Android签名验证简介

Android原生自带了个安装器（packages\apps\PackageInstaller），

通过其中的源码PackageParser.java (frameworks\base\core\java\android\content\pm)

我们大概就能知道其签名验证机制的验证过程。

其中主要涉及2个函数：

函数1

public boolean collectCertificates(Package pkg, int flags) {
        pkg.mSignatures = null;

        WeakReference<byte[]> readBufferRef;
        byte[] readBuffer = null;
        synchronized (mSync) {
            readBufferRef = mReadBuffer;
            if (readBufferRef != null) {
                mReadBuffer = null;
                readBuffer = readBufferRef.get();
            }
            if (readBuffer == null) {
                readBuffer = new byte[8192];
                readBufferRef = new WeakReference<byte[]>(readBuffer);
            }
        }

        try {
            JarFile jarFile = new JarFile(mArchiveSourcePath);

            Certificate[] certs = null;

            if ((flags&PARSE_IS_SYSTEM) != 0) {
                // If this package comes from the system image, then we
                // can trust it...  we'll just use the AndroidManifest.xml
                // to retrieve its signatures, not validating all of the
                // files.
                JarEntry jarEntry = jarFile.getJarEntry(ANDROID_MANIFEST_FILENAME);
                certs = loadCertificates(jarFile, jarEntry, readBuffer);
                if (certs == null) {
                    Slog.e(TAG, "Package " + pkg.packageName
                            + " has no certificates at entry "
                            + jarEntry.getName() + "; ignoring!");
                    jarFile.close();
                    mParseError = PackageManager.INSTALL_PARSE_FAILED_NO_CERTIFICATES;
                    return false;
                }
                if (DEBUG_JAR) {
                    Slog.i(TAG, "File " + mArchiveSourcePath + ": entry=" + jarEntry
                            + " certs=" + (certs != null ? certs.length : 0));
                    if (certs != null) {
                        final int N = certs.length;
                        for (int i=0; i<N; i++) {
                            Slog.i(TAG, "  Public key: "
                                    + certs[i].getPublicKey().getEncoded()
                                    + " " + certs[i].getPublicKey());
                        }
                    }
                }
            } else {
                Enumeration<JarEntry> entries = jarFile.entries();
                final Manifest manifest = jarFile.getManifest();
                while (entries.hasMoreElements()) {
                    final JarEntry je = entries.nextElement();
                    if (je.isDirectory()) continue;

                    final String name = je.getName();

                    if (name.startsWith("META-INF/"))
                        continue;

                    if (ANDROID_MANIFEST_FILENAME.equals(name)) {
                        final Attributes attributes = manifest.getAttributes(name);
                        pkg.manifestDigest = ManifestDigest.fromAttributes(attributes);
                    }

                    final Certificate[] localCerts = loadCertificates(jarFile, je, readBuffer);
                    if (DEBUG_JAR) {
                        Slog.i(TAG, "File " + mArchiveSourcePath + " entry " + je.getName()
                                + ": certs=" + certs + " ("
                                + (certs != null ? certs.length : 0) + ")");
                    }

                    if (localCerts == null) {
                        Slog.e(TAG, "Package " + pkg.packageName
                                + " has no certificates at entry "
                                + je.getName() + "; ignoring!");
                        jarFile.close();
                        mParseError = PackageManager.INSTALL_PARSE_FAILED_NO_CERTIFICATES;
                        return false;
                    } else if (certs == null) {
                        certs = localCerts;
                    } else {
                        // Ensure all certificates match.
                        for (int i=0; i<certs.length; i++) {
                            boolean found = false;
                            for (int j=0; j<localCerts.length; j++) {
                                if (certs[i] != null &&
                                        certs[i].equals(localCerts[j])) {
                                    found = true;
                                    break;
                                }
                            }
                            if (!found || certs.length != localCerts.length) {
                                Slog.e(TAG, "Package " + pkg.packageName
                                        + " has mismatched certificates at entry "
                                        + je.getName() + "; ignoring!");
                                jarFile.close();
                                mParseError = PackageManager.INSTALL_PARSE_FAILED_INCONSISTENT_CERTIFICATES;
                                return false;
                            }
                        }
                    }
                }
            }
            jarFile.close();

            synchronized (mSync) {
                mReadBuffer = readBufferRef;
            }

            if (certs != null && certs.length > 0) {
                final int N = certs.length;
                pkg.mSignatures = new Signature[certs.length];
                for (int i=0; i<N; i++) {
                    pkg.mSignatures[i] = new Signature(
                            certs[i].getEncoded());
                }
            } else {
                Slog.e(TAG, "Package " + pkg.packageName
                        + " has no certificates; ignoring!");
                mParseError = PackageManager.INSTALL_PARSE_FAILED_NO_CERTIFICATES;
                return false;
            }
        } catch (CertificateEncodingException e) {
            Slog.w(TAG, "Exception reading " + mArchiveSourcePath, e);
            mParseError = PackageManager.INSTALL_PARSE_FAILED_CERTIFICATE_ENCODING;
            return false;
        } catch (IOException e) {
            Slog.w(TAG, "Exception reading " + mArchiveSourcePath, e);
            mParseError = PackageManager.INSTALL_PARSE_FAILED_CERTIFICATE_ENCODING;
            return false;
        } catch (RuntimeException e) {
            Slog.w(TAG, "Exception reading " + mArchiveSourcePath, e);
            mParseError = PackageManager.INSTALL_PARSE_FAILED_UNEXPECTED_EXCEPTION;
            return false;
        }

        return true;
    }

 函数2

private Certificate[] loadCertificates(JarFile jarFile, JarEntry je,
            byte[] readBuffer) {
        try {
            // We must read the stream for the JarEntry to retrieve
            // its certificates.
            InputStream is = new BufferedInputStream(jarFile.getInputStream(je));
            while (is.read(readBuffer, 0, readBuffer.length) != -1) {
                // not using
            }
            is.close();
            return je != null ? je.getCertificates() : null;
        } catch (IOException e) {
            Slog.w(TAG, "Exception reading " + je.getName() + " in "
                    + jarFile.getName(), e);
        } catch (RuntimeException e) {
            Slog.w(TAG, "Exception reading " + je.getName() + " in "
                    + jarFile.getName(), e);
        }
        return null;
    }

 通过上面的代码，我们已经能够得到了签名的证书，通过证书我们就得到PublicKey，通过比较PublicKey我们就能比较签名是否一致，当然这里假设的是只有一个签名。

实例1

package edu.edut.robin.utils;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.security.PublicKey;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.util.Base64;

public class SigntureUtil
{
    final static String TAG = "Signture";

    public static String[] getPublicKeyString(PackageInfo pi)
    {
        PublicKey pubKeys[] = getPublicKey(pi);
        if (pubKeys == null || pubKeys.length == 0)
        {
            return null;
        }
        String[] strPubKeys = new String[pubKeys.length];
        for (int i = 0; i < pubKeys.length; i++)
            strPubKeys[i] = Base64.encodeToString(pubKeys[i].getEncoded(),
                    Base64.DEFAULT);
        return strPubKeys;
    }

    private static PublicKey[] getPublicKey(PackageInfo pi)
    {
        try
        {
            if (pi.signatures == null || pi.signatures.length == 0)
            {
                return null;
            }
            PublicKey[] publicKeys = new PublicKey[pi.signatures.length];
            for (int i = 0; i < publicKeys.length; i++)
            {
                byte[] signature = pi.signatures[i].toByteArray();
                CertificateFactory certFactory = CertificateFactory
                        .getInstance("X.509");
                InputStream is = new ByteArrayInputStream(signature);
                X509Certificate cert = (X509Certificate) certFactory
                        .generateCertificate(is);

                publicKeys[i] = cert.getPublicKey();
            }
        } catch (Exception ex)
        {

        }
        return null;
    }

    private static PublicKey[] getInstalledAppPublicKey(Context context,
            String packageName)
    {
        PackageManager pm = context.getPackageManager();
        PackageInfo pi;
        try
        {
            pi = pm.getPackageInfo(packageName, PackageManager.GET_SIGNATURES);
            if (pi != null && pi.versionName != null)
            {
                return getPublicKey(pi);
            }
        } catch (NameNotFoundException e)
        {
            // not installed
            return null;
        } catch (Exception e)
        {
            e.printStackTrace();
        }

        return null;
    }

    private static Certificate[] loadCertificates(JarFile jarFile, JarEntry je)
    {
        try
        {
            // We must read the stream for the JarEntry to retrieve
            // its certificates.
            byte[] readBuffer = new byte[1024];
            InputStream is = jarFile.getInputStream(je);
            while (is.read(readBuffer, 0, readBuffer.length) != -1)
                ;
            is.close();

            return (je != null) ? je.getCertificates() : null;
        } catch (IOException e)
        {
            e.printStackTrace();
        }
        return null;
    }

    public static boolean verifySignature(Context context, String packageName,
            String filePath)
    {
        boolean verifyed = true;
        try
        {
            PublicKey[] installedAppPubKeys = getInstalledAppPublicKey(context,
                    packageName);
            if (installedAppPubKeys == null||installedAppPubKeys.length==0)
            {
                // package not installed
                return true;
            }
            JarFile jarFile = new JarFile(filePath);
            verifyed = false;
            JarEntry je = jarFile.getJarEntry("classes.dex");
            Certificate[] certs = loadCertificates(jarFile, je);
            if (certs != null && certs.length > 0)
            {
                for (int i = 0; i < certs.length; i++)
                {
                    PublicKey pubKey = certs[i].getPublicKey();
                    for(int j=0;j<installedAppPubKeys.length;j++)
                    {
                        if (pubKey.equals(installedAppPubKeys[j]))
                        {
                            verifyed = true;
                            break;
                        }
                    }
                    if(verifyed)
                        break;
                }
            } else
            {
                verifyed = true;
            }

            jarFile.close();
        } catch (Exception e)
        {
            verifyed = true;
        }

        return verifyed;
    }

}

 关于数字签名的更多内容请阅读《数字签名简介》

关于java本身的数字签名和数字证书请参考《Java中的数字签名和数字证书》和《Jar文件的数字签名》

结束