Signing Apk files programmatically in java

Question

I need to modify preexisting .apk files present in the /data/app folder. After the modifications the signatures change in the Meta-INF folder. So in order to make sure the apk works properly I need to resign them with the correct md5sum.

Is it possible to resign the apks programmatically through java, generating private key and certs through code only?

Answer 1

I am using Bouncy Castle and this class. Re-sign example:

SignedJar bcApk = new SignedJar(
    new FileOutputStream("out.apk"), signChain, signCert, signKey);
JarFile jsApk = new JarFile(new File("in.apk"));
Enumeration<JarEntry> entries = jsApk.entries();
while (entries.hasMoreElements()) {
    JarEntry entry = entries.nextElement();
    String name = entry.getName();
    if (!entry.isDirectory() && !name.startsWith("META-INF/")) {
        InputStream eis = jsApk.getInputStream(entry);
        bcApk.addFileContents(name, IOUtils.toByteArray(eis));
        eis.close();
    }
}
jsApk.close();
bcApk.close();