Code Investigation Lab

Programming FoundationsLab 3 of 390–120 minutesLab included

Hands-on lab

Mission

Investigate an unfamiliar C source file, recover the accepted candidate, and explain every transformation without using a debugger or disassembler.

Download code-investigation-v1.0.0.tar. Expected SHA-256:

fcb574aa0878e046bbeb06aedfa13e28a59e8c9354d3acfddbf73df82ba38098

Verify, extract into ~/underdunn-labs/code-investigation, and enter the version directory. Before compiling, map main, the input boundary, accepts, the length check, loop, transformation, outputs, and exit statuses.

Compile and test only after recording predictions:

gcc -Wall -Wextra -Wpedantic -o investigate investigate.c
./investigate test
printf 'exit=%s\n' "$?"

The comparison XORs each candidate byte with one constant. XOR reverses itself, so apply the same constant to each stored byte and interpret the result as ASCII. Confirm the recovered candidate at runtime.

Replace its punctuation separator with an underscore and construct UNDERDUNN{first_second}. Expected flag hash:

d4da97fe320d060566ee1f2e956f60ad703ef90e6ae7a7b9cdd9df76c96c4249

Your evidence log must include the control-flow map, encoded bytes, inverse transformation, successful output, and exit status. Reset by re-extracting the verified archive.