静态分析java层

2014 ASIS Cyber Security Contest Finals Numdroid

逆向分析

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ArrayTools.each_with_index(buttons, new EachIndexAction<Integer>() { // from class: io.asis.ctf2014.numdriod.MainActivity.1
        @Override // io.asis.ctf2014.numdriod.tools.EachIndexAction
            public void action(final int i, Integer element) {
            ((Button) MainActivity.this.findViewById(element.intValue())).setOnClickListener(new View.OnClickListener() { // from class: io.asis.ctf2014.numdriod.MainActivity.1.1
                @Override // android.view.View.OnClickListener
                    public void onClick(View arg0) {
                    MainActivity.this.clicked(i);
                }
            });
        }
    });
    this.mScreen = (EditText) findViewById(R.id.editText1);
    this.mScreen.setEnabled(false);
    this.mOk = (ImageButton) findViewById(R.id.ok);
    this.mDel = (ImageButton) findViewById(R.id.del);
    this.mOk.setOnClickListener(new View.OnClickListener() { // from class: io.asis.ctf2014.numdriod.MainActivity.2
        @Override // android.view.View.OnClickListener
            public void onClick(View arg0) {
            MainActivity.this.ok_clicked();
        }
    });
    this.mDel.setOnClickListener(new View.OnClickListener() { // from class: io.asis.ctf2014.numdriod.MainActivity.3
        @Override // android.view.View.OnClickListener
            public void onClick(View arg0) {
            MainActivity.this.del_clicked();
        }
    });
}

首先遍历按钮数组，并进行初始化和设置点击事件 MainActivity.this.clicked(i);
然后对OK和del按钮进行初始化并设置点击事件分别为 MainActivity.this.ok_clicked(); 和 MainActivity.this.del_clicked();

public void clicked(int i) {
    DebugTools.log("number: " + i);
    this.mScreen.setText(this.mScreen.getText().append((CharSequence) Integer.toString(i)));
    DebugTools.log("current Pass: " + ((Object) this.mScreen.getText()));
}

点击按钮时候会先log记录下来，然后再将数字转为String显示到屏幕上，然后再log记录下当前的passwd

protected void ok_clicked() {
    DebugTools.log("clicked password: " + ((Object) this.mScreen.getText()));
    boolean result = Verify.isOk(this, this.mScreen.getText().toString());
    DebugTools.log("password is Ok? : " + result);
    if (result) {
        Intent i = new Intent(this, (Class<?>) LipSum.class);
        Bundle b = new Bundle();
        b.putString("flag", this.mScreen.getText().toString().substring(0, 7));
        i.putExtras(b);
        startActivity(i);
        return;
    }
    Toast.makeText(this, R.string.wrong, 1).show();
    this.mScreen.setText("");
}

点击OK按钮，会先log记录当前的passwd，然后通过Verify.isOk对其进行check，如果密码正确会进入到分支，然后会把flag放到屏幕上，显然这就是胜利条件了

第一个idea，对isOk进行hook，测试之后发现，他的flag是md5的密码，显然偷鸡失败（/(ㄒoㄒ)/~~

那么就要研究isOk函数的逻辑：

public static boolean isOk(Context c, String _password) {
    String password = _password;
    if (_password.length() > 7) {
        password = _password.substring(0, 7); // 只取前7个数字
    }
    String r = OneWayFunction(password);
    DebugTools.log("digest: " + password + " => " + r);
    return r.equals("be790d865f2cea9645b3f79c0342df7e");
}

password只取前7个数字进OneWayFunction函数，之后将其返回的值与一个hash进行比对

private static String OneWayFunction(final String password) {
    String[] hashes = {"MD2", "MD5", "SHA-1", "SHA-256", "SHA-384", "SHA-512"};
    List<byte[]> bytes = ArrayTools.map(ArrayTools.select(ArrayTools.map(hashes, new MapAction<String, byte[]>() { // from class: io.asis.ctf2014.numdriod.Verify.1
        @Override // io.asis.ctf2014.numdriod.tools.MapAction
            public byte[] action(String element) {
            try {
                MessageDigest digest = MessageDigest.getInstance(element);
                digest.update(password.getBytes());
                return digest.digest();
            } catch (NoSuchAlgorithmException e) {
                return null;
            }
        }
    }), new SelectAction<byte[]>() { // from class: io.asis.ctf2014.numdriod.Verify.2
        @Override // io.asis.ctf2014.numdriod.tools.SelectAction
            public boolean action(byte[] element) {
            return element != null;
        }
    }), new MapAction<byte[], byte[]>() { // from class: io.asis.ctf2014.numdriod.Verify.3
        @Override // io.asis.ctf2014.numdriod.tools.MapAction
            public byte[] action(byte[] element) {
            byte[] b = new byte[8];
            for (int i = 0; i < b.length / 2; i++) {
                b[i] = element[i];
            }
            for (int i2 = 0; i2 < b.length / 2; i2++) {
                b[(b.length / 2) + i2] = element[(element.length - i2) - 2];
            }
            return b;
        }
    });
    byte[] b2 = new byte[bytes.size() * 8];
    for (int i = 0; i < b2.length; i++) {
        b2[i] = bytes.get(i % bytes.size())[i / bytes.size()];
    }
    try {
        MessageDigest digest = MessageDigest.getInstance("MD5");
        digest.update(b2);
        byte[] messageDigest = digest.digest();
        StringBuilder hexString = new StringBuilder();
        for (byte aMessageDigest : messageDigest) {
            String h = Integer.toHexString(aMessageDigest & 255);
            while (h.length() < 2) {
                h = "0" + h;
            }
            hexString.append(h);
        }
        return hexString.toString();
    } catch (NoSuchAlgorithmException e) {
        return "";
    }
}

发现hash基本都是单向的，发现如果只是爆破的话只有10^7的大小，感觉可以尝试

方案1：

网上师傅的方案：

.line 26
  :cond_0
  const/4 v0, 0x0

  .local v0, "i":I
  :goto_0
  const v2, 0x98967f

  if-lt v0, v2, :cond_1

  .line 38
  return-void

  .line 28
  :cond_1
  invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;

  move-result-object v2

  invoke-static {v2}, Lcom/example/forloop/MainActivity;->isOk(Ljava/lang/String;)Z

  move-result v1

  .line 29
  .local v1, "ok":Z
  const v2, 0x186a0

  rem-int v2, v0, v2

  if-nez v2, :cond_2

  .line 31
  invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;

  move-result-object v2

  invoke-virtual {p0, v2}, Lcom/example/forloop/MainActivity;->log(Ljava/lang/String;)V

  .line 33
  :cond_2
  if-eqz v1, :cond_3

  .line 35
  invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;

  move-result-object v2

  invoke-virtual {p0, v2}, Lcom/example/forloop/MainActivity;->log(Ljava/lang/String;)V

  .line 26
  :cond_3
  add-int/lit8 v0, v0, 0x1

  goto :goto_0

:cond_0
const/4 v0, 0x0

.local v0, "i":I
:goto_0

这里首先初始化v0=0，然后初始化循环器i（存储在v0中）

1 2	const v2, 0x98967f # 加载最大值 9,999,999 (0x98967F) if-lt v0, v2, :cond_1 # 如果 i >= 9,999,999，跳转到 :cond_1（退出循环）

if v0 less than v2（即v0<v2）就会跳转到cond_1

invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;
move-result-object v2     # 将 i 转为字符串
invoke-static {v2}, Lcom/example/forloop/MainActivity;->isOk(Ljava/lang/String;)Z
move-result v1            # 调用 isOk() 并存储结果到 v1(ok)

v0转换为字符串，然后将结果存储到v2，之后调用isOk，参数是v2，然后将返回值放入v1

const v2, 0x186a0        # 加载 100,000 (0x186A0)
rem-int v2, v0, v2       # 计算 i % 100,000
if-nez v2, :cond_2       # 如果余数为0（每100,000次），执行打印

# 打印当前进度
invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;
move-result-object v2
invoke-virtual {p0, v2}, Lcom/example/forloop/MainActivity;->log(Ljava/lang/String;)V

if v2 no equal zero，就是v2!=0就会跳转到cond_2标签处执行，否则继续执行下一条指令

:cond_2
if-eqz v1, :cond_3       # 如果 isOk() 返回 true，执行成功逻辑

# 打印成功的数字
invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;
move-result-object v2
invoke-virtual {p0, v2}, Lcom/example/forloop/MainActivity;->log(Ljava/lang/String;)V

如果v1==0就会打印成功的数字，调用的是log进行打印

1
2
3

:cond_3
add-int/lit8 v0, v0, 0x1  # i++
goto :goto_0              # 跳回循环开头

如果没满足，就执行i++然后跳转回去

但是为了将其粘贴到apk中就要对其进行修改

const/4 v0, 0x0

.local v0, "i":I
:goto_3
const v2, 0x98967f

if-lt v0, v2, :cond_3
return-void

.line 28
:cond_3
invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;

move-result-object v2

invoke-static {p0, v2}, Lio/asis/ctf2014/numdriod/Verify;->isOk(Landroid/content/Context;Ljava/lang/String;)Z

move-result v1

.line 29
.local v1, "ok":Z

const v4, 0x186a0

rem-int v4, v0, v4

if-nez v4, :cond_6

.line 31
invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;

move-result-object v2
invoke-static {v2}, Lio/asis/ctf2014/numdriod/tools/DebugTools;->log(Ljava/lang/String;)V

:cond_6

if-eqz v1, :cond_2

goto :goto_4
.line 31
invoke-static {v0}, Ljava/lang/Integer;->toString(I)Ljava/lang/String;

move-result-object v2

invoke-static {v2}, Lio/asis/ctf2014/numdriod/tools/DebugTools;->log(Ljava/lang/String;)V

.line 26
:cond_2
add-int/lit8 v0, v0, 0x1

goto :goto_3

方案2：

这个方案是直接将Verify中加个main函数，然后修改一些报错，直接运行即可，参照https://gist.github.com/volpino/2edea8503822aefb4c9e

得到答案是

1 2	................> java .\sample\Verify.java FOUND!! 3130110

2014 Sharif University Quals CTF Commercial Application

private void checkLicenceKey(final Context context) {
      if (this.app.getDataHelper().getConfig().hasLicence()) { // 如果没有有效许可证
          showAlertDialog(context, OK_LICENCE_MSG);
          return;
      }
      LayoutInflater li = LayoutInflater.from(context);
      View promptsView = li.inflate(R.layout.propmt, (ViewGroup) null);
      AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(context);
      alertDialogBuilder.setView(promptsView);
      final EditText userInput = (EditText) promptsView.findViewById(R.id.editTextDialogUserInput);
      alertDialogBuilder.setCancelable(false).setPositiveButton("Continue", new DialogInterface.OnClickListener() { // from class: edu.sharif.ctf.activities.MainActivity.4
          @Override // android.content.DialogInterface.OnClickListener
          public void onClick(DialogInterface dialog, int id) {
              String userEnteredValue = userInput.getText().toString();
              String storedKey = MainActivity.this.app.getDataHelper().getConfig().getSecurityKey();
              String iv = MainActivity.this.app.getDataHelper().getConfig().getSecurityIv();
              boolean licenceKeyIsValid = KeyVerifier.isValidLicenceKey(userEnteredValue, storedKey, iv);
              if (licenceKeyIsValid) {
                  MainActivity.this.app.getDataHelper().updateLicence(2014);
                  MainActivity.isRegisterd = true;
                  MainActivity.this.showAlertDialog(context, MainActivity.OK_LICENCE_MSG);
                  return;
              }
              MainActivity.this.showAlertDialog(context, MainActivity.NOK_LICENCE_MSG);
          }
      }).setNegativeButton("Cancel", new DialogInterface.OnClickListener() { // from class: edu.sharif.ctf.activities.MainActivity.5
          @Override // android.content.DialogInterface.OnClickListener
          public void onClick(DialogInterface dialog, int id) {
              dialog.cancel();
          }
      });
      AlertDialog inputLicenceDialog = alertDialogBuilder.create();
      inputLicenceDialog.show();
  }

关键函数，处理key过程如下

按下continue之后，usrinput会被转为string进入

String userEnteredValue = userInput.getText().toString();
String storedKey = MainActivity.this.app.getDataHelper().getConfig().getSecurityKey();
String iv = MainActivity.this.app.getDataHelper().getConfig().getSecurityIv();
boolean licenceKeyIsValid = KeyVerifier.isValidLicenceKey(userEnteredValue, storedKey, iv);

会从配置中得到storedKey和iv，之后进入是否有效的判断

public static final String CIPHER_ALGORITHM = "AES/CBC/PKCS5Padding";
public static final String VALID_LICENCE = "29a002d9340fc4bd54492f327269f3e051619b889dc8da723e135ce486965d84";

public static boolean isValidLicenceKey(String userInput, String secretKey, String iv) {
    String encryptUserInputData = encrypt(userInput, secretKey, iv);
    return encryptUserInputData.equals(VALID_LICENCE);
}

public static String encrypt(String userInput, String secretKey, String iv) {
    try {
        SecretKeySpec secretKeySpec = new SecretKeySpec(hexStringToBytes(secretKey), "AES");
        Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
        IvParameterSpec ivSpec = new IvParameterSpec(iv.getBytes());
        cipher.init(1, secretKeySpec, ivSpec);
        byte[] encryptedBytes = cipher.doFinal(userInput.getBytes());
        String encryptedText = bytesToHexString(encryptedBytes);
        return encryptedText;
    } catch (Exception e) {
        e.printStackTrace();
        return "";
    }
}

public static String bytesToHexString(byte[] bytes) {
    StringBuilder sb = new StringBuilder();
    for (byte b : bytes) {
        sb.append(String.format("%02x", Integer.valueOf(b & 255)));
    }
    return sb.toString();
}

public static byte[] hexStringToBytes(String s) {
    int len = s.length();
    byte[] data = new byte[len / 2];
    for (int i = 0; i < len; i += 2) {
        data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i + 1), 16));
    }
    return data;
}

主要是通过encrypt函数进行加密，然后和invalid_license进行比较

在getconfig中

public AppConfig getConfig() {
    AppConfig agency = new AppConfig();
    Cursor cursor = this.myDataBase.rawQuery(SELECT_QUERY, null);
    if (cursor.moveToFirst()) {
        agency.setId(cursor.getInt(0));
        agency.setName(cursor.getString(1));
        agency.setInstallDate(cursor.getString(2));
        agency.setValidLicence(cursor.getInt(3) > 0);
        agency.setSecurityIv(cursor.getString(4));
        agency.setSecurityKey(cursor.getString(5));
        agency.setDesc(cursor.getString(7));
    }
    return agency;
}

可以发现在这里设置了iv和Key

private final Context myContext;
private SQLiteDatabase myDataBase;
private static String DB_PATH = "/data/data/edu.sharif.ctf/databases/";
private static String DB_NAME = "db.db";
private static String TABLE_NAME = "config";
public static final String UPDATE_QUERY = "UPDATE " + TABLE_NAME + " SET d=?";
public static final String SELECT_QUERY = "SELECT  * FROM " + TABLE_NAME + " WHERE a=1";

是从数据库中得到的，且有给出路径，那么直接

1	adb pull /data/data/edu.sharif.ctf/databases/db.db

获得数据库，然后就能得到iv和Key了

1 2	iv=a5efdbd57b84ca36 key=37eaae0141f1a3adf8a1dee655853714

因为AES CBC是对称加密的，所以加解密的Key都是一样的

写个解密AES/CBC/PKCS5Padding的java类即可

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class Main {
    public static final String iv="a5efdbd57b84ca36";
    public static final String Key="37eaae0141f1a3adf8a1dee655853714";
    public static final String en_text="29a002d9340fc4bd54492f327269f3e051619b889dc8da723e135ce486965d84";
    public static void main(String[] args) {
        String data=decrypt(en_text,Key,iv);
        System.out.println(data);
    }
    public static String decrypt(String paramString1, String paramString2, String paramString3) {
        try {
            SecretKeySpec localSecretKeySpec = new SecretKeySpec(hexStringToBytes(paramString2), "AES");
            Cipher localCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            localCipher.init(Cipher.DECRYPT_MODE, localSecretKeySpec, new IvParameterSpec(paramString3.getBytes()));
            byte[] bytes = localCipher.doFinal(hexStringToBytes(paramString1));
            String flag = "";
            for (byte b : bytes) {
                flag += (char) b;
            }
            return flag;
        } catch (Exception localException) {
            localException.printStackTrace();
        }
        return "";
    }
    public static String bytesToHexString(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) {
            sb.append(String.format("%02x", Integer.valueOf(b & 255)));
        }
        return sb.toString();
    }

    public static byte[] hexStringToBytes(String s) {
        int len = s.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i + 1), 16));
        }
        return data;
    }
}

成功得到fl-ag-IS-se-ri-al-NU-MB-ER

2015-0CTF-vezel

public void confirm(View v) {
    String s = getPackageName();
    String first = String.valueOf(getSig(s));
    String next = getCrc();
    String flag = "0CTF{" + first + next + "}";
    if (flag.equals(this.et.getText().toString())) {
        Toast.makeText(this, "Yes!", 0).show();
    } else {
        Toast.makeText(this, "0ops!", 0).show();
    }
}

主要代码如上，发现是通过getSig和getCrc来拼接获得flag的

那么考虑直接hook getSig和getCrc获得对应的值

Java.perform(function() {
    var MainActivity = Java.use('com.ctf.vezel.MainActivity');
    MainActivity.getSig.implementation = function(packageName) {
        var result = this.getSig(packageName);
        console.log("Signature hashCode: " + result);
        return result;
    };
    MainActivity.getCrc.implementation = function() {
        var result = this.getCrc();
        console.log("Crs: " + result);
        return result;
    };
});

1 2	Signature hashCode: -183971537 Crs: 1189242199

得到flag为0CTF{-1839715371189242199}

2017 XMAN HelloSmali2

package com.example.hellosmali.hellosmali;

/* loaded from: D:\android_re\CTF\wiki\hello\sec.dex */
public class Digest {
    public static boolean check(String input) {
        if (input != null && input.length() != 0) {
            char[] charinput = input.toCharArray();
            StringBuilder v2 = new StringBuilder();
            for (char c : charinput) {
                String intinput = Integer.toBinaryString(c);
                while (intinput.length() < 8) {
                    intinput = "0" + intinput;
                }
                v2.append(intinput);
            }
            while (v2.length() % 6 != 0) { // 字符串的长度要是6的倍数
                v2.append("0");
            }
            String v1 = String.valueOf(v2);
            char[] v4 = new char[v1.length() / 6];
            for (int i = 0; i < v4.length; i++) {
                int v6 = Integer.parseInt(v1.substring(0, 6), 2);
                v1 = v1.substring(6);
                v4[i] = "+/abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789".charAt(v6);
            }
            StringBuilder v3 = new StringBuilder(String.valueOf(v4));
            if (input.length() % 3 != 1) {
                if (input.length() % 3 == 2) {
                    v3.append("!");
                }
            } else {
                v3.append("!?");
            }
            String key = String.valueOf(v3);
            if (key.equals("xsZDluYYreJDyrpDpucZCo!?")) {
                return true;
            }
            return false;
        }
        return false;
    }
}

逆向函数：

public class re1 {
    public static void main(String[] args) {
        String key="xsZDluYYreJDyrpDpucZCo!?";
        String charset="+/abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        key=key.substring(0,key.length()-2);
        System.out.println(key);
        StringBuilder binary_string=new StringBuilder();
        for(int i=0;i<key.length();i++){
            char c=key.charAt(i);
            int index=charset.indexOf(c);
            String binary=String.format("%6s",Integer.toBinaryString(index)).replace(' ','0');
            binary_string.append(binary);
        }
        StringBuilder result=new StringBuilder();
        String binary=binary_string.toString();
        for(int i=0;i<binary.length();i+=8){
            if(i+8>binary.length()){
                break;
            }
            String byteStr=binary.substring(i,i+8);
            int charCode=Integer.parseInt(byteStr,2);
            result.append((char)charCode);
        }
        System.out.println(result);
    }
}

1 2	xsZDluYYreJDyrpDpucZCo eM_5m4Li_i4_Ea5y

得到结果

静态分析原生层

2015 - 海峡两岸 - 一个 APK，逆向试试吧

public native boolean testFlag(String str);

static {
    System.loadLibrary("mobicrackNDK");
}

@Override // android.support.v7.app.ActionBarActivity, android.support.v4.app.FragmentActivity, android.app.Activity
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_crack_me);
    this.inputButton = (Button) findViewById(R.id.input_button);
    this.pwdEditText = (EditText) findViewById(R.id.pwd);
    this.inputButton.setOnClickListener(new View.OnClickListener() { // from class: com.example.mobicrackndk.CrackMe.1
        @Override // android.view.View.OnClickListener
            public void onClick(View v) {
            CrackMe.this.input = CrackMe.this.pwdEditText.getText().toString();
            if (CrackMe.this.input != null) {
                if (CrackMe.this.testFlag(CrackMe.this.input)) {
                    Toast.makeText(CrackMe.this, CrackMe.this.input, 1).show();
                } else {
                    Toast.makeText(CrackMe.this, "Wrong flag", 1).show();
                }
            }
        }
    });
}

不难看出，testFlag就是核心的函数，加载的mobicrackNDK

但是so文件dump下来直接搜索符号是没有的，因此考虑寻找JNI_Onload函数（通过 JNI_OnLoad 动态注册）

jint JNI_OnLoad(JavaVM *vm, void *reserved)
{
  int v3; // r5
  char *v4; // r7
  int v5; // r1
  FILE *stream; // [sp+4h] [bp-24h]
  int v8; // [sp+Ch] [bp-1Ch] BYREF

  v8 = 0;
  printf("JNI_OnLoad");
  if ( (*vm)->GetEnv(vm, (void **)&v8, 65540) )
    goto LABEL_6;
  v3 = v8;
  v4 = classPathName[0];
  stream = (FILE *)((char *)&_sF + 168);
  fprintf((FILE *)((char *)&_sF + 168), "RegisterNatives start for '%s'", classPathName[0]);
  v5 = (*(int (__fastcall **)(int, char *))(*(_DWORD *)v3 + 24))(v3, v4);
  if ( !v5 )
  {
    fprintf(stream, "Native registration unable to find class '%s'", v4);
LABEL_6:
    fputs("GetEnv failed", (FILE *)((char *)&_sF + 168));
    return -1;
  }
  if ( (*(int (__fastcall **)(int, int, char **, int))(*(_DWORD *)v3 + 860))(v3, v5, off_400C, 2) < 0 )
  {
    fprintf(stream, "RegisterNatives failed for '%s'", v4);
    goto LABEL_6;
  }
  return 65540;
}

1	if ( ((int (__fastcall )(int, int, char , int))((_DWORD *)v3 + 860))(v3, v5, off_400C, 2) < 0 )

这就是注册的函数

.data:0000400C off_400C        DCD aTestflag           ; DATA XREF: JNI_OnLoad+60↑o
.data:0000400C                                         ; JNI_OnLoad+68↑o ...
.data:0000400C                                         ; "testFlag"
.data:00004010                 DCD aLjavaLangStrin_0   ; "(Ljava/lang/String;)Z"
.data:00004014                 DCD abcdefghijklmn+1
.data:00004018                 DCD aHello              ; "hello"
.data:0000401C                 DCD aLjavaLangStrin_1   ; "()Ljava/lang/String;"
.data:00004020                 DCD native_hello+1
.data:00004020 ; .data         ends

可以看到testFlag就是abcdefghijklmn函数，第二个参数括弧里的是参数，括弧外的是返回值的类型，可以看到testFlag函数的参数类型是String，参数返回类型是bool型

1	bool __fastcall abcdefghijklmn(int a1, int a2, int a3)

a1：JNIEnv* 指针（通过 jniEnv 全局变量缓存）
a2：未使用
a3：输入的 Java 字符串对象（jstring）

bool __fastcall abcdefghijklmn(JNIEnv *a1, int a2, void *a3)
{
  int v5; // r4
  size_t i; // r6
  jmethodID v7; // r2
  struct _jfieldID *key; // r4
  jobject v9; // r0
  const char *v10; // r5
  jclass v12; // [sp+4h] [bp-C4h]
  const char *user_input; // [sp+8h] [bp-C0h]
  char s2[12]; // [sp+14h] [bp-B4h] BYREF
  char v15[140]; // [sp+20h] [bp-A8h] BYREF

  if ( !jniEnv )
    jniEnv = a1;                                // 缓存JNIEnv指针
  memset(&v15[12], 0, 0x80u);
  user_input = (*jniEnv)->GetStringUTFChars(jniEnv, a3, 0);// 将java字符串转为c字符串
  v5 = 0;
  if ( strlen(user_input) == 0x10 )
  {
    for ( i = 0; i != 8; ++i )
      s2[i] = user_input[i] - i;                // 前8个字符减去索引值
    v5 = 0;
    s2[8] = 0;
    if ( !strcmp(seed[0], s2) )                 // 与seed[0]比较
    {
      v12 = (*jniEnv)->FindClass(jniEnv, "com/example/mobicrackndk/Calc");// 加载这个类
      if ( !v12 )
      {
        _android_log_print(4, "log", "class,failed");
        goto LABEL_11;
      }
      v7 = (*jniEnv)->GetStaticMethodID(jniEnv, v12, "calcKey", "()V");
      if ( !v7 )
      {
        _android_log_print(4, "log", "method,failed");
LABEL_11:
        exit(1);
      }
      _JNIEnv::CallStaticVoidMethod(jniEnv, v12, v7);// 调用 Java 层的 Calc.calcKey() 方法
      key = (*a1)->GetStaticFieldID(a1, v12, "key", "Ljava/lang/String;");// 获取该静态字段的jfieldID
      if ( !key )
        _android_log_print(4, "log", "fid,failed");
      v9 = (*a1)->GetStaticObjectField(a1, v12, key);// 获取目标类的静态字段值
      v10 = (*jniEnv)->GetStringUTFChars(jniEnv, v9, 0);
      while ( i < strlen(v10) + 8 )
      {
        s2[i + 4] = user_input[i] - i;          // s2[i+4]其实就是v15[i]
        ++i;
      }
      v15[8] = 0;
      return strcmp(v10, v15) == 0; //与key进行比较
    }
  }
  return v5;
}

逆向得到，我们的输入的前八个字节减去索引要与seed[0]相等，后八个字节减去索引要与key相同

package com.example.mobicrackndk;

/* loaded from: classes.dex */
public class Calc {
    public static String key;

    public static void calcKey() {
        StringBuffer sb = new StringBuffer("c7^WVHZ,");
        key = sb.reverse().toString();
    }
}

key=",ZHVW^7c"

所以写个脚本即可

public class My {
    public static void main(String[] args) {
        String key = "QflMn`fH,ZHVW^7c";
        char[] chars = key.toCharArray();
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < chars.length; i++) {
            result.append((char)(chars[i] + i));  // 每个字符减去索引值
        }

        System.out.println(result.toString());
    }
}

但是wp说这是错误的

发现是在_init_my中存在对seed的修改

size_t _init_my()
{
  size_t i; // r7
  size_t result; // r0

  for ( i = 0; ; ++i )
  {
    result = strlen(seed[0]);
    if ( i >= result )
      break;
    t[i] = seed[0][i] - 3;
  }
  seed[0] = t;
  byte_4038 = 0;
  return result;
}

都减了3，对脚本进行修改

public class My {
    public static void main(String[] args) {
        String key = "QflMn`fH,ZHVW^7c";
        char[] chars = key.toCharArray();
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < chars.length; i++) {
            if(i<8){
                chars[i]-=3;
            }
            result.append((char)(chars[i] + i));  // 每个字符减去索引值
        }

        System.out.println(result.toString());
    }
}

1	NdkMobiL4cRackEr

成功

静态分析综合题目

2017 ISCC Crackone

protected void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.activity_main);
     this.editFlag = (EditText) findViewById(R.id.textView3);
     this.button = (Button) findViewById(R.id.button);
     this.button.setOnClickListener(new View.OnClickListener() { // from class: org.isclab.iscc.MainActivity.1
         @Override // android.view.View.OnClickListener
         public void onClick(View v) {
             String flag = Digest.encode(MainActivity.this.editFlag.getText().toString()).trim();
             Log.i("ISCC", flag);
             int result = MainActivity.this.checkFlag(flag.getBytes(), flag.length());
             if (result == 1) {
                 Toast.makeText(MainActivity.this, "Flag验证成功！", 0).show();
             } else {
                 Toast.makeText(MainActivity.this, "Flag验证失败！", 0).show();
             }
         }
     });
 }

checkFlag为核心函数

_BOOL4 __cdecl native_checkFlag(JNIEnv *a1, int a2, void *usrinput, int size)
{
  char *usrinput_arr; // ebp
  int idx; // eax
  char *end; // edx
  char tmp; // [esp+2Bh] [ebp-21h]
  jbyte *src; // [esp+2Ch] [ebp-20h]

  src = (jbyte *)malloc(size);
  (*a1)->GetByteArrayRegion(a1, usrinput, 0, size, src);
  usrinput_arr = (char *)malloc(size + 1);
  memset(usrinput_arr, 0, size + 1);
  memcpy(usrinput_arr, src, size);
  if ( size / 2 > 0 )
  {
    idx = 0;
    end = &usrinput_arr[size];
    do
    {
      tmp = usrinput_arr[idx] - 5;
      usrinput_arr[idx++] = *(end - 1);
      *--end = tmp;
    }
    while ( idx != size / 2 );
  }
  usrinput_arr[size] = 0;
  free(usrinput_arr);
  free(src);
  return strcmp(usrinput_arr, "=0HWYl1SE5UQWFfN?I+PEo.UcshU") == 0;
}

逆向得到脚本：

public class My {
    public static void main(String[] args) {
        StringBuffer key = new StringBuffer("=0HWYl1SE5UQWFfN?I+PEo.UcshU");
        String re_key=key.reverse().toString();
        char[] chars = re_key.toCharArray();
        int idx=re_key.length();
        StringBuffer result=new StringBuffer();
        for(int i=0; i<idx;i++)
        {
            if(i<idx/2)
            {
                result.append((char)(chars[i]+5));
                continue;
            }
            result.append(chars[i]);
        }
        System.out.println(result);
    }
}

1	ZmxhZ3tJU0NDSkFWQU5ES1lYWH0=

但是在进入checkFlag之前，还对其进行了编码

package org.isclab.iscc;

/* loaded from: classes.dex */
public class Digest {
    private static final String TAG = "Util/Digest";
    private static String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    public static String encode(String srcStr) {
        if (srcStr != null && srcStr.length() != 0) {
            char[] srcStrCh = srcStr.toCharArray();
            StringBuilder asciiBinStrB = new StringBuilder();
            for (char c : srcStrCh) {
                String asciiBin = Integer.toBinaryString(c);
                while (asciiBin.length() < 8) {
                    asciiBin = "0" + asciiBin;
                }
                asciiBinStrB.append(asciiBin);
            }
            while (asciiBinStrB.length() % 6 != 0) {
                asciiBinStrB.append("0");
            }
            String asciiBinStr = String.valueOf(asciiBinStrB);
            char[] codeCh = new char[asciiBinStr.length() / 6];
            for (int i = 0; i < codeCh.length; i++) {
                int index = Integer.parseInt(asciiBinStr.substring(0, 6), 2);
                asciiBinStr = asciiBinStr.substring(6);
                codeCh[i] = str.charAt(index);
            }
            StringBuilder code = new StringBuilder(String.valueOf(codeCh));
            if (srcStr.length() % 3 == 1) {
                code.append("==");
            } else if (srcStr.length() % 3 == 2) {
                code.append("=");
            }
            for (int i2 = 76; i2 < code.length(); i2 += 76) {
                code.insert(i2, "\r\n");
            }
            code.append("\r\n");
            return String.valueOf(code);
        }
        return srcStr;
    }
}

简单分析，可以发现是标准base64，就不用自己写脚本了，cyberchef得到

1	flag{ISCCJAVANDKYXX}

成功

2018 强网杯 picture lock

在android中，onActivityResult是一个android.app.Activity类预先定义好的回调函数，只有当内部方法调用startActivityForResult(Intent intent, int requestCode)来启动另一个Activity的时候才会调用这个回调函数，被启动的Activity必须在结束前调用setResult来设置返回结果和finish来关闭自己，关闭完之后原Activity就会调用onActivityResult方法，并将之前启动的Activity的resultCode和intent以及一开始调用新Activity传入的requestCode一起传入onActivityResult

MediaStore内容提供器中，_data代表绝对路径

逆向分析：

private String j() {
    try { // 获取该包的签名信息
        Signature[] signatureArr = getPackageManager().getPackageInfo("com.a.sample.picturelock", 64).signatures; // 获取该包的签名信息
        MessageDigest messageDigest = MessageDigest.getInstance("MD5"); // 初始化MD5计算器
        for (Signature signature : signatureArr) {
            messageDigest.update(signature.toByteArray()); // 遍历所有签名并更新哈希值
        }
        byte[] digest = messageDigest.digest(); // 最终md5哈希
        StringBuilder sb = new StringBuilder();
        for (byte b : digest) { // 将字节数组转换为十六进制字符串
            int i = b & 255;
            if (i < 16) {
                sb.append("0");
            }
            sb.append(Integer.toHexString(i));
        }
        return sb.toString(); // 返回string
    } catch (PackageManager.NameNotFoundException | NoSuchAlgorithmException e) {
        return "";
    }
}

@Override // android.support.v4.a.k, android.app.Activity
protected void onActivityResult(int i, int i2, Intent intent) {
    super.onActivityResult(i, i2, intent);
    switch (i) {
        case 1:
            if (intent != null) {
                String[] strArr = {"_data"};
                Cursor query = getContentResolver().query(intent.getData(), strArr, null, null, null);
                query.moveToFirst();
                String file_path = query.getString(query.getColumnIndex(strArr[0])); // 源文件路径
                query.close();
                enc(file_path, getFilesDir().getAbsolutePath() + file_path.substring(file_path.lastIndexOf("/")) + ".lock", j());
                i();
                Toast.makeText(this, String.format("%s encrypting", file_path), 1).show();
                break;
            }
            break;
    }
}

@Override // android.support.v7.app.c, android.support.v4.a.k, android.app.Activity
protected void onCreate(Bundle bundle) {
    super.onCreate(bundle);
    setContentView(R.layout.activity_main);
    findViewById(R.id.encrypt).setOnClickListener(new View.OnClickListener() { // from class: com.a.sample.picturelock.MainActivity.1
        @Override // android.view.View.OnClickListener
        public void onClick(View view) {
            if (a.a(this, "android.permission.WRITE_EXTERNAL_STORAGE") != 0) { // 判断是否有写入外部存储权限
                android.support.v4.a.a.a((Activity) this, new String[]{"android.permission.WRITE_EXTERNAL_STORAGE"}, 1);
                return;
            }
            Intent intent = new Intent("android.intent.action.PICK", (Uri) null); // 动作
            intent.setDataAndType(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, "image/*"); // 间接调用了MediaStore内容提供器
            MainActivity.this.startActivityForResult(intent, 1);
        }
    });
    findViewById(R.id.refresh).setOnClickListener(new View.OnClickListener() { // from class: com.a.sample.picturelock.MainActivity.2
        @Override // android.view.View.OnClickListener
        public void onClick(View view) {
            MainActivity.this.i();
        }
    });
    i();
}

看native层的enc函数参数(文件的真实路径，目标路径，文件签名的md5)，第三个参数可以hook看一眼即可得到：f8c49056e4ccf9a11e090eaf471f418d

不hook也可以直接得到

PS D:\android_re\CTF\wiki\picture> apksigner verify --verbose --print-certs picturelock.apk
Verifies
Verified using v1 scheme (JAR signing): true
Verified using v2 scheme (APK Signature Scheme v2): true
Verified using v3 scheme (APK Signature Scheme v3): false
Verified using v3.1 scheme (APK Signature Scheme v3.1): false
Verified using v4 scheme (APK Signature Scheme v4): false
Verified for SourceStamp: false
Number of signers: 1
Signer #1 certificate DN: CN=a, OU=b, O=c, L=d, ST=e, C=ff
Signer #1 certificate SHA-256 digest: ba12c13fd60e0def17ae3aee4e6a816782d0367ff02e37ccad5d6e86870c8e38
Signer #1 certificate SHA-1 digest: 48e7045ee60d9d8a257c5275e3650609a5cca13e
Signer #1 certificate MD5 digest: f8c49056e4ccf9a11e090eaf471f418d
Signer #1 key algorithm: RSA
Signer #1 key size (bits): 2048
Signer #1 public key SHA-256 digest: 4de55872bc804bf5fccc61c6e42377b24cd6eefc183a800c5807f759f7f9796d
Signer #1 public key SHA-1 digest: dba8196f6f49a1d1291e4c03102bc7225b6f1f25
Signer #1 public key MD5 digest: d246e0ae52179dfe9daca889ee3133ef

看到Signer #1 certificate MD5 digest: f8c49056e4ccf9a11e090eaf471f418d就能得到

so程序的enc程序在调试的时候，老是出现错误，因此就在此留下一个小坑吧，等我变强之后再回来搞定😎

android逆向之动态调试

java层调试

工具：android studio、apktools、smalidea、已经root的手机

首先apktools反编译apk为output

1	apktool d app.apk -o output

然后

adb shell #adb进入命令行模式
su #切换至超级用户
magisk resetprop ro.debuggable 1
stop
start #一定要通过该方式重启

设置手机的ro.debuggable为1，这样任何程序都可以在我们的手机上进行调试（但是缺点就是每次重启都会失效，因此在启动之后都要设置一次

1	adb shell ps

找到对应的调试进程

1	u0_a137 9261 7805 1120068 56804 SyS_epoll_wait 0 S com.a.sample.picturelock

PID为9261

因此设置

1 2	PS C:\Users\Lenovo> adb forward tcp:8700 jdwp:9261 8700

这个8700是android studio中设置的

来到android studio中

设置如上的部分，output是apktool反编译apk为smali的文件，其中output中的smali文件夹要将其Mark为Sources Root权限

之后直接到output中进行调试即可

原生层调试

1	adb shell am start -D -n com.a.sample.picturelock/.MainActivity

然后在adb shell中push进去ida/dbgsrv下对应的server，运行，自动监听 23946 port

然后

1	adb forward tcp:23946 tcp:23946

将PC端的端口转发到手机上对应的服务端口

之后ida

Debug->attach->localhost:23946

选中对应的服务即成功attack上

然后android studio也attach上java层即可