The scene
Harbour Festival · Accreditation deskThe ticket office received a false instruction to close the accreditation queue. The message came from one of three internal terminals and carried a code identifying its sender.
The system conceals that code with two transformations, always the same and always in the same order. The printed record is enough to reverse them if you remember to undo the last operation first.
What we know for certain
One of these people sent the instruction from their assigned terminal. There was no shared access, printing error or manual alteration. The codes have four letters, and the system uses only the transformation rules described.
The three accounts
Núria Font
Visitor coordinator«My terminal's original code is ABCA.»
Ivo Gil
Group coordinator«My terminal uses CABA; at first glance, it looks like some of the others.»
Rocío Mas
Ticket coordinator«Mine has the code BACB. I did not share my access.»
Examine the evidence
0 of 5 openedOpening these five clues does not cost points.
01The received strip
The false instruction arrived marked with the printed code BCBA, in that exact order. The complete four-letter strip was kept.
02The first transformation
The system simultaneously replaces each letter using this cycle: A becomes B, B becomes C and C becomes A. Each letter is replaced exactly once.
03The second transformation
After replacing all four letters, it reverses their entire order: the last becomes first, the next-to-last becomes second, and so on.
04The original codes
The terminal directory lists ABCA for Núria, CABA for Ivo and BACB for Rocío. These are different codes and have not changed that week.
05The single output
Every message retains its own terminal's code. The ticket office does not transform the strip again and receives no codes from terminals other than these three.