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  1. #1
    Registered User
    Join Date
    Jul 2006

    Self-signed CA certificate

    Apologies in advance for what will be a long post: this has taken a bit of work.

    I've written a J2ME application (using Netbeans and the Sun WTK2.2) and have successfully tested it in the emulator. The application is reasonably small (20K) but its data set is 250K (which I put in a J2ME record store). For testing, I initially simply put the data set in a file and included it in the jar and that worked fine in the emulator, but my phone (a stock Nokia 6101 from T-Mobile USA) has a limit of 166K on applications and so that doesn't really work. I switched to a remote download of the data file and that was where the problem arose, because the phone will not allow me to download anything in an unsigned app. After running around a bit and realizing that (at this time) I'm uninterested in paying for a code-signing certificate, I started looking into self signing.

    I checked out the Nokia specs at http://www.forum.nokia.com/info/sw.n..._8_en.pdf.html which lists all the mime types supported by the various phones, and concluded that the only way to get a certificate on the phone would be using the application/vnd.wap.hashed-certificate format. I looked at the Open Mobile Alliance specifications at http://www.openmobilealliance.org/te.../wapindex.html and after reading through a couple of the wireless security specifications, I tried to build my own CA certificate that I could install in the phone to let me sign applications.

    Specifically, this is what I did:
    1. Create using OpenSSL a new CA certificate (details on this abound on the web: Google is your friend).
    2. Convert the PEM-encoded certificate into a DER-encoded certificate (binary) using OpenSSL.
    3. Modified my apache installation with this line:
    AddType application/vnd.wap.hashed-certificate .whc

    The extension was arbitrarily chosen as something obscure.
    4. Created using java a certificate file based on the wireless security specs.
    5. Tried to download it to the phone using the browser.

    Now I'm halfway there: the phone tries to install my binary file and then complains about the Authority certificate being corrupt (which makes perfect sense: I have no real clue what I'm doing in terms of generating the certificate file, so I'd have been extremely impressed if it accepted it). What I'm looking for is insight/knowledge/wisdom from anyone who's had experience with a properly encoded CA certificate to shed some light on exactly what a properly structured wap hashed certificate file looks like. If anyone has access to one such file that they could give me to deconstruct, I'll gladly document and donate the knowledge back. Right now, I'm using the following Java code to generate the wap hashed certificate input.

    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.ByteArrayOutputStream;

    import com.ideasynthesis.utilities.Base64Utils;

    public class createCert
    public static void main(String[] args) throws IOException
    ByteArrayOutputStream fos = new ByteArrayOutputStream(2048);

    // write pieces
    // the version (1)

    // the certificate display name
    String displayName = "My Personal CA";

    // character set (106: UTF-8)
    fos.write(106 >> 8);

    // size
    byte[] data = displayName.getBytes("UTF-8");
    int size = data.length;

    // data

    // certificate
    File inputCert = new File(args[0]);
    FileInputStream fis = new FileInputStream(inputCert);

    // format (x509 certificate)

    // size
    size = (int)inputCert.length();

    // certificate data
    int ch;
    while((ch = fis.read()) != -1) fos.write(ch);

    // url
    String cainfo_url = "www.nokia.com";
    size = cainfo_url.length();

    // size

    // url data
    for(ch=0;ch<size;ch++) fos.write(cainfo_url.charAt(ch));

    // hash

    // output it
    FileOutputStream os = new FileOutputStream(args[1]);
    data = fos.toByteArray();
    size = data.length;
    //char[] output = Base64Utils.encode(data);

    private static int topbyte(int input){ return input >> 24; }
    private static int thirdbyte(int input){ return input >> 16; }
    private static int hibyte(int input){ return input >> 8; }

    Important questions:

    1. The spec doesn't say whether or not it needs to be Base64 encoded: anyone know if that's a necessary step or not?
    2. This takes a DER encoded input file (args[1]). Is the DER encoding the proper certificate encoding?
    3. If you're looking at the specs, I'm basing my output on page 19 of the WPKI definition document (WAP-217-WPKI) and on pages 63, 64 and 67 of the WTLS spec (WAP-261-WTLS) of the openmobilaalliance link I placed above. I was a little fuzzy on the structure definitions used in the WTLS spec, so clarification from any informed souls would be appreciated.

    Thanks for reading this far,

  2. #2
    Super Contributor
    Join Date
    Dec 2005

    Re: Self-signed CA certificate

    hi black,
    i'm not expert at all, but does that thread:
    summary simply state that you cannot self-sign java application for s40 device?
    (also in your linked thread there is a mention about T-mobile proprieptary solution for signing),


  3. #3
    Nokia Developer Champion
    Join Date
    Apr 2003
    USA, CA

    Re: Self-signed CA certificate

    You cannot add certificates on to the S40 devices which you could then use for application signing, sorry.

    Is there any way you could make the data set smaller?


  4. #4
    Registered User
    Join Date
    Jul 2006

    Re: Self-signed CA certificate

    hartti, peter,
    thanks for the responses. I wasn't aware that the phone explicitly forbids adding new authority certificates that permit code signing, but looking through the menu options is appears that on some certificates the options are available to activate or enable App signing, cross-certification (what is that, pray tell) and server authentication (which I'm assuming is SSL for either use in the browser or use in an appropriately signed application). Since one can obviously install new authority certificates, I'd like to know if you have any idea how the phone decides whether or not to allow app-signing by a particular authority certificate: is this something that's in one of the fields on the certificate, or is this a fixed list that is set when the phone is shipped to/activated by the carrier.
    Unfortunately the dataset is kinda immune to further size reduction: its an index for a search application and is about as small as it can be and still be useful. I guess I'll have to bite the bullet and pay Thawte the $199 for the certificate. Still sticks in my throat, though: its my damn phone, and I'm paying for the data service. I should be able to make it jump through hoops if I so choose.
    Alright, diatribe over. However, I'm STILL interested in the authority certificate format: any pointers on how to make a valid wap hashed certificate from an OpenSSL certificate, regardless of whether or not it can be used with code-signing? I'm kinda confused that the spec is so opaque (well, not really: someone wants to make money off it and the easiest way to do that is to make the spec opaque) and since it appears that most of the newer devices are deprecating x-x509 it would seem to be a useful thing (from a developer perspective) to be able to build private authority certificates.

  5. #5
    Nokia Developer Champion
    Join Date
    Apr 2003
    USA, CA

    Re: Self-signed CA certificate

    "I wasn't aware that the phone explicitly forbids adding new authority certificates that permit code signing"

    For Java application signing that is recommended policy as written in MIDP spec.
    In this case T-Mobile has a little more stricter policies in place for unsigned and even for signed 3rd party midlets and therefore the problem arises (you need sigining to get net access). On generic phone, there should be always at least "Ask every time" option available.


  6. #6
    Regular Contributor
    Join Date
    Mar 2003

    Re: Self-signed CA certificate

    I don't know how to solve the signing problem on that phone but maybe I have an idea how you could get the needed data into the phone:

    Could you split the application into two (or more) MIDlets? The first MIDlet "installs " (a part of) the data to the RMS. When you install the second MIDlet (which is named the same but has a higher version number) the user has to select the option to keep the MIDlet data (=RMS, Don't know if S40 devices support this, at least on S60 this works) and install the "new" version (the real application which uses data from RMS).

    Don't know if I explained this approach good enough to get an idea of it. It's also not to easy to use for an average user but at least it could work - without signing.

    Maybe this helps.

    Best Regards

  7. #7
    Nokia Developer Champion
    Join Date
    Mar 2003
    Quote Originally Posted by blackbuddha
    it appears that most of the newer devices are deprecating x-x509 it would seem to be a useful thing (from a developer perspective) to be able to build private authority certificates.
    No, most phones support X.509 in DER. Just these Nokia Series 40 2nd Edition ones need these terrible vnd.wap.hashed-certificates. A user has to enter the whole hash manually. What for a garbage. Older ones only support WTLS, some nothing, most X.509.

    I have send you a link to my one in a direct message, however, I recommend to use Valimo's WPKI Certificate Encoder.

    In the Nokia Series 40 Platform SDKs you can play with the certificate installation. There – in the Nokia 6230i emulator – you are allowed to use self-signed certificates even for code-signing. Good for testing.

    Finally, yes, in Nokia Series 40 only certificates installed with the firmware are allowed for code-signing.

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