这篇文章上次修改于 958 天前，可能其部分内容已经发生变化，如有疑问可询问作者。
原文 -> https://blog.csdn.net/qq_38851536/article/details/118794351
前言
这是SO逆向入门实战教程的第十一篇，总共会有十一篇，十三十一个实战（PS：更多实战在龙哥星球
- 出于学习和研究的目的，对shield的模拟执行和算法分析，本篇不会太过详细，只会讲解关键点
unidbg 模拟执行
shield的模拟执行并没什么难度，依照此前所述，JNItrace 就能基本解决问题
因为shield通过拦截器去完成参数的封装，所以为了更加优雅的实现，我们在代码中引入OkHttp库
但这并不是必须的，只是这样做更优雅
package com.article13;
import com.github.unidbg.AndroidEmulator;
import com.github.unidbg.Module;
import com.github.unidbg.linux.android.AndroidEmulatorBuilder;
import com.github.unidbg.linux.android.AndroidResolver;
import com.github.unidbg.linux.android.SystemPropertyHook;
import com.github.unidbg.linux.android.SystemPropertyProvider;
import com.github.unidbg.linux.android.dvm.*;
import com.github.unidbg.linux.android.dvm.array.ByteArray;
import com.github.unidbg.memory.Memory;
import okhttp3.*;
import okio.Buffer;
import okio.BufferedSink;
import org.apache.commons.codec.binary.Base64;
import java.awt.geom.RectangularShape;
import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
public class xhs extends AbstractJni {
private final AndroidEmulator emulator;
private final VM vm;
private final Module module;
private Headers headers;
private Request request;
private String url;
xhs(){
emulator = AndroidEmulatorBuilder.for32Bit().setProcessName("com.xhs").build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分
final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口
memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析
vm = emulator.createDalvikVM(new File("E:\\unidbg-master\\unidbg-master\\unidbg-android\\src\\test\\resources\\example_binaries\\xhs\\xhs-armv7.apk"));
vm.setVerbose(true);
DalvikModule dm = vm.loadLibrary(new File("E:\\unidbg-master\\unidbg-master\\unidbg-android\\src\\test\\resources\\example_binaries\\xhs\\libshield.so"), true);
vm.setJni(this);
module = dm.getModule();
System.out.println("call JNIOnLoad");
dm.callJNI_OnLoad(emulator);
url = "https://edith.xiaohongshu.com/api/sns/v6/homefeed?oid=homefeed_recommend&cursor_score=&geo=eyJsYXRpdHVkZSI6MC4wMDAwMDAsImxvbmdpdHVkZSI6MC4wMDAwMDB9%0A&trace_id=7e9cea5d-3e7c-3240-bf3d-20e221557b61¬e_index=0&refresh_type=1&client_volume=0.60&preview_ad=&loaded_ad=%7B%22ads_id_list%22%3A%5B%5D%7D&personalization=1&pin_note_id=&pin_note_source=&unread_begin_note_id=60da0881000000002103ef52&unread_end_note_id=60e2abe5000000000102aced&unread_note_count=6";
request = new Request.Builder()
.url(url)
.addHeader("X-B3-TraceId", "4a4a3a065c180b0f")
.addHeader("xy-common-params", "fid=16254550111059c4b478ba32dc122790a4f7e9261f0e&device_fingerprint=20210101000953d097cda53c248c488cadcce5ec7882880173338edc38b45d&device_fingerprint1=20210101000953d097cda53c248c488cadcce5ec7882880173338edc38b45d&launch_id=1625473798&tz=Asia%2FShanghai&channel=PMgdt19935737&versionName=6.97.0.1&deviceId=1d41ebdc-86dd-33ea-9ceb-e9210babd74e&platform=android&sid=session.1625455019284508278852&identifier_flag=4&t=1625473812&project_id=ECFAAF&build=6970181&x_trace_page_current=explore_feed&lang=zh-Hans&app_id=ECFAAF01&uis=light")
.addHeader("User-Agent", "Dalvik/2.1.0 (Linux; U; Android 10; MIX 2S MIUI/V12.0.2.0.QDGCNXM) Resolution/1080*2160 Version/6.97.0.1 Build/6970181 Device/(Xiaomi;MIX 2S) discover/6.97.0.1 NetType/CellNetwork")
.build();
}
// 第一个初始化函数
public void callinitializeNative(){
List<Object> list = new ArrayList<>(10);
list.add(vm.getJNIEnv()); // 第一个参数是env
list.add(0); // 第二个参数，实例方法是jobject，静态方法是jclazz，可以填0，但最好是构造一下
module.callFunction(emulator, 0x6c11d, list.toArray());
};
// 第二个初始化函数
public long callinitialize(){
List<Object> list = new ArrayList<>(10);
list.add(vm.getJNIEnv()); // 第一个参数是env
list.add(0); // 第二个参数，实例方法是jobject，静态方法是jclazz，可以填0，但最好是构造一下
list.add(vm.addLocalObject(new StringObject(vm, "main")));
Number number = module.callFunction(emulator, 0x6b801, list.toArray())[0];
return number.longValue();
}
// 目标函数
public void callintercept(long ptr){
List<Object> list = new ArrayList<>(10);
list.add(vm.getJNIEnv()); // 第一个参数是env
list.add(0); // 第二个参数，实例方法是jobject，静态方法是jclazz，可以填0，但最好是构造一下
DvmObject<?> chain = vm.resolveClass("okhttp3/Interceptor$Chain").newObject(null);
list.add(vm.addLocalObject(chain));
list.add(ptr);
module.callFunction(emulator, 0x6b9e9, list.toArray());
};
public static void main(String[] args) {
xhs test = new xhs();
test.callinitializeNative();
long ptr = test.callinitialize();
System.out.println("call intercept");
test.callintercept(ptr);
}
@Override
public DvmObject<?> getStaticObjectField(BaseVM vm, DvmClass dvmClass, String signature) {
switch (signature){
case "com/xingin/shield/http/ContextHolder->sLogger:Lcom/xingin/shield/http/ShieldLogger;":{
return vm.resolveClass("com/xingin/shield/http/ShieldLogger").newObject(signature);
}
case "com/xingin/shield/http/ContextHolder->sDeviceId:Ljava/lang/String;":{
return new StringObject(vm, "1d41ebdc-86dd-33ea-9ceb-e9210babd74e");
}
}
return super.getStaticObjectField(vm, dvmClass, signature);
}
@Override
public void callVoidMethodV(BaseVM vm, DvmObject<?> dvmObject, String signature, VaList vaList) {
switch (signature){
case "com/xingin/shield/http/ShieldLogger->nativeInitializeStart()V":{
return;
}
case "com/xingin/shield/http/ShieldLogger->nativeInitializeEnd()V": {
return;
}
case "com/xingin/shield/http/ShieldLogger->initializeStart()V": {
return;
}
case "com/xingin/shield/http/ShieldLogger->initializedEnd()V": {
return;
}
case "com/xingin/shield/http/ShieldLogger->buildSourceStart()V": {
return;
}
case "okhttp3/RequestBody->writeTo(Lokio/BufferedSink;)V": {
BufferedSink bufferedSink = (BufferedSink) vaList.getObjectArg(0).getValue();
RequestBody requestBody = (RequestBody) dvmObject.getValue();
if(requestBody != null){
try {
requestBody.writeTo(bufferedSink);
} catch (IOException e) {
e.printStackTrace();
}
}
return;
}
case "com/xingin/shield/http/ShieldLogger->buildSourceEnd()V": {
return;
}
case "com/xingin/shield/http/ShieldLogger->calculateStart()V": {
System.out.println("calculateStart —— 开始计算");
return;
}
case "com/xingin/shield/http/ShieldLogger->calculateEnd()V": {
System.out.println("calculateEnd —— 结束计算");
return;
}
}
super.callVoidMethodV(vm, dvmObject, signature, vaList);
}
@Override
public DvmObject<?> callStaticObjectMethodV(BaseVM vm, DvmClass dvmClass, String signature, VaList vaList) {
switch (signature){
case "java/nio/charset/Charset->defaultCharset()Ljava/nio/charset/Charset;":{
return vm.resolveClass("java/nio/charset/Charset").newObject(Charset.defaultCharset());
}
case "com/xingin/shield/http/Base64Helper->decode(Ljava/lang/String;)[B":{
String input = (String) vaList.getObjectArg(0).getValue();
byte[] result = Base64.decodeBase64(input);
return new ByteArray(vm, result);
}
}
return super.callStaticObjectMethodV(vm, dvmClass, signature, vaList);
}
@Override
public int getIntField(BaseVM vm, DvmObject<?> dvmObject, String signature) {
switch (signature){
case "android/content/pm/PackageInfo->versionCode:I":{
return 6970181;
}
}
return super.getIntField(vm, dvmObject, signature);
}
@Override
public int getStaticIntField(BaseVM vm, DvmClass dvmClass, String signature) {
switch (signature){
case "com/xingin/shield/http/ContextHolder->sAppId:I":{
return -319115519;
}
}
return super.getStaticIntField(vm, dvmClass, signature);
}
@Override
public DvmObject<?> callObjectMethodV(BaseVM vm, DvmObject<?> dvmObject, String signature, VaList vaList) {
switch (signature) {
case "android/content/Context->getSharedPreferences(Ljava/lang/String;I)Landroid/content/SharedPreferences;":
return vm.resolveClass("android/content/SharedPreferences").newObject(vaList.getObjectArg(0));
case "android/content/SharedPreferences->getString(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;": {
if(((StringObject) dvmObject.getValue()).getValue().equals("s")){
System.out.println("getString :"+vaList.getObjectArg(0).getValue());
if (vaList.getObjectArg(0).getValue().equals("main")) {
return new StringObject(vm, "");
}
if(vaList.getObjectArg(0).getValue().equals("main_hmac")){
return new StringObject(vm, "eSwKRbpB4OfG+D8ofTHooZrXr1b0B+ZDVsxHEr7K7yTWiiVX/bZl0E8D6+6645aLIAZ0+geJrjMLyyrXA99xApWvssdRm01Cg8PRVJhEvWqyHNAS73/z0OLspXVmhaSs");
}
}
}
case "okhttp3/Interceptor$Chain->request()Lokhttp3/Request;": {
DvmClass clazz = vm.resolveClass("okhttp3/Request");
return clazz.newObject(request);
}
case "okhttp3/Request->url()Lokhttp3/HttpUrl;": {
DvmClass clazz = vm.resolveClass("okhttp3/HttpUrl");
Request request = (Request) dvmObject.getValue();
return clazz.newObject(request.url());
}
case "okhttp3/HttpUrl->encodedPath()Ljava/lang/String;": {
HttpUrl httpUrl = (HttpUrl) dvmObject.getValue();
return new StringObject(vm, httpUrl.encodedPath());
}
case "okhttp3/HttpUrl->encodedQuery()Ljava/lang/String;": {
HttpUrl httpUrl = (HttpUrl) dvmObject.getValue();
return new StringObject(vm, httpUrl.encodedQuery());
}
case "okhttp3/Request->body()Lokhttp3/RequestBody;": {
Request request = (Request) dvmObject.getValue();
return vm.resolveClass("okhttp3/RequestBody").newObject(request.body());
}
case "okhttp3/Request->headers()Lokhttp3/Headers;": {
Request request = (Request) dvmObject.getValue();
return vm.resolveClass("okhttp3/Headers").newObject(request.headers());
}
case "okio/Buffer->writeString(Ljava/lang/String;Ljava/nio/charset/Charset;)Lokio/Buffer;": {
System.out.println("write to my buffer:"+vaList.getObjectArg(0).getValue());
Buffer buffer = (Buffer) dvmObject.getValue();
buffer.writeString(vaList.getObjectArg(0).getValue().toString(), (Charset) vaList.getObjectArg(1).getValue());
return dvmObject;
}
case "okhttp3/Headers->name(I)Ljava/lang/String;": {
Headers headers = (Headers) dvmObject.getValue();
return new StringObject(vm, headers.name(vaList.getIntArg(0)));
}
case "okhttp3/Headers->value(I)Ljava/lang/String;": {
Headers headers = (Headers) dvmObject.getValue();
return new StringObject(vm, headers.value(vaList.getIntArg(0)));
}
case "okio/Buffer->clone()Lokio/Buffer;": {
Buffer buffer = (Buffer) dvmObject.getValue();
return vm.resolveClass("okio/Buffer").newObject(buffer.clone());
}
case "okhttp3/Request->newBuilder()Lokhttp3/Request$Builder;": {
Request request = (Request) dvmObject.getValue();
return vm.resolveClass("okhttp3/Request$Builder").newObject(request.newBuilder());
}
case "okhttp3/Request$Builder->header(Ljava/lang/String;Ljava/lang/String;)Lokhttp3/Request$Builder;": {
Request.Builder builder = (Request.Builder) dvmObject.getValue();
builder.header(vaList.getObjectArg(0).getValue().toString(), vaList.getObjectArg(1).getValue().toString());
return dvmObject;
}
case "okhttp3/Request$Builder->build()Lokhttp3/Request;": {
Request.Builder builder = (Request.Builder) dvmObject.getValue();
return vm.resolveClass("okhttp3/Request").newObject(builder.build());
}
case "okhttp3/Interceptor$Chain->proceed(Lokhttp3/Request;)Lokhttp3/Response;": {
return vm.resolveClass("okhttp3/Response").newObject(null);
}
}
return super.callObjectMethodV(vm, dvmObject, signature, vaList);
}
@Override
public DvmObject<?> newObjectV(BaseVM vm, DvmClass dvmClass, String signature, VaList vaList) {
switch (signature){
case "okio/Buffer-><init>()V":
return dvmClass.newObject(new Buffer());
}
return super.newObjectV(vm, dvmClass, signature, vaList);
}
@Override
public int callIntMethodV(BaseVM vm, DvmObject<?> dvmObject, String signature, VaList vaList) {
switch (signature){
case "okhttp3/Headers->size()I":
Headers headers = (Headers) dvmObject.getValue();
return headers.size();
case "okhttp3/Response->code()I":
return 200;
case "okio/Buffer->read([B)I":
Buffer buffer = (Buffer) dvmObject.getValue();
return buffer.read((byte[]) vaList.getObjectArg(0).getValue());
}
return super.callIntMethodV(vm, dvmObject, signature, vaList);
}
}全部的内容都在前述文章中有讲述
unidbg算法还原
网上也有不少shield的算法还原文章，一些是IDA F5扣下来伪代码，所以我们有必要再说说
算法用到了现代密码学算法(AES+HMAC MD5)来保证强度，以及古典加密(查表替换，类似于凯撒密码之类的)来保证独特性
其中 AES 和 HMAC MD5 都经过了魔改，代码本身没有经过混淆，这极大的降低了难度，但开发者对密码学显然有一定了解，算法魔改的很好
MD5主要修改了IV(ABCD颠倒)、运算中循环左移的位数、K值、运算的顺序，在我见过的样本里，是是对MD5的魔改程度很彻底的了，粒度也很细
如下是Python版本的代码，感兴趣的可以和正常MD5进行对比
import binascii
SV = [0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee, 0xf57c0faf,
0x4787c62a, 0xa8304613, 0xfd469501, 0x698098d8, 0x8b44f7af,
0xffff5bb1, 0x895cd7be, 0x6b901122, 0xfd987193, 0xa679438e,
0x49b40821, 0xf61e2562&0xFF00FF00, 0xc040b340, 0x265e5a51, 0xe9b6c7aa& 0xFF0011FF,
0xd62f105d, 0x2441453, 0xd8a1e681, 0xe7d3fbc8, 0x21e1cde6,
0xc33707d6, 0xf4d50d87, 0x455a14ed, 0xa9e3e905, 0xfcefa3f8 & 0xFF110011,
0x676f02d9, 0x8d2a4c8a, 0xfffa3942, 0x8771f681, 0x6d9d6122,
0xfde5380c, 0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x4881d05, 0xd9d4d039,
0xe6db99e5, 0x1fa27cf8, 0xc4ac5665, 0xf4292244, 0x432aff97,
0xab9423a7, 0xfc93a039, 0x655b59c3, 0x8f0ccc92, 0xffeff47d,
0x85845dd1, 0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391]
# 根据ascil编码把字符转成对应的二进制
def binvalue(val, bitsize):
binval = bin(val)[2:] if isinstance(val, int) else bin(ord(val))[2:]
if len(binval) > bitsize:
raise ("binary value larger than the expected size")
while len(binval) < bitsize:
binval = "0" + binval
return binval
def string_to_bit_array(text):
array = list()
for char in text:
binval = binvalue(char, 8)
array.extend([int(x) for x in list(binval)])
return array
# 循环左移
def leftCircularShift(k, bits):
bits = bits % 32
k = k % (2 ** 32)
upper = (k << bits) % (2 ** 32)
result = upper | (k >> (32 - (bits)))
return (result)
# 分块
def blockDivide(block, chunks):
result = []
size = len(block) // chunks
for i in range(0, chunks):
result.append(int.from_bytes(block[i * size:(i + 1) * size], byteorder="little"))
return result
# F函数作用于“比特位”上
# if x then y else z
def F(X, Y, Z):
compute = ((X & Y) | ((~X) & Z))
return compute
# if z then x else y
def G(X, Y, Z):
return ((X & Z) | (Y & (~Z)))
# if X = Y then Z else ~Z
def H(X, Y, Z):
return (X ^ Y ^ Z)
def I(X, Y, Z):
return (Y ^ (X | (~Z)))
# 四个F函数
def FF(a, b, c, d, M, s, t):
xhsTemp = leftCircularShift((a + F(b, c, d) + M + t), s)
result = b + xhsTemp
return (result)
def GG(a, b, c, d, M, s, t):
result = b + leftCircularShift((a + G(b, c, d) + M + t), s)
return (result)
def HH(a, b, c, d, M, s, t):
result = b + leftCircularShift((a + H(b, c, d) + M + t), s)
# print(hex(leftCircularShift((a + H(b, c, d) + M + t), s)))
return (result)
def HH1(a, b, c, d, M, s, t):
result = b + leftCircularShift((a + H(b, c, d) + M + t), s)
return (result)
def II(a, b, c, d, M, s, t):
result = b + leftCircularShift((a + I(b, c, d) + M + t), s)
return (result)
# 数据转换
def fmt8(num):
bighex = "{0:08x}".format(num)
binver = binascii.unhexlify(bighex)
result = "{0:08x}".format(int.from_bytes(binver, byteorder='little'))
return (result)
# 计算比特长度
def bitlen(bitstring):
return len(bitstring) * 8
def md5sum(msg):
# 计算比特长度，如果内容过长，64个比特放不下，就取低64bit
msgLen = bitlen(msg) % (2 ** 64)
# 先填充一个0x80，其实是先填充一个1，后面跟对应个数的0，因为一个明文的编码至少需要8比特，所以直接填充 0b10000000即0x80
msg = msg + b'\x80' # 0x80 = 1000 0000
zeroPad = (448 - (msgLen + 8) % 512) % 512
zeroPad //= 8
# msg = msg + b'\x00' * zeroPad + bytes.fromhex('4022000000000000')
print(msgLen)
msg = msg + b'\x00' * zeroPad + msgLen.to_bytes(8, byteorder='little')
# 计算循环轮数，512个为一轮
msgLen = bitlen(msg)
iterations = msgLen // 512
# 初始化变量
# 算法魔改的第一个点，也是最明显的点
D = 0x67452301
C = 0xefcdab89
B = 0x98badcfe
A = 0x10325476
# main loop
for i in range(0, 2):
a = A
b = B
c = C
d = D
block = msg[i * 64:(i + 1) * 64]
M = blockDivide(block, 16)
# Rounds
a = FF(a, b, c, d, M[0], 6, SV[0])
d = FF(d, a, b, c, M[1], 13, SV[1])
c = FF(c, d, a, b, M[2], 17, SV[2])
b = FF(b, c, d, a, M[3], 21, SV[3])
a = FF(a, b, c, d, M[4], 7, SV[4])
d = FF(d, a, b, c, M[5], 12, SV[5])
c = FF(c, d, a, b, M[6], 17, SV[6])
b = FF(b, c, d, a, M[7], 20, SV[7])
a = FF(a, b, c, d, M[8], 7, SV[8])
d = FF(d, a, b, c, M[9], 12, SV[9])
c = FF(c, d, a, b, M[10], 16, SV[10])
b = FF(b, c, d, a, M[11], 22, SV[11])
a = FF(a, b, c, d, M[12], 7, SV[12])
d = FF(d, a, b, c, M[13], 13, SV[13])
c = FF(c, d, a, b, M[14], 17, SV[14])
b = FF(b, c, d, a, M[15], 22, SV[15])
a = GG(a, b, c, d, M[1], 5, SV[16])
d = GG(d, a, b, c, M[6], 9, SV[17])
c = GG(c, d, a, b, M[11], 14, SV[18])
b = GG(b, c, d, a, M[0], 20, SV[19])
a = GG(a, b, c, d, M[5], 5, SV[20]) # 21 step
d = GG(d, a, b, c, M[10], 9, SV[21]) # 22 step
c = GG(c, d, a, b, M[15], 14, SV[22]) # 23 step
b = GG(b, c, d, a, M[4], 20, SV[23])
a = GG(a, b, c, d, M[9], 5, SV[24])
d = GG(d, a, b, c, M[14], 9, SV[25])
c = GG(c, d, a, b, M[3], 14, SV[26]) # 27 step
b = GG(b, c, d, a, M[8], 20, SV[27])
a = GG(a, b, c, d, M[13], 5, SV[28]) # 29 step
d = GG(d, a, b, c, M[2], 9, SV[29]) # 30 step
c = GG(c, d, a, b, M[7], 14, SV[30])
b = GG(b, c, d, a, M[12], 20, SV[31])
a = HH(a, b, c, d, M[5], 4, SV[32]) # 33 step
d = HH(d, a, b, c, M[8], 11, SV[33])
c = HH(c, d, a, b, M[11], 16, SV[34])
b = HH(b, c, d, a, M[14], 23, SV[35]) # 36
a = HH(a, b, c, d, M[1], 4, SV[36]) # 37
d = HH(d, a, b, c, M[4], 11, SV[37]) # 38
c = HH(c, d, a, b, M[7], 16, SV[38]) # 39
# 正常的第40步
# b = HH(b, c, d, a, M[10], 23, SV[39])
a = HH(a, b, c, d, M[13], 4, SV[40]) # 第40步
b = HH(b, c, a, d, M[10], 23, SV[39]) # 第41步
c = HH(c, d, a, b, M[3], 16, SV[42]) # 第42步
d = HH(d, a, b, c, M[0], 11, SV[41]) # 43
b = HH(b, c, d, a, M[6], 23, SV[43]) # 44
a = HH(a, b, c, d, M[9], 4, SV[44]) # 45
d = HH(d, a, b, c, M[12], 11, SV[45]) # 46
c = HH(c, d, a, b, M[15], 16, SV[46]) # 47
b = HH(b, c, d, a, M[2], 23, SV[47]) # 48
a = II(a, b, c, d, M[0], 6, SV[48])
d = II(d, a, b, c, M[7], 10, SV[49])
c = II(c, d, a, b, M[14], 15, SV[50])
b = II(b, c, d, a, M[5], 21, SV[51]) # 52
a = II(a, b, c, d, M[12], 6, SV[52])
d = II(d, a, b, c, M[3], 10, SV[53])
c = II(c, d, a, b, M[10], 15, SV[54])
b = II(b, c, d, a, M[1], 21, SV[55]) #56
a = II(a, b, c, d, M[8], 6, SV[56])
d = II(d, a, b, c, M[15], 10, SV[57])
c = II(c, d, a, b, M[6], 15, SV[58])
b = II(b, c, d, a, M[13], 21, SV[59]) # 60
a = II(a, b, c, d, M[4], 6, SV[60])
d = II(d, a, b, c, M[11], 10, SV[61])
c = II(c, d, a, b, M[2], 15, SV[62])# 63
b = II(b, c, d, a, M[9], 21, SV[63])
A = (A + a) % (2 ** 32)
B = (B + b) % (2 ** 32)
C = (C + c) % (2 ** 32)
D = (D + d) % (2 ** 32)
result = fmt8(A) + fmt8(B) + fmt8(C) + fmt8(D)
return result
if __name__ == "__main__":
data = bytes.fromhex("d7ab505697331bfab20a1d121157e174b2a4939f375fe5a9c1aeb06f8118c65264470147c736f2a298e66cf40589c1d57852aa3469596f9e755a0752c50297038a06f86db83b6932f1d4a55bfdeb79ac")
print("plainText: ", data)
print("result: ", md5sum(data))第二个就是AES的魔改，AES在工程中，主要有三个思路实现
- 标准实现（标准S盒和各种逆S盒）
- 表合并实现 （空间换时间，将运算转变成查表）
- 白盒AES（难、复杂）
其中三种实现之间是有密切联系的，AES每轮的具体运算有四个步骤，列混淆、S盒替换、和密钥异或 以及循环左移
标准实现就是老老实实去做每一步，标准AES的代码最好懂，也好排查问题，逆向也是它最好分析
表合并法将列混淆、循环左移、S盒替换这三步整合到一起去，但是AES最后一轮并不是完整的，所以最后一轮还是类似于标准实现
白盒AES简单理解就是四步合一，将密钥埋藏在了加密中，防止人直接得到密钥
从标准实现到表合并发，是为了提高运算速度，代价是原本SO里只要S盒和逆S盒，现在要多出八个大的合并表
从前两种到白盒AES，则是为了隐藏密钥，应对反编译
Shield采用的是表合并实现的AES，仔细瞧瞧的话，感觉样本像是改的OpenSSL的代码
AES魔改点选择的也很隐蔽，修改了密钥扩展中需要用到的Rcon，硬编码在了样本中，非常的好
除此之外并没有别的什么很有意思了
HMAC-MD5中的HMAC方法也是标准的
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