Broken Signals Zeroed PNG signature

forensics
flag hiCTF{h34d3r_r3p41r_m4st3r}

Category: forensics / file repair · Artifact: extracted/broken_signal.dat

Hint

"…it appears corrupted. The file cannot be opened by any standard application. Something is wrong with the file itself - can you repair it…?"

Solve

file says data, but the structure is a PNG with a damaged header: the 4-byte PNG signature has been zeroed out while the rest (chunk lengths, IHDR, CRCs) is intact.

bash 
1xxd broken_signal.dat | head -1
2# 00000000: 0000 0000 0d0a 1a0a 0000 000d 4948 4452  ............IHDR
3
4python3 - <<'EOF'
5d = bytearray(open('broken_signal.dat','rb').read())
6d[0:4] = b'\x89PNG'                 # restore the PNG magic
7open('fixed.png','wb').write(d)
8EOF

Open fixed.png (400x300, 16-bit RGBA). The image itself renders the answer:

output 
SIGNAL  INTERCEPTED
hiCTF{h34d3r_r3p41r_m4st3r}

The repaired PNG, reading SIGNAL INTERCEPTED with the flag underneath

Flag

output 
hiCTF{h34d3r_r3p41r_m4st3r}