了解反编译的Android方法

Question

我刚刚完成了一项任务，即在一年前对一家咨询公司开发的应用程序进行逆向工程。他们没有源代码，这就是为什么我必须这样做。

无论如何，有一个令牌从一个字符串转换为另一个字符串。

示例：

From:
H0zRNCGT4fnxPUaR0zuFO8HSWTZKYczetXf8vgfWgOAfZBwfE201MLgkbNu0lRuahspqLtrvMTMTivVxH6htYj+VGAbgJydH1OssYfW/RK4Acyxu1C/fCvlW1ccOePwzoboO9WLXj4781ahE+zQAVA==.

To:
H0zRNCGT4fnxPUaR0zuFO8HSWTZKYczetXf8vgfWgOAfZBwfE201MLgksNu0lRuahspqLtrvMTMTivVxH6htYj+VGAbgJydH1OsbYfW/RK4Acyxu1C/fCvlW1ccOePwzoboO9WLXj4781ahE+zQAVA==.

它们看起来一样，但是2个字符已被替换，我不知道是什么原因。

使用空格

可以更清楚地看出差异

From:
H0zRNCGT4fnxPUaR0zuFO8HSWTZKYczetXf8vgfWgOAfZBwfE201MLgk b Nu0lRuahspqLtrvMTMTivVxH6htYj+VGAbgJydH1Os s YfW/RK4Acyxu1C/fCvlW1ccOePwzoboO9WLXj4781ahE+zQAVA==.

To:
H0zRNCGT4fnxPUaR0zuFO8HSWTZKYczetXf8vgfWgOAfZBwfE201MLgk s Nu0lRuahspqLtrvMTMTivVxH6htYj+VGAbgJydH1Os b YfW/RK4Acyxu1C/fCvlW1ccOePwzoboO9WLXj4781ahE+zQAVA==.

我已使用apktool以及dex2jar来反编译代码

来自dex2jar的java代码没有意义，它为你提供了一些线索，但它没有正常工作的代码。

这是java代码

private String b;

private String h()
    {
        int i = 56;
        int j = 0;
        String str;
        if (this.b == null)
            str = "";
        do
        {
            str = this.b;
        }
        while (str.length() <= 100);
        switch (str.charAt(71) % '\r')
        {
        case 2:
        case 3:
        case 4:
        case 6:
        default:
            i = 0;
        case 1:
        case 5:
        case 7:
        case 8:
        }
        while (j != 0)
        {
            char c = str.charAt(j);
            return methodA(methodA(str, j, str.charAt(i)), i, c);
            j = 99;
            continue;
            j = 81;
            i = 50;
            continue;
            j = 45;
            i = 80;
            continue;
            j = 76;
        }
    }

    private static String methodA(String paramString, int paramInt, char paramChar)
    {
        StringBuffer localStringBuffer = new StringBuffer(paramString);
        localStringBuffer.setCharAt(paramInt, paramChar);
        return localStringBuffer.toString();
    }

这是来自apktool

的smali代码

# instance fields
.field private b:Ljava/lang/String;


.method private h()Ljava/lang/String;
    .locals 5

    .prologue
    const/16 v1, 0x38

    const/4 v2, 0x0

    .line 138
    iget-object v0, p0, Lcom/example/MainActivity;->b:Ljava/lang/String;

    if-nez v0, :cond_1

    .line 139
    const-string v0, ""

    .line 185
    :cond_0
    :goto_0
    return-object v0

    .line 142
    :cond_1
    iget-object v0, p0, Lcom/example/MainActivity;->b:Ljava/lang/String;

    .line 143
    invoke-virtual {v0}, Ljava/lang/String;->length()I

    move-result v3

    const/16 v4, 0x64

    if-le v3, v4, :cond_0

    .line 145
    const/16 v3, 0x47

    invoke-virtual {v0, v3}, Ljava/lang/String;->charAt(I)C

    move-result v3

    rem-int/lit8 v3, v3, 0xd

    .line 150
    packed-switch v3, :pswitch_data_0

    :pswitch_0
    move v1, v2

    .line 170
    :goto_1
    if-eqz v2, :cond_0

    .line 177
    invoke-virtual {v0, v2}, Ljava/lang/String;->charAt(I)C

    move-result v3

    .line 178
    invoke-virtual {v0, v1}, Ljava/lang/String;->charAt(I)C

    move-result v4

    .line 180
    invoke-static {v0, v2, v4}, Lcom/example/MainActivity;->methodA(Ljava/lang/String;IC)Ljava/lang/String;

    move-result-object v0

    .line 181
    invoke-static {v0, v1, v3}, Lcom/example/MainActivity;->methodA(Ljava/lang/String;IC)Ljava/lang/String;

    move-result-object v0

    goto :goto_0

    .line 153
    :pswitch_1
    const/16 v2, 0x63

    .line 155
    goto :goto_1

    .line 158
    :pswitch_2
    const/16 v2, 0x51

    .line 159
    const/16 v1, 0x32

    .line 160
    goto :goto_1

    .line 163
    :pswitch_3
    const/16 v2, 0x2d

    .line 164
    const/16 v1, 0x50

    .line 165
    goto :goto_1

    .line 168
    :pswitch_4
    const/16 v2, 0x4c

    .line 169
    goto :goto_1

    .line 150
    nop

    :pswitch_data_0
    .packed-switch 0x1
        :pswitch_1
        :pswitch_0
        :pswitch_0
        :pswitch_0
        :pswitch_2
        :pswitch_0
        :pswitch_3
        :pswitch_4
    .end packed-switch
.end method



.method private static methodA(Ljava/lang/String;IC)Ljava/lang/String;
    .locals 1

    .prologue
    .line 189
    new-instance v0, Ljava/lang/StringBuffer;

    invoke-direct {v0, p0}, Ljava/lang/StringBuffer;-><init>(Ljava/lang/String;)V

    .line 190
    invoke-virtual {v0, p1, p2}, Ljava/lang/StringBuffer;->setCharAt(IC)V

    .line 191
    invoke-virtual {v0}, Ljava/lang/StringBuffer;->toString()Ljava/lang/String;

    move-result-object v0

    return-object v0
.end method

如果有人能够弄清楚这里发生了什么，我会非常感激。