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I'm working on a challenge where I was given an encoded string:

VFRJZ2NuM2ROZU1fTFNNQ0Z6R0Bfbk8xR2RwTlMwX2hfdUJSb19JM31Ve1ozZF8zXzdORWZu

I know this is Base64-URL encoded because it contains characters like _ instead of /.

I get this result when I decode it:

TTIgcn3dNeM_LSMCFzG@_nO1GdpNS0_h_uBRo_I3}U{Z3d_3_7NEfn

However, I was expecting a flag in the format:

TMUCTF{...}

It's clear that the Base64 decoding is just the first step, and there seems to be another layer of encoding or encryption.

I've tried checking for common patterns like:

XOR with a key ROT or Caesar ciphers Re-encoding with another base (Base85, hex, etc.) But I haven’t been able to figure out the correct approach.

Could anyone provide insights into:

How to identify the next step in decoding? What tools or techniques are commonly used in such scenarios to retrieve the expected flag format? Any guidance or suggestions would be greatly appreciated!

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    Just by eyeball, it appears that the characters are what you'd expect in a leet-encoded flag message, it's even got the '{}' characters inside of which the flag would be. However, the position of the characters has been scrambled. Perhaps there is a clue to this position scrambling elsewhere in the CTF problem or in a previous CTF problem if this is part of group. Otherwise, you can try various tricks, like writing the string of characters as a matrix of various widths, and take a look at it and see if something pops out. Commented Jan 9 at 14:10
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