次のクラスは、Android クラスの問題を軽減するのに役立ちますSecureRandom
。このコードはテキストの代わりに作成されました。
/**
* A strengthener that can be used to generate and re-seed random number
* generators that do not seed themselves appropriately.
*
* @author owlstead
*/
public class SecureRandomStrengthener {
private static final String DEFAULT_PSEUDO_RANDOM_NUMBER_GENERATOR = "SHA1PRNG";
private static final EntropySource TIME_ENTROPY_SOURCE = new EntropySource() {
final ByteBuffer timeBuffer = ByteBuffer.allocate(Long.SIZE / Byte.SIZE
* 2);
@Override
public ByteBuffer provideEntropy() {
this.timeBuffer.clear();
this.timeBuffer.putLong(System.currentTimeMillis());
this.timeBuffer.putLong(System.nanoTime());
this.timeBuffer.flip();
return this.timeBuffer;
}
};
private final String algorithm;
private final List<EntropySource> entropySources = new LinkedList<EntropySource>();
private final MessageDigest digest;
private final ByteBuffer seedBuffer;
/**
* Generates an instance of a {@link SecureRandomStrengthener} that
* generates and re-seeds instances of {@code "SHA1PRNG"}.
*
* @return the strengthener, never null
*/
public static SecureRandomStrengthener getInstance() {
return new SecureRandomStrengthener(
DEFAULT_PSEUDO_RANDOM_NUMBER_GENERATOR);
}
/**
* Generates an instance of a {@link SecureRandomStrengthener} that
* generates instances of the given argument. Note that the availability of
* the given algorithm arguments in not tested until generation.
*
* @param algorithm
* the algorithm indicating the {@link SecureRandom} instance to
* use
* @return the strengthener, never null
*/
public static SecureRandomStrengthener getInstance(final String algorithm) {
return new SecureRandomStrengthener(algorithm);
}
private SecureRandomStrengthener(final String algorithm) {
if (algorithm == null || algorithm.length() == 0) {
throw new IllegalArgumentException(
"Please provide a PRNG algorithm string such as SHA1PRNG");
}
this.algorithm = algorithm;
try {
this.digest = MessageDigest.getInstance("SHA1");
} catch (final NoSuchAlgorithmException e) {
throw new IllegalStateException(
"MessageDigest to create seed not available", e);
}
this.seedBuffer = ByteBuffer.allocate(this.digest.getDigestLength());
}
/**
* Add an entropy source, which will be called for each generation and
* re-seeding of the given random number generator.
*
* @param source
* the source of entropy
*/
public void addEntropySource(final EntropySource source) {
if (source == null) {
throw new IllegalArgumentException(
"EntropySource should not be null");
}
this.entropySources.add(source);
}
/**
* Generates and seeds a random number generator of the configured
* algorithm. Calls the {@link EntropySource#provideEntropy()} method of all
* added sources of entropy.
*
* @return the random number generator
*/
public SecureRandom generateAndSeedRandomNumberGenerator() {
final SecureRandom secureRandom;
try {
secureRandom = SecureRandom.getInstance(this.algorithm);
} catch (final NoSuchAlgorithmException e) {
throw new IllegalStateException("PRNG is not available", e);
}
reseed(secureRandom);
return secureRandom;
}
/**
* Re-seeds the random number generator. Calls the
* {@link EntropySource#provideEntropy()} method of all added sources of
* entropy.
*
* @param secureRandom
* the random number generator to re-seed
*/
public void reseed(final SecureRandom secureRandom) {
this.seedBuffer.clear();
secureRandom.nextBytes(this.seedBuffer.array());
for (final EntropySource source : this.entropySources) {
final ByteBuffer entropy = source.provideEntropy();
if (entropy == null) {
continue;
}
final ByteBuffer wipeBuffer = entropy.duplicate();
this.digest.update(entropy);
wipe(wipeBuffer);
}
this.digest.update(TIME_ENTROPY_SOURCE.provideEntropy());
this.digest.update(this.seedBuffer);
this.seedBuffer.clear();
// remove data from seedBuffer so it won't be retrievable
// reuse
try {
this.digest.digest(this.seedBuffer.array(), 0,
this.seedBuffer.capacity());
} catch (final DigestException e) {
throw new IllegalStateException(
"DigestException should not be thrown", e);
}
secureRandom.setSeed(this.seedBuffer.array());
wipe(this.seedBuffer);
}
private void wipe(final ByteBuffer buf) {
while (buf.hasRemaining()) {
buf.put((byte) 0);
}
}
}
そして、これは次の小さなインターフェイスですEntropySource
。
/**
* A simple interface that can be used to retrieve entropy from any source.
*
* @author owlstead
*/
public interface EntropySource {
/**
* Retrieves the entropy.
* The position of the ByteBuffer must be advanced to the limit by any users calling this method.
* The values of the bytes between the position and limit should be set to zero by any users calling this method.
*
* @return entropy within the position and limit of the given buffer
*/
ByteBuffer provideEntropy();
}
クラスの出力はランダム性についてテストされていないことに注意してください (ただし、これは主に返されたクラスに依存するSecureRandom
ため、問題ないはずです)。
最後に、私は Android 1.6 ランタイムの準備ができていないので、互換性のために誰かがこのバージョンまたはそれ以前のバージョンに対してテストする必要があります (!)。