diff options
| -rw-r--r-- | src/se/leap/bitmaskclient/Dashboard.java | 3 | ||||
| -rw-r--r-- | src/se/leap/bitmaskclient/PRNGFixes.java | 338 |
2 files changed, 340 insertions, 1 deletions
diff --git a/src/se/leap/bitmaskclient/Dashboard.java b/src/se/leap/bitmaskclient/Dashboard.java index 601428e2..fd8d6be6 100644 --- a/src/se/leap/bitmaskclient/Dashboard.java +++ b/src/se/leap/bitmaskclient/Dashboard.java @@ -75,7 +75,8 @@ public class Dashboard extends Activity implements LogInDialog.LogInDialogInterf super.onCreate(savedInstanceState); app = this; - + + PRNGFixes.apply(); ConfigHelper.setSharedPreferences(getSharedPreferences(SHARED_PREFERENCES, MODE_PRIVATE)); preferences = ConfigHelper.shared_preferences; diff --git a/src/se/leap/bitmaskclient/PRNGFixes.java b/src/se/leap/bitmaskclient/PRNGFixes.java new file mode 100644 index 00000000..a046f01f --- /dev/null +++ b/src/se/leap/bitmaskclient/PRNGFixes.java @@ -0,0 +1,338 @@ +package se.leap.bitmaskclient; + +/* + * This software is provided 'as-is', without any express or implied + * warranty. In no event will Google be held liable for any damages + * arising from the use of this software. + * + * Permission is granted to anyone to use this software for any purpose, + * including commercial applications, and to alter it and redistribute it + * freely, as long as the origin is not misrepresented. + * + * Source: http://android-developers.blogspot.de/2013/08/some-securerandom-thoughts.html + */ + +import android.os.Build; +import android.os.Process; +import android.util.Log; + +import java.io.ByteArrayOutputStream; +import java.io.DataInputStream; +import java.io.DataOutputStream; +import java.io.File; +import java.io.FileInputStream; +import java.io.FileOutputStream; +import java.io.IOException; +import java.io.OutputStream; +import java.io.UnsupportedEncodingException; +import java.security.NoSuchAlgorithmException; +import java.security.Provider; +import java.security.SecureRandom; +import java.security.SecureRandomSpi; +import java.security.Security; + +/** + * Fixes for the output of the default PRNG having low entropy. + * + * The fixes need to be applied via {@link #apply()} before any use of Java + * Cryptography Architecture primitives. A good place to invoke them is in the + * application's {@code onCreate}. + */ +public final class PRNGFixes { + + private static final int VERSION_CODE_JELLY_BEAN = 16; + private static final int VERSION_CODE_JELLY_BEAN_MR2 = 18; + private static final byte[] BUILD_FINGERPRINT_AND_DEVICE_SERIAL = + getBuildFingerprintAndDeviceSerial(); + + /** Hidden constructor to prevent instantiation. */ + private PRNGFixes() {} + + /** + * Applies all fixes. + * + * @throws SecurityException if a fix is needed but could not be applied. + */ + public static void apply() { + applyOpenSSLFix(); + installLinuxPRNGSecureRandom(); + } + + /** + * Applies the fix for OpenSSL PRNG having low entropy. Does nothing if the + * fix is not needed. + * + * @throws SecurityException if the fix is needed but could not be applied. + */ + private static void applyOpenSSLFix() throws SecurityException { + if ((Build.VERSION.SDK_INT < VERSION_CODE_JELLY_BEAN) + || (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2)) { + // No need to apply the fix + return; + } + + try { + // Mix in the device- and invocation-specific seed. + Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto") + .getMethod("RAND_seed", byte[].class) + .invoke(null, generateSeed()); + + // Mix output of Linux PRNG into OpenSSL's PRNG + int bytesRead = (Integer) Class.forName( + "org.apache.harmony.xnet.provider.jsse.NativeCrypto") + .getMethod("RAND_load_file", String.class, long.class) + .invoke(null, "/dev/urandom", 1024); + if (bytesRead != 1024) { + throw new IOException( + "Unexpected number of bytes read from Linux PRNG: " + + bytesRead); + } + } catch (Exception e) { + throw new SecurityException("Failed to seed OpenSSL PRNG", e); + } + } + + /** + * Installs a Linux PRNG-backed {@code SecureRandom} implementation as the + * default. Does nothing if the implementation is already the default or if + * there is not need to install the implementation. + * + * @throws SecurityException if the fix is needed but could not be applied. + */ + private static void installLinuxPRNGSecureRandom() + throws SecurityException { + if (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2) { + // No need to apply the fix + return; + } + + // Install a Linux PRNG-based SecureRandom implementation as the + // default, if not yet installed. + Provider[] secureRandomProviders = + Security.getProviders("SecureRandom.SHA1PRNG"); + if ((secureRandomProviders == null) + || (secureRandomProviders.length < 1) + || (!LinuxPRNGSecureRandomProvider.class.equals( + secureRandomProviders[0].getClass()))) { + Security.insertProviderAt(new LinuxPRNGSecureRandomProvider(), 1); + } + + // Assert that new SecureRandom() and + // SecureRandom.getInstance("SHA1PRNG") return a SecureRandom backed + // by the Linux PRNG-based SecureRandom implementation. + SecureRandom rng1 = new SecureRandom(); + if (!LinuxPRNGSecureRandomProvider.class.equals( + rng1.getProvider().getClass())) { + throw new SecurityException( + "new SecureRandom() backed by wrong Provider: " + + rng1.getProvider().getClass()); + } + + SecureRandom rng2; + try { + rng2 = SecureRandom.getInstance("SHA1PRNG"); + } catch (NoSuchAlgorithmException e) { + throw new SecurityException("SHA1PRNG not available", e); + } + if (!LinuxPRNGSecureRandomProvider.class.equals( + rng2.getProvider().getClass())) { + throw new SecurityException( + "SecureRandom.getInstance(\"SHA1PRNG\") backed by wrong" + + " Provider: " + rng2.getProvider().getClass()); + } + } + + /** + * {@code Provider} of {@code SecureRandom} engines which pass through + * all requests to the Linux PRNG. + */ + private static class LinuxPRNGSecureRandomProvider extends Provider { + + public LinuxPRNGSecureRandomProvider() { + super("LinuxPRNG", + 1.0, + "A Linux-specific random number provider that uses" + + " /dev/urandom"); + // Although /dev/urandom is not a SHA-1 PRNG, some apps + // explicitly request a SHA1PRNG SecureRandom and we thus need to + // prevent them from getting the default implementation whose output + // may have low entropy. + put("SecureRandom.SHA1PRNG", LinuxPRNGSecureRandom.class.getName()); + put("SecureRandom.SHA1PRNG ImplementedIn", "Software"); + } + } + + /** + * {@link SecureRandomSpi} which passes all requests to the Linux PRNG + * ({@code /dev/urandom}). + */ + public static class LinuxPRNGSecureRandom extends SecureRandomSpi { + + /* + * IMPLEMENTATION NOTE: Requests to generate bytes and to mix in a seed + * are passed through to the Linux PRNG (/dev/urandom). Instances of + * this class seed themselves by mixing in the current time, PID, UID, + * build fingerprint, and hardware serial number (where available) into + * Linux PRNG. + * + * Concurrency: Read requests to the underlying Linux PRNG are + * serialized (on sLock) to ensure that multiple threads do not get + * duplicated PRNG output. + */ + + private static final File URANDOM_FILE = new File("/dev/urandom"); + + private static final Object sLock = new Object(); + + /** + * Input stream for reading from Linux PRNG or {@code null} if not yet + * opened. + * + * @GuardedBy("sLock") + */ + private static DataInputStream sUrandomIn; + + /** + * Output stream for writing to Linux PRNG or {@code null} if not yet + * opened. + * + * @GuardedBy("sLock") + */ + private static OutputStream sUrandomOut; + + /** + * Whether this engine instance has been seeded. This is needed because + * each instance needs to seed itself if the client does not explicitly + * seed it. + */ + private boolean mSeeded; + + @Override + protected void engineSetSeed(byte[] bytes) { + try { + OutputStream out; + synchronized (sLock) { + out = getUrandomOutputStream(); + } + out.write(bytes); + out.flush(); + } catch (IOException e) { + // On a small fraction of devices /dev/urandom is not writable. + // Log and ignore. + Log.w(PRNGFixes.class.getSimpleName(), + "Failed to mix seed into " + URANDOM_FILE); + } finally { + mSeeded = true; + } + } + + @Override + protected void engineNextBytes(byte[] bytes) { + if (!mSeeded) { + // Mix in the device- and invocation-specific seed. + engineSetSeed(generateSeed()); + } + + try { + DataInputStream in; + synchronized (sLock) { + in = getUrandomInputStream(); + } + synchronized (in) { + in.readFully(bytes); + } + } catch (IOException e) { + throw new SecurityException( + "Failed to read from " + URANDOM_FILE, e); + } + } + + @Override + protected byte[] engineGenerateSeed(int size) { + byte[] seed = new byte[size]; + engineNextBytes(seed); + return seed; + } + + private DataInputStream getUrandomInputStream() { + synchronized (sLock) { + if (sUrandomIn == null) { + // NOTE: Consider inserting a BufferedInputStream between + // DataInputStream and FileInputStream if you need higher + // PRNG output performance and can live with future PRNG + // output being pulled into this process prematurely. + try { + sUrandomIn = new DataInputStream( + new FileInputStream(URANDOM_FILE)); + } catch (IOException e) { + throw new SecurityException("Failed to open " + + URANDOM_FILE + " for reading", e); + } + } + return sUrandomIn; + } + } + + private OutputStream getUrandomOutputStream() throws IOException { + synchronized (sLock) { + if (sUrandomOut == null) { + sUrandomOut = new FileOutputStream(URANDOM_FILE); + } + return sUrandomOut; + } + } + } + + /** + * Generates a device- and invocation-specific seed to be mixed into the + * Linux PRNG. + */ + private static byte[] generateSeed() { + try { + ByteArrayOutputStream seedBuffer = new ByteArrayOutputStream(); + DataOutputStream seedBufferOut = + new DataOutputStream(seedBuffer); + seedBufferOut.writeLong(System.currentTimeMillis()); + seedBufferOut.writeLong(System.nanoTime()); + seedBufferOut.writeInt(Process.myPid()); + seedBufferOut.writeInt(Process.myUid()); + seedBufferOut.write(BUILD_FINGERPRINT_AND_DEVICE_SERIAL); + seedBufferOut.close(); + return seedBuffer.toByteArray(); + } catch (IOException e) { + throw new SecurityException("Failed to generate seed", e); + } + } + + /** + * Gets the hardware serial number of this device. + * + * @return serial number or {@code null} if not available. + */ + private static String getDeviceSerialNumber() { + // We're using the Reflection API because Build.SERIAL is only available + // since API Level 9 (Gingerbread, Android 2.3). + try { + return (String) Build.class.getField("SERIAL").get(null); + } catch (Exception ignored) { + return null; + } + } + + private static byte[] getBuildFingerprintAndDeviceSerial() { + StringBuilder result = new StringBuilder(); + String fingerprint = Build.FINGERPRINT; + if (fingerprint != null) { + result.append(fingerprint); + } + String serial = getDeviceSerialNumber(); + if (serial != null) { + result.append(serial); + } + try { + return result.toString().getBytes("UTF-8"); + } catch (UnsupportedEncodingException e) { + throw new RuntimeException("UTF-8 encoding not supported"); + } + } +} |