压缩是在加密后发生的吗

Question

在审查加密方案时，我遇到了以下代码：

@Override
public OutputStream encrypt(OutputStream outputStream) throws Exception {
// generate the IV for encryption
final byte[] encryptionIV = KeyFileUtil.randomBytes(16);
outputStream.write(encryptionIV);
// now create the encryption cipher
final Cipher cipher = Cipher.getInstance(ENCRYPTION_ALGORITHM);
cipher.init(Cipher.ENCRYPT_MODE, getKey(), new GCMParameterSpec(128, encryptionIV));
// The CipherOutputStream shouldn't close the underlying stream
outputStream = new FilterOutputStream(outputStream) {
@Override
public void close() throws IOException {
// Do nothing
}
};
final CipherOutputStream cos = new CipherOutputStream(outputStream, cipher);
if (useZip) {
final ZipOutputStream zipOutputStream = new ZipOutputStream(cos) {
@Override
public void finish() throws IOException {
super.finish();
def.end();
}
@Override
public void flush() {
// Do nothing.
}
@Override
public void close() throws IOException {
try {
super.flush();
} catch (final IOException exception) {
// Continue and try to close.
}
super.close();
}
};
zipOutputStream.putNextEntry(new ZipEntry("ResourceContents"));
return zipOutputStream;
}
return cos;
}

据我所知，流的顺序是先加密数据，然后(无用地(压缩数据。这是正确的吗？还是我误解了OutputStreams上的排序方式？

感谢

Answer 1

是的，您误解(或阅读(了排序的工作原理。

在new ZipOutputStream(cos)，CipherOutputStream被ZOS包裹，因此数据首先被压缩，然后传递到包裹的流，包裹的流将加密数据，然后将其传递到下一个包裹的流中，依此类推

最外层的流首先访问数据，如果启用了压缩，则调用return zipOutputStream;，zipstream是最外层的数据流。这是FilterOutputStream的惯用用法。