Dizzy
This is a writeup of the crypto challenge Dizzy from the TFC CTF
Points: 50
Premise
Embark on ‘Dizzy’, a carousel ride through cryptography! This warmup challenge spins you around the basics of ciphers and keys. Sharpen your mind, find the flag, and remember - in crypto, it’s fun to get a little dizzy!
T4 l16 _36 510 _27 s26 _11 320 414 {6 }39 C2 T0 m28 317 y35 d31 F1 m22 g19 d38 z34 423 l15 329 c12 ;37 19 h13 _30 F5 t7 C3 325 z33 _21 h8 n18 132 k24
Challenge chiphertext:
T4 l16 _36 510 _27 s26 _11 320 414 {6 }39 C2 T0 m28 317 y35 d31 F1 m22 g19 d38 z34 423 l15 329 c12 ;37 19 h13 _30 F5 t7 C3 325 z33 _21 h8 n18 132 k24
Observations
We can attempt to identify what cipher is used with the cipher identifier from dcode.fr, which gives us letters positions as its top result.
Solution
When decoding the ciphertext in the letters positionsdecoder, we get the following result:
TFCCTF{th_chllng_mks_m_dzzy_;d}, which looks like a flag, but its not a complete one.
The cipher we have is one were a characters position in the string comes directly after the letter.
As we can see, the string we have doesnt contain any number, but as we can see from the following entries in the ciphertext 510 320 414 317 423 329 19 325 132, we can see that we’re missing a 5 in position 10, 3 in position 20 and so on.
Placing these numbers into the partial flag found earlier gives us the actual flag:
TFCCTF{th15_ch4ll3ng3_m4k3s_m3_d1zzy_;d}