Wednesday, October 04, 2017

The case of the different jsch 0.1.54 binaries

As part of the Apache NetBeans IP clearance we are combing through all the code and dependencies.

One interesting thing we bumped into was that the jsch 0.1.54 binary JAR we are using has a different hash (and size) than the binary JAR from Maven Central.

The old hash is 0D7D8ABA0D11E8CD2F775F47CD3A6CFBF2837DA4, the new one is DA3584329A263616E277E15462B387ADDD1B208D.

The binaries are 278,612 bytes vs 280,515 bytes in Maven Central.

Our version is actually the same as the one found on http://www.jcraft.com/jsch/

Also, the Maven JAR is properly signed with the author's CA7FA1F0 key.

This is where it becomes clear that reproducible builds are important. You do not want to have to wonder why a binary differs, especially years later when you are doing a review. And this one is a library doing SSH!

So, why the different binaries?

It seems the original JAR was compiled on Aug 30, 2016 with Java 1.4 (major version 48) while the Maven Central JAR was compiled Sep 3, 2016 with Java 5 (major version 49).

The original JAR also concatenates strings using StringBuffer while the Maven Central JAR uses the newly introduced in 1.5 StringBuilder. Which should also be a bit faster since it's not synchronized.

Next, most of the cypher classes use some reflection via a static static java.lang.Class class$(java.lang.String) method.

What is this? It's just the way class literals worked in Java 1.4. As explained here, in Java 5 the ldc_w instruction was introduced to load a Class object.

In 1.4 the class literal was helped by the compiler by actually introducing the helper Class class$(java.lang.String className) method and replacing the Person.class with a class$("Person") call.

It conclusion, it seems that excluding the Java 1.4 to Java 5 compiler changes, the two JARs are identical. With the Maven Central JAR even a bit better due to StringBuilder being used.

There is no check so far that the sources do produce the specific JAR. This is an exercise left for the reader.

Note: I have also cross-posted this blog post to the Apache NetBeans blog.

Tuesday, June 20, 2017

Processing a generic Data.Array matrix

I had an interesting Haskell problem the other week: work on columns and rows of a Data.Array i e.

You only have the Ix i, Ord e class constraints, which make sense because the index must be a Data.Ix. The elements also must be Ord to be able to process them.

The thing about Data.Ix is that it's very opaque. It only extends Ord. There is nothing matrix-related in it. One could use Data.Array for a lot of data structures!

But if you do know it's a matrix, although you have no explicit class constraint, there is a nice trick to use: two neighbouring cells will have a Data.Ix.rangeSize of 2!

So, the rows may be extracted by this little function:

byRows :: Ix i => [i] -> [[i]]
byRows indices = incGroupBy isNeighbour $ indices
    where isNeighbour x y = 2 == rangeSize (x, y)

which is called like

process :: (Ix i, Ord e) => Array i e -> Something
process matrix =

    let rows = byRows $ indices matrix
    ...

Note the unknown incGroupBy which is a groupBy that takes pairs incrementally.

That's it! I had a lot of ideas about using rangeSize to figure out the matrix dimensions, but pairing cells this way was really clean.

Thursday, March 30, 2017

Retina work

These past months I have done a NetBeans patch for the Apple Retina Display and also made a small Wiki-like site to help me and anyone else interested with finding matching font icons for the NetBeans icons: https://nextbeans.com/retina

The nextbeans.com stack is Angular, Prime NG, nginx, Jetty, Servlets, Spring Framework JDBC, HSQLDB. SSL via Let's Encrypt.  Hosted at Scaleway.

It's a fun project since I got to learn Angular, find a bug and submit a patch for Prime NG, see how Let's Encrypt does free SSL certificates, learn about the EU cookie warning and all the many tiny things that are needed for a site.

Angular in particular and the whole webdev ecosystem was a lot of new information for me. I was changing project configuration as Angular progressed along! Which reminds me: @angular/cli reached 1.0 and I should probably see if I need to tweak something.

Read on JAXenter a longer article about my work.

Tuesday, January 31, 2017

Machine learning everywhere!

Samsung announced a while back that they used a "Neural Net based predictor" for their CPU branch prediction.

Shortly after that an Intel person claimed it's no big deal because they have also been using a perceptron for some time.

But to me this seemed a rather big discovery! Previously I would have assumed that branch prediction is a super complex algorithm.

Learning that branch prediction is a basic perceptron reduces Intel's perceived strength.

So companies are openly and covertly using machine learning everywhere.

Machine learning is also a perfect fit for companies because there is no moral filter on a neural network and no chance of whistle blowing.

Volkswagen truly missed a golden opportunity here with their diesel scandal.

They should have just trained a neural network on passing the diesel criteria and then have perfect plausible deniability: "the neural network disabled the pollution filters all by itself!"

The case of the different jsch 0.1.54 binaries

As part of the Apache NetBeans IP clearance we are combing through all the code and dependencies. One interesting thing we bumped into wa...