SEC-3002: Add new option for AES encryption with GCM

The Galois Counter Mode (GCM) is held to be superior than the current
default CBC. This change adds an extra parameter to the constructor
of AesBytesEncryptor and a new convenience method in Encryptors.

crypto/src/test/java/org/springframework/security/crypto/encrypt/EncryptorsTests.java

@@ -9,6 +9,17 @@ import org.junit.Test;
 
 public class EncryptorsTests {
 
+	@Test
+	public void stronger() throws Exception {
+		BytesEncryptor encryptor = Encryptors.stronger("password", "5c0744940b5c369b");
+		byte[] result = encryptor.encrypt("text".getBytes("UTF-8"));
+		assertNotNull(result);
+		assertFalse(new String(result).equals("text"));
+		assertEquals("text", new String(encryptor.decrypt(result)));
+		assertFalse(new String(result).equals(new String(encryptor.encrypt("text"
+				.getBytes()))));
+	}
+
 	@Test
 	public void standard() throws Exception {
 		BytesEncryptor encryptor = Encryptors.standard("password", "5c0744940b5c369b");
@@ -20,6 +31,16 @@ public class EncryptorsTests {
 				.getBytes()))));
 	}
 
+	@Test
+	public void preferred() {
+		TextEncryptor encryptor = Encryptors.delux("password", "5c0744940b5c369b");
+		String result = encryptor.encrypt("text");
+		assertNotNull(result);
+		assertFalse(result.equals("text"));
+		assertEquals("text", encryptor.decrypt(result));
+		assertFalse(result.equals(encryptor.encrypt("text")));
+	}
+
 	@Test
 	public void text() {
 		TextEncryptor encryptor = Encryptors.text("password", "5c0744940b5c369b");