某车联网App 通讯协议加密分析(四) Trace Code
一、目标
之前我们已经通过Trace Block 来比对了Unidbg和App跑的结果。现在他们运行的流程都差不多了，但是结果还是不对，今天我们就要通过Trace Code进行更细致的对比。
v6.1.0
二、步骤
缩小Trace的范围
Trace Code那么好使，我们为什么不一上来就Trace一遍？
因为Trace Code的粒度太细了，一上来就搞，跑出几百万行结果，根本没法看。
我们通过Trace Block已经在逐步缩小范围了。
JNIEnv->GetStringUtfChars("FlK6XicivmCwPSE3sk6b71m9WbWd/gYZtlajqGXhEXXjmWEZziR51rVWSEDwUUi4UN9RnoCGbLNmqI80Fiog4Sw==") was called from [email protected][libencrypt.so]0x2b744
sub_2b8b8
sub_2b800
sub_2b800
sub_2b800
sub_2b800
sub_2b828
sub_ab6c
sub_a528
sub_ab9c
sub_a848
sub_a7e8
sub_a7c4
sub_8ee4
sub_7334
sub_8f40
sub_95e0
........
sub_a7c4
sub_8ee4
sub_7334
sub_8f40
sub_96bc
sub_9a2c
sub_9268
sub_a818
sub_a90c
sub_a928
sub_2b854
JNIEnv->ReleaseStringUTFChars("FlK6XicivmCwPSE3sk6b71m9WbWd/gYZtlajqGXhEXXjmWEZziR51rVWSEDwUUi4UN9RnoCGbLNmqI80Fiog4Sw==") was called from [email protected][libencrypt.so]0x2b86c
我们的目标大概率是在 0x7000 → 0xa000 这个地址范围之类。
定位Trace Code目标
翻一翻IDA里面的导出表
1:ida
比较合眼缘的就这三个了，0x7184 ,0x77A4 貌似都没有被Trace Block命中，感觉幕后大boss应该就是这个 0x8EE4
Tip:
可以在怀疑的几个函数上加个hook，看看是否命中。
Unidbg Trace Code
emulator.attach().addBreakPoint(module.base + 0x8EE4 , new BreakPointCallback() {
@Override
public boolean onHit(Emulator<?> emulator, long address) {
System.out.println(" ====== traceCode ====== ");
UnidbgPointer pX = UnidbgPointer.register(emulator, Arm64Const.UC_ARM64_REG_X1);
byte[] bData = pX.getByteArray(0,16);
String strLabel = String.format("x0值 0x%08x", pX.peer);
Inspector.inspect(bData,strLabel);
try {
emulator.traceCode(module.base + 0x8EE4, module.base + 0x9C0C).setRedirect(new PrintStream(new File("traceCodeCar.log")));
} catch (IOException e) {
throw new IllegalStateException(e);
}
return true;
});
}
先在 0x8EE4 加个断点，然后开始Trace Code。 参数是Trace的起始地址和结束地址，已经保存的结果文件。
从这个Trace结果来看，每16个字节去做解密。典型的AES。
Frida Trace Code
Stalker的好处很多，最大的功能是可以过反调试，所以基于Stalker去写Trace Code,写了好几个版本，一直不大满意。
前几天发现了
http://github.com/IIIImmmyyy/frida-trace
比较帅，拿来改了改。效果很好。(只支持Arm64)
let moduleBase;
let isFirstIn = true;
let pre_regs;
let infoMap = new Map();
let detailInsMap = new Map();
function parserNextAddr(ins) {
let s = JSON.stringify(ins);
let address = ins.address;
// log("address:"+address)
let offset = address - moduleBase;
let s1 = (offset).toString(16);
let entity = {};
entity.address = offset;
return s1;
}
const byteToHex = [];
for (let n = 0; n <= 0xff; ++n) {
const hexOctet = n.toString(16).padStart(2, "0");
byteToHex.push(hexOctet);
}
function hex(arrayBuffer) {
const buff = new Uint8Array(arrayBuffer);
const hexOctets = [];
for (let i = 0; i < buff.length; ++i)
hexOctets.push(byteToHex[buff[i]]);
return hexOctets.join("");
}
function formatArm64Regs(context) {
let regs = [];
regs.push(context.x0);
regs.push(context.x1);
regs.push(context.x2);
regs.push(context.x3);
regs.push(context.x4);
regs.push(context.x5);
regs.push(context.x6);
regs.push(context.x7);
regs.push(context.x8);
regs.push(context.x9);
regs.push(context.x10);
regs.push(context.x11);
regs.push(context.x12);
regs.push(context.x13);
regs.push(context.x14);
regs.push(context.x15);
regs.push(context.x16);
regs.push(context.x17);
regs.push(context.x18);
regs.push(context.x19);
regs.push(context.x20);
regs.push(context.x21);
regs.push(context.x22);
regs.push(context.x23);
regs.push(context.x24);
regs.push(context.x25);
regs.push(context.x26);
regs.push(context.x27);
regs.push(context.x28);
regs.push(context.fp);
regs.push(context.lr);
regs.push(context.sp);
regs.push(context.pc);
return regs;
}
function getPcReg(regs) {
return regs[32];
}
function isRegsChange(context, ins) {
let currentRegs = formatArm64Regs(context);
let logInfo = "";
for (let i = 0; i < 32; i++) {
if (i === 30) {
continue;
}
let preReg = pre_regs[i];
let currentReg = currentRegs[i];
if (Number(preReg) !== Number(currentReg)) {
if (logInfo === "") {
//尝试读取string
let changeString = "";
try {
let nativePointer = new NativePointer(currentReg);
changeString = nativePointer.readCString();
}
catch (e) {
changeString = "";
}
if (changeString !== "") {
currentReg = currentReg + " (" + changeString + ")";
}
logInfo = "\t " + getRegsString(i) + " = " + preReg + " --> " + currentReg;
}
else {
logInfo = logInfo + "\t " + getRegsString(i) + " = " + preReg + " --> " + currentReg;
}
}
}
//打印PC寄存器
let parse = JSON.parse(ins);
let mnemonic = parse.mnemonic; //补充str
if (mnemonic === "str") {
let strParams = getStrParams(parse, currentRegs);
logInfo = logInfo + strParams;
}
else if (mnemonic === "cmp") {
let cmpParams = getCmpParams(parse, currentRegs);
logInfo = logInfo + cmpParams;
}
else if (mnemonic === "b.gt" || mnemonic === "b.le" || mnemonic === "b.eq" || mnemonic === "b.ne" || mnemonic === "b") {
// log(ins)
let bgtAddr = getbgtAddr(parse, currentRegs);
logInfo = logInfo + bgtAddr;
}
let entity = {};
entity.info = logInfo;
let address = parse.address;
if (lastAddr === undefined) {
entity.color = getColor();
lastAddr = address;
}
else {
let number = address - lastAddr;
if (number === 0x4) {
entity.color = getColor();
}
else {
currentIndex++;
entity.color = getColor();
}
lastAddr = address;
}
pre_regs = currentRegs;
return entity;
}
let lastAddr = undefined;
let currentIndex = 0;
function getColor() {
return "";
if (currentIndex > 1) {
currentIndex = 0;
}
if (currentIndex === 0) {
return "C35"; // logger_1.LogColor.C35;
}
else if (currentIndex === 1) {
return "C97"; // logger_1.LogColor.C97;
}
else if (currentIndex === 2) {
return "C97"; // logger_1.LogColor.C97;
}
}
function getRegsString(index) {
let reg;
if (index === 31) {
reg = "sp";
}
else {
reg = "x" + index;
}
return reg;
}
function getbgtAddr(parser, currentRegs) {
let bgtAddr = "";
let operands = parser.operands;
for (let i = 0; i < operands.length; i++) {
let operand = operands[i];
if (operand.type === "imm") {
let value = operand.value;
let number = value - moduleBase;
bgtAddr = "\t block addr:" + number.toString(16);
break;
}
}
return bgtAddr;
}
function getStrParams(parser, currentRegs) {
let operands = parser.operands;
for (let i = 0; i < operands.length; i++) {
let operand = operands[i];
if (operand.type === "reg") {
//获取value
let value = operand.value;
if (value === "wzr") {
return "\t " + "str = 0";
}
else {
let replace = value.replace("w", "");
let index = replace.replace("x", "");
let index_reg = currentRegs[index];
let changeString = "";
try {
let nativePointer = new NativePointer(index_reg);
changeString = nativePointer.readCString();
}
catch (e) {
changeString = "";
}
//读取值
if (changeString !== "") {
index_reg = index_reg + " (" + changeString + ")";
}
return "\t " + "str = " + index_reg;
}
}
}
}
function getCmpParams(parser, currentRegs) {
let operands = parser.operands;
let cmpInfo = "";
for (let i = 0; i < operands.length; i++) {
let operand = operands[i];
if (operand.type === "reg") {
let value = operand.value;
let replace = value.replace("w", "");
let index = replace.replace("x", "");
let index_reg = currentRegs[index];
let changeString = "";
try {
let nativePointer = new NativePointer(index_reg);
changeString = nativePointer.readCString();
}
catch (e) {
changeString = "";
}
//读取值
if (changeString !== "") {
index_reg = index_reg + " (" + changeString + ")";
}
cmpInfo = cmpInfo + "\t " + value + " = " + index_reg;
}
}
return cmpInfo;
}
function ZY_unTraceAddrEnd(){
var tid = Process.getCurrentThreadId();
Stalker.unfollow(tid);
Stalker.garbageCollect();
console.log(TAG + " ======== unTraceAddr_End");
}
function ZY_trace_Stalker_begin(soname, addr, size) {
let module = Process.findModuleByName(soname);
moduleBase = module.base;
console.log(TAG + JSON.stringify(module));
console.log(TAG + "addr = " + addr);
console.log(TAG + "size = " + size);
Interceptor.attach(moduleBase.add(addr), {
onEnter: function (args) {
this.pid = Process.getCurrentThreadId();
// console.log(TAG + " ==== ZY_trace_Stalker_begin ==== ");
//看下结构体的值
Stalker.follow(this.pid, {
events:{
call:false,
ret:false,
exec:false,
block:false,
compile:false
},
onReceive:function(events){
},
transform: function (iterator) {
let lastInfo;
const instruction = iterator.next();
let startAddress = instruction.address;
// console.log(TAG + "startAddress:" + startAddress + " base:" + module.base );
if (size === 0) {
size = module.size;
addr = 0;
}
const isModuleCode = startAddress.compare(moduleBase.add(addr)) >= 0 &&
startAddress.compare(moduleBase.add(addr).add(size)) < 0;
do {
if (isModuleCode) {
// console.log(TAG + instruction.address + ":" + instruction);
let s = parserNextAddr(instruction);
let address = instruction.address;
let offset = address - moduleBase;
let lastInfo = s.toString(16) + "\t\t" + instruction;
detailInsMap.set(offset, JSON.stringify(instruction));
infoMap.set(offset, lastInfo);
iterator.putCallout(function (context) {
let regs = JSON.stringify(context);
if (isFirstIn) {
isFirstIn = false;
//保存寄存器
pre_regs = formatArm64Regs(context);
}
else {
//打印的实际是上一次的 这样延迟一次可以打印出寄存器变化
let pcReg = getPcReg(pre_regs);
let offset = Number(pcReg) - moduleBase;
let logInfo = infoMap.get(offset);
let detailIns = detailInsMap.get(offset);
// log("detailIns:"+detailIns)
let entity = isRegsChange(context, detailIns);
console.log(TAG + logInfo + " ; " + entity.info, entity.color);
}
});
}
iterator.keep();
} while (iterator.next() != null);
},
});
},
onLeave: function (ret) {
// libtprt.saveStringMapTofile();
Stalker.unfollow(this.pid);
console.log(TAG + "ret:" + ret);
}
});
}
调用方法
ZY_trace_Stalker_begin('libencrypt.so',0x8EF4, 0x9C0C - 0x8EF4);
Tip:
Trace之前可以先匹配入参，只Trace指定的密文。然后unidbg 去 Trace 同样的密文，这样有利于比对。
对比结果
前戏铺垫的太长了，总算拿到Trace Code的结果了。
1:main
这里有个很奇怪的地方，
9608: "ldr w8, [x9, x8, lsl #2]" x9=0x40147510 x8=0x9094 => w8=0xf54de125
0x40147510 这个地址是在so的数据段。 这段代码的意思是 从 0x40147510+(0x9094<<2) = 0x4016B760 这个地址取数据
m0x4016B760 >-----------------------------------------------------------------------------< [11:57:20 551][email protected][libencrypt.so]0x16b760, md5=cc2b1f1f88429f40f84599a613cf3143, hex=25e14df5a6ea8219a148998cebd3d9b5e55522c3109f9bd0347f27854da2729b83f3a390ce0c318645a588f14b339626692918f7119819acb36b0f92cd0dc4d596a74b1bc8f1263f2841c72757b265b4b1692c56a24a9c8f528a41e0d1d95149e25a0120a9e884147d223f7323eb4ff2 size: 112 0000: 25 E1 4D F5 A6 EA 82 19 A1 48 99 8C EB D3 D9 B5 %.M......H...... 0010: E5 55 22 C3 10 9F 9B D0 34 7F 27 85 4D A2 72 9B .U".....4.'.M.r.
从unidbg里面打印一下，没毛病。 就是 25 E1 4D F5
但是对应的App的结果就有点意思了
9608 ldr w8, [x9, x8, lsl #2] ; x8 = 0x90f7 --> 0x73b55372
0x40147510+(0x90f7<<2) = 0x4016B8EC
m0x4016B8EC >-----------------------------------------------------------------------------< [12:00:52 810][email protected][libencrypt.so]0x16b8ec, md5=cd71edc06f5f49b56a700c1f6e541610, hex=e35324c7bb9b61e3b06ee0f4f571fb062a44630bc501d369b49e3e2cee56eaeb463ab0c57e5c3b12a8abf8f81264047dd98a871bc1b84e9d807db83241a8ee1d0be8aeecd8e1328a7311b4a73e2c9b925f24946cc35eacb6953472a0b4cdc9baebce5c65701ab7afa0f48251f1e5afab size: 112 0000: E3 53 24 C7 BB 9B 61 E3 B0 6E E0 F4 F5 71 FB 06 .S$...a..n...q.. 0010: 2A 44 63 0B C5 01 D3 69 B4 9E 3E 2C EE 56 EA EB *Dc....i..>,.V..
这个地址对应的结果不对。 难道App会在内存中变异？
m0x4017B8EC >-----------------------------------------------------------------------------< [12:01:51 113][email protected][libencrypt.so]0x17b8ec, md5=09b5524828f471a42a3e75beed7b23a8, hex=7253b573f596a2d945a40787a842b3a0e46eadcc761474b12000e2a1ec0ab7053cca47f537ed81c4b823dc9866cc99a7b5b4b4adb3fffa867aa45080ea698ddb04e771872ee075f999b9ba241908bc5ac29666eb5f6a7800abee8213d52a28f19321df19b077a1716dbf3ae72a10f33f size: 112 0000: 72 53 B5 73 F5 96 A2 D9 45 A4 07 87 A8 42 B3 A0 rS.s....E....B.. 0010: E4 6E AD CC 76 14 74 B1 20 00 E2 A1 EC 0A B7 05 .n..v.t. .......
在unidbg的内存里面搜索了一下，发现加上 0x10000 之后的值恰好是App里显示的一致。
真相只有一个
pc时代过来的老同学就很敏感了。这个so并不是原始so，而是我们在内存中dump出来的。
我们观察下原始so的节表
fenfei$ greadelf -l libencrypt.so
Elf file type is DYN (Shared object file)
Entry point 0x3210
There are 5 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x000000000002f288 0x000000000002f288 R E 0x10000
LOAD 0x000000000002fba0 0x000000000003fba0 0x000000000003fba0
0x0000000000194a08 0x0000000000194ab8 RW 0x10000
DYNAMIC 0x00000000001c5b90 0x000000000003fc00 0x000000000003fc00
0x0000000000000210 0x0000000000000210 RW 0x8
readelf: Error: no .dynamic section in the dynamic segment
GNU_EH_FRAME 0x000000000002cd10 0x000000000002cd10 0x000000000002cd10
0x000000000000048c 0x000000000000048c R 0x4
LOAD 0x00000000001c5078 0x00000000001d5078 0x00000000001d5078
0x0000000000000afc 0x0000000000000afc R E 0x1000
文件地址 0x2fba0 映射到了 内存地址 0x3fba0
所以我们dump出来的so要修复这个映射
Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x000000000002f288 0x000000000002f288 R E 0x10000
LOAD 0x000000000003fba0 0x000000000003fba0 0x000000000003fba0
0x0000000000194a08 0x0000000000194ab8 RW 0x10000
DYNAMIC 0x00000000001c5b90 0x000000000003fc00 0x000000000003fc00
0x0000000000000210 0x0000000000000210 RW 0x8
readelf: Error: no .dynamic section in the dynamic segment
GNU_EH_FRAME 0x000000000002cd10 0x000000000002cd10 0x000000000002cd10
0x000000000000048c 0x000000000000048c R 0x4
LOAD 0x00000000001c5078 0x00000000001d5078 0x00000000001d5078
0x0000000000000afc 0x0000000000000afc R E 0x1000
把我们dump出的so头里面的 0x2fba0 改成 0x3fba0
这次终于可以成功解密了
call decheckcode: {"code":"0","message":"success","respondData":{"serverTime":1663643024410,"timeSpan":"5","loginFlag":0}}
三、总结
忙活了老半天，其实最后只做了一下修复so文件头。严格意义上只改了3个字节。
改3个字节很简单，分析并知道如何改，再哪改，才是我们的重点。
Trace Function 、Trace Block 、Trace Code。逐渐缩小范围来定位。
还可以通过不同的入参来TraceCode，对比一下更有助于分析算法。
1:ffshow
纵浪大化中 不喜亦不惧 应尽便须尽 无复独多虑
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