStream();
+
+        c1 = new Connection(i,new FastPipedOutputStream(j));
+        c2 = new Connection(j,new FastPipedOutputStream(i));
+    }
+
+    @Test
+    public void testEncyrpt() throws Throwable {
+        final SecretKey sessionKey = new SecretKeySpec(new byte[16],"AES");
+
+        Thread t1 = new Thread() {
+            @Override
+            public void run() {
+                try {
+                    c1.encryptConnection(sessionKey,"AES/CFB8/NoPadding").writeUTF("Hello");
+                } catch (Throwable x) {
+                    e = x;
+                }
+            }
+        };
+        t1.start();
+
+        Thread t2 = new Thread() {
+            @Override
+            public void run() {
+                try {
+                    String data = c2.encryptConnection(sessionKey,"AES/CFB8/NoPadding").readUTF();
+                    assertEquals("Hello", data);
+                } catch (Throwable x) {
+                    e = x;
+                }
+            }
+        };
+        t2.start();
+
+        t1.join(3000);
+        t2.join(3000);
+
+        if (t1.isAlive() || t2.isAlive()) {
+            t1.interrupt();
+            t2.interrupt();
+            throw new Error("thread is still alive");
+        }
+
+        if (e!=null)    throw e;
+    }
+}