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MITMH2022
Public Access

Solution to Please Prove You Are Human

Noirleans

Answer: PHOTOSHOOT
by James Sugrono

Solvers are presented with a number of CAPTCHAs, each with an audio "CAPTCHA", which they need to solve in order to proceed. Though some CAPTCHAs function correctly, solvers encounter a number of CAPTCHAs where attempting to select the named objects does not allow them to proceed.

To solve the puzzle, solvers need to figure out that some CAPTCHAs are "broken" in a specific way, and then in those cases select images matching the alternate rule.

PromptRule (if broken)Actual prompt (if broken)Audio
LAKESierra
ISLANDQuebec
BECUNAROT13ORPHANUniform
SHELLAlfa
BEZOARChange all vowels to ABAZAARRomeo
TABLEEcho
EGGMike
AGLETPrepend EEAGLETEcho
NOTEBOOKTango
TRAPRomeo
IRONSANDmove last three letters to the frontANDIRONSOscar
WOLFreverse order of lettersFLOWNovember
ORGANBravo
BONEAlfa
PANSpanish to EnglishBREADYankee
RABBITAlfa
RANGEPrepend OORANGENovember
SWORDReplace a sword with a penPENCharlie
OCTOPUSAlfa
FIREReplace words with oppositesICEFoxtrot
KNIFEEcho
ENVELOPECharlie
RUTUT to OOTROOTLima
WORMWOODSwap first and second half of wordWOODWORMIndia
NEEDLEMike
WRITINGPartial replacement with GreekGRAPHINGBravo
SCREWSierra

The first letters of the "working" CAPTCHAs spell LISTENTOBROKENS. The letters spelled by the broken CAPTCHA audio gives the seemingly nonsensical string UREONYNCFLIB, which needs to be transformed using each of the broken steps again.

Captcha #RuleResulting string
UREONYNCFLIB
ORPHANROT13HERBALAPSYVO
BAZAARChange all vowels to AHARBALAPSYVA
EAGLETPrepend EEHARBALAPSYVA
ANDIRONSmove last three letters to the frontYVAEHARBALAPS
FLOWreverse order of lettersSPALABRAHEAVY
BREADSPANISH > ENGLISHSWORDHEAVY
ORANGEPrepend OOSWORDHEAVY
PENReplace SWORD with PENOPENHEAVY
ICEReplace words with oppositesSHUTLIGHT
ROOTReplace UT with OOTSHOOTLIGHT
WOODWORMSwap first and second half of wordLIGHTSHOOT
GRAPHINGPartial replacement with GreekPHOTOSHOOT

Applying the rules in order as shown above, yields the answer PHOTOSHOOT.

Author’s Notes

Doesn’t everyone love CAPTCHAs? No? Well, me neither.

However, this still seemed like a fun idea for a different puzzle, and it started off being much more straightforward and without the audio component — the ROT13 prompt was also just NAG/ANT, which was much easier.

In deploying this to production, we identified a number of bugs and potential enhancements which maybe remediated and implemented in PPYAHv2 (rePPYAH).