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Progress on PGPainless Development

Not much time has passed since I last wrote about my progress on the PGPainless library. However, I feel like its time for an update.

Since the big 0.2.0 release, 4 further releases, 0.2.1 through 0.2.4 have been published. Taken together, the changes are quite substantial, so let me summarize.

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Photo by Raphael Koh on Unsplash

Modular SOP Implementation

The (in my opinion) most exciting change is that there now is an experimental module of java interfaces that model the Stateless OpenPGP Protocol (SOP). This module named sop-java is completely independent from PGPainless and has no external dependencies whatsoever. Its basically a port of Sequoia-PGP’s sop crate (which in term is based around the Stateless OpenPGP Command Line Interface specification) to Java.

Applications that want to execute basic OpenPGP operations can depend on this interface and decide on the concrete implementation later without locking themselves in with one fixed implementation. Remember:

The Database Is a Detail. […] The Web Is a Detail. […] Frameworks Are Details.

Uncle Bob – Clean Architecture

The module sop-java-picocli contains a CLI frontend for sop-java. It uses the picocli library to closely model the Stateless OpenPGP Command Line Interface (SOP-CLI) specification (version 1 for now).

The exciting part is that this module too is independent from PGPainless, but it can be used by any library that implements sop-java.

Next up, the contents of pgpainless-sop drastically changed. While up until recently it contained a fully fledged SOP-CLI application which used pgpainless-core directly, it now no longer contains command line application code, but instead an implementation of sop-java using pgpainless-core. Therefore pgpainless-sop can be used as a drop-in for sop-java, making it the first java-based SOP implementation (to my knowledge).

Lastly, pgpainless-cli brings sop-java-picocli and pgpainless-sop together. The code does little more than to plug pgpainless-sop as SOP backend into the command line application, resulting in a fully functional OpenPGP command line application (basically what pgpainless-sop was up until release 0.2.3, just better :P).

$ ./pgpainless-cli help
Usage: pgpainless-cli [COMMAND]
  help          Displays help information about the specified command
  armor         Add ASCII Armor to standard input
  dearmor       Remove ASCII Armor from standard input
  decrypt       Decrypt a message from standard input
  encrypt       Encrypt a message from standard input
  extract-cert  Extract a public key certificate from a secret key from
                  standard input
  generate-key  Generate a secret key
  sign          Create a detached signature on the data from standard input
  verify        Verify a detached signature over the data from standard input
  version       Display version information about the tool

The exciting part about this modular design is that if YOU are working on an OpenPGP library for Java, you don’t need to re-implement a CLI frontend on your own. Instead, you can implement the sop-java interface and benefit from the CLI provided by sop-java-picocli for free.

If you are a library consumer, depending on sop-java instead of pgpainless-core would allow you to swap out PGPainless for another library, should any emerge in the future. It also means that porting your application to other platforms and languages might become easier, thanks to the more or less fixed API provided by the SOP protocol.

Further Changes

There are some more exciting changes worth mentioning.

The whole PGPainless suite can now be built reproducibly!

$ gradle --quiet clean build &> /dev/null && md5sum {.,pgpainless-core,pgpainless-sop,pgpainless-cli,sop-java,sop-java-picocli}/build/libs/*.jar

e7e9f45eb9d74540092920528bb0abf0  ./build/libs/PGPainless-0.2.4.jar
8ab68285202c8a303692c7332d15c2b2  pgpainless-core/build/libs/pgpainless-core-0.2.4.jar
a9c1d7b4a47d5ec66fc65131c14f4848  pgpainless-sop/build/libs/pgpainless-sop-0.2.4.jar
08cfb620a69015190e45d66548b8ea0f  pgpainless-cli/build/libs/pgpainless-cli-0.2.4.jar
e309d5a8d3a9439c6fae1c56150d9d07  sop-java/build/libs/sop-java-0.2.4.jar
9901849535f57f04b615afb06216ae5c  sop-java-picocli/build/libs/sop-java-picocli-0.2.4.jar

It actually was not hard at all to achieve reproducibility. The command line application has a version command, which extracted the current application version by accessing a file which would be written during the Gradle build.

Unfortunately, Java’s implementation of the Properties class includes a timestamp when writing out the object into a PrintStream. Therefore the result was not reproducible. The fix was to write the file manually, without using a Properties object.

Furthermore, the APIs for decryption/verification were further simplified, following the example of the encryption API. Instead of chained builder subclasses, there now is a single builder class which is used to receive decryption keys and public key certificates etc.

If you need more details about what changed in PGPainless, there now is a changelog file.

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