Archived Challenges - December 2025

Submit the flag

ictf{has_it_really_been_5_years?}

If you are in the discord server, enable developer mode → copy server ID → Discord snowflake decoder → get Unix timestamp. Alternatively, search for the discord server on https://discord.com/servers → https://discord.com/servers/imaginaryctf-732308165265326080 → the snowflake ID is the numerical part → Decode → get Unix timestamp.

ictf{1594666272}

The key is between 0 and 23, try all of them and decrypt (subtract first, then XOR). The correct key is 23

ictf{23_days_till_Christmas!}

if you combine vigenere ciphers of different lengths you just get another vigenere cipher whose length is just the lcm of the input lengths

ictf{if_terra_hadnt_blocked_croix_du_nord_he_wouldve_won_totally_not_cope}

just brute force the key for each block going in reverse order, you'll know you have the right key because it will fully decrypt that block of the flag which is plain english

ictf{couldve_just_been_an_equinox_victim_but_bro_just_keeps_winning_now_that_his_rivals_retired}

by author request writeup will be posted next month

ictf{https://www.youtube.com/watch?v=CQXPc-O82Dc}

caesar cipher along the diagonal, should be findable since only the diagonal has any special characters

ictf{she_was_also_one_of_the_greatest_broodmares_in_jra_history}

file has some hidden binary data encoded as 50ms pulses at 11.9 kHz, use ffts to recover them, or if you're very fancy you can look into goertzels algorithm

ictf{she_produced_3_g1_winning_children}

Find the image source, https://idolhorse.com/wp-content/uploads/2024/07/SodashiWW.jpg , since you know the blur parameters and font you can just go character by character in the flag to compare outputs, whichever minimizes the difference between them is the correct character

ictf{this_horse_is_kinda_majestic_frfr}