CRACK Solution

AA Scramble

CRACK single-key XOR 0xAA cipher

In-game screenshot of AA Scramble
In-game view
FamilyCRACK Graph0.239 DifficultyEasy Ring02 IDllama_xor_aa

Prerequisites

TONE BURSTROTARY DECODE

Unlocks

DOTTED RAMP

Accepted input BYTE
Techniquesingle-key XOR 0xAA cipher Rulenonzero SampleBYTE

Walkthrough

Recover the accepted input below, then submit it to the CRACK verifier.

Reject Samples

  • BYT
  • BYTES
  • byte
  • CYTE
Verifier Listing 
; llama_xor_aa: single-key XOR with 0xAA (10101010, alternating bits). Each
; input byte is XORed with 0xAA and compared to a stored target. XOR is self-
; inverse. Technique: single-key XOR with 0xAA. r0 = 1 on accept. Accept: nonzero.
;
; targets = 0xE8 0xF3 0xFE 0xEF  (after ^0xAA)  ->  password "BYTE".

        len   r1
        cmp   r1, 4
        jnz   bad           ; exactly 4 bytes

        mov   r7, 0
        ldb   r0, [r7]
        xor   r0, 0xaa
        cmp   r0, 0xe8
        jnz   bad
        inc   r7
        ldb   r0, [r7]
        xor   r0, 0xaa
        cmp   r0, 0xf3
        jnz   bad
        inc   r7
        ldb   r0, [r7]
        xor   r0, 0xaa
        cmp   r0, 0xfe
        jnz   bad
        inc   r7
        ldb   r0, [r7]
        xor   r0, 0xaa
        cmp   r0, 0xef
        jnz   bad

        mov   r0, 1
        ret
bad:    mov   r0, 0
        ret