我正在尝试开发一款涉及加密的Android应用程序。计划使用AES-CTR模式和Whirlpool的PBKDF2进行密钥拉伸。
我打算实现一个新的Bouncy Castle（密码工具库）实现，而不是Android内置的旧实现，以确保在任何Android版本上都能按预期运行。
但是我遇到了一些问题，无法找到一种可靠的方法来生成盐和密钥的随机数。我曾经看到有人说Android内置的安全随机数在一些旧的Android版本上存在漏洞，并且我也听说大多数Android手机很难保持/dev/random中高熵和常见的块。这难道对/dev/urandom的安全性没有巨大影响吗？因此，我正在寻找利用手机传感器收集更多熵的好方法。
SecureRandom类的问题。这段代码是为了避免小细节而创建的，而不是文本。/**
* 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);
}
}
}
这是一个名为EntropySource的小接口：
/**
* 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();
}
SecureRandom类，因此应该没有问题）。flip()方法。 - Maarten Bodewes/dev/urandom读取，除了4.2 / 4.3已经这样做（但搞砸了初始种子）。他们使用了比时间更多的熵源。不幸的是，他们通过写入/dev/urandom进行种子生成，在某些CyanogenMod和最新的Galaxy S4固件上失败，因为它们拒绝写入。在您的代码和由内核随时间重新播种的/dev/urandom之间，我不知道该使用什么了。 - Barend