Question

I am building an Android application that needs to keep track of some of the other applications installed on the device.

For a given application (package) I need to compute a hash values such that:

• The value is different for different versions of the same application
• The value is the same for the same version of the same application installed on different devices

Is there a way of doing this efficiently?

Thank you

Answer 1

Simply load the apk as a file and compute the MD5 hash of the file with:

public String md5(String s) {
    try {
        // Create MD5 Hash
        MessageDigest digest = java.security.MessageDigest.getInstance("MD5");
        digest.update(s.getBytes());
        byte messageDigest[] = digest.digest();

        // Create Hex String
        StringBuffer hexString = new StringBuffer();
        for (int i=0; i<messageDigest.length; i++)
            hexString.append(Integer.toHexString(0xFF & messageDigest[i]));
        return hexString.toString();

    } catch (NoSuchAlgorithmException e) {
        e.printStackTrace();
    }
    return "";
}

Taken from: http://www.androidsnippets.com/create-a-md5-hash-and-dump-as-a-hex-string

Update:
Are you simply trying to see if a newer version of an App has been installed why not use the PackageManager.getPackageInfo method? It returns a PackageInfo object that contains the version number of the application. You can track these values and when they change it means that an app has been updated. See this: http://developer.android.com/reference/android/content/pm/PackageManager.html