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最近项目有需求: 只有使用特定签名签的apk才可以安装,其他任何apk都不能安装(root版,使用adb push进去的除外)。n多度娘、google之后最终实现,把实现代码罗列一下,以供以后参考.
1、使用工具自己制作签名文件,这个签名就是需要提供给apk制作者签名使用的。
可以参考源码路径 build/target/product/security/README 文件
development/tools/make_key testkey ‘/C=CN/ST=ShangHai/L=ShangHai/O=xxx/OU=MTK/CN=China/emailAddress=xxx@qq'
2、使用制作好的签名文件签名一个内置的apk,本例采用使用 com.mediatek.factorymode 作为以后签名的对比对象
mediatek/packages/apps/FactoryMode/Android.mk
增加
[java] view plain copy- ifeq ($(XHW_SIGNATURE_CONFIG),yes)
- LOCAL_CERTIFICATE := testkey
- endif
3、在安装过程中对比签名,如果签名相同的话就继续安装,否则给出一个错误号,弹一个消息框
frameworks/base/services/java/com/android/server/pm/PackageManagerService.java
[java] view plain copy- private PackageParser.Package scanPackageLI(PackageParser.Package pkg,
- int parseFlags, int scanMode, long currentTime, UserHandle user) {
- ...
- if (!verifySignaturesLP(pkgSetting, pkg)) {
- ...
- }
- //add start
- if(com.mediatekmon.featureoption.FeatureOption.XHW_SIGNATURE_CONFIG) {
- // is xhw signatures
- Signature[] xhwSignatures = getXWHSignatures();
- if (xhwSignatures != null) {
- if (compareSignatures(xhwSignatures, pkg.mSignatures) != PackageManager.SIGNATURE_MATCH) {
- mLastScanError = PackageManager.INSTALL_FAILED_INVALID_SIGNATURES;
- return null;
- }
- }
- }
- //add end
- // Verify that this new package doesn't have any content providers
- // that conflict with existing packages. Only do this if the
- // package isn't already installed, since we don't want to break
- // things that are installed.
- if ((scanMode&SCAN_NEW_INSTALL) != 0) {
- ...
- }
因为在启动是也要走 scanPackageLI 函数,故增加一个变量 mIsInstallApkFlag 判断是否是安装过程
[java] view plain copy- private void installPackageLI(InstallArgs args,
- boolean newInstall, PackageInstalledInfo res) {
- ...
- Log.i(TAG, "Start installation for package: " + pkg.packageName);
- //add start
- if(com.mediatekmon.featureoption.FeatureOption.XHW_SIGNATURE_CONFIG) {
- Log.i(TAG, "installPackageLI-111- mIsInstallApkFlag="+mIsInstallApkFlag);
- mIsInstallApkFlag = true;
- Log.i(TAG, "installPackageLI-222- mIsInstallApkFlag="+mIsInstallApkFlag);
- }
- //add end
- if (replace) {
- replacePackageLI(pkg, parseFlags, scanMode, args.user,
- installerPackageName, res);
- } else {
- installNewPackageLI(pkg, parseFlags, scanMode, args.user,
- installerPackageName, res);
- }
- Log.i(TAG, "Installation done for package: " + pkg.packageName);
- ...
- }
增加的函数为: [java] view plain copy
- //add start
- private boolean mIsInstallApkFlag = false;
- private Signature[] getXWHSignatures(){
- if(!mIsInstallApkFlag) return null;
- // 取得xhw签名
- Signature[] xhwSigns = null;
- String packageName = "com.mediatek.factorymode";
- /* try {
- //PackageInfo xhwPackageInfo = mContext.getPackageManager().getPackageInfo("com.mediatek.factorymode", PackageManager.GET_SIGNATURES); //-- 只能取得已安装的apk 签名
- PackageInfo xhwPackageInfo = getPackageInfo("com.mediatek.factorymode", PackageManager.GET_SIGNATURES, Process.SYSTEM_UID);
- if(xhwPackageInfo != null){
- xhwSigns = xhwPackageInfo.signatures;
- }
- } catch (Exception e) {
- e.printStackTrace();
- }
- if(xhwSigns != null) Log.e(TAG, "....----getXWHSignatures--xhw_Signs[0]="+xhwSigns[0].toCharsString());
- */
- //another method
- PackageSetting ps = mSettings.mPackages.get(packageName);
- if (ps != null) {
- PackageParser.Package pkg = ps.pkg;
- if (pkg == null) {
- pkg = new PackageParser.Package(packageName);
- pkg.applicationInfo.packageName = packageName;
- pkg.applicationInfo.flags = ps.pkgFlags | ApplicationInfo.FLAG_IS_DATA_ONLY;
- pkg.applicationInfo.publicSourceDir = ps.resourcePathString;
- pkg.applicationInfo.sourceDir = ps.codePathString;
- pkg.applicationInfo.dataDir = getDataPathForPackage(packageName, 0).getPath();
- pkg.applicationInfo.nativeLibraryDir = ps.nativeLibraryPathString;
- }
- PackageInfo xhwPackageInfo2 = generatePackageInfo(pkg, PackageManager.GET_SIGNATURES, UserHandle.getCallingUserId());
- if(xhwPackageInfo2 != null){
- xhwSigns = xhwPackageInfo2.signatures;
- }
- }
- // reset flag
- mIsInstallApkFlag = false;
- return xhwSigns;
- }
- //add end
上面代码中 PackageManager.INSTALL_FAILED_INVALID_SIGNATURES 是自己增加的错误代码,以供弹出消息使用
[java] view plain copy- +++ frameworks/base/core/java/android/content/pm/PackageManager.java (revision 471)
- @@ -553,7 +553,17 @@
- */
- public static final int INSTALL_FAILED_VERSION_DOWNGRADE = -25;
- +
- /**
- + * Installation return code: this is passed to the {@link IPackageInstallObserver} by
- + * {@link #installPackage(android.Uri, IPackageInstallObserver, int)} if
- + * the installed package hasn't the expected signature
- + * @hide
- + */
- + public static final int INSTALL_FAILED_INVALID_SIGNATURES = -26; //jimbo add
- +
- +
- + /**
- * Installation parse return code: this is passed to the {@link IPackageInstallObserver} by
- * {@link #installPackage(android.Uri, IPackageInstallObserver, int)}
- * if the parser was given a path that is not a file, or does not end with the expected
4、 弹出错误提示
packages/apps/PackageInstaller/src/com/android/packageinstaller/InstallAppProgress.java
- private Handler mHandler = new Handler() {
- public void handleMessage(Message msg) {
- switch (msg.what) {
- ...
- //add start
- } else if (msg.arg1 == PackageManager.INSTALL_FAILED_INVALID_SIGNATURES){
- // Generic error handling for all other error codes.
- centerTextDrawable.setLevel(1);
- centerExplanationLabel = getExplanationFromErrorCode(msg.arg1);
- centerTextLabel = R.string.install_failed_invalid_signature;
- mLaunchButton.setVisibility(View.INVISIBLE);
- //add end
- } else {
- // Generic error handling for all other error codes.
- centerTextDrawable.setLevel(1);
- centerExplanationLabel = getExplanationFromErrorCode(msg.arg1);
- centerTextLabel = R.string.install_failed;
- mLaunchButton.setVisibility(View.INVISIBLE);
- }
- ...
windows下给apk签名的方法:
制作一个批处理文件 Auto_Sign.bat 内容:
- @echo off
- :menu
- cls
- color 0b
- echo.
- echo *****************************************************
- echo Android platform auto-sign tool V0.2 by imchange
- echo Please select your choice then press ENTER
- echo *****************************************************
- echo.
- echo 1. Sign ROM files (*.zip)
- echo.
- echo 2. Sign program files (*.apk)
- echo.
- echo 3. Sign ALL (*.zip/*.apk)
- echo.
- echo 4. Exit
- echo.
- set /p choice=Please select:
- if /i "%choice%"=="1" goto rom
- if /i "%choice%"=="2" goto apk
- if /i "%choice%"=="3" goto all
- if /i "%choice%"=="4" exit
- goto menu
- :rom
- set filename=*.zip
- goto sign
- :apk
- set filename=*.apk
- goto sign
- :all
- set filename=*.zip *.apk
- goto sign
- :sign
- echo.
- echo Please wait while signing...
- echo The signed files will be placed into subfolder 'Signed'...
- echo.
- if not exist .\Signed mkdir .\Signed
- for /f "delims=" %%i in ('dir/b %filename%') do (
- java -jar signapk.jar testkey.x509.pem testkey.pk8 "%%i" ".\Signed\%%~ni_signed%%~xi")
- echo.
- echo Completed. Press any key to exit.
- pause >nul
- exit
readme.txt
[java] view plain copy- Android platform ROM/program files auto-sign batch tool
- Created by imchange
- Usage:
- Place your ROM files (*.zip) or program files (*.apk) to this folder, execute Auto_Sign.bat by double click, then select the type of files you want to sign. The signed files are placed into subfolder 'Signed'.
- 用法:
- 将ROM文件(*.zip)或程序(*.apk)放到本文件夹,双击执行Auto_Sign.bat,选择要签名的文件类型。签名后的文件放置在Signed文件夹内。
- Changelog:
- V0.2
- -All functions merge into one batch file
- -Add select menu
- V0.1
- -The first version
signapk.jar
[java] view plain copy
- package com.android.signapk;
- import java.io.BufferedReader;
- import java.io.ByteArrayOutputStream;
- import java.io.DataInputStream;
- import java.io.File;
- import java.io.FileInputStream;
- import java.io.FileOutputStream;
- import java.io.FilterOutputStream;
- import java.io.IOException;
- import java.io.InputStream;
- import java.io.InputStreamReader;
- import java.io.OutputStream;
- import java.io.PrintStream;
- import java.security.DigestOutputStream;
- import java.security.GeneralSecurityException;
- import java.security.Key;
- import java.security.KeyFactory;
- import java.security.MessageDigest;
- import java.security.PrivateKey;
- import java.security.Signature;
- import java.security.SignatureException;
- import java.security.cert.CertificateFactory;
- import java.security.cert.X509Certificate;
- import java.security.spec.InvalidKeySpecException;
- import java.security.spec.KeySpec;
- import java.security.spec.PKCS8EncodedKeySpec;
- import java.util.Enumeration;
- import java.util.Map;
- import java.util.Map.Entry;
- import java.util.jar.Attributes;
- import java.util.jar.JarEntry;
- import java.util.jar.JarFile;
- import java.util.jar.JarOutputStream;
- import java.util.jar.Manifest;
- import javax.crypto.Cipher;
- import javax.crypto.EncryptedPrivateKeyInfo;
- import javax.crypto.SecretKeyFactory;
- import javax.crypto.spec.PBEKeySpec;
- import javax.security.auth.x500.X500Principal;
- import sun.misc.BASE64Encoder;
- import sun.security.pkcs.ContentInfo;
- import sun.security.pkcs.PKCS7;
- import sun.security.pkcs.SignerInfo;
- import sun.security.x509.AlgorithmId;
- import sun.security.x509.X500Name;
- class SignApk
- {
- private static X509Certificate readPublicKey(File file)
- throws IOException, GeneralSecurityException
- {
- FileInputStream input = new FileInputStream(file);
- try {
- CertificateFactory cf = CertificateFactory.getInstance("X.509");
- return (X509Certificate)cf.generateCertificate(input);
- } finally {
- input.close();
- }
- }
- private static String readPassword(File keyFile)
- {
- System.out.print("Enter password for " + keyFile + " (password will not be hidden): ");
- System.out.flush();
- BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
- try {
- return stdin.readLine(); } catch (IOException ex) {
- }
- return null;
- }
- private static KeySpec decryptPrivateKey(byte[] encryptedPrivateKey, File keyFile)
- throws GeneralSecurityException
- {
- EncryptedPrivateKeyInfo epkInfo;
- try
- {
- epkInfo = new EncryptedPrivateKeyInfo(encryptedPrivateKey);
- }
- catch (IOException ex) {
- return null;
- }
- char[] password = readPassword(keyFile).toCharArray();
- SecretKeyFactory skFactory = SecretKeyFactory.getInstance(epkInfo.getAlgName());
- Key key = skFactory.generateSecret(new PBEKeySpec(password));
- Cipher cipher = Cipher.getInstance(epkInfo.getAlgName());
- cipher.init(2, key, epkInfo.getAlgParameters());
- try
- {
- return epkInfo.getKeySpec(cipher);
- } catch (InvalidKeySpecException ex) {
- System.err.println("signapk: Password for " + keyFile + " may be bad.");
- throw ex;
- }
- }
- private static PrivateKey readPrivateKey(File file)
- throws IOException, GeneralSecurityException
- {
- DataInputStream input = new DataInputStream(new FileInputStream(file));
- try {
- byte[] bytes = new byte[(int)file.length()];
- input.read(bytes);
- KeySpec spec = decryptPrivateKey(bytes, file);
- if (spec == null) {
- spec = new PKCS8EncodedKeySpec(bytes);
- }
- try
- {
- return KeyFactory.getInstance("RSA").generatePrivate(spec);
- } catch (InvalidKeySpecException ex) {
- return KeyFactory.getInstance("DSA").generatePrivate(spec);
- }
- } finally {
- input.close();
- }
- }
- private static Manifest addDigestsToManifest(JarFile jar)
- throws IOException, GeneralSecurityException
- {
- Manifest input = jar.getManifest();
- Manifest output = new Manifest();
- Attributes main = output.getMainAttributes();
- if (input != null) {
- main.putAll(input.getMainAttributes());
- } else {
- main.putValue("Manifest-Version", "1.0");
- main.putValue("Created-By", "1.0 (Android SignApk)");
- }
- BASE64Encoder base64 = new BASE64Encoder();
- MessageDigest md = MessageDigest.getInstance("SHA1");
- byte[] buffer = new byte[4096];
- for (Enumeration e = jar.entries(); e.hasMoreElements(); ) {
- JarEntry entry = (JarEntry)e.nextElement();
- String name = entry.getName();
- if ((!entry.isDirectory()) && (!name.equals("META-INF/MANIFEST.MF"))) {
- InputStream data = jar.getInputStream(entry);
- int num;
- while ((num = data.read(buffer)) > 0) {
- md.update(buffer, 0, num);
- }
- Attributes attr = null;
- if (input != null) attr = input.getAttributes(name);
- attr = attr != null ? new Attributes(attr) : new Attributes();
- attr.putValue("SHA1-Digest", base64.encode(md.digest()));
- output.getEntries().put(name, attr);
- }
- }
- return output;
- }
- private static void writeSignatureFile(Manifest manifest, OutputStream out)
- throws IOException, GeneralSecurityException
- {
- Manifest sf = new Manifest();
- Attributes main = sf.getMainAttributes();
- main.putValue("Signature-Version", "1.0");
- main.putValue("Created-By", "1.0 (Android SignApk)");
- BASE64Encoder base64 = new BASE64Encoder();
- MessageDigest md = MessageDigest.getInstance("SHA1");
- PrintStream print = new PrintStream(new DigestOutputStream(new ByteArrayOutputStream(), md), true, "UTF-8");
- manifest.write(print);
- print.flush();
- main.putValue("SHA1-Digest-Manifest", base64.encode(md.digest()));
- Map entries = manifest.getEntries();
- for (Map.Entry entry : entries.entrySet())
- {
- print.print("Name: " + (String)entry.getKey() + "\r\n");
- for (Map.Entry att : ((Attributes)entry.getValue()).entrySet()) {
- print.print(att.getKey() + ": " + att.getValue() + "\r\n");
- }
- print.print("\r\n");
- print.flush();
- Attributes sfAttr = new Attributes();
- sfAttr.putValue("SHA1-Digest", base64.encode(md.digest()));
- sf.getEntries().put(entry.getKey(), sfAttr);
- }
- sf.write(out);
- }
- private static void writeSignatureBlock(Signature signature, X509Certificate publicKey, OutputStream out)
- throws IOException, GeneralSecurityException
- {
- SignerInfo signerInfo = new SignerInfo(new X500Name(publicKey.getIssuerX500Principal().getName()), publicKey.getSerialNumber(), AlgorithmId.get("SHA1"), AlgorithmId.get("RSA"), signature.sign());
- PKCS7 pkcs7 = new PKCS7(new AlgorithmId[] { AlgorithmId.get("SHA1") }, new ContentInfo(ContentInfo.DATA_OID, null), new X509Certificate[] { publicKey }, new SignerInfo[] { signerInfo });
- pkcs7.encodeSignedData(out);
- }
- private static void copyFiles(Manifest manifest, JarFile in, JarOutputStream out)
- throws IOException
- {
- byte[] buffer = new byte[4096];
- Map entries = manifest.getEntries();
- for (String name : entries.keySet()) {
- JarEntry inEntry = in.getJarEntry(name);
- if (inEntry.getMethod() == 0)
- {
- out.putNextEntry(new JarEntry(inEntry));
- }
- else {
- out.putNextEntry(new JarEntry(name));
- }
- InputStream data = in.getInputStream(inEntry);
- int num;
- while ((num = data.read(buffer)) > 0) {
- out.write(buffer, 0, num);
- }
- out.flush();
- }
- }
- public static void main(String[] args) {
- if (args.length != 4) {
- System.err.println("Usage: signapk publickey.x509[.pem] privatekey.pk8 input.jar output.jar");
- System.exit(2);
- }
- JarFile inputJar = null;
- JarOutputStream outputJar = null;
- try
- {
- X509Certificate publicKey = readPublicKey(new File(args[0]));
- PrivateKey privateKey = readPrivateKey(new File(args[1]));
- inputJar = new JarFile(new File(args[2]), false);
- outputJar = new JarOutputStream(new FileOutputStream(args[3]));
- outputJar.setLevel(9);
- Manifest manifest = addDigestsToManifest(inputJar);
- manifest.getEntries().remove("META-INF/CERT.SF");
- manifest.getEntries().remove("META-INF/CERT.RSA");
- outputJar.putNextEntry(new JarEntry("META-INF/MANIFEST.MF"));
- manifest.write(outputJar);
- Signature signature = Signature.getInstance("SHA1withRSA");
- signature.initSign(privateKey);
- outputJar.putNextEntry(new JarEntry("META-INF/CERT.SF"));
- writeSignatureFile(manifest, new SignatureOutputStream(outputJar, signature));
- outputJar.putNextEntry(new JarEntry("META-INF/CERT.RSA"));
- writeSignatureBlock(signature, publicKey, outputJar);
- copyFiles(manifest, inputJar, outputJar);
- } catch (Exception e) {
- e.printStackTrace();
- System.exit(1);
- } finally {
- try {
- if (inputJar != null) inputJar.close();
- if (outputJar != null) outputJar.close();
- }
- catch (IOException e) { e.printStackTrace();
- System.exit(1);
- }
- }
- }
- private static class SignatureOutputStream extends FilterOutputStream
- {
- private Signature mSignature;
- public SignatureOutputStream(OutputStream out, Signature sig)
- {
- super();
- this.mSignature = sig;
- }
- public void write(int b) throws IOException
- {
- try {
- this.mSignature.update((byte)b);
- } catch (SignatureException e) {
- throw new IOException("SignatureException: " + e);
- }
- super.write(b);
- }
- public void write(byte[] b, int off, int len) throws IOException
- {
- try {
- this.mSignature.update(b, off, len);
- } catch (SignatureException e) {
- throw new IOException("SignatureException: " + e);
- }
- super.write(b, off, len);
- }
- }
- }
附:参考文章
http://www.blogjava/zh-weir/archive/2011/07/19/354663.html
Android APK 签名比对
发布过Android应用的朋友们应该都知道,Android APK的发布是需要签名的。签名机制在Android应用和框架中有着十分重要的作用。
例如,Android系统禁止更新安装签名不一致的APK;如果应用需要使用system权限,必须保证APK签名与Framework签名一致,等等。在《APK Crack》一文中,我们了解到,要破解一个APK,必然需要重新对APK进行签名。而这个签名,一般情况无法再与APK原先的签名保持一致。(除非APK原作者的私钥泄漏,那已经是另一个层次的软件安全问题了。)
简单地说,签名机制标明了APK的发行机构。因此,站在软件安全的角度,我们就可以通过比对APK的签名情况,判断此APK是否由“官方”发行,而不是被破解篡改过重新签名打包的“盗版软件”。
Android签名机制
为了说明APK签名比对对软件安全的有效性,我们有必要了解一下Android APK的签名机制。为了更易于大家理解,我们从Auto-Sign工具的一条批处理命令说起。
在《APK Crack》一文中,我们了解到,要签名一个没有签名过的APK,可以使用一个叫作Auto-sign的工具。Auto-sign工具实际运行的是一个叫做Sign.bat的批处理命令。用文本编辑器打开这个批处理文件,我们可以发现,实现签名功能的命令主要是这一行命令:
java -jar signapk.jar testkey.x509.pem testkey.pk8 update.apk update_signed.apk
这条命令的意义是:通过signapk.jar这个可执行jar包,以“ testkey.x509.pem ”这个公钥文件和“ testkey.pk8 ”这个私钥文件对“ update.apk ”进行签名,签名后的文件保存为“ update_signed.apk ”。
对于此处所使用的私钥和公钥的生成方式,这里就不做进一步介绍了。这方面的资料大家可以找到很多。我们这里要讲的是signapk.jar到底做了什么。
signapk.jar是Android源码包中的一个签名工具。由于Android是个开源项目,所以,很高兴地,我们可以直接找到signapk.jar的源码!路径为/build/tools/signapk/SignApk.java。
对比一个没有签名的APK和一个签名好的APK,我们会发现,签名好的APK包中多了一个叫做META-INF的文件夹。里面有三个文件,分别名为MANIFEST.MF、CERT.SF和CERT.RSA。signapk.jar就是生成了这几个文件(其他文件没有任何改变。因此我们可以很容易去掉原有签名信息)。
通过阅读signapk源码,我们可以理清签名APK包的整个过程。
1、 生成MANIFEST.MF文件:
程序遍历update.apk包中的所有文件(entry),对非文件夹非签名文件的文件,逐个生成SHA1的数字签名信息,再用Base64进行编码。具体代码见这个方法:
private static Manifest addDigestsToManifest(JarFile jar)
关键代码如下:
1 for (JarEntry entry: byName.values()) {2 String name = entry.getName();
3 if (!entry.isDirectory() && !name.equals(JarFile.MANIFEST_NAME) &&
4 !name.equals(CERT_SF_NAME) && !name.equals(CERT_RSA_NAME) &&
5 (stripPattern == null ||!stripPattern.matcher(name).matches())) {
6 InputStream data = jar.getInputStream(entry);
7 while ((num = data.read(buffer)) > 0) {
8 md.update(buffer, 0, num);
9 }
10 Attributes attr = null;
11 if (input != null) attr = input.getAttributes(name);
12 attr = attr != null ? new Attributes(attr) : new Attributes();
13 attr.putValue("SHA1-Digest", base64.encode(md.digest()));
14 output.getEntries().put(name, attr);
15 }
16 }
之后将生成的签名写入MANIFEST.MF文件。关键代码如下:
1 Manifest manifest = addDigestsToManifest(inputJar);
2 je = new JarEntry(JarFile.MANIFEST_NAME);
3 je.setTime(timestamp);
4 outputJar.putNextEntry(je);
5 manifest.write(outputJar);
这里简单介绍下SHA1数字签名。简单地说,它就是一种安全哈希算法,类似于MD5算法。它把任意长度的输入,通过散列算法变成固定长度的输出(这里我们称作“摘要信息”)。你不能仅通过这个摘要信息复原原来的信息。另外,它保证不同信息的摘要信息彼此不同。因此,如果你改变了apk包中的文件,那么在apk安装校验时,改变后的文件摘要信息与MANIFEST.MF的检验信息不同,于是程序就不能成功安装。
2、 生成CERT.SF文件:
对前一步生成的Manifest,使用SHA1-RSA算法,用私钥进行签名。关键代码如下:
1 Signature signature = Signature.getInstance("SHA1withRSA");2 signature.initSign(privateKey);
3 je = new JarEntry(CERT_SF_NAME);
4 je.setTime(timestamp);
5 outputJar.putNextEntry(je);
6 writeSignatureFile(manifest,
7 new SignatureOutputStream(outputJar, signature));
RSA是一种非对称加密算法。用私钥通过RSA算法对摘要信息进行加密。在安装时只能使用公钥才能解密它。解密之后,将它与未加密的摘要信息进行对比,如果相符,则表明内容没有被异常修改。
3、 生成CERT.RSA文件:
生成MANIFEST.MF没有使用密钥信息,生成CERT.SF文件使用了私钥文件。那么我们可以很容易猜测到,CERT.RSA文件的生成肯定和公钥相关。
CERT.RSA文件中保存了公钥、所采用的加密算法等信息。核心代码如下:
1 je = new JarEntry(CERT_RSA_NAME);
2 je.setTime(timestamp);
3 outputJar.putNextEntry(je);
4 writeSignatureBlock(signature, publicKey, outputJar);
其中writeSignatureBlock的代码如下:
1 private static void writeSignatureBlock(
2 Signature signature, X509Certificate publicKey, OutputStream out)
3 throws IOException, GeneralSecurityException {
4 SignerInfo signerInfo = new SignerInfo(
5 new X500Name(publicKey.getIssuerX500Principal().getName()),
6 publicKey.getSerialNumber(),
7 AlgorithmId.get("SHA1"),
8 AlgorithmId.get("RSA"),
9 signature.sign());
10
11 PKCS7 pkcs7 = new PKCS7(
12 new AlgorithmId[] { AlgorithmId.get("SHA1") },
13 new ContentInfo(ContentInfo.DATA_OID, null),
14 new X509Certificate[] { publicKey },
15 new SignerInfo[] { signerInfo });
16
17 pkcs7.encodeSignedData(out);
18 }
好了,分析完APK包的签名流程,我们可以清楚地意识到:
1、 Android签名机制其实是对APK包完整性和发布机构唯一性的一种校验机制。
2、 Android签名机制不能阻止APK包被修改,但修改后的再签名无法与原先的签名保持一致。(拥有私钥的情况除外)。
3、 APK包加密的公钥就打包在APK包内,且不同的私钥对应不同的公钥。换句话言之,不同的私钥签名的APK公钥也必不相同。所以我们可以根据公钥的对比,来判断私钥是否一致。
APK签名比对的实现方式
好了,通过Android签名机制的分析,我们从理论上证明了通过APK公钥的比对能判断一个APK的发布机构。并且这个发布机构是很难伪装的,我们暂时可以认为是不可伪装的。
有了理论基础后,我们就可以开始实践了。那么如何获取到APK文件的公钥信息呢?因为Android系统安装程序肯定会获取APK信息进行比对,所以我们可以通过Android源码获得一些思路和帮助。
源码中有一个隐藏的类用于APK包的解析。这个类叫PackageParser,路径为frameworks\base\core\java\android\content\pm\PackageParser.java。当我们需要获取APK包的相关信息时,可以直接使用这个类,下面代码就是一个例子函数:
1 private PackageInfo parsePackage(String archiveFilePath, int flags){
2
3 PackageParser packageParser = new PackageParser(archiveFilePath);
4 DisplayMetrics metrics = new DisplayMetrics();
5 metrics.setToDefaults();
6 final File sourceFile = new File(archiveFilePath);
7 PackageParser.Package pkg = packageParser.parsePackage(
8 sourceFile, archiveFilePath, metrics, 0);
9 if (pkg == null) {
10 return null;
11 }
12
13 packageParser.collectCertificates(pkg, 0);
14
15 return PackageParser.generatePackageInfo(pkg, null, flags, 0, 0);
16 }
其中参数archiveFilePath指定APK文件路径;flags需设置PackageManager.GET_SIGNATURES位,以保证返回证书签名信息。
具体如何通过PackageParser获取签名信息在此处不做详述,具体代码请参考PackageParser中的public boolean collectCertificates(Package pkg, int flags)和private Certificate[] loadCertificates(JarFile jarFile, JarEntry je, byte[] readBuffer)方法。至于如何在Android应用开发中使用隐藏的类及方法,可以参看我的这篇文章:《Android应用开发中如何使用隐藏API》。
紧接着,我们就可以通过packageInfo.signatures来访问到APK的签名信息。还需要说明的是 Android中Signature和Java中Certificate的对应关系。它们的关系如下面代码所示:
1 pkg.mSignatures = new Signature[certs.length];
2 for ( int i=0; i<N; i++) {
3 pkg.mSignatures[i] = new Signature(
4 certs[i].getEncoded());
5 }
也就是说signature = new Signature(certificate.getEncoded()); certificate证书中包含了公钥和证书的其他基本信息。公钥不同,证书肯定互不相同。我们可以通过certificate的getPublicKey方法获取公钥信息。所以比对签名证书本质上就是比对公钥信息。
OK,获取到APK签名证书之后,就剩下比对了。这个简单,功能函数如下所示:
1 private boolean IsSignaturesSame(Signature[] s1, Signature[] s2) {2 if (s1 == null) {
3 return false;
4 }
5 if (s2 == null) {
6 return false;
7 }
8 HashSet<Signature> set1 = new HashSet<Signature>();
9 for (Signature sig : s1) {
10 set1.add(sig);
11 }
12 HashSet<Signature> set2 = new HashSet<Signature>();
13 for (Signature sig : s2) {
14 set2.add(sig);
15 }
16 // Make sure s2 contains all signatures in s1.
17 if (set1.equals(set2)) {
18 return true;
19 }
20 return false;
21 }
APK签名比对的应用场景
经过以上的论述,想必大家已经明白签名比对的原理和我的实现方式了。那么什么时候什么情况适合使用签名对比来保障Android APK的软件安全呢?
个人认为主要有以下三种场景:
1、 程序自检测。在程序运行时,自我进行签名比对。比对样本可以存放在APK包内,也可存放于云端。缺点是程序被破解时,自检测功能同样可能遭到破坏,使其失效。
2、 可信赖的第三方检测。由可信赖的第三方程序负责APK的软件安全问题。对比样本由第三方收集,放在云端。这种方式适用于杀毒安全软件或者APP Market之类的软件下载市场。缺点是需要联网检测,在无网络情况下无法实现功能。(不可能把大量的签名数据放在移动设备本地)。
3、 系统限定安装。这就涉及到改Android系统了。限定仅能安装某些证书的APK。软件发布商需要向系统发布上申请证书。如果发现问题,能追踪到是哪个软件发布商的责任。适用于系统提供商或者终端产品生产商。缺点是过于封闭,不利于系统的开放性。
以上三种场景,虽然各有缺点,但缺点并不是不能克服的。例如,我们可以考虑程序自检测的功能用native method的方法实现等等。软件安全是一个复杂的课题,往往需要多种技术联合使用,才能更好的保障软件不被恶意破坏。
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