tsundere (160 pts)

Problem

Solution

1. Reverse some of the bytecode manually to try and figure out what its doing.
2. The flag text must consist of only lowercase acsii characters and numbers.
3. The regex splits up the flag string into chunks of 4 characters. It calls the routine1 function on each chunk of 5 characters, and concatenates the results, checking if the final result is equal to the String TODO - Put right string here
4. Guess that the routine1 function is a hashing function. It contains a sin/cos call, 4 "secret" numbers, and a bit rotateLeft call, so we guess that it is md5, based on this source code for md5 in java.
5. Split the final string into chunks of 32 characters, and brute force md5 hashes of chunks of 5 lowercase characters and numbers, to reverse each hash. We can easily plug the hashes into hashkiller for the individual hashes, which we concatenate into the flag.

Flag

tjctf{j4hbjllsqyndjonfn6czn40f322p2ttgvbtg1m9pi33o8gmu368dkzpk7nldb8ztcdi3nb6ovjtawtovmmna2a67rjjoz6oun1if}