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[原创] 看雪CTF.TSRC 2018 团队赛 第五题 交响曲
2018-12-9 18:07 1251

[原创] 看雪CTF.TSRC 2018 团队赛 第五题 交响曲

2018-12-9 18:07
1251

拿到一个apk,拖到jadx里面,拿到源码。

package cn.kwaiching.crackme;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class CrackMe extends AppCompatActivity {
    int[] a = new int[]{16, 6, 7, 10, 9, 16, 10, 8, 8, 9, 6, 6};
    int[] b = new int[]{5, 10, 8, 15, 16, 15, 8, 16, 8, 16, 9, 17, 8, 17, 10, 8, 9, 18, 5, 15, 10, 9, 8, 9, 15, 18, 7, 8, 16, 6};
    int[] c = new int[]{6, 7, 18, 9, 5, 16, 9, 15, 18, 8, 9, 5};
    int[] d = new int[]{7, 7, 9, 12, 8, 7, 13, 5, 14, 5, 9, 17, 5, 7, 12, 8, 8, 6, 19, 6, 8, 16, 10, 6, 12, 9, 6, 7, 12, 5, 9, 8, 7, 8, 15, 9, 16, 8, 8, 19, 12, 6, 8, 7, 5, 15, 6, 16, 15, 7, 9, 12, 10, 7, 15, 6, 5, 14, 14, 9};
    int e;
    int f;
    int g;
    int h;
    int i;
    int j;
    int k;
    String[] l = new String[73];
    String[] m = new String[]{"23to01", "01to03", "03to05", "05to07", "07to09", "09to11", "11to13", "13to15", "15to17", "17to19", "19to21", "21to23"};
    TextView n;

    protected void onCreate(Bundle bundle) {
        super.onCreate(bundle);
        setContentView((int) R.layout.activity_fate_me);
        b();
        this.n = (TextView) findViewById(R.id.fate);
        ((Button) findViewById(R.id.ok)).setOnClickListener(new OnClickListener() {
            public void onClick(View view) {
                try {
                    CrackMe.this.a();
                } catch (Exception unused) {
                    CrackMe.this.n.setText(CrackMe.this.getString(R.string.notMe));
                }
            }
        });
    }

    private void a() {
        try {
            c();
            if (this.j == 0 || this.i == 0 || this.h == 0) {
                this.n.setText(getString(R.string.notMe));
                return;
            }
            d();
            a(((e() + f()) + g()) + h());
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
        }
    }

    private void b() {
        for (int i = 0; i <= 72; i++) {
            if (i != 34) {
                this.l[i] = getResources().getString(R.string.success00);
            } else {
                this.l[i] = getResources().getString(R.string.success34);
            }
        }
    }

    private void c() {
        try {
            String obj = ((EditText) findViewById(R.id.code)).getText().toString();
            this.j = 0;
            this.i = 0;
            this.h = 0;
            this.j = Integer.parseInt(obj.length() > 4 ? obj.substring(0, 4) : obj);
            if (this.j > 0 && this.j < 189) {
                this.j = 0;
            }
            if (this.j <= 1983 || this.j >= 2007) {
                this.j = 0;
            }
            this.i = Integer.parseInt(obj.length() > 6 ? obj.substring(4, 6) : obj);
            if (this.i < 1 || this.i > 12) {
                this.i = 0;
            }
            if (obj.length() > 8) {
                obj = obj.substring(6, 8);
            }
            this.h = Integer.parseInt(obj);
            if (this.h < 1 || this.h > 31) {
                this.h = 0;
            }
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
        }
    }

    private void d() {
        try {
            if (this.j == 1989 || this.j == 2004) {
                this.h = 31;
            }
            if (this.i == 1 || this.i == 4 || this.i == 5 || this.i == 7 || this.i == 10 || this.i == 11 || this.i == 12) {
                this.j = 1999;
            }
            if (this.j <= 1994 && (this.i == 2 || this.i == 6 || this.i == 8)) {
                this.i = 3;
            }
            if (this.j >= 1996 && (this.i == 2 || this.i == 6 || this.i == 8)) {
                this.i = 9;
            }
            if (this.j == 1995 && (this.h > this.i + 2 || this.i == this.h)) {
                this.i = 6;
            }
            this.g = this.j;
            this.f = this.i;
            this.e = this.h;
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
        }
    }

    private void a(int i) {
        if (i > 34 || i < 34) {
            this.n.setText(getString(R.string.notMe));
            return;
        }
        try {
            this.n.setText(String.format("%s%s", new Object[]{getString(R.string.me), this.l[i]}));
            ((Button) findViewById(R.id.ok)).setEnabled(false);
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
        }
    }

    private int e() {
        try {
            return this.d[(this.g - 1900) % 60];
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
            return 0;
        }
    }

    private int f() {
        try {
            return this.c[this.f - 1];
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
            return 0;
        }
    }

    private int g() {
        try {
            return this.b[this.e - 1];
        } catch (Exception unused) {
            this.n.setText(getString(R.string.notMe));
            return 0;
        }
    }

    /* JADX WARNING: Removed duplicated region for block: B:17:0x0050 A:{Catch:{ Exception -> 0x005c }} */
    private int h() {
        /*
        r6 = this;
        r0 = 2131165227; // 0x7f07002b float:1.7944665E38 double:1.0529355243E-314;
        r1 = 2131427370; // 0x7f0b002a float:1.8476354E38 double:1.05306504E-314;
        r2 = 0;
        r0 = r6.findViewById(r0);     Catch:{ Exception -> 0x005c }
        r0 = (android.widget.EditText) r0;     Catch:{ Exception -> 0x005c }
        r0 = r0.getText();     Catch:{ Exception -> 0x005c }
        r0 = r0.toString();     Catch:{ Exception -> 0x005c }
        r3 = 8;
        r4 = r0.length();     Catch:{ Exception -> 0x005c }
        r0 = r0.substring(r3, r4);     Catch:{ Exception -> 0x005c }
        r3 = r6.f;     Catch:{ Exception -> 0x005c }
        r4 = 0;
    L_0x0022:
        r5 = r6.m;     Catch:{ Exception -> 0x005c }
        r5 = r5.length;     Catch:{ Exception -> 0x005c }
        if (r4 >= r5) goto L_0x004d;
    L_0x0027:
        r5 = r6.m;     Catch:{ Exception -> 0x005c }
        r5 = r5[r4];     Catch:{ Exception -> 0x005c }
        r5 = r0.equals(r5);     Catch:{ Exception -> 0x005c }
        if (r5 == 0) goto L_0x004a;
    L_0x0031:
        r5 = 2;
        if (r3 != r5) goto L_0x0042;
    L_0x0034:
        r3 = r6.m;     Catch:{ Exception -> 0x005c }
        r5 = 6;
        r3 = r3[r5];     Catch:{ Exception -> 0x005c }
        r0 = r0.equals(r3);     Catch:{ Exception -> 0x005c }
        if (r0 == 0) goto L_0x0042;
    L_0x003f:
        r0 = 63;
        return r0;
    L_0x0042:
        r0 = r6.a;     Catch:{ Exception -> 0x005c }
        r0 = r0[r4];     Catch:{ Exception -> 0x005c }
        r6.k = r0;     Catch:{ Exception -> 0x005c }
        r0 = 1;
        goto L_0x004e;
    L_0x004a:
        r4 = r4 + 1;
        goto L_0x0022;
    L_0x004d:
        r0 = 0;
    L_0x004e:
        if (r0 != 0) goto L_0x0059;
    L_0x0050:
        r0 = r6.n;     Catch:{ Exception -> 0x005c }
        r3 = r6.getString(r1);     Catch:{ Exception -> 0x005c }
        r0.setText(r3);     Catch:{ Exception -> 0x005c }
    L_0x0059:
        r0 = r6.k;     Catch:{ Exception -> 0x005c }
        return r0;
    L_0x005c:
        r0 = r6.n;
        r1 = r6.getString(r1);
        r0.setText(r1);
        return r2;
        */
        throw new UnsupportedOperationException("Method not decompiled: cn.kwaiching.crackme.CrackMe.h():int");
    }
}

可以看到,除了h()函数外,反编译结果非常友好。

 

看起来是要求输入一个日期,对年月日、时刻进行判断,进行一些神秘处理后,执行a(((e() + f()) + g()) + h())a()的逻辑非常简单,就是判断参数是不是34。所以我们的目标就是e() + f()) + g()) + h() == 34。而这几个函数就是单纯查表,所以直接遍历所有的日期和时刻即可。

 

然后就开始复制粘贴外加一些替换和修改,得脚本如下:

a = [16, 6, 7, 10, 9, 16, 10, 8, 8, 9, 6, 6]
day_table = [5, 10, 8, 15, 16, 15, 8, 16, 8, 16, 9, 17, 8, 17, 10, 8, 9, 18, 5, 15, 10, 9, 8, 9, 15, 18, 7, 8, 16, 6]
month_table = [6, 7, 18, 9, 5, 16, 9, 15, 18, 8, 9, 5]
year_table = [7, 7, 9, 12, 8, 7, 13, 5, 14, 5, 9, 17, 5, 7, 12, 8, 8, 6, 19, 6, 8, 16, 10, 6, 12, 9, 6, 7, 12, 5, 9, 8, 7, 8, 15, 9, 16, 8, 8, 19, 12, 6, 8, 7, 5, 15, 6, 16, 15, 7, 9, 12, 10, 7, 15, 6, 5, 14, 14, 9]
tail_table = ["23to01", "01to03", "03to05", "05to07", "07to09", "09to11", "11to13", "13to15", "15to17", "17to19", "19to21", "21to23"]
def xx(year, month, day):
    if (year == 1989 or year == 2004):
        day = 31
    if (month == 1 or month == 4 or month == 5 or month == 7 or month == 10 or month == 11 or month == 12):
        year = 1999
    if (year <= 1994 and (month == 2 or month == 6 or month == 8)):
        month = 3 # <= 1994, month[2,6,8] -> 3
    if (year >= 1996 and (month == 2 or month == 6 or month == 8)):
        month = 9 # >= 1996, month[2,6,8] -> 9
    if (year == 1995 and (day > month + 2 or month == day)):
        month = 6 # == 1995 month[<day-2, day] -> 6    
    return (year, month, day)

for year in range(1984, 2007):
    for month in range(1, 13):
        for day in range(1, 32):
            for k in range(len(tail_table)):
                year_, month_, day_ = xx(year, month, day)
                #print year_, month_, day_
                try:
                    i = 0
                    i += year_table[(year_ - 1900) % 60]
                    i += month_table[month_ - 1]
                    i += day_table[day_ - 1]
                    if month_ != 2:
                        i += a[k]
                    else:
                        if k != 6:
                            i += a[k]
                    #print i,
                    if i == 34:
                        print year, month, day, tail_table[k]
                except:
                    pass

运行后给出结果1995 2 3 05to07,所以答案是1995020305to07


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最后于 2018-12-9 18:09 被diycode编辑 ,原因:
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