一、前言
今天是元旦,也是Single Dog的嚎叫之日,只能写博客来祛除寂寞了,今天我们继续来看一下Android中的签名机制的姊妹篇:android中是如何验证一个Apk的签名。在前一篇文章中我们介绍了,Android中是如何对程序进行签名的,不了解的同学可以转战:
http://blog.****.net/jiangwei0910410003/article/details/50402000
当然在了解我们今天说到的知识点,这篇文章也是需要了解的,不然会有些知识点有些困惑的。
二、知识摘要
在我们没有开始这篇文章之前,我们回顾一下之前说到的签名机制流程:
1、对Apk中的每个文件做一次算法(数据摘要+Base64编码),保存到MANIFEST.MF文件中
2、对MANIFEST.MF整个文件做一次算法(数据摘要+Base64编码),存放到CERT.SF文件的头属性中,在对MANIFEST.MF文件中各个属性块做一次算法(数据摘要+Base64编码),存到到一个属性块中。
3、对CERT.SF文件做签名,内容存档到CERT.RSA中
所以通过上面的流程可以知道,我们今天来验证签名流程也是这三个步骤
三、代码分析
我们既然要了解Android中的应用程序的签名验证过程的话,那么我们肯定需要从一个类来开始看起,那就是PackageManagerService.Java,因为这个类是Apk在安装的过程中核心类:frameworks\base\services\core\java\com\android\server\pm\PackageManagerService.java
-
private void installPackageLI(InstallArgs args, PackageInstalledInfo res) {
-
……
-
PackageParser pp = new PackageParser();
-
……
-
try {
-
pp.collectCertificates(pkg, parseFlags);
-
pp.collectManifestDigest(pkg);
-
} catch (PackageParserException e) {
-
res.setError("Failed collect during installPackageLI", e);
-
return;
-
}
-
……
我们可以看到,有一个核心类:PackageParser
frameworks\base\core\java\android\content\pm\PackageParser.java
这个类也是见名知意,就是需要解析Apk包,那么就会涉及到签名信息了,下面我们就从这个类开始入手:
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_BAD_MANIFEST;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_BAD_PACKAGE_NAME;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_CERTIFICATE_ENCODING;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_INCONSISTENT_CERTIFICATES;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_MANIFEST_MALFORMED;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_NOT_APK;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_NO_CERTIFICATES;
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION;
我们看到了几个我们很熟悉的信息:
-
import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_NO_CERTIFICATES;
这个是在安装apk包的时候出现的错误,没有证书:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzUxNC9iOWExYTViMWE1OGUzYWZhMDhhNTUyY2FjMGM2ZWE4Mi5wbmc=)
那么我们就先来查找一下这个字段:
-
private static void collectCertificates(Package pkg, File apkFile, int flags)
-
throws PackageParserException {
-
final String apkPath = apkFile.getAbsolutePath();
-
-
StrictJarFile jarFile = null;
-
try {
-
jarFile = new StrictJarFile(apkPath);
-
-
// Always verify manifest, regardless of source
-
final ZipEntry manifestEntry = jarFile.findEntry(ANDROID_MANIFEST_FILENAME);
-
if (manifestEntry == null) {
-
throw new PackageParserException(INSTALL_PARSE_FAILED_BAD_MANIFEST,
-
"Package " + apkPath + " has no manifest");
-
}
-
-
final List<ZipEntry> toVerify = new ArrayList<>();
-
toVerify.add(manifestEntry);
-
-
// If we're parsing an untrusted package, verify all contents
-
if ((flags & PARSE_IS_SYSTEM) == 0) {
-
final Iterator<ZipEntry> i = jarFile.iterator();
-
while (i.hasNext()) {
-
final ZipEntry entry = i.next();
-
-
if (entry.isDirectory()) continue;
-
if (entry.getName().startsWith("META-INF/")) continue;
-
if (entry.getName().equals(ANDROID_MANIFEST_FILENAME)) continue;
-
-
toVerify.add(entry);
-
}
-
}
-
-
// Verify that entries are signed consistently with the first entry
-
// we encountered. Note that for splits, certificates may have
-
// already been populated during an earlier parse of a base APK.
-
for (ZipEntry entry : toVerify) {
-
final Certificate[][] entryCerts = loadCertificates(jarFile, entry);
-
if (ArrayUtils.isEmpty(entryCerts)) {
-
throw new PackageParserException(INSTALL_PARSE_FAILED_NO_CERTIFICATES,
-
"Package " + apkPath + " has no certificates at entry "
-
+ entry.getName());
-
}
-
final Signature[] entrySignatures = convertToSignatures(entryCerts);
-
-
if (pkg.mCertificates == null) {
-
pkg.mCertificates = entryCerts;
-
pkg.mSignatures = entrySignatures;
-
pkg.mSigningKeys = new ArraySet<PublicKey>();
-
for (int i=0; i < entryCerts.length; i++) {
-
pkg.mSigningKeys.add(entryCerts[i][0].getPublicKey());
-
}
-
} else {
-
if (!Signature.areExactMatch(pkg.mSignatures, entrySignatures)) {
-
throw new PackageParserException(
-
INSTALL_PARSE_FAILED_INCONSISTENT_CERTIFICATES, "Package " + apkPath
-
+ " has mismatched certificates at entry "
-
+ entry.getName());
-
}
-
}
-
}
-
} catch (GeneralSecurityException e) {
-
throw new PackageParserException(INSTALL_PARSE_FAILED_CERTIFICATE_ENCODING,
-
"Failed to collect certificates from " + apkPath, e);
-
} catch (IOException | RuntimeException e) {
-
throw new PackageParserException(INSTALL_PARSE_FAILED_NO_CERTIFICATES,
-
"Failed to collect certificates from " + apkPath, e);
-
} finally {
-
closeQuietly(jarFile);
-
}
-
}
这里看到了,当有异常的时候就会提示这个信息,我们在跟进去看看:
-
// Verify that entries are signed consistently with the first entry
-
// we encountered. Note that for splits, certificates may have
-
// already been populated during an earlier parse of a base APK.
-
for (ZipEntry entry : toVerify) {
-
final Certificate[][] entryCerts = loadCertificates(jarFile, entry);
-
if (ArrayUtils.isEmpty(entryCerts)) {
-
throw new PackageParserException(INSTALL_PARSE_FAILED_NO_CERTIFICATES,
-
"Package " + apkPath + " has no certificates at entry "
-
+ entry.getName());
-
}
-
final Signature[] entrySignatures = convertToSignatures(entryCerts);
-
-
if (pkg.mCertificates == null) {
-
pkg.mCertificates = entryCerts;
-
pkg.mSignatures = entrySignatures;
-
pkg.mSigningKeys = new ArraySet<PublicKey>();
-
for (int i=0; i < entryCerts.length; i++) {
-
pkg.mSigningKeys.add(entryCerts[i][0].getPublicKey());
-
}
-
} else {
-
if (!Signature.areExactMatch(pkg.mSignatures, entrySignatures)) {
-
throw new PackageParserException(
-
INSTALL_PARSE_FAILED_INCONSISTENT_CERTIFICATES, "Package " + apkPath
-
+ " has mismatched certificates at entry "
-
+ entry.getName());
-
}
-
}
-
}
这里有一个重要的方法:loadCertificates
-
private static Certificate[][] loadCertificates(StrictJarFile jarFile, ZipEntry entry)
-
throws PackageParserException {
-
InputStream is = null;
-
try {
-
// We must read the stream for the JarEntry to retrieve
-
// its certificates.
-
is = jarFile.getInputStream(entry);
-
readFullyIgnoringContents(is);
-
return jarFile.getCertificateChains(entry);
-
} catch (IOException | RuntimeException e) {
-
throw new PackageParserException(INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION,
-
"Failed reading " + entry.getName() + " in " + jarFile, e);
-
} finally {
-
IoUtils.closeQuietly(is);
-
}
-
}
这个方法是加载证书内容的
1、验证Apk中的每个文件的算法(数据摘要+Base64编码)和MANIFEST.MF文件中的对应属性块内容是否配对
首先获取StrictJarFile文件中的InputStream对象
StrictJarFile这个类:libcore\luni\src\main\java\java\util\jar\StrictJarFile.java
-
public InputStream getInputStream(ZipEntry ze) {
-
final InputStream is = getZipInputStream(ze);
-
-
if (isSigned) {
-
JarVerifier.VerifierEntry entry = verifier.initEntry(ze.getName());
-
if (entry == null) {
-
return is;
-
}
-
-
return new JarFile.JarFileInputStream(is, ze.getSize(), entry);
-
}
-
-
return is;
-
}
1》获取到VerifierEntry对象entry
在JarVerifier.java:libcore\luni\src\main\java\java\util\jar\JarVerifier.java
-
VerifierEntry initEntry(String name) {
-
// If no manifest is present by the time an entry is found,
-
// verification cannot occur. If no signature files have
-
// been found, do not verify.
-
if (manifest == null || signatures.isEmpty()) {
-
return null;
-
}
-
Attributes attributes = manifest.getAttributes(name);
-
// entry has no digest
-
if (attributes == null) {
-
return null;
-
}
-
ArrayList<Certificate[]> certChains = new ArrayList<Certificate[]>();
-
Iterator<Map.Entry<String, HashMap<String, Attributes>>> it = signatures.entrySet().iterator();
-
while (it.hasNext()) {
-
Map.Entry<String, HashMap<String, Attributes>> entry = it.next();
-
HashMap<String, Attributes> hm = entry.getValue();
-
if (hm.get(name) != null) {
-
// Found an entry for entry name in .SF file
-
String signatureFile = entry.getKey();
-
Certificate[] certChain = certificates.get(signatureFile);
-
if (certChain != null) {
-
certChains.add(certChain);
-
}
-
}
-
}
-
// entry is not signed
-
if (certChains.isEmpty()) {
-
return null;
-
}
-
Certificate[][] certChainsArray = certChains.toArray(new Certificate[certChains.size()][]);
-
for (int i = 0; i < DIGEST_ALGORITHMS.length; i++) {
-
final String algorithm = DIGEST_ALGORITHMS[i];
-
final String hash = attributes.getValue(algorithm + "-Digest");
-
if (hash == null) {
-
continue;
-
}
-
byte[] hashBytes = hash.getBytes(StandardCharsets.ISO_8859_1);
-
try {
-
return new VerifierEntry(name, MessageDigest.getInstance(algorithm), hashBytes,
-
certChainsArray, verifiedEntries);
-
} catch (NoSuchAlgorithmException ignored) {
-
}
-
}
-
return null;
-
}
就是构造一个VerifierEntry对象:
-
/**
-
* Stores and a hash and a message digest and verifies that massage digest
-
* matches the hash.
-
*/
-
static class VerifierEntry extends OutputStream {
-
private final String name;
-
private final MessageDigest digest;
-
private final byte[] hash;
-
private final Certificate[][] certChains;
-
private final Hashtable<String, Certificate[][]> verifiedEntries;
-
VerifierEntry(String name, MessageDigest digest, byte[] hash,
-
Certificate[][] certChains, Hashtable<String, Certificate[][]> verifedEntries) {
-
this.name = name;
-
this.digest = digest;
-
this.hash = hash;
-
this.certChains = certChains;
-
this.verifiedEntries = verifedEntries;
-
}
-
/**
-
* Updates a digest with one byte.
-
*/
-
@Override
-
public void write(int value) {
-
digest.update((byte) value);
-
}
-
/**
-
* Updates a digest with byte array.
-
*/
-
@Override
-
public void write(byte[] buf, int off, int nbytes) {
-
digest.update(buf, off, nbytes);
-
}
-
/**
-
* Verifies that the digests stored in the manifest match the decrypted
-
* digests from the .SF file. This indicates the validity of the
-
* signing, not the integrity of the file, as its digest must be
-
* calculated and verified when its contents are read.
-
*
-
* @throws SecurityException
-
* if the digest value stored in the manifest does <i>not</i>
-
* agree with the decrypted digest as recovered from the
-
* <code>.SF</code> file.
-
*/
-
void verify() {
-
byte[] d = digest.digest();
-
if (!MessageDigest.isEqual(d, Base64.decode(hash))) {
-
throw invalidDigest(JarFile.MANIFEST_NAME, name, name);
-
}
-
verifiedEntries.put(name, certChains);
-
}
-
}
要构造这个对象,必须事先准备好参数。第一个参数很简单,就是要验证的文件名,直接将name传进来就好了。第二个参数是计算摘要的对象,可以通过MessageDigest.getInstance获得,不过要先告知到底要用哪个摘要算法,同样也是通过查看MANIFEST.MF文件中对应名字的属性值来决定的:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzEzMS83ZTNmYjljMTM3MmU4NWFkMzFkNGY5MWMwMDg5OGU5Yi5KUEVH)
所以可以知道所用的摘要算法是SHA1。第三个参数是对应文件的摘要值,这是通过读取MANIFEST.MF文件获得的:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzM3MC9jZjQ2MDViMDdhMDg0NDY1Nzk1NDZkNDJiNjk2MDhiMi5KUEVH)
第四个参数是证书链,即对该apk文件签名的所有证书链信息。为什么是二维数组呢?这是因为Android允许用多个证书对apk进行签名,但是它们的证书文件名必须不同,这个知识点,我在之前的一篇文章中:签名过程详解 中有提到。
最后一个参数是已经验证过的文件列表,VerifierEntry在完成了对指定文件的摘要验证之后会将该文件的信息加到其中。
2》再去JarFile的JarFileInputStream类中看看:
-
static final class JarFileInputStream extends FilterInputStream {
-
private long count;
-
-
private ZipEntry zipEntry;
-
-
private JarVerifier.VerifierEntry entry;
-
-
private boolean done = false;
-
-
JarFileInputStream(InputStream is, ZipEntry ze,
-
JarVerifier.VerifierEntry e) {
-
super(is);
-
zipEntry = ze;
-
count = zipEntry.getSize();
-
entry = e;
-
}
-
-
@Override
-
public int read() throws IOException {
-
if (done) {
-
return -1;
-
}
-
if (count > 0) {
-
int r = super.read();
-
if (r != -1) {
-
entry.write(r);
-
count--;
-
} else {
-
count = 0;
-
}
-
if (count == 0) {
-
done = true;
-
entry.verify();
-
}
-
return r;
-
} else {
-
done = true;
-
entry.verify();
-
return -1;
-
}
-
}
-
-
@Override
-
public int read(byte[] buf, int off, int nbytes) throws IOException {
-
if (done) {
-
return -1;
-
}
-
if (count > 0) {
-
int r = super.read(buf, off, nbytes);
-
if (r != -1) {
-
int size = r;
-
if (count < size) {
-
size = (int) count;
-
}
-
entry.write(buf, off, size);
-
count -= size;
-
} else {
-
count = 0;
-
}
-
if (count == 0) {
-
done = true;
-
entry.verify();
-
}
-
return r;
-
} else {
-
done = true;
-
entry.verify();
-
return -1;
-
}
-
}
-
-
@Override
-
public int available() throws IOException {
-
if (done) {
-
return 0;
-
}
-
return super.available();
-
}
-
-
@Override
-
public long skip(long byteCount) throws IOException {
-
return Streams.skipByReading(this, byteCount);
-
}
-
}
3》PackageParser的readFullyIgnoringContents方法:
-
public static long readFullyIgnoringContents(InputStream in) throws IOException {
-
byte[] buffer = sBuffer.getAndSet(null);
-
if (buffer == null) {
-
buffer = new byte[4096];
-
}
-
-
int n = 0;
-
int count = 0;
-
while ((n = in.read(buffer, 0, buffer.length)) != -1) {
-
count += n;
-
}
-
-
sBuffer.set(buffer);
-
return count;
-
}
得到第二步之后的一个InputStream对象,然后就开始read操作,这里我没发现什么猫腻,但是我们从第一件事做完之后可以发现,这里的InputStream对象其实是JarInputStream,所以我们可以去看一下他的read方法的实现:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzgzNC85YjVkN2RlZjc2OTNiZDdiZTZiMTZkYWU3M2Q1N2QyYS5KUEVH)
玄机原来在这里,这里的JarFileInputStream.read确实会调用其父类的read读取指定的apk内文件的内容,并且将其传给JarVerifier.VerifierEntry.write函数。当文件读完后,会接着调用JarVerifier.VerifierEntry.verify函数对其进行验证。JarVerifier.VerifierEntry.write函数非常简单:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzEwNi8wNzYyZWNmOTcyYmEyMmFmNmE4YTVmZTAxY2U2ZDEyYS5KUEVH)
就是将读到的文件的内容传给digest,这个digest就是前面在构造JarVerifier.VerifierEntry传进来的,对应于在MANIFEST.MF文件中指定的摘要算法。万事具备,接下来想要验证就很简单了:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzQzMi9mZDAyOWYxMjUyOThmMDg1OTRjZDg2MDM0ZjZhYjcwMC5KUEVH)
通过digest就可以算出apk内指定文件的真实摘要值。而记录在MANIFEST.MF文件中对应该文件的摘要值,也在构造JarVerifier.VerifierEntry时传递给了hash变量。不过这个hash值是经过Base64编码的。所以在比较之前,必须通过Base64解码。如果不一致的话,会抛出SecurityException异常:
-
private static SecurityException invalidDigest(String signatureFile, String name,
-
String jarName) {
-
throw new SecurityException(signatureFile + " has invalid digest for " + name +
-
" in " + jarName);
-
}
到这里我们就分析了,Android中是如何验证MANIFEST.MF文件中的内容的,我们这里再来看一下,这里抛出异常出去:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzkwOS83ZjY1NDg0NDQyNTBiMzYyYWVmNGFlNTFjNjY0MzZkNS5KUEVH)
这里捕获到异常之后,会在抛异常出去:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzU4Ny81YThiNWMxZTZhYzYwOGFhOWY1NmExN2VkY2ZmZjI5Yi5KUEVH)
在这里就会抛出异常信息,所以如果我们修改了一个Apk中的一个文件内容的话,这里肯定是安装不上的。
2、验证CERT.SF文件的签名信息和CERT.RSA中的内容是否一致
1》我们就来看看StrictJarFile中的getCertificateChains方法:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzgyMC9lMjIzNmZhZTc2NjY2NTI4NWFlOTRiNmVjMjI0OWUzNC5KUEVH)
-
/**
-
* Return all certificate chains for a given {@link ZipEntry} belonging to this jar.
-
* This method MUST be called only after fully exhausting the InputStream belonging
-
* to this entry.
-
*
-
* Returns {@code null} if this jar file isn't signed or if this method is
-
* called before the stream is processed.
-
*/
-
public Certificate[][] getCertificateChains(ZipEntry ze) {
-
if (isSigned) {
-
return verifier.getCertificateChains(ze.getName());
-
}
-
-
return null;
-
}
这里有一个变量判断:isSigned,他是在构造方法中赋值的:
-
public StrictJarFile(String fileName) throws IOException {
-
this.nativeHandle = nativeOpenJarFile(fileName);
-
this.raf = new RandomAccessFile(fileName, "r");
-
-
try {
-
// Read the MANIFEST and signature files up front and try to
-
// parse them. We never want to accept a JAR File with broken signatures
-
// or manifests, so it's best to throw as early as possible.
-
HashMap<String, byte[]> metaEntries = getMetaEntries();
-
this.manifest = new Manifest(metaEntries.get(JarFile.MANIFEST_NAME), true);
-
this.verifier = new JarVerifier(fileName, manifest, metaEntries);
-
-
isSigned = verifier.readCertificates() && verifier.isSignedJar();
-
} catch (IOException ioe) {
-
nativeClose(this.nativeHandle);
-
throw ioe;
-
}
-
-
guard.open("close");
-
}
去verifier中看看这两个方法:
-
/**
-
* If the associated JAR file is signed, check on the validity of all of the
-
* known signatures.
-
*
-
* @return {@code true} if the associated JAR is signed and an internal
-
* check verifies the validity of the signature(s). {@code false} if
-
* the associated JAR file has no entries at all in its {@code
-
* META-INF} directory. This situation is indicative of an invalid
-
* JAR file.
-
* <p>
-
* Will also return {@code true} if the JAR file is <i>not</i>
-
* signed.
-
* @throws SecurityException
-
* if the JAR file is signed and it is determined that a
-
* signature block file contains an invalid signature for the
-
* corresponding signature file.
-
*/
-
synchronized boolean readCertificates() {
-
if (metaEntries.isEmpty()) {
-
return false;
-
}
-
Iterator<String> it = metaEntries.keySet().iterator();
-
while (it.hasNext()) {
-
String key = it.next();
-
if (key.endsWith(".DSA") || key.endsWith(".RSA") || key.endsWith(".EC")) {
-
verifyCertificate(key);
-
it.remove();
-
}
-
}
-
return true;
-
}
这个方法其实很简单,就是判断metaEntries中是否为空,说白了,就是判断Apk中的META-INF文件夹中是否为空,只有文件就返回true。再来看看isSignedJar方法:
-
/**
-
* Returns a <code>boolean</code> indication of whether or not the
-
* associated jar file is signed.
-
*
-
* @return {@code true} if the JAR is signed, {@code false}
-
* otherwise.
-
*/
-
boolean isSignedJar() {
-
return certificates.size() > 0;
-
}
这个方法直接判断certificates这个集合是否为空。我们全局搜索一下这个集合在哪里存入的数据的地方,找到了verifyCertificate方法,同时我们发现,在上面的readCertificates方法中,就调用了这个方法,其实这个方法就是读取证书信息的。
下面来看一下verifyCertificate方法:
-
/**
-
* @param certFile
-
*/
-
private void verifyCertificate(String certFile) {
-
// Found Digital Sig, .SF should already have been read
-
String signatureFile = certFile.substring(0, certFile.lastIndexOf('.')) + ".SF";
-
byte[] sfBytes = metaEntries.get(signatureFile);
-
if (sfBytes == null) {
-
return;
-
}
-
byte[] manifestBytes = metaEntries.get(JarFile.MANIFEST_NAME);
-
// Manifest entry is required for any verifications.
-
if (manifestBytes == null) {
-
return;
-
}
-
byte[] sBlockBytes = metaEntries.get(certFile);
-
try {
-
Certificate[] signerCertChain = JarUtils.verifySignature(
-
new ByteArrayInputStream(sfBytes),
-
new ByteArrayInputStream(sBlockBytes));
-
if (signerCertChain != null) {
-
certificates.put(signatureFile, signerCertChain);
-
}
-
} catch (IOException e) {
-
return;
-
} catch (GeneralSecurityException e) {
-
throw failedVerification(jarName, signatureFile);
-
}
-
// Verify manifest hash in .sf file
-
Attributes attributes = new Attributes();
-
HashMap<String, Attributes> entries = new HashMap<String, Attributes>();
-
try {
-
ManifestReader im = new ManifestReader(sfBytes, attributes);
-
im.readEntries(entries, null);
-
} catch (IOException e) {
-
return;
-
}
-
// Do we actually have any signatures to look at?
-
if (attributes.get(Attributes.Name.SIGNATURE_VERSION) == null) {
-
return;
-
}
-
boolean createdBySigntool = false;
-
String createdBy = attributes.getValue("Created-By");
-
if (createdBy != null) {
-
createdBySigntool = createdBy.indexOf("signtool") != -1;
-
}
-
// Use .SF to verify the mainAttributes of the manifest
-
// If there is no -Digest-Manifest-Main-Attributes entry in .SF
-
// file, such as those created before java 1.5, then we ignore
-
// such verification.
-
if (mainAttributesEnd > 0 && !createdBySigntool) {
-
String digestAttribute = "-Digest-Manifest-Main-Attributes";
-
if (!verify(attributes, digestAttribute, manifestBytes, 0, mainAttributesEnd, false, true)) {
-
throw failedVerification(jarName, signatureFile);
-
}
-
}
-
// Use .SF to verify the whole manifest.
-
String digestAttribute = createdBySigntool ? "-Digest" : "-Digest-Manifest";
-
if (!verify(attributes, digestAttribute, manifestBytes, 0, manifestBytes.length, false, false)) {
-
Iterator<Map.Entry<String, Attributes>> it = entries.entrySet().iterator();
-
while (it.hasNext()) {
-
Map.Entry<String, Attributes> entry = it.next();
-
Manifest.Chunk chunk = manifest.getChunk(entry.getKey());
-
if (chunk == null) {
-
return;
-
}
-
if (!verify(entry.getValue(), "-Digest", manifestBytes,
-
chunk.start, chunk.end, createdBySigntool, false)) {
-
throw invalidDigest(signatureFile, entry.getKey(), jarName);
-
}
-
}
-
}
-
metaEntries.put(signatureFile, null);
-
signatures.put(signatureFile, entries);
-
}
2》获取证书信息,并且验证CERT.SF文件的签名信息和CERT.RSA中的内容是否一致。
-
// Found Digital Sig, .SF should already have been read
-
String signatureFile = certFile.substring(0, certFile.lastIndexOf('.')) + ".SF";
-
byte[] sfBytes = metaEntries.get(signatureFile);
-
if (sfBytes == null) {
-
return;
-
}
-
byte[] manifestBytes = metaEntries.get(JarFile.MANIFEST_NAME);
-
// Manifest entry is required for any verifications.
-
if (manifestBytes == null) {
-
return;
-
}
-
byte[] sBlockBytes = metaEntries.get(certFile);
-
try {
-
Certificate[] signerCertChain = JarUtils.verifySignature(
-
new ByteArrayInputStream(sfBytes),
-
new ByteArrayInputStream(sBlockBytes));
-
if (signerCertChain != null) {
-
certificates.put(signatureFile, signerCertChain);
-
}
-
} catch (IOException e) {
-
return;
-
} catch (GeneralSecurityException e) {
-
throw failedVerification(jarName, signatureFile);
-
}
这里首先获取到,签名文件。我们在之前的一篇文章中说到了,签名文件和证书文件的名字是一样的。
同时这里还调用了JarUtils类:libcore\luni\src\main\java\org\apache\harmony\security\utils\JarUtils.java
中的verifySignature方法来获取证书,这里就不做太多的解释了,如何从一个RSA文件中获取证书,这样的代码网上也是有的,而且后面我会演示一下,如何获取。
-
/**
-
* This method handle all the work with PKCS7, ASN1 encoding, signature verifying,
-
* and certification path building.
-
* See also PKCS #7: Cryptographic Message Syntax Standard:
-
* http://www.ietf.org/rfc/rfc2315.txt
-
* @param signature - the input stream of signature file to be verified
-
* @param signatureBlock - the input stream of corresponding signature block file
-
* @return array of certificates used to verify the signature file
-
* @throws IOException - if some errors occurs during reading from the stream
-
* @throws GeneralSecurityException - if signature verification process fails
-
*/
-
public static Certificate[] verifySignature(InputStream signature, InputStream
-
signatureBlock) throws IOException, GeneralSecurityException {
-
-
BerInputStream bis = new BerInputStream(signatureBlock);
-
ContentInfo info = (ContentInfo)ContentInfo.ASN1.decode(bis);
-
SignedData signedData = info.getSignedData();
-
if (signedData == null) {
-
throw new IOException("No SignedData found");
-
}
-
Collection<org.apache.harmony.security.x509.Certificate> encCerts
-
= signedData.getCertificates();
-
if (encCerts.isEmpty()) {
-
return null;
-
}
-
X509Certificate[] certs = new X509Certificate[encCerts.size()];
-
int i = 0;
-
for (org.apache.harmony.security.x509.Certificate encCert : encCerts) {
-
certs[i++] = new X509CertImpl(encCert);
-
}
-
-
List<SignerInfo> sigInfos = signedData.getSignerInfos();
-
SignerInfo sigInfo;
-
if (!sigInfos.isEmpty()) {
-
sigInfo = sigInfos.get(0);
-
} else {
-
return null;
-
}
-
-
// Issuer
-
X500Principal issuer = sigInfo.getIssuer();
-
-
// Certificate serial number
-
BigInteger snum = sigInfo.getSerialNumber();
-
-
// Locate the certificate
-
int issuerSertIndex = 0;
-
for (i = 0; i < certs.length; i++) {
-
if (issuer.equals(certs[i].getIssuerDN()) &&
-
snum.equals(certs[i].getSerialNumber())) {
-
issuerSertIndex = i;
-
break;
-
}
-
}
-
if (i == certs.length) { // No issuer certificate found
-
return null;
-
}
-
-
if (certs[issuerSertIndex].hasUnsupportedCriticalExtension()) {
-
throw new SecurityException("Can not recognize a critical extension");
-
}
-
-
// Get Signature instance
-
Signature sig = null;
-
String da = sigInfo.getDigestAlgorithm();
-
String dea = sigInfo.getDigestEncryptionAlgorithm();
-
String alg = null;
-
if (da != null && dea != null) {
-
alg = da + "with" + dea;
-
try {
-
sig = Signature.getInstance(alg, OpenSSLProvider.PROVIDER_NAME);
-
} catch (NoSuchAlgorithmException e) {}
-
}
-
if (sig == null) {
-
alg = da;
-
if (alg == null) {
-
return null;
-
}
-
try {
-
sig = Signature.getInstance(alg, OpenSSLProvider.PROVIDER_NAME);
-
} catch (NoSuchAlgorithmException e) {
-
return null;
-
}
-
}
-
sig.initVerify(certs[issuerSertIndex]);
-
......
这里返回的是一个证书的数组。
3、MANIFEST.MF整个文件签名在CERT.SF文件中头属性中的值是否匹配以及验证MANIFEST.MF文件中的各个属性块的签名在CERT.SF文件中是否匹配
1》第一件事是:验证MANIFEST.MF整个文件签名在CERT.SF文件中头属性中的值是否匹配
-
// Use .SF to verify the mainAttributes of the manifest
-
// If there is no -Digest-Manifest-Main-Attributes entry in .SF
-
// file, such as those created before java 1.5, then we ignore
-
// such verification.
-
if (mainAttributesEnd > 0 && !createdBySigntool) {
-
String digestAttribute = "-Digest-Manifest-Main-Attributes";
-
if (!verify(attributes, digestAttribute, manifestBytes, 0, mainAttributesEnd, false, true)) {
-
throw failedVerification(jarName, signatureFile);
-
}
-
}
这里的manifestBytes:
-
byte[] manifestBytes = metaEntries.get(JarFile.MANIFEST_NAME);
就是MANIFEST.MF文件内容。继续看一下verify方法:
-
private boolean verify(Attributes attributes, String entry, byte[] data,
-
int start, int end, boolean ignoreSecondEndline, boolean ignorable) {
-
for (int i = 0; i < DIGEST_ALGORITHMS.length; i++) {
-
String algorithm = DIGEST_ALGORITHMS[i];
-
String hash = attributes.getValue(algorithm + entry);
-
if (hash == null) {
-
continue;
-
}
-
MessageDigest md;
-
try {
-
md = MessageDigest.getInstance(algorithm);
-
} catch (NoSuchAlgorithmException e) {
-
continue;
-
}
-
if (ignoreSecondEndline && data[end - 1] == '\n' && data[end - 2] == '\n') {
-
md.update(data, start, end - 1 - start);
-
} else {
-
md.update(data, start, end - start);
-
}
-
byte[] b = md.digest();
-
byte[] hashBytes = hash.getBytes(StandardCharsets.ISO_8859_1);
-
return MessageDigest.isEqual(b, Base64.decode(hashBytes));
-
}
-
return ignorable;
-
}
这个方法其实很简单,就是验证传入的data数据块的数据摘要算法和传入的attributes中的算法块的值是否匹配,比如这里:
-
String algorithm = DIGEST_ALGORITHMS[i];
-
String hash = attributes.getValue(algorithm + entry);
这里的algorithm是算法:
-
private static final String[] DIGEST_ALGORITHMS = new String[] {
-
"SHA-512",
-
"SHA-384",
-
"SHA-256",
-
"SHA1",
-
};
这里的entry也是传入的,我们看到传入的是:-Digest
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzcyNC8yMzRkOGE2NDkzYTQ0YTlmZTgzNWJkYTdkNzg5NjE2NC5KUEVH)
这样就是CERT.SF文件中的一个条目:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzEzMS83ZTNmYjljMTM3MmU4NWFkMzFkNGY5MWMwMDg5OGU5Yi5KUEVH)
2》第二件事是:验证MANIFEST.MF文件中的各个属性块的签名在CERT.SF文件中是否匹配
-
// Use .SF to verify the whole manifest.
-
String digestAttribute = createdBySigntool ? "-Digest" : "-Digest-Manifest";
-
if (!verify(attributes, digestAttribute, manifestBytes, 0, manifestBytes.length, false, false)) {
-
Iterator<Map.Entry<String, Attributes>> it = entries.entrySet().iterator();
-
while (it.hasNext()) {
-
Map.Entry<String, Attributes> entry = it.next();
-
Manifest.Chunk chunk = manifest.getChunk(entry.getKey());
-
if (chunk == null) {
-
return;
-
}
-
if (!verify(entry.getValue(), "-Digest", manifestBytes,
-
chunk.start, chunk.end, createdBySigntool, false)) {
-
throw invalidDigest(signatureFile, entry.getKey(), jarName);
-
}
-
}
-
}
这里我们可以看到也是同样调用verify方法来验证CERT.SF中的条目信息的。
最后我们再看一下是如何配对签名信息的,在PackageParser中的collectCertificates方法:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzg1OC9lZTY0ZTRjNmI1NDZlNzNmNTY3ZjE0ODM3MDEwNjVlMi5KUEVH)
这里会比对已经安装的apk的签名和准备要安装的apk的签名是否一致,如果不一致的话,就会报错:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzc0Lzc1ZThjZjBjYjg2MDkzOGE4OTNmYTQ4MTcxMDUzYzVhLnBuZw==)
这个错,也是我们经常会遇到的,就是同样的apk,签名不一致导致的问题。
我们从上面的分析代码中可以看到,这里的Signature比对签名,其实就是比对证书中的公钥信息:
上面我们就看完了Android中验证签名信息的流程,下面我们再来梳理一下流程吧:
所有有关apk文件的签名验证工作都是在JarVerifier里面做的,一共分成三步:
1、JarVerifier.VerifierEntry.verify做了验证,即保证apk文件中包含的所有文件,对应的摘要值与MANIFEST.MF文件中记录的一致。
2、JarVeirifer.verifyCertificate使用证书文件(在META-INF目录下,以.DSA、.RSA或者.EC结尾的文件)检验签名文件(在META-INF目录下,和证书文件同名,但扩展名为.SF的文件)是没有被修改过的。这里我们可以注意到,Android中在验证的过程中对SF喝RSA文件的名字并不关心,这个在之前的 签名过程 文章中介绍到了。
3、JarVeirifer.verifyCertificate中使用签名文件CERT.SF,检验MANIFEST.MF文件中的内容也没有被篡改过
综上所述:
首先,如果你改变了apk包中的任何文件,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,于是验证失败,程序就不能成功安装。
其次,如果你对更改的过的文件相应的算出新的摘要值,然后更改MANIFEST.MF文件里面对应的属性值,那么必定与CERT.SF文件中算出的摘要值不一样,照样验证失败。
这里都会提示安装失败信息:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzUxNC9iOWExYTViMWE1OGUzYWZhMDhhNTUyY2FjMGM2ZWE4Mi5wbmc=)
如果你还不死心,继续计算MANIFEST.MF的摘要值,相应的更改CERT.SF里面的值.
那么数字签名值必定与CERT.RSA文件中记录的不一样,还是失败。
这里的失败信息:
![Android签名机制之---签名验证过程详解 Android签名机制之---签名验证过程详解](/default/index/img?u=aHR0cHM6Ly9waWFuc2hlbi5jb20vaW1hZ2VzLzc0Lzc1ZThjZjBjYjg2MDkzOGE4OTNmYTQ4MTcxMDUzYzVhLnBuZw==)
那么能不能继续伪造数字签名呢?不可能,因为没有数字证书对应的私钥。
所以,如果要重新打包后的应用程序能再Android设备上安装,必须对其进行重签名。
从上面的分析可以得出,只要修改了Apk中的任何内容,就必须重新签名,不然会提示安装失败,当然这里不会分析,后面一篇文章会注重分析为何会提示安装失败。
总结
到这里我们就介绍完了Android中的apk的签名验证过程,再结合之前的一篇文章,我们可以了解到了Android中的签名机制了。这个也是对Android中的安全机制的一个深入了解吧,新年快乐~~