Android学习心得（21） --- apk签名源码解析

来源：互联网发布：telnet打开端口命令编辑：程序博客网时间：2024/05/02 08:14

新博客地址

blog.marssecure.com

重打包检测

对于apk重打包检测中，验证签名是一种很简单、很快捷的方法，为了更好理解签名，这一章主要讲解apk中签名文件内容

签名：

每一个apk发布之前都需要进行签名，不然不能进行安装，我们使用winrar来查看一个apk包

我们可以看到其目录结构，关注一下META-INF这个文件，里面包含三个文件

下面我们来解压缩，打开看看里面内容

源码位置：

/build/tools/signapk/SignApk.java

MANIFEST.MF：

我们可以看到，该文件包含了多个Name和SHA1-Digest，其中name是文件名称，而SHA1-Digest则是其Base64格式的SHA1的哈希值

来看看源码中的实现

// Main函数中调用Manifest manifest = addDigestsToManifest(inputJar, hashes);  // 计算文件的hash值并放入Manifest中  // addDigestsToManifest函数    private static Manifest addDigestsToManifest(JarFile jar, int hashes)       ...       ...       ...        TreeMap<String, JarEntry> byName = new TreeMap<String, JarEntry>();        for (Enumeration<JarEntry> e = jar.entries(); e.hasMoreElements(); ) {            JarEntry entry = e.nextElement();            byName.put(entry.getName(), entry);        }        // 依次进行哈希值计算        for (JarEntry entry: byName.values()) {            String name = entry.getName();            if (!entry.isDirectory() &&                (stripPattern == null || !stripPattern.matcher(name).matches())) {                InputStream data = jar.getInputStream(entry);                // 哈希操作                while ((num = data.read(buffer)) > 0) {                    if (md_sha1 != null) md_sha1.update(buffer, 0, num);                    if (md_sha256 != null) md_sha256.update(buffer, 0, num);                }                // 添加name hash-digest属性                Attributes attr = null;                if (input != null) attr = input.getAttributes(name);                attr = attr != null ? new Attributes(attr) : new Attributes();                // 计算过程                if (md_sha1 != null) {                    attr.putValue("SHA1-Digest",                                  new String(Base64.encode(md_sha1.digest()), "ASCII"));                }                if (md_sha256 != null) {                    attr.putValue("SHA-256-Digest",                                  new String(Base64.encode(md_sha256.digest()), "ASCII"));                }                output.getEntries().put(name, attr);            }        }        return output;    }// copyFile存放manifestcopyFiles(manifest, inputJar, outputJar, timestamp); // 根据Manifest中name依次将input中文件放入output中

主要的计算过程是在addDigestsToManifest函数中，先生成TreeMap

CERT.SF：

打开看到该文件基本上也和MANIFEST.MF一样

来看看源码中的实现

// Main方法中调用signFile函数signFile(manifest, inputJar, publicKey, privateKey, outputJar);// 查看signFile函数private static void signFile(Manifest manifest, JarFile inputJar,                                 X509Certificate[] publicKey, PrivateKey[] privateKey,                                 JarOutputStream outputJar)        throws Exception {        // Assume the certificate is valid for at least an hour.        long timestamp = publicKey[0].getNotBefore().getTime() + 3600L * 1000;  // 时间戳        // MANIFEST.MF        JarEntry je = new JarEntry(JarFile.MANIFEST_NAME);        je.setTime(timestamp);        outputJar.putNextEntry(je);        manifest.write(outputJar);        int numKeys = publicKey.length;        for (int k = 0; k < numKeys; ++k) {            // CERT.SF / CERT#.SF            // 生成CERT.SF文件            je = new JarEntry(numKeys == 1 ? CERT_SF_NAME :                              (String.format(CERT_SF_MULTI_NAME, k)));            je.setTime(timestamp);            outputJar.putNextEntry(je);            ByteArrayOutputStream baos = new ByteArrayOutputStream();            writeSignatureFile(manifest, baos, getAlgorithm(publicKey[k]));            byte[] signedData = baos.toByteArray();            outputJar.write(signedData);        }    }

主要的过程是在signFile中调用writeSignatureFile这个函数

 /** Write a .SF file with a digest of the specified manifest. */    private static void writeSignatureFile(Manifest manifest, OutputStream out,                                           int hash)        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)");        MessageDigest md = MessageDigest.getInstance(            hash == USE_SHA256 ? "SHA256" : "SHA1");        PrintStream print = new PrintStream(            new DigestOutputStream(new ByteArrayOutputStream(), md),            true, "UTF-8");        // Digest of the entire manifest        manifest.write(print);        print.flush();        main.putValue(hash == USE_SHA256 ? "SHA-256-Digest-Manifest" : "SHA1-Digest-Manifest",                      new String(Base64.encode(md.digest()), "ASCII"));        Map<String, Attributes> entries = manifest.getEntries();        for (Map.Entry<String, Attributes> entry : entries.entrySet()) {            // Digest of the manifest stanza for this entry.            print.print("Name: " + entry.getKey() + "\r\n");            for (Map.Entry<Object, Object> att : entry.getValue().entrySet()) {                print.print(att.getKey() + ": " + att.getValue() + "\r\n");            }            print.print("\r\n");            print.flush();            Attributes sfAttr = new Attributes();            sfAttr.putValue(hash == USE_SHA256 ? "SHA-256-Digest" : "SHA1-Digest-Manifest",                            new String(Base64.encode(md.digest()), "ASCII"));            sf.getEntries().put(entry.getKey(), sfAttr);        }        CountOutputStream cout = new CountOutputStream(out);        sf.write(cout);        if ((cout.size() % 1024) == 0) {            cout.write('\r');            cout.write('\n');        }    }

将manifest中的所有value再做一次哈希计算，目的是验证MANIFEST.MF中值是否已经变化。
for (Map.Entry

CERT.RSA：

该文件是X.509格式证书，可以使用openssl进行查看

来看看源代码

// main函数中调用signFile函数signFile(manifest, inputJar, publicKey, privateKey, outputJar);// 调用writeSignatureBlock函数writeSignatureBlock(new CMSProcessableByteArray(signedData),                                publicKey[k], privateKey[k], outputJar);// 调用writeSignatureBlock函数private static void writeSignatureBlock(    CMSTypedData data, X509Certificate publicKey, PrivateKey privateKey,    OutputStream out)    throws IOException,           CertificateEncodingException,           OperatorCreationException,           CMSException {    // 公钥    ArrayList<X509Certificate> certList = new ArrayList<X509Certificate>(1);    certList.add(publicKey);    JcaCertStore certs = new JcaCertStore(certList);    // 私钥信息    CMSSignedDataGenerator gen = new CMSSignedDataGenerator();    ContentSigner signer = new JcaContentSignerBuilder(        getAlgorithm(publicKey) == USE_SHA256 ? "SHA256withRSA" : "SHA1withRSA")        .setProvider(sBouncyCastleProvider)        .build(privateKey);+9    gen.addSignerInfoGenerator(        new JcaSignerInfoGeneratorBuilder(            new JcaDigestCalculatorProviderBuilder()            .setProvider(sBouncyCastleProvider)            .build())        .setDirectSignature(true)        .build(signer, publicKey));    // 添加公钥信息    gen.addCertificates(certs);    CMSSignedData sigData = gen.generate(data, false);    ASN1InputStream asn1 = new ASN1InputStream(sigData.getEncoded());    DEROutputStream dos = new DEROutputStream(out);    dos.writeObject(asn1.readObject());}