#import "@preview/grape-suite:2.0.0": exercise
#import exercise: project, task, subtask
#import "@preview/codly:1.3.0": *
#import "@preview/codly-languages:0.1.1": *
#show: codly-init.with()

#let task = task.with(numbering-format: (..n) => numbering("1", ..n))
#let subtask = subtask.with(markers: ("a)", "1)"))

#show: project.with(
    no: 3,
    type: "Average",
    //suffix-title: "",

    university: [HES-SO Master],
    institute: [MSE],
    seminar: [SRE],

    author: "Rémi Heredero",

    show-solutions: false,
    show-hints: false,

    task-type: [],

    date: datetime.today()
)

#task[
  What is the algorithm used to check the validity of a password?
][][
  The algorithm is in 2 parts:
  - Part 1: Lot of instructions (~30k) to calculate some constants.
  - Part 2: Use these constants to calculate each of the 12 letters of the passwords.
]

#task[
  This program relies on a specific trick. How does it work?
][][
  Most of the code is useless. Only the last instruction is useful.
  At the end, the algorithm doesn't provide directly the letters of the password, but the index on a character array.
]

#task[
  Can you recover the secret password? You must send 1 the valid password by email to pascal+sre25\@mod-p.ch before Apr. 28th, 2025, 12h00 CET to validate this lab and get 10 points.
][][
  JFuzhFSI4YShfqE7
]

#task[
  Difficulties encountered during the lab
][][
  I didn't encounter particular difficulties. I quickly identified the main function for the algorithm with Ghidra. I copy past this main function in my IDE (Zed) and change the end of the function with the code bellow to as directly the right password:

  #[
    #set text(size: 8pt)
    ```c
    pw[0] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar6 >> 0x1a];
    pw[1] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar6 >> 0x14 & 0x3f];
    pw[2] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar6 >> 0xe & 0x3f];
    pw[3] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar6 >> 8 & 0x3f];
    pw[4] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar6 >> 2 & 0x3f];
    pw[5] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[(uVar6 & 3) << 4 | uVar4 >> 0x1c];
    pw[6] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar4 >> 0x16 & 0x3f];
    pw[7] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar4 >> 0x10 & 0x3f];
    pw[8] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar4 >> 10 & 0x3f];
    pw[9] = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar4 >> 4 & 0x3f];
    pw[10]= "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar5 >> 0x1e | (uVar4 & 0xf) << 2];
    pw[11]= "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar5 >> 0x18 & 0x3f];
    pw[12]= "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar5 >> 0x12 & 0x3f];
    pw[13]= "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar5 >> 0xc & 0x3f];
    pw[14]= "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar5 >> 6 & 0x3f];
    pw[15]= "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ+-"[uVar5 & 0x3f];
    ```
  ]

  With that I only print the passowrd at then end

  #[
    #set text(size: 8pt)
    ```c
    printf("%s\n", password);
    ```
  ]

  I test it, and it's work!

]