Bytectf2022
题的质量都很高，而且绝大部分知识点都是我不会的，所以接下来一个月，抽时间就来复现。
OhMySolidity
这个题是一个智能合约题，第一次接触这种类型的题，发现反编译出来的东西很抽象。
给了一个txt文件
我们将第一段input输入https://ethervm.io/这个网站就可以得到反编译后的样子：
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| contract Contract {
function main() {
memory[0x40:0x60] = 0x80;
var var0 = msg.value;
if (var0) { revert(memory[0x00:0x00]); }
if (msg.data.length < 0x04) { revert(memory[0x00:0x00]); }
var0 = msg.data[0x00:0x20] >> 0xe0;
if (var0 == 0x14edb54d) {
// Dispatch table entry for k1()
var var1 = 0x006f;
var var2 = k1();
var temp0 = memory[0x40:0x60];
memory[temp0:temp0 + 0x20] = var2 & 0xffffffff;
var temp1 = memory[0x40:0x60];
return memory[temp1:temp1 + (temp0 + 0x20) - temp1];
} else if (var0 == 0x58f5382e) {
// Dispatch table entry for challenge(string)
var1 = 0x014a;
var2 = 0x04;
var var3 = msg.data.length - var2;
if (var3 < 0x20) { revert(memory[0x00:0x00]); }
var1 = challenge(var2, var3);
var temp2 = memory[0x40:0x60];
var2 = temp2;
var3 = var2;
var temp3 = var3 + 0x20;
memory[var3:var3 + 0x20] = temp3 - var3;
var temp4 = var1;
memory[temp3:temp3 + 0x20] = memory[temp4:temp4 + 0x20];
var var4 = temp3 + 0x20;
var var6 = memory[temp4:temp4 + 0x20];
var var5 = temp4 + 0x20;
var var7 = var6;
var var8 = var4;
var var9 = var5;
var var10 = 0x00;
if (var10 >= var7) {
label_018A:
var temp5 = var6;
var4 = temp5 + var4;
var5 = temp5 & 0x1f;
if (!var5) {
var temp6 = memory[0x40:0x60];
return memory[temp6:temp6 + var4 - temp6];
} else {
var temp7 = var5;
var temp8 = var4 - temp7;
memory[temp8:temp8 + 0x20] = ~(0x0100 ** (0x20 - temp7) - 0x01) & memory[temp8:temp8 + 0x20];
var temp9 = memory[0x40:0x60];
return memory[temp9:temp9 + (temp8 + 0x20) - temp9];
}
} else {
label_0178:
var temp10 = var10;
memory[var8 + temp10:var8 + temp10 + 0x20] = memory[var9 + temp10:var9 + temp10 + 0x20];
var10 = temp10 + 0x20;
if (var10 >= var7) { goto label_018A; }
else { goto label_0178; }
}
} else if (var0 == 0x93eed093) {
// Dispatch table entry for 0x93eed093 (unknown)
var1 = 0x01cd;
var2 = func_056F();
var temp11 = memory[0x40:0x60];
memory[temp11:temp11 + 0x20] = var2 & 0xffffffff;
var temp12 = memory[0x40:0x60];
return memory[temp12:temp12 + (temp11 + 0x20) - temp12];
} else if (var0 == 0x9577a145) {
// Dispatch table entry for 0x9577a145 (unknown)
var1 = 0x0251;
var2 = 0x04;
var3 = msg.data.length - var2;
if (var3 < 0x80) { revert(memory[0x00:0x00]); }
func_0205(var2, var3);
stop();
} else if (var0 == 0xa7f81e6a) {
// Dispatch table entry for k2()
var1 = 0x025b;
var2 = k2();
var temp13 = memory[0x40:0x60];
memory[temp13:temp13 + 0x20] = var2 & 0xffffffff;
var temp14 = memory[0x40:0x60];
return memory[temp14:temp14 + (temp13 + 0x20) - temp14];
} else if (var0 == 0xf0407ca7) {
// Dispatch table entry for 0xf0407ca7 (unknown)
var1 = 0x0285;
var2 = func_0623();
var temp15 = memory[0x40:0x60];
memory[temp15:temp15 + 0x20] = var2 & 0xffffffff;
var temp16 = memory[0x40:0x60];
return memory[temp16:temp16 + (temp15 + 0x20) - temp16];
} else { revert(memory[0x00:0x00]); }
}
function challenge(var arg0, var arg1) returns (var r0) {
var temp0 = arg0;
arg0 = temp0 + arg1;
arg1 = temp0;
var var1 = msg.data[arg1:arg1 + 0x20];
var var0 = arg1 + 0x20;
if (var1 > 0x0100000000) { revert(memory[0x00:0x00]); }
var temp1 = arg1 + var1;
var1 = temp1;
if (var1 + 0x20 > arg0) { revert(memory[0x00:0x00]); }
var temp2 = var1;
var temp3 = msg.data[temp2:temp2 + 0x20];
var1 = temp3;
var temp4 = var0;
var0 = temp2 + 0x20;
var var2 = temp4;
if ((var1 > 0x0100000000) | (var0 + var1 > arg0)) { revert(memory[0x00:0x00]); }
var temp5 = var1;
var temp6 = memory[0x40:0x60];
memory[0x40:0x60] = temp6 + (temp5 + 0x1f) / 0x20 * 0x20 + 0x20;
memory[temp6:temp6 + 0x20] = temp5;
var temp7 = temp6 + 0x20;
memory[temp7:temp7 + temp5] = msg.data[var0:var0 + temp5];
memory[temp7 + temp5:temp7 + temp5 + 0x20] = 0x00;
arg0 = temp6;
arg1 = 0x60;
var0 = arg0;
var1 = 0x00;
var2 = 0x08;
var var3 = memory[var0:var0 + 0x20];
if (!var2) { assert(); }
if (var3 % var2 != var1) { revert(memory[0x00:0x00]); }
var1 = 0x60;
var temp8 = memory[var0:var0 + 0x20];
var temp9 = memory[0x40:0x60];
var2 = temp9;
var3 = temp8;
memory[var2:var2 + 0x20] = var3;
memory[0x40:0x60] = var2 + (var3 + 0x1f & ~0x1f) + 0x20;
if (!var3) {
var1 = var2;
var2 = 0xdeadbeef;
var3 = 0x00;
if (var3 >= memory[var0:var0 + 0x20]) {
label_0563:
return var1;
} else {
label_032D:
var var4 = 0x00;
var var5 = 0x00;
var var6 = 0x00;
var var7 = 0x00;
if (var7 & 0xff >= 0x04) {
label_03CD:
var7 = 0x00;
if (var7 & 0xff >= 0x20) {
label_047F:
var7 = 0x00;
if (var7 & 0xff >= 0x04) {
label_0554:
var3 = var3 + 0x08;
if (var3 >= memory[var0:var0 + 0x20]) { goto label_0563; }
else { goto label_032D; }
} else {
label_0493:
var temp10 = var7;
var var8 = (((var5 & 0xffffffff) >> (0x03 - temp10 * 0x08 & 0xff)) & 0xff) << 0xf8;
var var9 = var1;
var var10 = var3 + (temp10 & 0xff);
if (var10 >= memory[var9:var9 + 0x20]) { assert(); }
memory[var10 + 0x20 + var9:var10 + 0x20 + var9 + 0x01] = byte(var8 & ~0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff, 0x00);
var temp11 = var7;
var8 = (((var6 & 0xffffffff) >> (0x03 - temp11 * 0x08 & 0xff)) & 0xff) << 0xf8;
var9 = var1;
var10 = var3 + (temp11 & 0xff) + 0x04;
if (var10 >= memory[var9:var9 + 0x20]) { assert(); }
memory[var10 + 0x20 + var9:var10 + 0x20 + var9 + 0x01] = byte(var8 & ~0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff, 0x00);
var7 = var7 + 0x01;
if (var7 & 0xff >= 0x04) { goto label_0554; }
else { goto label_0493; }
}
} else {
label_03E1:
var temp12 = var4 + var2;
var4 = temp12;
var temp13 = var6;
var temp14 = var5 + (((temp13 & 0xffffffff) << 0x04) + (storage[0x00] & 0xffffffff) ~ temp13 + var4 ~ ((temp13 & 0xffffffff) >> 0x05) + (storage[0x00] / 0x0100 ** 0x04 & 0xffffffff));
var5 = temp14;
var6 = temp13 + (((var5 & 0xffffffff) << 0x04) + (storage[0x00] / 0x0100 ** 0x08 & 0xffffffff) ~ var5 + var4 ~ ((var5 & 0xffffffff) >> 0x05) + (storage[0x00] / 0x0100 ** 0x0c & 0xffffffff));
var7 = var7 + 0x01;
if (var7 & 0xff >= 0x20) { goto label_047F; }
else { goto label_03E1; }
}
} else {
label_034E:
var temp15 = var7;
var8 = 0x03 - temp15 * 0x08 & 0xff;
var9 = var0;
var10 = var3 + (temp15 & 0xff);
if (var10 >= memory[var9:var9 + 0x20]) { assert(); }
var5 = var5 + (((((memory[var10 + 0x20 + var9:var10 + 0x20 + var9 + 0x20] >> 0xf8) << 0xf8) >> 0xf8) & 0xff) << var8);
var temp16 = var7;
var8 = 0x03 - temp16 * 0x08 & 0xff;
var9 = var0;
var10 = var3 + (temp16 & 0xff) + 0x04;
if (var10 >= memory[var9:var9 + 0x20]) { assert(); }
var6 = var6 + (((((memory[var10 + 0x20 + var9:var10 + 0x20 + var9 + 0x20] >> 0xf8) << 0xf8) >> 0xf8) & 0xff) << var8);
var7 = var7 + 0x01;
if (var7 & 0xff >= 0x04) { goto label_03CD; }
else { goto label_034E; }
}
}
} else {
var temp17 = var3;
memory[var2 + 0x20:var2 + 0x20 + temp17] = code[code.length:code.length + temp17];
var1 = var2;
var2 = 0xdeadbeef;
var3 = 0x00;
if (var3 >= memory[var0:var0 + 0x20]) { goto label_0563; }
else { goto label_032D; }
}
}
function func_0205(var arg0, var arg1) {
var temp0 = arg0;
var temp1 = temp0 + 0x20;
arg0 = msg.data[temp0:temp0 + 0x20] & 0xffffffff;
var temp2 = temp1 + 0x20;
arg1 = msg.data[temp1:temp1 + 0x20] & 0xffffffff;
var var0 = msg.data[temp2:temp2 + 0x20] & 0xffffffff;
var var1 = msg.data[temp2 + 0x20:temp2 + 0x20 + 0x20] & 0xffffffff;
storage[0x00] = (arg0 & 0xffffffff) | (storage[0x00] & ~0xffffffff);
storage[0x00] = (arg1 & 0xffffffff) * 0x0100 ** 0x04 | (storage[0x00] & ~(0xffffffff * 0x0100 ** 0x04));
storage[0x00] = (var0 & 0xffffffff) * 0x0100 ** 0x08 | (storage[0x00] & ~(0xffffffff * 0x0100 ** 0x08));
storage[0x00] = (var1 & 0xffffffff) * 0x0100 ** 0x0c | (storage[0x00] & ~(0xffffffff * 0x0100 ** 0x0c));
}
function k1() returns (var r0) { return storage[0x00] / 0x0100 ** 0x04 & 0xffffffff; }
function func_056F() returns (var r0) { return storage[0x00] & 0xffffffff; }
function k2() returns (var r0) { return storage[0x00] / 0x0100 ** 0x08 & 0xffffffff; }
function func_0623() returns (var r0) { return storage[0x00] / 0x0100 ** 0x0c & 0xffffffff; }
}
|
看这个东西，要看if中的语句，比如下面，当输入0x93eed093时，会调用func_056F函数
我们的第二段输入
0x9577a1450000000000000000000000000000000000000000000000000000000010000000000000000000000000000876543210000000000000002345678000000000000000000000000000000000000000000000000000000000000000000000aabbccdd0000000000000000000000000000000000000000000000000000000044332211
我们直接看func_0205函数
这就要猜了，能看出是赋值了4个值到storage，四个值分别对应0x12345678、0x87654321、0xaabbccdd、0x44332211
第三次输入时challenge方法：输入0x59f5382e，并输出了0xa625e97482f83d2b7fc5125763dcbbffd8115b208c4754eee8711bdfac9e3377622bbf0cbb785e612b82c7f5143d5333
challeng函数是一个魔改的tea
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| #include <stdio.h>
#include <stdint.h>
void encrypt (uint32_t* v, uint32_t* k) {
uint32_t v0=v[0], v1=v[1], sum=0, i;
uint32_t delta=0x9e3779b9;
uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];
for (i=0; i < 32; i++) {
sum += delta;
v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);
}
v[0]=v0; v[1]=v1;
}
void decrypt (uint32_t* v, uint32_t* k) {
uint32_t v0=v[0], v1=v[1], sum=0xdeadbeef*32, i;
uint32_t delta=0xdeadbeef;
uint32_t k0=k[0], k1=k[1], k2=k[2], k3=k[3];
for (i=0; i<32; i++) {
v1 -= ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);
v0 -= ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
sum -= delta;
}
v[0]=v0; v[1]=v1;
}
int main()
{
uint32_t v[12]={0xa625e974,0x82f83d2b,0x7fc51257,0x63dcbbff,0xd8115b20,0x8c4754ee,0xe8711bdf,0xac9e3377,0x622bbf0c,0xbb785e61,0x2b82c7f5,0x143d5333},k[4]={0x12345678,0x87654321,0xaabbccdd,0x44332211};
for(int i = 0; i < 6; i+=2)
{
decrypt(v + i, k);
printf("decode:%x %x\n",v[i],v[i + 1]);
}
return 0;
}
|
1
| bytectf{f2d9e0b6-274d-47e0-bc4c-40967015ba79273}
|
maze6d
这个混淆看了一天，里面涉及到好多不清楚的地方，还有很多之前没搞明白的地方。
第一个点是GOT和PLT表：
GOT表是一个存储外部函数地址的表，PLT表是一个代码片段组成的表，每一个都能跳到GOT表项。众所周知，链接时要进行一个重定位，链接做的事情：对同名section进行合并，对代码段和数据段进行地址分配，进行重定位。
重定位是这样的：如果时在中间文件中定义好的函数，连接时直接可以重定位到函数地址，如果是动态链接库中的函数，只能生成额外的小段代码，就是PLT表，然后重定位到该代码片段。
运行时重定位：运行后加载动态库，把动态库中的相应函数地址填入GOT表
延迟重定位：只有动态库被调用时才会进行地址解析和重定位工作，这时候动态库函数地址被写到GOT表项中。
第一步由函数跳到PLT表中，第二步PLT表跳到GOT表（jmp），第三步GOT跳到PLT(push)，并进行压栈，把代表函数的id压栈，第四步跳到公共PLT表项中（jmp），第五步进入GOT表，然后_dl_runtime_resolve对动态函数进行地址解析和重定位，第七步把动态函数真实的地址写入GOT表项，然后执行函数并retn。
