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#808080 - Grey Code Wheel Decoder

Miscellaneous 50 pts

Challenge

  • Category: Miscellaneous
  • Points: 50 (dynamic)
  • Description: "gray code ? nah grey code" with a binary string and a web interface

Solution

The challenge presents a "Binary Wheel Decoder" web interface at http://chall.ehax.in:8076/ with:

  • A wheel cipher with 5 rings and 32 slices
  • A binary string to decode: 0010111100011010000101111111110110010010000100010111011001000110010000011111101101100111010000010101011001111110010000000111010001111110010000011

Key Insight

The wheel validation requires all 32 five-bit values to be unique. Since 2^5 = 32, this means ALL possible 5-bit combinations must appear exactly once - this is a Gray code arrangement.

Steps

  1. Generated the standard 5-bit reflected binary Gray code (32 values where adjacent values differ by 1 bit)
  2. The standard ordering validated but gave garbled text
  3. Tried all 32 rotations of the wheel - rotation 4 produced the flag