PRNG fixes were a nop ever since we switched to 4.4+
This commit is contained in:
Daniel Gultsch
parent
521bb7846c
commit
f23311ab3f
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@ -1,327 +0,0 @@
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package eu.siacs.conversations.utils;
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import android.os.Build;
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import android.os.Process;
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import android.util.Log;
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import java.io.ByteArrayOutputStream;
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import java.io.DataInputStream;
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import java.io.DataOutputStream;
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import java.io.File;
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import java.io.FileInputStream;
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import java.io.FileOutputStream;
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import java.io.IOException;
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import java.io.OutputStream;
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import java.io.UnsupportedEncodingException;
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import java.security.NoSuchAlgorithmException;
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import java.security.Provider;
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import java.security.SecureRandom;
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import java.security.SecureRandomSpi;
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import java.security.Security;
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/**
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* Fixes for the output of the default PRNG having low entropy.
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*
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* The fixes need to be applied via {@link #apply()} before any use of Java
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* Cryptography Architecture primitives. A good place to invoke them is in the
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* application's {@code onCreate}.
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*/
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public final class PRNGFixes {
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private static final int VERSION_CODE_JELLY_BEAN = 16;
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private static final int VERSION_CODE_JELLY_BEAN_MR2 = 18;
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private static final byte[] BUILD_FINGERPRINT_AND_DEVICE_SERIAL = getBuildFingerprintAndDeviceSerial();
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/** Hidden constructor to prevent instantiation. */
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private PRNGFixes() {
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}
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/**
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* Applies all fixes.
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*
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* @throws SecurityException
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* if a fix is needed but could not be applied.
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*/
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public static void apply() {
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applyOpenSSLFix();
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installLinuxPRNGSecureRandom();
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}
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/**
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* Applies the fix for OpenSSL PRNG having low entropy. Does nothing if the
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* fix is not needed.
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*
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* @throws SecurityException
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* if the fix is needed but could not be applied.
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*/
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private static void applyOpenSSLFix() throws SecurityException {
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if ((Build.VERSION.SDK_INT < VERSION_CODE_JELLY_BEAN)
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|| (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2)) {
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// No need to apply the fix
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return;
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}
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try {
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// Mix in the device- and invocation-specific seed.
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Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto")
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.getMethod("RAND_seed", byte[].class)
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.invoke(null, generateSeed());
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// Mix output of Linux PRNG into OpenSSL's PRNG
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int bytesRead = (Integer) Class
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.forName(
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"org.apache.harmony.xnet.provider.jsse.NativeCrypto")
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.getMethod("RAND_load_file", String.class, long.class)
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.invoke(null, "/dev/urandom", 1024);
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if (bytesRead != 1024) {
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throw new IOException(
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"Unexpected number of bytes read from Linux PRNG: "
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+ bytesRead);
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}
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} catch (Exception e) {
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throw new SecurityException("Failed to seed OpenSSL PRNG", e);
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}
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}
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/**
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* Installs a Linux PRNG-backed {@code SecureRandom} implementation as the
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* default. Does nothing if the implementation is already the default or if
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* there is not need to install the implementation.
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*
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* @throws SecurityException
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* if the fix is needed but could not be applied.
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*/
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private static void installLinuxPRNGSecureRandom() throws SecurityException {
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if (Build.VERSION.SDK_INT > VERSION_CODE_JELLY_BEAN_MR2) {
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// No need to apply the fix
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return;
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}
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// Install a Linux PRNG-based SecureRandom implementation as the
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// default, if not yet installed.
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Provider[] secureRandomProviders = Security
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.getProviders("SecureRandom.SHA1PRNG");
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if ((secureRandomProviders == null)
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|| (secureRandomProviders.length < 1)
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|| (!LinuxPRNGSecureRandomProvider.class
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.equals(secureRandomProviders[0].getClass()))) {
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Security.insertProviderAt(new LinuxPRNGSecureRandomProvider(), 1);
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}
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// Assert that new SecureRandom() and
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// SecureRandom.getInstance("SHA1PRNG") return a SecureRandom backed
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// by the Linux PRNG-based SecureRandom implementation.
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SecureRandom rng1 = new SecureRandom();
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if (!LinuxPRNGSecureRandomProvider.class.equals(rng1.getProvider()
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.getClass())) {
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throw new SecurityException(
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"new SecureRandom() backed by wrong Provider: "
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+ rng1.getProvider().getClass());
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}
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SecureRandom rng2;
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try {
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rng2 = SecureRandom.getInstance("SHA1PRNG");
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} catch (NoSuchAlgorithmException e) {
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throw new SecurityException("SHA1PRNG not available", e);
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}
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if (!LinuxPRNGSecureRandomProvider.class.equals(rng2.getProvider()
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.getClass())) {
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throw new SecurityException(
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"SecureRandom.getInstance(\"SHA1PRNG\") backed by wrong"
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+ " Provider: " + rng2.getProvider().getClass());
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}
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}
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/**
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* {@code Provider} of {@code SecureRandom} engines which pass through all
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* requests to the Linux PRNG.
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*/
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private static class LinuxPRNGSecureRandomProvider extends Provider {
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public LinuxPRNGSecureRandomProvider() {
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super("LinuxPRNG", 1.0,
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"A Linux-specific random number provider that uses"
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+ " /dev/urandom");
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// Although /dev/urandom is not a SHA-1 PRNG, some apps
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// explicitly request a SHA1PRNG SecureRandom and we thus need to
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// prevent them from getting the default implementation whose output
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// may have low entropy.
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put("SecureRandom.SHA1PRNG", LinuxPRNGSecureRandom.class.getName());
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put("SecureRandom.SHA1PRNG ImplementedIn", "Software");
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}
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}
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/**
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* {@link SecureRandomSpi} which passes all requests to the Linux PRNG (
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* {@code /dev/urandom}).
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*/
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public static class LinuxPRNGSecureRandom extends SecureRandomSpi {
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/*
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* IMPLEMENTATION NOTE: Requests to generate bytes and to mix in a seed
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* are passed through to the Linux PRNG (/dev/urandom). Instances of
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* this class seed themselves by mixing in the current time, PID, UID,
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* build fingerprint, and hardware serial number (where available) into
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* Linux PRNG.
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*
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* Concurrency: Read requests to the underlying Linux PRNG are
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* serialized (on sLock) to ensure that multiple threads do not get
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* duplicated PRNG output.
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*/
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private static final File URANDOM_FILE = new File("/dev/urandom");
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private static final Object sLock = new Object();
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/**
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* Input stream for reading from Linux PRNG or {@code null} if not yet
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* opened.
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*
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* @GuardedBy("sLock")
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*/
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private static DataInputStream sUrandomIn;
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/**
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* Output stream for writing to Linux PRNG or {@code null} if not yet
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* opened.
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*
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* @GuardedBy("sLock")
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*/
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private static OutputStream sUrandomOut;
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/**
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* Whether this engine instance has been seeded. This is needed because
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* each instance needs to seed itself if the client does not explicitly
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* seed it.
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*/
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private boolean mSeeded;
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@Override
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protected void engineSetSeed(byte[] bytes) {
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try {
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OutputStream out;
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synchronized (sLock) {
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out = getUrandomOutputStream();
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}
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out.write(bytes);
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out.flush();
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} catch (IOException e) {
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// On a small fraction of devices /dev/urandom is not writable.
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// Log and ignore.
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Log.w(PRNGFixes.class.getSimpleName(),
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"Failed to mix seed into " + URANDOM_FILE);
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} finally {
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mSeeded = true;
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}
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}
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@Override
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protected void engineNextBytes(byte[] bytes) {
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if (!mSeeded) {
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// Mix in the device- and invocation-specific seed.
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engineSetSeed(generateSeed());
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}
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try {
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DataInputStream in;
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synchronized (sLock) {
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in = getUrandomInputStream();
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}
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synchronized (in) {
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in.readFully(bytes);
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}
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} catch (IOException e) {
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throw new SecurityException("Failed to read from "
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+ URANDOM_FILE, e);
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}
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}
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@Override
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protected byte[] engineGenerateSeed(int size) {
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byte[] seed = new byte[size];
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engineNextBytes(seed);
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return seed;
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}
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private DataInputStream getUrandomInputStream() {
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synchronized (sLock) {
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if (sUrandomIn == null) {
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// NOTE: Consider inserting a BufferedInputStream between
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// DataInputStream and FileInputStream if you need higher
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// PRNG output performance and can live with future PRNG
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// output being pulled into this process prematurely.
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try {
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sUrandomIn = new DataInputStream(new FileInputStream(
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URANDOM_FILE));
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} catch (IOException e) {
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throw new SecurityException("Failed to open "
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+ URANDOM_FILE + " for reading", e);
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}
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}
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return sUrandomIn;
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}
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}
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private OutputStream getUrandomOutputStream() throws IOException {
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synchronized (sLock) {
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if (sUrandomOut == null) {
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sUrandomOut = new FileOutputStream(URANDOM_FILE);
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}
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return sUrandomOut;
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}
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}
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}
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/**
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* Generates a device- and invocation-specific seed to be mixed into the
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* Linux PRNG.
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*/
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private static byte[] generateSeed() {
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try {
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ByteArrayOutputStream seedBuffer = new ByteArrayOutputStream();
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DataOutputStream seedBufferOut = new DataOutputStream(seedBuffer);
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seedBufferOut.writeLong(System.currentTimeMillis());
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seedBufferOut.writeLong(System.nanoTime());
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seedBufferOut.writeInt(Process.myPid());
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seedBufferOut.writeInt(Process.myUid());
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seedBufferOut.write(BUILD_FINGERPRINT_AND_DEVICE_SERIAL);
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seedBufferOut.close();
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return seedBuffer.toByteArray();
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} catch (IOException e) {
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throw new SecurityException("Failed to generate seed", e);
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}
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}
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/**
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* Gets the hardware serial number of this device.
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*
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* @return serial number or {@code null} if not available.
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*/
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private static String getDeviceSerialNumber() {
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// We're using the Reflection API because Build.SERIAL is only available
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// since API Level 9 (Gingerbread, Android 2.3).
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try {
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return (String) Build.class.getField("SERIAL").get(null);
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} catch (Exception ignored) {
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return null;
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}
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}
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private static byte[] getBuildFingerprintAndDeviceSerial() {
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StringBuilder result = new StringBuilder();
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String fingerprint = Build.FINGERPRINT;
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if (fingerprint != null) {
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result.append(fingerprint);
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}
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String serial = getDeviceSerialNumber();
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if (serial != null) {
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result.append(serial);
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}
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try {
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return result.toString().getBytes("UTF-8");
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} catch (UnsupportedEncodingException e) {
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throw new RuntimeException("UTF-8 encoding not supported");
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}
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}
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}
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