public class foo {
public byte[] encrypt(String message) throws Exception {
final MessageDigest md = MessageDigest.getInstance("md5");
final byte[] digestOfPassword = md.digest("HG58YZ3CR9"
.getBytes("utf-8"));
final byte[] keyBytes = Arrays.copyOf(digestOfPassword, 24);
for (int j = 0, k = 16; j < 8;) {
keyBytes[k++] = keyBytes[j++];
}
final SecretKey key = new SecretKeySpec(keyBytes, "DESede");
final IvParameterSpec iv = new IvParameterSpec(new byte[8]);
final Cipher cipher = Cipher.getInstance("DESede/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, key, iv);
final byte[] plainTextBytes = message.getBytes("utf-8");
final byte[] cipherText = cipher.doFinal(plainTextBytes);
// final String encodedCipherText = new sun.misc.BASE64Encoder()
// .encode(cipherText);
return cipherText;
}
}
// Q1: "md5" (in line 3) encryption is vulnerable to length extension attack. (True or False)
// A1: True
// Q2: To avoid this kind of attack, ____ encryption methods can be used to replace "md5". (multi-choice)
// A. SHA-1 B. SHA-2 C. SHA-256 D. Whirlpool E. BLAKE2
// A2: B C E
// Q3: The true descriptions about "secret key", "message", "cipher", "padding" are ____. (multi-choice)
// A. message is encrypted into cipher by using secret key
// B. secret key is encrypted into message by using cipher
// C. padding is used to make encryption more secret
// D. padding will increse overhead
// A3: A C D
class Foo {
public static void adjustHue(ColorMatrix cm, float value)
{
value = cleanValue(value, 180f) / 180f * (float) Math.PI;
if (value == 0)
{
return;
}
float cosVal = (float) Math.cos(value);
float sinVal = (float) Math.sin(value);
float lumR = 0.213f;
float lumG = 0.715f;
float lumB = 0.072f;
float[] mat = new float[]
{
lumR + cosVal * (1 - lumR) + sinVal * (-lumR), lumG + cosVal * (-lumG) + sinVal * (-lumG), lumB + cosVal * (-lumB) + sinVal * (1 - lumB), 0, 0,
lumR + cosVal * (-lumR) + sinVal * (0.143f), lumG + cosVal * (1 - lumG) + sinVal * (0.140f), lumB + cosVal * (-lumB) + sinVal * (-0.283f), 0, 0,
lumR + cosVal * (-lumR) + sinVal * (-(1 - lumR)), lumG + cosVal * (-lumG) + sinVal * (lumG), lumB + cosVal * (1 - lumB) + sinVal * (lumB), 0, 0,
0f, 0f, 0f, 1f, 0f,
0f, 0f, 0f, 0f, 1f };
cm.postConcat(new ColorMatrix(mat));
}
}
// Q1: The 180 (in line 4) can be modified to the values that are multiples of 60. (True/False, give the reason if false)
// A1: False. 180 is used to transform from degree to radian.
// Q2: The 180 (in line 4) is relevant to "Math.PI". (True/False, give the reason if false)
// A2: True.
// Q3: The true descriptions about lumR, lumG, lumB (line 11-13) are ____. (multi-choice)
// A. they are the values of RGB
// B. they can be modified to any other values
// C. they can be modified to other three values whose sum is 1.0
// D. they can not be modified
// A3: D
public class foo {
protected String wifiIpAddress(Context context) {
WifiManager wifiManager = (WifiManager) context.getSystemService(WIFI_SERVICE);
int ipAddress = wifiManager.getConnectionInfo().getIpAddress();
// Convert little-endian to big-endian if needed
if (ByteOrder.nativeOrder().equals(ByteOrder.LITTLE_ENDIAN)) {
ipAddress = Integer.reverseBytes(ipAddress);
}
byte[] ipByteArray = BigInteger.valueOf(ipAddress).toByteArray();
String ipAddressString;
try {
ipAddressString = InetAddress.getByAddress(ipByteArray).getHostAddress();
} catch (UnknownHostException ex) {
Log.e("WIFIIP", "Unable to get host address.");
ipAddressString = null;
}
return ipAddressString;
}
}
// Q1: We need to convert little-endian to big-endian in line 6-9, because networking protocals are often ____ and device memories are often ____.
// A1: big-endianness little-endianness
public class foo {
public HttpClient getNewHttpClient() {
try {
KeyStore trustStore = KeyStore.getInstance(KeyStore.getDefaultType());
trustStore.load(null, null);
MySSLSocketFactory sf = new MySSLSocketFactory(trustStore);
sf.setHostnameVerifier(SSLSocketFactory.ALLOW_ALL_HOSTNAME_VERIFIER);
HttpParams params = new BasicHttpParams();
HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);
HttpProtocolParams.setContentCharset(params, HTTP.UTF_8);
SchemeRegistry registry = new SchemeRegistry();
registry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));
registry.register(new Scheme("https", sf, 443));
ClientConnectionManager ccm = new ThreadSafeClientConnManager(params, registry);
return new DefaultHttpClient(ccm, params);
} catch (Exception e) {
return new DefaultHttpClient();
}
}
}
// Q1: The input recieved by an HTTP client is ____.
// A1: url
// Q2: If the input starts with ____, HTTP client use http schema; if the input starts with _____, the client use https schema.
// A2: http: https:
// Q3: Compared to http schema, https schema has an additional _____ layer for _____.
// A3: secure socket layer encryption
public class foo {
public static String hsvToRgb(float hue, float saturation, float value) {
int h = (int)(hue * 6);
float f = hue * 6 - h;
float p = value * (1 - saturation);
float q = value * (1 - f * saturation);
float t = value * (1 - (1 - f) * saturation);
switch (h) {
case 0: return rgbToString(value, t, p);
case 1: return rgbToString(q, value, p);
case 2: return rgbToString(p, value, t);
case 3: return rgbToString(p, q, value);
case 4: return rgbToString(t, p, value);
case 5: return rgbToString(value, p, q);
default: throw new RuntimeException("Something went wrong when converting from HSV to RGB. Input was " + hue + ", " + saturation + ", " + value);
}
}
}
// Q1: We can change the number (in line 4) from 6 to 7. (True/False, give the reason if false)
// A1: False, according to the formula.
// Q2: We can add another case in "switch" block. (True/False, give the reason if false)
// A2: False, according to the formula.
// Q3: We can change the order of the six cases in "switch" block. (True/False, give the reason if false)
// A3: False, according to the formula.
