NDIAS 2026 - Real KeeLoq Garage: Next HOP

Challenge Overview

Category: Keyfob Files: capture_c7c8.bin, memo_c7c8.txt Flag format: flag{FRAMEHEX}

Reuse the DeviceKey from Normal Learn to predict the next valid logical OPEN frame.

1. Inputs

• DeviceKey = 0xBF61DA58FE545128
• SERIAL = 0x107A4C3D
• Last observed hop (press 4) = 0x13472C1C
• Last decrypted plaintext = 0x103D 0043 → counter = 0x0043, DISC = 0x103D

2. Wire vs Logical Frame

The wire frame is 90 bits at a 250 µs Manchester chip period:

bits[ 0..15]  preamble 1010_1010_1010_1010 (= AA AA)
bits[16..23]  sync     0xD5
bits[24..55]  HOP (32 bits, MSB-first)
bits[56..57]  status   "00" (VLOW=0, RPT=0)
bits[58..89]  SERIAL   0x107A4C3D (32 bits, MSB-first)

The challenge asks for the logical frame, not the raw wire bits — so the 2 inter-field status bits are not part of the answer. The logical frame is just the meaningful fields concatenated:

preamble | sync | HOP | SERIAL
=
AA AA | D5 | hh hh hh hh | 10 7A 4C 3D

That’s 11 bytes total.

3. Prediction

Increment the counter, keep DISC and BTN the same:

plaintext_next = 0x103D 0044
hop_next       = KeeLoq_encrypt(0x103D0044, 0xBF61DA58FE545128)
               = 0x2675F6FA

So the predicted logical frame is:

AA AA D5 | 26 75 F6 FA | 10 7A 4C 3D

Flag

flag{AAAAD52675F6FA107A4C3D}