re-java

Use CFR with the command java -jar cfr.jar app.jar --outputdir cfr_out/ to decompile an entire jar into Java source. JD-GUI provides a GUI alternative where you open the jar and use File > Save All Sources to export.

CFR handles lambdas and modern bytecode better and runs from the command line, while JD-GUI works well for older code with a graphical browser. Cross-validate critical classes with both since no decompiler produces perfectly accurate output.

ProGuard renames classes and methods to a/b/c, so start from plaintext strings: grep for URLs or prompt messages in the decompiled output, find the classes referencing them, and trace the call chain to recover semantics.

The class file's major version is higher than your installed JDK supports. Compute the target Java version as major minus 44 (e.g., 61 = Java 17), then install a matching or newer JDK to run javap.

No, Android DEX bytecode is handled by the re-apk skill. Once DEX is converted to jar format, this skill's CFR/JD-GUI decompilation workflow applies to the resulting classes.

Locate the StringEncryptor decryption class and its key/algorithm statically, then replicate it in Python to batch-decrypt strings. If static analysis stalls, run the sample in a sandbox and use JDB eval or Frida to capture decrypted plaintext at runtime.