cryptography - Slow AES GCM encryption and decryption with Java 8u20

Question

I am trying to encrypt and decrypt data using AES/GCM/NoPadding. I installed the JCE Unlimited Strength Policy Files and ran the (simple minded) benchmark below. I've done the same using OpenSSL and was able to achieve more than 1 GB/s encryption and decryption on my PC.

With the benchmark below I'm only able to get 3 MB/s encryption and decryption using Java 8 on the same PC. Any idea what I am doing wrong?

public static void main(String[] args) throws Exception {
    final byte[] data = new byte[64 * 1024];
    final byte[] encrypted = new byte[64 * 1024];
    final byte[] key = new byte[32];
    final byte[] iv = new byte[12];
    final Random random = new Random(1);
    random.nextBytes(data);
    random.nextBytes(key);
    random.nextBytes(iv);

    System.out.println("Benchmarking AES-256 GCM encryption for 10 seconds");
    long javaEncryptInputBytes = 0;
    long javaEncryptStartTime = System.currentTimeMillis();
    final Cipher javaAES256 = Cipher.getInstance("AES/GCM/NoPadding");
    byte[] tag = new byte[16];
    long encryptInitTime = 0L;
    long encryptUpdate1Time = 0L;
    long encryptDoFinalTime = 0L;
    while (System.currentTimeMillis() - javaEncryptStartTime < 10000) {
        random.nextBytes(iv);
        long n1 = System.nanoTime();
        javaAES256.init(Cipher.ENCRYPT_MODE, new SecretKeySpec(key, "AES"), new GCMParameterSpec(16 * Byte.SIZE, iv));
        long n2 = System.nanoTime();
        javaAES256.update(data, 0, data.length, encrypted, 0);
        long n3 = System.nanoTime();
        javaAES256.doFinal(tag, 0);
        long n4 = System.nanoTime();
        javaEncryptInputBytes += data.length;

        encryptInitTime = n2 - n1;
        encryptUpdate1Time = n3 - n2;
        encryptDoFinalTime = n4 - n3;
    }
    long javaEncryptEndTime = System.currentTimeMillis();
    System.out.println("Time init (ns): "     + encryptInitTime);
    System.out.println("Time update (ns): "   + encryptUpdate1Time);
    System.out.println("Time do final (ns): " + encryptDoFinalTime);
    System.out.println("Java calculated at " + (javaEncryptInputBytes / 1024 / 1024 / ((javaEncryptEndTime - javaEncryptStartTime) / 1000)) + " MB/s");

    System.out.println("Benchmarking AES-256 GCM decryption for 10 seconds");
    long javaDecryptInputBytes = 0;
    long javaDecryptStartTime = System.currentTimeMillis();
    final GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(16 * Byte.SIZE, iv);
    final SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
    long decryptInitTime = 0L;
    long decryptUpdate1Time = 0L;
    long decryptUpdate2Time = 0L;
    long decryptDoFinalTime = 0L;
    while (System.currentTimeMillis() - javaDecryptStartTime < 10000) {
        long n1 = System.nanoTime();
        javaAES256.init(Cipher.DECRYPT_MODE, keySpec, gcmParameterSpec);
        long n2 = System.nanoTime();
        int offset = javaAES256.update(encrypted, 0, encrypted.length, data, 0);
        long n3 = System.nanoTime();
        javaAES256.update(tag, 0, tag.length, data, offset);
        long n4 = System.nanoTime();
        javaAES256.doFinal(data, offset);
        long n5 = System.nanoTime();
        javaDecryptInputBytes += data.length;

        decryptInitTime += n2 - n1;
        decryptUpdate1Time += n3 - n2;
        decryptUpdate2Time += n4 - n3;
        decryptDoFinalTime += n5 - n4;
    }
    long javaDecryptEndTime = System.currentTimeMillis();
    System.out.println("Time init (ns): " + decryptInitTime);
    System.out.println("Time update 1 (ns): " + decryptUpdate1Time);
    System.out.println("Time update 2 (ns): " + decryptUpdate2Time);
    System.out.println("Time do final (ns): " + decryptDoFinalTime);
    System.out.println("Total bytes processed: " + javaDecryptInputBytes);
    System.out.println("Java calculated at " + (javaDecryptInputBytes / 1024 / 1024 / ((javaDecryptEndTime - javaDecryptStartTime) / 1000)) + " MB/s");
}

EDIT: I leave it as a fun exercise to improve this simple minded benchmark.

I've tested some more using the ServerVM, removed nanoTime calls and introduced warmup, but as I expected none of this had any improvement on the benchmark results. It is flat-lined at 3 megabytes per second.

Answer 1

Micro-benchmarking aside, the performance of the GCM implementation in JDK 8 (at least up to 1.8.0_25) is crippled.

I can consistently reproduce the 3MB/s (on a Haswell i7 laptop) with a more mature micro-benchmark.

From a code dive, this appears to be due to a naive multiplier implementation and no hardware acceleration for the GCM calculations.

By comparison AES (in ECB or CBC mode) in JDK 8 uses an AES-NI accelerated intrinsic and is (for Java at least) very quick (in the order of 1GB/s on the same hardware), but the overall AES/GCM performance is completely dominated by the broken GCM performance.

There are plans to implement hardware acceleration, and there have been third party submissions to improve the performance with, but these haven't made it to a release yet.

Something else to be aware of is that the JDK GCM implementation also buffers the entire plaintext on decryption until the authentication tag at the end of the ciphertext is verified, which cripples it for use with large messages.

Bouncy Castle has (at the time of writing) faster GCM implementations (and OCB if you're writing open source software of not encumbered by software patent laws).

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Updated July 2015 - 1.8.0_45 and JDK 9

JDK 8+ will get an improved (and constant time) Java implementation (contributed by Florian Weimer of RedHat) - this has landed in JDK 9 EA builds, but apparently not yet in 1.8.0_45. JDK9 (since EA b72 at least) also has GCM intrinsics - AES/GCM speed on b72 is 18MB/s without intrinsics enabled and 25MB/s with intrinsics enabled, both of which are disappointing - for comparison the fastest (not constant time) BC implementation is ~60MB/s and the slowest (constant time, not fully optimised) is ~26MB/s.

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Updated Jan 2016 - 1.8.0_72:

Some performance fixes landed in JDK 1.8.0_60 and performance on the same benchmark now is 18MB/s - a 6x improvement from the original, but still much slower than the BC implementations.