cryptography - Decoding Base64-URL Ciphertext to Retrieve Expected Flag Format - Stack Overflow

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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!

本文标签： cryptographyDecoding Base64URL Ciphertext to Retrieve Expected Flag FormatStack Overflow