Krakatau VS dnscat2

Since Java bytecode uses MUTF-8, which encodes astral characters as surrogate pairs, I've had to implement this conversion in Python multiple times, in Krakatau and Enjarify.

Not sure how applicable this is for your project since my compiler was written in Python, but I used Krakatau.

Here is one that disassembles the bytecodes and reassembles them https://github.com/Storyyeller/Krakatau .

There's an additional problem that unlike regular assembly or LLVM assembly where there's some fully supported standard format, Jasmin is a third party program and different JVM assemblers and disassemblers disagree on so many things. There are also some newer assemblers and disassemblers like Krakatau you could try instead. Krakatau has different syntax than Jasmin or javap.

Krakatau - Java decompiler and disassembler.

The compiler outputs bytecode in a text format, which can be assembled into .class files using the Krakatau assembler. Figuring out how to translate features like nested functions and nonlocals to JVM was pretty interesting, and having access to Java’s standard library made the whole thing much easier than expected.

Dnscat2 - Hosts communication through DNS.

dnscat2 - Tool designed to create an encrypted command and control channel over the DNS protocol, which is an effective tunnel out of almost every network.

Another commonly used tool is dnscat. I’ve seen it successfully used by adversaries and during pentests.