Android签名机制之---签名验证过程详解
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.csdn.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
[java] view plain copy
- 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;
- }
- ……
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:
[java] view plain copy- 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;
[java] view plain copy
- import static android.content.pm.PackageManager.INSTALL_PARSE_FAILED_NO_CERTIFICATES;
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
toVerify = new ArrayList<>(); - toVerify.add(manifestEntry);
- // If we're parsing an untrusted package, verify all contents
- if ((flags & PARSE_IS_SYSTEM) == 0) {
- final Iterator
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
(); - 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);
- }
- }
- // 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
(); - 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());
- }
- }
- }
[java] view plain copy
- 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);
- }
- }
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
[java] view plain copy
- 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
[java] view plain copy- 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
certChains = new ArrayList (); - Iterator
>> it = signatures.entrySet().iterator(); - while (it.hasNext()) {
- Map.Entry
> entry = it.next(); - HashMap
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;
- }
- /**
- * 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
verifiedEntries; - VerifierEntry(String name, MessageDigest digest, byte[] hash,
- Certificate[][] certChains, Hashtable
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 not
- * agree with the decrypted digest as recovered from the
- *
.SF
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);
- }
- }
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:
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。
[java] view plain copy
- 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);
- }
- }
- 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;
- }
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:
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:
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:
[java] view plain copy
- private static SecurityException invalidDigest(String signatureFile, String name,
- String jarName) {
- throw new SecurityException(signatureFile + " has invalid digest for " + name +
- " in " + jarName);
- }
这里捕获到异常之后,会在抛异常出去:
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:
[java] view plain copy
- /**
- * 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;
- }
- 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
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");
- }
- /**
- * 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.
- *
- * Will also return {@code true} if the JAR file is not
- * 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
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;
- }
- /**
- * Returns a
boolean
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;
- }
下面来看一下verifyCertificate方法:
[java] view plain copy- /**
- * @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
entries = new HashMap (); - 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
> it = entries.entrySet().iterator(); - while (it.hasNext()) {
- Map.Entry
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。
[java] view plain copy- // 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。
[java] view plain copy- /**
- * 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
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
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
[java] view plain copy
- // 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);
- }
- }
[java] view plain copy
- byte[] manifestBytes = metaEntries.get(JarFile.MANIFEST_NAME);
- 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;
- }
- String algorithm = DIGEST_ALGORITHMS[i];
- String hash = attributes.getValue(algorithm + entry);
- 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
这样就是CERT.SF文件中的一个条目:
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
[java] view plain copy- // Use .SF to verify the whole manifest.
- String digestAttribute = createdBySigntool ? "-Digest" : "-Digest-Manifest";
- if (!verify(attributes, digestAttribute, manifestBytes, 0, manifestBytes.length, false, false)) {
- Iterator
> it = entries.entrySet().iterator(); - while (it.hasNext()) {
- Map.Entry
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);
- }
- }
- }
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:
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:
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:
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:
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~~
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