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[原创]2019看雪CTF 晋级赛Q1 第2题
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2019-3-23 22:50 3705
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一、分析apk和dex文件
本题是一道android题目。首先分析apk文件
程序入口：com.zhuotong.crackme.MainActivity
入口类继承AppCompiatActivity
public class MainActivity extends AppCompiatActivity
我们看一下AppCompiatActivity内的关键信息：
1、加载liboo000oo.so
static {
System.loadLibrary("oo000oo");
}
2、native 函数声明
protected native boolean eq(String arg1) {}
3、onStart（）中的关键逻辑
protected void onStart() {
super.onStart();
this.login = this.findViewById(2131165260);
this.login.setOnClickListener(new View$OnClickListener() {
public void onClick(View arg5) {
AppCompiatActivity.this.mName = AppCompiatActivity.this.name.getText().toString();
AppCompiatActivity.this.mPassword = AppCompiatActivity.this.password.getText().toString();
if(!TextUtils.isEmpty(AppCompiatActivity.this.mName)) {
if(TextUtils.isEmpty(AppCompiatActivity.this.mPassword)) {
}
else {
int v1 = 0;
AppCompiatActivity.this.login.setEnabled(false);
if(AppCompiatActivity.this.eq(AppCompiatActivity.this.mPassword)) {
byte[] v5 = AppCompiatActivity.this.mPassword.getBytes();
int v3 = 24;
if(v5.length != v3) {
byte[] v2 = new byte[v3];
while(v1 < v2.length) {
byte v3_1 = v1 < v5.length ? v5[v1] : ((byte)v1);
v2[v1] = v3_1;
++v1;
}
v5 = v2;
}
v5 = AppCompiatActivity.dec(v5, "2ggdrsLgM7iPNYPQrD58Rg==".getBytes());
AppCompiatActivity v1_1 = AppCompiatActivity.this;
StringBuilder v2_1 = new StringBuilder();
v2_1.append("flag{");
v2_1.append(new String(v5));
v2_1.append("}");
Toast.makeText(((Context)v1_1), v2_1.toString(), 1).show();
}
else {
Toast.makeText(AppCompiatActivity.this, "error", 1).show();
}
return;
}
}
Toast.makeText(AppCompiatActivity.this, "用户名或密码为空", 1).show();
}
});
this.name = this.findViewById(2131165265);
this.name.setEnabled(false);
this.password = this.findViewById(2131165277);
}
}
从onStart（）方法中可以看出，方法eq(mPassword)进行输入密码判断。为真，进行长度为24的pw字符串拷贝，pw长度不够时，序号补齐。紧跟着后面使用我们输入的pw作为key使用dec（）方法进行解密。最终显示解密的flag字串。
二、分析so文件
通过上面的分析可以发现，此题的关键是eq()函数。
1、我们先静态分析一下liboo000oo.so。
如何真机调试？如何定位JNI_OnLoad这里就不说了，不熟悉的同学可以参考这两篇文章：
定位JNI_OnLoad
搭建Android真机调试环境
signed int __fastcall JNI_OnLoad(JavaVM *JVM)
{
int v1; // r8
signed int result; // r0
JNIEnv *Env_1; // r5
int jcalss; // r6
JNIEnv *Env; // [sp+0h] [bp-18h]
int v6; // [sp+4h] [bp-14h]
int v7; // [sp+8h] [bp-10h]
v7 = v1;
Env = 0;
if ( !((int (*)(void))(*JVM)->GetEnv)() )
goto LABEL_4;
LABEL_2:
result = -1;
while ( _stack_chk_guard != v6 )
{
LABEL_4:
Env_1 = Env;
jcalss = ((int (__fastcall *)(JNIEnv *, void *))(*Env)->FindClass)(Env, off_4010);
dword_4110 = ((int (__fastcall *)(JNIEnv *, int))(*Env_1)->NewGlobalRef)(Env_1, jcalss);
if ( !jcalss
|| ((int (__fastcall *)(JNIEnv *, int, char **, signed int))(*Env_1)->RegisterNatives)(Env_1, jcalss, off_4014, 1) <= -1 )
{
goto LABEL_2;
}
result = 0x10006;
}
return result;
}
JNI_OnLoad 注册了一个native函数sub_784（）该函数应该就是eq（）函数
2、动态调试eq（）函数
int __fastcall sub_784(int a1)
{
size_t constLen; // r10
unsigned __int8 *constVerBuf; // r6
_BYTE *constNo45Buf; // r8
_BYTE *constIndexBuf; // r11
int constNo45BufLen; // r0
size_t constLen1; // r2
char *g_const11; // r1
int v8; // r3
int v9; // r1
unsigned int v10; // r2
int v11; // r3
int v12; // r0
int v13; // r4
unsigned __int8 v14; // r0
_BYTE *constIndexBuf_1; // r3
_BYTE *v16; // r5
char *keyDataIndex; // r4
int v18; // r5
int v19; // r1
int v20; // r0
signed int v21; // r1
int v22; // r2
size_t psswordLen; // r0
unsigned int psswordLen_1; // r8
unsigned int v25; // r5
_BYTE *mallocBuf; // r0
int v27; // r3
int v28; // r10
unsigned int index; // r2
int v30; // r12
bool v31; // zf
_BYTE *BASE_CODE1; // r1
bool v33; // zf
int v34; // r3
int v35; // r1
unsigned __int8 keyData; // r11
unsigned int v37; // lr
char v38; // r1
char *v39; // r2
int v40; // t1
unsigned int v42; // [sp+4h] [bp-234h]
unsigned int v43; // [sp+8h] [bp-230h]
unsigned int step_ox33; // [sp+10h] [bp-228h]
char *pssword; // [sp+14h] [bp-224h]
char constKey[256]; // [sp+18h] [bp-220h]
char cosntIndex256Buf[256]; // [sp+118h] [bp-120h]
int v48; // [sp+218h] [bp-20h]
pssword = (char *)(*(int (**)(void))(*(_DWORD *)a1 + 676))();
constLen = strlen(g_const1); // 650f909c-7217-3647-9331-c82df8b98e98
constVerBuf = (unsigned __int8 *)malloc(constLen);
constNo45Buf = malloc(constLen);
constIndexBuf = malloc(constLen);
_aeabi_memclr(constVerBuf, constLen);
_aeabi_memclr(constNo45Buf, constLen);
_aeabi_memclr(constIndexBuf, constLen);
if ( constLen )
{
constNo45BufLen = 0;
constLen1 = constLen;
g_const11 = g_const1;
do
{
v8 = (unsigned __int8)*g_const11++; // 650f909c721736479331c82df8b98e98
if ( v8 != 45 )
constNo45Buf[constNo45BufLen++] = v8;
--constLen1;
}
while ( constLen1 );
if ( constNo45BufLen >= 1 )
{
v9 = constNo45BufLen - 1;
v10 = -8;
v11 = 0;
v12 = 0;
do
{
if ( (v11 | (v10 >> 2)) > 3 )
{
v13 = v12;
}
else
{
v13 = v12 + 1;
constVerBuf[v12] = 0x2D;
}
v14 = constNo45Buf[v9--];
v11 += 0x40000000;
constVerBuf[v13] = v14;
++v10;
v12 = v13 + 1; // constVerBuf = 89e89b8f-d28c-1339-7463-7127c909f056
}
while ( v9 != -1 );
if ( v13 >= 0 )
{
constIndexBuf_1 = constIndexBuf; // 对2409715836dbeafc索引
while ( 1 )
{
v16 = (_BYTE *)*constVerBuf;
if ( (unsigned __int8)((_BYTE)v16 - 'a') <= 5u )
break;
if ( (unsigned __int8)((_BYTE)v16 - '0') <= 9u )
{
v16 = (char *)&unk_23DE + (_DWORD)v16 - '0';// dbeafc2409715836
goto LABEL_18;
}
LABEL_19:
*constIndexBuf_1++ = (_BYTE)v16;
--v12;
++constVerBuf;
if ( !v12 )
goto LABEL_20;
}
v16 = (char *)&unk_23D8 + (_DWORD)v16 - 'a';// dbeafc2409715836
LABEL_18:
LOBYTE(v16) = *v16;
goto LABEL_19;
} // constIndexBuf_1 = 36f36b3c-a03e-4996-8759-8408e626c215
}
}
LABEL_20:
_aeabi_memcpy8(constKey, &unk_23E8, 256);
keyDataIndex = cosntIndex256Buf;
v18 = 0;
do
{
sub_D20(v18, constLen);
cosntIndex256Buf[v18++] = constIndexBuf[v19];// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f36b3c-a03e-4996-8759-8408e626c215
// 36f3
}
while ( v18 != 256 );
v20 = (unsigned __int8)(cosntIndex256Buf[0] - 0x29);
constKey[0] = constKey[v20];
constKey[v20] = 0xD7u;
v21 = 1;
do
{
v22 = (unsigned __int8)constKey[v21];
v20 = (v20 + (unsigned __int8)cosntIndex256Buf[v21] + v22) % 256;
constKey[v21++] = constKey[v20];
constKey[v20] = v22;
}
while ( v21 != 256 ); // 00 00 00 00 B9 00 00 00 00 40 00 00 00 00 6F 00
// 00 00 1E 00 00 3D 34 05 00 00 53 00 04 00 01 00
// 00 4F FF 00 00 00 00 06 C0 00 00 B9 00 00 00 9F
// 00 00 FF 03 00 FC 00 04 3E 00 00 00 01 00 00 6F
// 00 78 47 48 00 00 00 00 00 FF B4 00 00 5C 1A FF
// EF 00 00 F3 FF FF 00 B9 00 04 3C 52 00 01 00 00
// 05 00 00 00 00 00 00 00 00 00 00 00 0A 00 01 01
// FB 01 00 01 00 1C 6F 00 01 00 00 00 00 A6 01 0B
// 6F 0E AC 00 00 00 00 00 01 00 00 00 00 00 00 A6
// 48 00 00 00 00 9C 10 00 00 00 00 5C F0 A6 01 00
// 48 00 00 01 00 00 00 00 00 00 B9 00 84 00 00 00
// 74 00 00 00 00 00 3E FF 00 00 BC 6F B9 00 00 FF
// 00 A6 00 00 00 1B 00 00 00 F0 00 00 00 19 05 00
// 00 15 05 FE 00 FF 00 00 FF 00 00 00 FF 00 FF 00
// 83 00 68 FD 00 6F B6 00 00 59 A6 01 00 00 00 D7
// 01 00 00 00 00 00 00 1D FF 04 00 08 D8 00 00 B6
psswordLen = strlen(pssword); 在此之前都是算法的准备阶段，与输入PW无关
psswordLen_1 = psswordLen;
v25 = (unsigned __int8)constIndexBuf[3];
v43 = 8 * (3 - -3 * (psswordLen / 3));
v42 = v25 + v43 / 6;
mallocBuf = malloc(v42 + 1);
if ( psswordLen_1 )
{
v28 = 0;
index = 0;
v30 = 0;
step_ox33 = v25;
do
{
v28 = (v28 + 1) % 256;
v35 = (unsigned __int8)constKey[v28];
v30 = (v30 + v35) % 256;
constKey[v28] = constKey[v30];
constKey[v30] = v35;
keyDataIndex = (char *)(unsigned __int8)constKey[v28];
keyData = constKey[(unsigned __int8)(v35 + (_BYTE)keyDataIndex)] ^ pssword[index];
if ( index && (v27 = 0xAAAAAAAB * (unsigned __int64)index >> 32, v37 = 3 * (index / 3), v37 != index) )
{
v31 = index == 1;
if ( index != 1 )
v31 = v37 + 1 == index;
if ( v31 )
{
BASE_CODE1 = BASE_CODE;
mallocBuf[step_ox33 + index] = BASE_CODE[(unsigned __int8)mallocBuf[step_ox33 + index] | ((unsigned int)keyData >> 4)];
keyDataIndex = &mallocBuf[step_ox33 + index];
v27 = 4 * keyData & 0x3C;
keyDataIndex[1] = v27;
if ( index + 1 >= psswordLen_1 )
goto LABEL_53;
}
else
{
v33 = index == 2;
if ( index != 2 )
v33 = v37 + 2 == index;
if ( v33 )
{
keyDataIndex = (char *)(keyData & 0xC0);
v34 = step_ox33++ + index;
mallocBuf[v34] = BASE_CODE[(unsigned __int8)mallocBuf[v34] | ((unsigned int)keyDataIndex >> 6)] ^ 0xF;
v27 = (int)&mallocBuf[v34];
*(_BYTE *)(v27 + 1) = BASE_CODE[keyData & 0x3F];
}
}
}
else
{
mallocBuf[step_ox33 + index] = BASE_CODE[(unsigned int)keyData >> 2] ^ 7;
keyDataIndex = &mallocBuf[step_ox33 + index];
v27 = 16 * keyData & 0x30;
keyDataIndex[1] = v27;
if ( index + 1 >= psswordLen_1 )
{
v38 = BASE_CODE[v27];
*((_WORD *)keyDataIndex + 1) = 0x3B3B;
goto LABEL_43;
}
}
++index;
}
while ( index < psswordLen_1 );
}
while ( 1 )
{
if ( v43 )
{
BASE_CODE1 = (_BYTE *)(&dword_0 + 1);
keyDataIndex = (char *)v42;
v39 = &byte_24E8;
do
{
v27 = (unsigned __int8)mallocBuf[v25++];
v40 = (unsigned __int8)*v39++;
if ( v40 != v27 )
BASE_CODE1 = 0;
}
while ( v25 < v42 );
}
else
{
BASE_CODE1 = (_BYTE *)(&dword_0 + 1);
}
mallocBuf = (_BYTE *)(_stack_chk_guard - v48);
if ( _stack_chk_guard == v48 )
break;
LABEL_53:
v38 = BASE_CODE1[v27];
keyDataIndex[2] = 0x34;
LABEL_43:
keyDataIndex[1] = v38;
}
return (unsigned __int8)BASE_CODE1;
}
如代码中的注释，代码的前半部分是算法的准备工作，与输入的password没有关系，后面才开始对password进行转换。转换是一个类似BASE解码的3变4的操作，最后与字符串“{98gal!Tn?@#fj'j$\g;;”进行比对，相等返回真。
三、爆破
通过上面的分析，每3位password的字符生成4目标结果字符。因此选择爆破还原。
修改一下sub_784（char *inputKeyStr, int index）函数，使其可以以三位为一组进行相等验证。
int sub_784(char *inputKeyStr, int index)
{
size_t len; // r10
_BYTE *pbuf1; // r6
_BYTE *pbuf2; // r8
_BYTE *pbuf3; // r11
int v5; // r0
size_t len_1; // r2
_BYTE *g_buf; // r1
int oneChar; // r3
int v9; // r1
unsigned int v10; // r2
int v11; // r3
int v12; // r0
int v13; // r4
unsigned __int8 v14; // r0
_BYTE *v15; // r3
_BYTE *pbuf1_1; // r5
_BYTE *ppp; // r4
unsigned int v18; // r5
int v19; // r1
int v20; // r0
signed int v21; // r1
int v22; // r2
size_t inputKeyLen; // r0
unsigned int inputKeyLen_1; // r8
unsigned int offset0x33; // r5
_BYTE *pNewBuf; // r0
int v27; // r3
int a; // r10
unsigned int indexOfKey; // r2
int b; // r12
bool state; // zf
int v32; // r1
bool v33; // zf
int v34; // r3
int Valindexa; // r1
unsigned __int8 valBox1xorInputKey; // r11
unsigned int v37; // lr
char v38; // r1
_BYTE *pGoal; // r2
int v40; // t1
unsigned int v42; // [sp+4h] [bp-234h]
unsigned int v43; // [sp+8h] [bp-230h]
unsigned int offset0x33_1; // [sp+10h] [bp-228h]
char box2[256]; // [sp+118h] [bp-120h]
int v48; // [sp+218h] [bp-20h]
char box1[256] = {
0xF0, 0x37, 0xE1, 0x9B, 0x2A, 0x15, 0x17, 0x9F,
0xD7, 0x58, 0x4D, 0x6E, 0x33, 0xA0, 0x39, 0xAE, 0x04, 0xD0, 0xBE, 0xED, 0xF8, 0x66, 0x5E, 0x00,
0xD6, 0x91, 0x2F, 0xC3, 0x10, 0x4C, 0xF7, 0xA6, 0xC1, 0xEC, 0x6D, 0x0B, 0x50, 0x65, 0xBB, 0x34,
0xFA, 0xA4, 0x2D, 0x3B, 0x23, 0xA1, 0x96, 0xD5, 0x1D, 0x38, 0x56, 0x0A, 0x5D, 0x4F, 0xE4, 0xCC,
0x24, 0x0D, 0x12, 0x87, 0x35, 0x85, 0x8E, 0x6F, 0xC6, 0x13, 0x9A, 0xD3, 0xFC, 0xE7, 0x08, 0xAC,
0xB7, 0xE9, 0xB0, 0xE8, 0x41, 0xAA, 0x55, 0x53, 0xC2, 0x42, 0xBC, 0xE6, 0x0F, 0x8A, 0x86, 0xA8,
0xCF, 0x84, 0xC5, 0x48, 0x74, 0x36, 0x07, 0xEB, 0x88, 0x51, 0xF6, 0x7F, 0x57, 0x05, 0x63, 0x3E,
0xFE, 0xB8, 0xC9, 0xF5, 0xAF, 0xDF, 0xEA, 0x82, 0x44, 0xF9, 0xCD, 0x06, 0xBA, 0x30, 0x47, 0x40,
0xDE, 0xFD, 0x1C, 0x7C, 0x11, 0x5C, 0x02, 0x31, 0x2C, 0x9C, 0x5F, 0x46, 0x27, 0xC4, 0x83, 0x73,
0x16, 0x90, 0x20, 0x76, 0x7B, 0xF2, 0xE3, 0xF3, 0x77, 0x52, 0x80, 0x25, 0x09, 0x26, 0x3F, 0xC7,
0x18, 0x1B, 0xA3, 0xFF, 0xFB, 0xCB, 0xA9, 0x8C, 0x54, 0x7A, 0x68, 0xB4, 0x70, 0x4B, 0xE2, 0x49,
0x22, 0x7E, 0xA5, 0xB6, 0x81, 0x9D, 0x4E, 0x67, 0xF1, 0xA7, 0x3C, 0xD9, 0x94, 0xEF, 0x32, 0x6B,
0x1F, 0xB1, 0x60, 0xB9, 0x64, 0x59, 0x01, 0xB3, 0x7D, 0xE0, 0x6C, 0xAD, 0x97, 0x19, 0xB5, 0x3A,
0xF4, 0xD8, 0x8D, 0x98, 0x03, 0x93, 0x1A, 0xDC, 0x1E, 0x4A, 0xC0, 0x5A, 0xE5, 0xD1, 0x3D, 0x14,
0xC8, 0x79, 0xBD, 0x43, 0xDB, 0x69, 0xD2, 0x61, 0x95, 0x9E, 0x21, 0x45, 0x89, 0x2B, 0xAB, 0x29,
0xA2, 0x8B, 0x2E, 0xD4, 0x0E, 0x62, 0xCA, 0x28, 0xDA, 0x5B, 0x72, 0x8F, 0x99, 0x75, 0xEE, 0x78,
0x0C, 0x71, 0xBF, 0xDD, 0xCE, 0x92, 0x6A, 0xB2,
};
inputKeyLen = strlen(inputKeyStr);
inputKeyLen_1 = inputKeyLen;
offset0x33 = 0x33; // 0x33
v43 = 8 * (3 - -3 * (inputKeyLen / 3)); // 8*(3--3*8)
v42 = offset0x33 + v43 / 6;
pNewBuf = (_BYTE*)malloc(v42 + 1);
if (inputKeyLen_1)
{
a = 0;
indexOfKey = 0;
b = 0;
offset0x33_1 = offset0x33; // 0x33
do
{
a = (a + 1) % 256;
Valindexa = (unsigned __int8)box1[a];
b = (b + Valindexa) % 256;
box1[a] = box1[b];
box1[b] = Valindexa; // a,b交换
ppp = (_BYTE *)(unsigned __int8)box1[a];
valBox1xorInputKey = box1[(unsigned __int8)(Valindexa + (_BYTE)ppp)] ^ inputKeyStr[indexOfKey];
if (indexOfKey
&& (v27 = 0xAAAAAAAB * (unsigned __int64)indexOfKey >> 32, v37 = 3 * (indexOfKey / 3), v37 != indexOfKey))
{
state = indexOfKey == 1;
if (indexOfKey != 1) // 1处理
state = v37 + 1 == indexOfKey;
if (state)
{
//v32 = byte_4050;
pNewBuf[offset0x33_1 + indexOfKey] = byte_4050[(unsigned __int8)pNewBuf[offset0x33_1 + indexOfKey] | ((unsigned int)valBox1xorInputKey >> 4)];
ppp = &pNewBuf[offset0x33_1 + indexOfKey];
v27 = 4 * valBox1xorInputKey & 0x3C; // 取后四位5643
ppp[1] = v27;
if (indexOfKey + 1 >= inputKeyLen_1)
goto LABEL_53;
}
else
{ // 2处理
v33 = indexOfKey == 2;
if (indexOfKey != 2)
v33 = v37 + 2 == indexOfKey;
if (v33)
{
ppp = (_BYTE *)(valBox1xorInputKey & 0xC0);// 高两位7，6
v34 = offset0x33_1++ + indexOfKey; // offset++了
pNewBuf[v34] = byte_4050[(unsigned __int8)pNewBuf[v34] | ((unsigned int)ppp >> 6)] ^ 0xF;// index高位前两bit
v27 = (int)&pNewBuf[v34];
*(_BYTE *)(v27 + 1) = byte_4050[valBox1xorInputKey & 0x3F];
}
}
}
else
{
pNewBuf[offset0x33_1 + indexOfKey] = byte_4050[(unsigned int)valBox1xorInputKey >> 2] ^ 7;// 低位前两个bit
ppp = &pNewBuf[offset0x33_1 + indexOfKey];
v27 = 16 * valBox1xorInputKey & 0x30; // 低位后两个bit
ppp[1] = v27;
if (indexOfKey + 1 >= inputKeyLen_1)
{
v38 = byte_4050[v27];
*((_WORD *)ppp + 1) = 0x3B3B;
//goto LABEL_43;
}
}
++indexOfKey;
} while (indexOfKey < inputKeyLen_1);
}
int cmpLen = offset0x33 + index;
while (1)
{
if (v43)
{
v32 = 1;
ppp = (_BYTE *)v42;
pGoal = byte_24E8;
do
{
v27 = (unsigned __int8)pNewBuf[offset0x33++];
v40 = (unsigned __int8)*pGoal++;
if (v40 != v27)
v32 = 0;
} while (offset0x33 < v42);
//while (offset0x33 < cmpLen);
}
else
{
v32 = 1;
}
break;
#if 1
LABEL_53:
v38 = byte_4050[v27];
ppp[2] = '4';
LABEL_43 :
int xx = 1;
ppp[1] = v38;
#endif
} // end whie(1)
return v32;
}
前三位爆破调用
for (i = 0; i < 62; i++)
{
p[0] = constString[i];
{
for (int j = 0; j < 62; j++)
{
p[1] = constString[j];
for (int k = 0; k < 62; k++)
{
p[2] = constString[k];
if (sub_784(p, 4)) //index=4，只和“{9*8ga*l!Tn?@#fj'j$\g;;”前4位校验
{
strcpy(resultB[resultBCnt], p);
resultBCnt++;
}
}
}
}
}
返回结果“fu0XXXXXXXXXXXXXXXXXXXXX”
依次求解，最终获得flag。
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