you have raw bytes: how to understand the used lossless algorithm?

[DiTBho]

Code: [Select]

.                        _____
  hidden source --------|     |            __________
                        |     |           |          |
                        | mux |-------- x | blackbox | y ------
                        |     |           | y = f(x) |
external source --------|_____|           |__________|
                                              ^
                                              |
                                            compress level
                                            value {1 .. 5}

ummm, it looks like I set the mux incorrectly, so the blackbox ignored the external source and processed the hidden source but, this time, no compression. I have to recreate the packet sequence for this, because it is very interesting and it is the first time that it emits something uncompressed.

Anyway, I issued an hardware reset, set the mux to the external source, and captured the compressed packet.

This time it should be right.

 image.tar (15.12 kB - downloaded 47 times.)

[DiTBho]

@Mechatrommer
which program are you using to decode pictures?
here I have implemented a very wild program for x11

Code: [Select]

    for (y = 0; y < ysize; y++)
    {
        for (x = 0; x < xsize; x++)
        {
            if (i < data_size)
            {
                R = data[i + 0];
                G = data[i + 1];
                B = data[i + 2];
            }
            else
            {
                R = 0;
                G = 0;
                B = 0;
            }

            x11_point_color(R, G, B);
            x11_point_draw(x, y);

            i += 3;
        }
    }


[golden_labels]

Wait, do you have something to see a decoded image? If yes, just introduce modifications. Flip a bit or increment some octet and see what happens.

As for the theoretical part: with zero knowledge about the content of the message and the encoding mechanism, you can never decode it. That is because you have no way of discerning valid decodings. Which is why one-time-pad is provably unbreakable encryption even if you could bruteforce all possible keys. Same goes for single blocks of many block ciphers.

IMO communicating with extraterrestial species would be much worse than just trouble with encoding. If both sides had the same goals while designing the communication methods, both would probably end up with something recognizable to the other side. The true obstacle may be of different nature. No concepts shared. Humans love to model ETs as “just an exotic civilization”, but in reality they may have been shaped to use concepts completely unfamiliar to humans. Make a simple thought experiment that doesn’t even require involving other planets. How would you talk with ants or trees, given you had a chance to do so? You may argue they are not complex enough and sure I do not ask about having a debate on philosophy with a nearby ant hill. But if you consider them horribly dense and only want to communicate simple things… you still can’t. Their and your pereception of everything is just too different to share any kind of information.

[Mechatrommer]

Hollywood makes first contact with aliens a breeze, but it's not.

because most aliens there speak english, and with decades of mixed culture, you can quickly tell if raising a hand is a hi or an insult watching too much "Marvel" grade movies is not good for your cryptanalyst's health, even experts will stuggle on others' creations in reality... if you want to watch movies instead of learning most decoding (encryption and compression) schemes in real life and try to invent one yourself, may i suggest  history movies such as Midway(2019) or The Imitation Game(2014). cheers

@Mechatrommer
which program are you using to decode pictures?

its my diy tool i made a while ago to extract plain image resources from some apps, it supports simple pixel and width padding and non 8-bit aligned data. also can be used to see data compressibility or randomness (information's entropy) in visual color form...

[DiTBho]

what do you think, guys, about the last binary image (compression level 5) I uploaded?

I captured a document that mentions "AVI", which somehow gives more clues.
However AVI is only a container, which can use:
- MPEG-1
- MPEG-2
- MPEG-4
- WMV
- RealVideo
- Theora
- Flash

OMG 

[Mechatrommer]

I captured a document that mentions "AVI", which somehow gives more clues.
However AVI is only a container, which can use:
- MPEG-1
- MPEG-2
- MPEG-4
- WMV
- RealVideo
- Theora
- Flash

OMG 

thats life. avi is an old format that has seen many new compression schemes coming in... backward compatibility has to be preserved.

[DiTBho]

I am trying with lz77&C compression-algorithms 

[Mechatrommer]

I am trying with lz77&C compression-algorithms 

i suggest start in chronological order, such as RLE and then huffman encoding and to more advanced dictionary based with tree traversing etc etc... so you can understand why things happened as it happened. its a long story cant easily being told in a single forum. good luck!

[DiTBho]

i suggest start in chronological order, such as RLE and then huffman encoding and to more advanced dictionary based with tree traversing etc etc... so you can understand why things happened as it happened. its a long story cant easily being told in a single forum. good luck!

eheh, and it will be a solid-rock learning experience this way!

Good idea! Thanks