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2024 | MoveCTF

EasyGame

#move

题目

easy_game.move 
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module movectf::easy_game {
    use std::vector;
    use sui::math;
    use sui::transfer;
    use sui::tx_context::TxContext;
    use sui::object::{Self,UID};
    use sui::event;

    struct Challenge has key, store {
        id: UID,
        initial_part: vector<u64>, 
        target_amount: u64, 
    }

    struct Flag has copy, drop {
        user: address,
        flag: bool
    }

    fun init( ctx: &mut sui::tx_context::TxContext) {
        let initial_part = vector::empty<u64>();
        vector::push_back(&mut initial_part, 1);
        vector::push_back(&mut initial_part, 2);
        vector::push_back(&mut initial_part, 4);
        vector::push_back(&mut initial_part, 5);
        vector::push_back(&mut initial_part, 1);
        vector::push_back(&mut initial_part, 3);
        vector::push_back(&mut initial_part, 6);
        vector::push_back(&mut initial_part, 7);

        let challenge = Challenge {
            id: object::new(ctx),
            initial_part: initial_part,
            target_amount: 22,
        };
        transfer::share_object(challenge);

    }

    public fun submit_solution(user_input: vector<u64>,rc: &mut Challenge,ctx: &mut TxContext ){
        let sender = sui::tx_context::sender(ctx);

        let houses = rc.initial_part;
        vector::append(&mut houses, user_input);

        let amount_robbed = rob(&houses);

        let result = amount_robbed == rc.target_amount;
        if  (result) {
            event::emit(Flag { user: sender, flag: true });
        };
    }
    public fun rob(houses: &vector<u64>):u64{
        let n = vector::length(houses);
        if (n ==0){
            0;
        };
        let v = vector::empty<u64>();
        vector::push_back(&mut v, *vector::borrow(houses, 0));
        if (n>1){
            vector::push_back(&mut v, math::max(*vector::borrow(houses, 0), *vector::borrow(houses, 1)));
        };
        let i = 2;
        while (i < n) {
            let dp_i_1 = *vector::borrow(&v, i - 1);
            let dp_i_2_plus_house = *vector::borrow(&v, i - 2) + *vector::borrow(houses, i);
            vector::push_back(&mut v, math::max(dp_i_1, dp_i_2_plus_house));
            i = i + 1;
        }
        ;
        *vector::borrow(&v, n - 1)
    }
}
Move.toml 
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[package]
name = "easy_game"
version = "0.0.1"

[dependencies]
Sui = { git = "https://github.com/MystenLabs/sui.git", subdir = "crates/sui-framework/packages/sui-framework", rev = "framework/testnet" }

[addresses]
movectf =  "0x0"
sui =  "0x0000000000000000000000000000000000000002"

解题思路

  • 为触发 Flag 事件需要 amount_robbed 为 \(22\)，即 rob() 的返回值

  • 对于给定的数组 houses，rob() 将新建数组 v 并添加元素 houses[0] 和 max(houses[0], houses[1])。随后依次计算 max(v[i-1], v[i-2] + houses[i]) (2 <= i < n) 并加入到数组 v 中，最终返回数组 v 的最后一个值

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    public fun rob(houses: &vector<u64>):u64{
    let n = vector::length(houses);
    if (n == 0) {
        0;
    };
    let v = vector::empty<u64>();
    vector::push_back(&mut v, *vector::borrow(houses, 0));
    if (n > 1) {
        vector::push_back(&mut v, math::max(*vector::borrow(houses, 0), *vector::borrow(houses, 1)));
    };
    let i = 2;
    while (i < n) {
        let dp_i_1 = *vector::borrow(&v, i - 1);
        let dp_i_2_plus_house = *vector::borrow(&v, i - 2) + *vector::borrow(houses, i);
        vector::push_back(&mut v, math::max(dp_i_1, dp_i_2_plus_house));
        i = i + 1;
    };
    *vector::borrow(&v, n - 1)
}

  • 根据 init()，houses 数组为 [1, 2, 4, 5, 1, 3, 6, 7, user_input]，可以推出数组 v 需要满足 [1, 2, 5, 7, 7, 10, 13, 17, 22]，由此可知 user_input 为 \(22-13=9\)

Exploitation

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$ sui client tx-block <digest>    # get Challenge objectID
$ sui client call --function submit_solution --args [9] <objectId> --module easy_game --package <packageId> --gas-budget 300000000

Flag

flag{yUH6yansnMpi}_EasyGame

最后更新: 2024年3月9日 00:20:22
Contributors: YanhuiJessica

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