Android逆向-获取APP签名

Android逆向-获取APP签名

本文转自Taardisaa 并作补充

很久以前开的blog，关于如何获取APP签名。不知道为啥要写这个了。

Android逆向-APP签名

生成JKS签名

Android studio 如何生成jks签名文件 - 简书 (jianshu.com)

打开AndroidStudio

1
Build-->Generate Signed APK-->APK

然后Key store path选择Create New

然后设置好存储路径，密码也设置一下（偷懒写个123456）

Key的别名就叫key，密码一样简单。

然后剩下的Certificate全填taardis，Country Code填11451。

反正创建成功后，就在选定路径下出现了jks密钥文件。

APK签名

将APK魔改，重新打包后，需要重新签名。

参考：Android之通过 apksigner 对 apk 进行 手动签名_恋恋西风的博客-CSDN博客

1
apksigner.bat sign --verbose --ks D:\Android\Keystore\taardis.jks --v1-signing-enabled false --v2-signing-enabled true --ks-key-alias key --ks-pass pass:123456 --key-pass pass:123456 --out D:\Android\Frida\gadget\bs.apk D:\Android\Frida\gadget\b.apk

成功后提示：

1
Signed

获取APK签名

首先APK解包：

1
apktool d <apk>

然后在 META-INF 文件夹拿到 CERT.RSA 文件。之后：

1
keytool -printcert -file CERT.RSA

不过Keytool似乎是Java的工具，不管了现在用不上。

JEB/JADX

这种反编译器也能直接看到APK的签名信息。

MT APP签名检查及绕过

L-JINBIN/ApkSignatureKillerEx: 新版MT去签及对抗 (github.com)

从“去除签名验证”说起 - 腾讯云开发者社区-腾讯云 (tencent.com)

过签名校验(2) – MT 的 IO 重定向实践 - 『移动安全区』 - 吾爱破解 - LCG - LSG |安卓破解|病毒分析|www.52pojie.cn

MT提供的签名绕过方式能够实现对API和APK方式的绕过。但是对于SVC的则无能为力。

1
2
3
4
String signatureExpected = "3bf8931788824c6a1f2c6f6ff80f6b21";
String signatureFromAPI = md5(signatureFromAPI());
String signatureFromAPK = md5(signatureFromAPK());
String signatureFromSVC = md5(signatureFromSVC());

API检测

用PackageManager直接获得签名。

1
2
3
4
5
6
7
8
9
private byte[] signatureFromAPI() {
    try {
        @SuppressLint("PackageManagerGetSignatures")
        PackageInfo info = getPackageManager().getPackageInfo(getPackageName(), PackageManager.GET_SIGNATURES);
        return info.signatures[0].toByteArray();
    } catch (PackageManager.NameNotFoundException e) {
        throw new RuntimeException(e);
    }
}

APK检测

找到APP私有文件夹下的base.apk，然后得到签名

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
private byte[] signatureFromAPK() {
    try (ZipFile zipFile = new ZipFile(getPackageResourcePath())) {
        Enumeration<? extends ZipEntry> entries = zipFile.entries();
        while (entries.hasMoreElements()) {
            ZipEntry entry = entries.nextElement();
            if (entry.getName().matches("(META-INF/.*)\\.(RSA|DSA|EC)")) {
                InputStream is = zipFile.getInputStream(entry);
                CertificateFactory certFactory = CertificateFactory.getInstance("X509");
                X509Certificate x509Cert = (X509Certificate) certFactory.generateCertificate(is);
                return x509Cert.getEncoded();
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

SVC检测

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
private byte[] signatureFromSVC() {
    try (ParcelFileDescriptor fd = ParcelFileDescriptor.adoptFd(openAt(getPackageResourcePath()));
         ZipInputStream zis = new ZipInputStream(new FileInputStream(fd.getFileDescriptor()))) {
        ZipEntry entry;
        while ((entry = zis.getNextEntry()) != null) {
            if (entry.getName().matches("(META-INF/.*)\\.(RSA|DSA|EC)")) {
                CertificateFactory certFactory = CertificateFactory.getInstance("X509");
                X509Certificate x509Cert = (X509Certificate) certFactory.generateCertificate(zis);
                return x509Cert.getEncoded();
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}

绕过

Java层的东西不多

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
private static void killOpen(String packageName) {
    try {
        // Native层Hook
        System.loadLibrary("SignatureKiller");
    } catch (Throwable e) {
        System.err.println("Load SignatureKiller library failed");
        return;
    }
    // 读取/proc/self/maps读取APP路径
    String apkPath = getApkPath(packageName);
    if (apkPath == null) {
        System.err.println("Get apk path failed");
        return;
    }
    // 读取自身APK文件（私有目录下的base.apk）
    File apkFile = new File(apkPath);
    // 在APP私有目录下创建origin.apk文件
    File repFile = new File(getDataFile(packageName), "origin.apk");
    try (ZipFile zipFile = new ZipFile(apkFile)) {
        // 将APK中的origin.apk给提取出来（origin.apk是MT去签是生成的，是初始没有被去签的APK）
        String name = "assets/SignatureKiller/origin.apk";
        ZipEntry entry = zipFile.getEntry(name);
        if (entry == null) {
            System.err.println("Entry not found: " + name);
            return;
        }
        // 读取出来
        if (!repFile.exists() || repFile.length() != entry.getSize()) {
            try (InputStream is = zipFile.getInputStream(entry); OutputStream os = new FileOutputStream(repFile)) {
                byte[] buf = new byte[102400];
                int len;
                while ((len = is.read(buf)) != -1) {
                    os.write(buf, 0, len);
                }
            }
        }
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
    // 传入底层so Hook
    hookApkPath(apkFile.getAbsolutePath(), repFile.getAbsolutePath());
}

然后看Native层，实际上是XHook，用于替换libc函数。

1
mt_jni.c

实际上就做了个字符串替换，有意将原本要打开的APK替换成origin.apk。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
const char *apkPath__;
const char *repPath__;

int (*old_open)(const char *, int, mode_t);
static int openImpl(const char *pathname, int flags, mode_t mode) {
    //XH_LOG_ERROR("open: %s", pathname);
    if (strcmp(pathname, apkPath__) == 0){
        //XH_LOG_ERROR("replace -> %s", repPath__);
        return old_open(repPath__, flags, mode);
    }
    return old_open(pathname, flags, mode);
}

JNIEXPORT void JNICALL
Java_bin_mt_signature_KillerApplication_hookApkPath(JNIEnv *env, __attribute__((unused)) jclass clazz, jstring apkPath, jstring repPath) {
    apkPath__ = (*env)->GetStringUTFChars(env, apkPath, 0);
    repPath__ = (*env)->GetStringUTFChars(env, repPath, 0);

    xhook_register(".*\\.so$", "openat64", openat64Impl, (void **) &old_openat64);
    xhook_register(".*\\.so$", "openat", openatImpl, (void **) &old_openat);
    xhook_register(".*\\.so$", "open64", open64Impl, (void **) &old_open64);
    xhook_register(".*\\.so$", "open", openImpl, (void **) &old_open);

    xhook_refresh(0);
}

通过Hook open函数，可以把基于APK读取的签名方式给绕过。

下面提供一个绕过基于PackageManager的：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
private static void killPM(String packageName, String signatureData) {
    // 构造一个假的签名
    Signature fakeSignature = new Signature(Base64.decode(signatureData, Base64.DEFAULT));
    Parcelable.Creator<PackageInfo> originalCreator = PackageInfo.CREATOR;
    Parcelable.Creator<PackageInfo> creator = new Parcelable.Creator<PackageInfo>() {
        @Override
        public PackageInfo createFromParcel(Parcel source) {
            PackageInfo packageInfo = originalCreator.createFromParcel(source);
            if (packageInfo.packageName.equals(packageName)) { //
                if (packageInfo.signatures != null && packageInfo.signatures.length > 0) {
                    packageInfo.signatures[0] = fakeSignature; // 将虚假的签名放入packageInfo，取代原来的
                }
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
                    if (packageInfo.signingInfo != null) {
                        Signature[] signaturesArray = packageInfo.signingInfo.getApkContentsSigners();
                        if (signaturesArray != null && signaturesArray.length > 0) {
                            signaturesArray[0] = fakeSignature;
                        }
                    }
                }
            }
            return packageInfo;
        }

        @Override
        public PackageInfo[] newArray(int size) {
            return originalCreator.newArray(size);
        }
    };
    try {
        // 用假的creator替换原来的PackageInfo.CREATOR
        findField(PackageInfo.class, "CREATOR").set(null, creator);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
        // 解除某些Android系统API的使用限制？
        HiddenApiBypass.addHiddenApiExemptions("Landroid/os/Parcel;", "Landroid/content/pm", "Landroid/app");
    }
    try {
        // 清空签名缓存
        Object cache = findField(PackageManager.class, "sPackageInfoCache").get(null);
        // noinspection ConstantConditions
        cache.getClass().getMethod("clear").invoke(cache);
    } catch (Throwable ignored) {
    }
    try {
        // 清空签名缓存
        Map<?, ?> mCreators = (Map<?, ?>) findField(Parcel.class, "mCreators").get(null);
        // noinspection ConstantConditions
        mCreators.clear();
    } catch (Throwable ignored) {
    }
    try {
        // 清空签名缓存
        Map<?, ?> sPairedCreators = (Map<?, ?>) findField(Parcel.class, "sPairedCreators").get(null);
        // noinspection ConstantConditions
        sPairedCreators.clear();
    } catch (Throwable ignored) {
    }
}

参考

Java Keytool 介绍 - 且行且码 - 博客园 (cnblogs.com)

获取Android应用签名的几种方式 - 简书 (jianshu.com)

Android studio 如何生成jks签名文件 - 简书 (jianshu.com)

apktool重新打包时报错_apktool 忽略错误信息__y4nnl2的博客-CSDN博客

Android之通过 apksigner 对 apk 进行 手动签名_恋恋西风的博客-CSDN博客

apksigner | Android 开发者 | Android Developers (google.cn)