Example: Try to find T such that X as a 6-digit string (pad with leading zeros) has digit sum 24. We can brute over possible T (0..2359) and compute X, then pad to 6 digits, sum digits.
adb install apktime-graveyard-pin.apk Running the app shows a gothic-themed screen with a graveyard image and a PIN entry field. No source code is provided — only the APK. 3.1 Decompilation with jadx jadx -d output apktime-graveyard-pin.apk Open output/sources/com/ctf/graveyardpin/ – the main activity is MainActivity.java . apk time graveyard pin
return (pinInt ^ timeInt) == 0xDEADBEEF; // Wait — this is suspicious } Example: Try to find T such that X
pin ^ time = 0xCA7 (within low 16 bits) => pin = time ^ 0xCA7 But pin must be 6 digits (100000 to 999999) and digits sum to 24. Suppose current time = 14:45 → timeInt = 1445 . No source code is provided — only the APK
Pseudo-code:
current_time = <current HHMM> pin = (current_time ^ 0xCA7) % 1000000 Enter as 6-digit with leading zeros. Example at 12:34:
(X ^ T) & 0xFFFF = 0xCA7 => X ^ T = 0xCA7 (mod 65536) => X = T ^ 0xCA7 (mod 65536) So X is between 0 and 65535, but we need a 6-digit decimal representation with digit sum 24.