CSCBE ‐ Complex Encodings Challenge

Complex encoding(s)

Somebody gave me this piece of data and warned me it has multiple layers of encoding. Can you figure out how to decode it ? Apparently, not every decoding tool can do it...

1Oh6axLwfecHErbVpRbtNj8t5JACsSQrofdnnMdQtBmoU8cQj6EyLcVRsQLz1MyWfXbqQDIc9wGy
yBuH7uV95lBVpFGn3syGIw0IVLx8wJr4ABsIH9Q71hBH4AvIgljx7XnfjfmafahBNrPMDkK3dsJF
0r41nzyMnOf7l36NcllAOgRLoB6Qh0APotZu6plYpkSiRCAkDKowOFm0mybKp336TAJe4JiDecD9
hNbl5fBDLkGNYhmSkzOQzLBH1aPumW4o

Hints

1. Basically, the first stage is not what it seems...
2. For the 3rd stage, random bytes could simply be compressed data, no ?
3. The 4th stage has something to do with the Bitcoin.
4. For the last stage, characters may be in the wrong order...

Explanation

This piece of data is made with codext using the following command:

$ echo -en 'CSC{mult1pl3_l4y3rs_m4k3s_1t_h4rd3r!}' | codext encode hex reverse base58 gzip uu base62

A few traps per stage:

1. The first stage could be mistakenly interpreted as Base64 while it is Base62, hence Hint 1.
2. From what I've seen, CyberChef does not handle UU-encoding. However, this step is straighforward when using a search engine.
3. For the next stage, here is where it becomes complex. The next stage with Gzip looks random and far harder to figure out, hence Hint 2.
4. This stage can be visually guessed by figuring out it is a base and trying multiple BaseX out. Hint 3 narrows the scope to Base58 Bitcoin.
5. The fifth stage is a trap just before the very last step. Decoding it as hex (or Base16) will give garbage, hence Hint 4.
6. No trap here, the last stage is a simple hex transformation.

Solution

The whole challenge can be solved with CodExt.

Per stage:

1. This can for instance be found using CyberChef and trying multiple bases and then recognizing the word "begin" which is the starting word for the next stage.
2. This should be solved by Googling, figuring out that it is UU-encode then using an online decoder or eventually using another tool like Ciphey.
3. As the data looks random from here, a guessing tool should do the trick.
4. The characters set doesn't let many solutions, unless we dive into trying to solve it with statistical analysis and substitutions, a Base should be one of the first guesses. The guess mode of CodExt can be used from here to find the final solution, requiring to read the documentation in order to know how to tune AI algorithm's parameters.
5. If the fourth stage was guessed manually, once again, the guess mode of a decoding tool supporting this can easily find the suite of encodings "reverse" and "hex".
6. The last step is straightforward ; we can decode as hex and it gives the flag.

$ cat input | codext decode base62 uu gzip base58 reverse hex

Flag: CSC{mult1pl3_l4y3rs_m4k3s_1t_h4rd3r!}