Posts for Tag: thinkpad

Thinkpad X250 - SMS and GPS via Python

When I was messing around trying to get the 4G modem working on my Thinkpad X250 for this post I ended up doing a little debugging by connecting to the modem over serial using cu:

    $ cu -h -l /dev/ttyACM0
    Connected.
    AT^M
    OK

It turns out that the Sierra EM7345 modem in my Thinkpad can be controlled through AT commands sent over serial. Over at zukota.com there's a guy who's done a seriously good job of experimenting with this modem and documenting what was previously not very well documented.  

For example if we wanted to use a SIM locked with the PIN "1234", then send the message "Hello, world!" to the Czech number 775123456, we would connect as above and enter the following:

    AT+CPIN="1234"^M

    OK
    AT+CMGS="+420775356278"^M
    > Hello, world!^Z^M
    +CMGS: 40

    OK

Getting the GPS position involved issuing the XLCSLSR at command and parsing it's output. This is a little more complicated, since there's a slight delay in the response, and the response contains dozens of fields (I've included the request/response in its entirety below so you can see):

    AT+XLCSLSR=1,1,,,,,,,,,,^M
    +XLCSLSR: request id 2

    OK

    +XLCSLSR: 2, 49.195669 N, 16.606075 E, 119.996932, 48.743179, 39.616302,143, 100.997169,67,2016/05/10,18:38:22,0,1,75.45,2.28,-0.25,2.20,0.64,239919,239919.74,,,4.50,2.50,3.50,118.92,62.80,100.98,,,1,1896,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,4,73.04,70.04,21.00,1,,,,21 ,61.03,283.14,41.00,1,,,,16 ,20.01,173.09,30.00,1,,,,10 ,17.01,100.05,32.00,1,,,,29 

    OK

I was delighted when I found this out, as I had recently discovered the pyserial library, and realised I could interact with the modem and explore/expose some of the modem's functionality via a Python library.

em73xx

I rolled up my sleeves and wrote a library called em73xx (PyPI, GitHub) which will issue the necessary AT commands to send and receive SMS messages, and retrieve the current location using the modem's GPS functionality.

To install the library either retrieve from pypi using pip:

    $ pip install em73xx

... or you can clone the smcl/em73xx repo and install using setup.py:

    $ git clone https://github.com/smcl/py-em73xx
    $ cd py-em73xx
    $ python setup.py install

Once it's installed you can use em73xx by importing the Modem class and instantiating it with the path to the serial device on your system (probably /dev/ttyACM0, as below) and optionally specify the PIN for the sim inserted:

    from em73xx import Modem
    modem = Modem("/dev/ttyACM0", pin="1234")

To retrieve all the SMS messages on the SIM, and print them to stdout we can use the getSMS method:

    messages = modem.getSMS()
    for m in messages:
        print("from %s: % (m.sender))
        print("\t%s" % (m.message))

If we want to send a message we can use the sendSMS method:

    # request an 60 minute tram ticket in brno!
    modem.sendSMS("90206", "BRNO")

And finally if we want to retrieve the current GPS position, we can use the getGPS method - note that the modem can fail to get a GPS fix, and will return None if so:

    gps = modem.getGPS()
    if gps:
        print(gps.latitude)
        print(gps.longitude)

xsms

Ultimately I started this because I wanted to have a simple utility that integrated with xmobar which would inform me whether I had received a new SMS, and would allow me to reply to existing messages or compose an entirely new one. To achieve this I wrote xsms which is a utility that will either print to stdout the number of unread messages (for xmobar) or launch a GUI, depending on the command line switches used.

Again you can either retrieve xsms from pypi using pip:

    $ pip install xsms

... or clone the smcl/xsms repo from github and install using setup.py:

    $ git clone https://github.com/smcl/xsms
    $ cd xsms
    $ python setup.py install

Once xsms is installed you can either launch it standalone.

    $ python -m xsms --device=/dev/ttyACM0

And if you want to have a little indicator in your xmobar you can use something like the below (which takes advantage of the ability to specify the font via tags to easily get some icons from Font Awesome):

    -- assumes you have Font Awesome installed and used here:
    -- additionalFonts = ["xft:FontAwesome-10"],
    Run Com "/usr/bin/python" [ "-m", "xsms", "-d", "/dev/ttyACM0", "-p", "1234", "-r", "", "-u", " %d" ] "xsms" 600,

So when you add %sms% to your xmobarrc's template and restart you'll see something like this:

... and if you want to be able to click the icon to raise the GUI, you can surround it with an <action> which invokes xsms:

  template = "%StdinReader% }{ ... stuff ... <action=`python -m xsms -g -d /dev/ttyACM0 -p 1234`>%xsms%</action> ... "

Conclusion

This is an idea that sat half-finished in my ~/dev folder for about 6 months, and I'm really glad that I was able to take it from a single hacky one-shot script to two fully-fledged packages released on PyPI and ready to be used. There is still some additional functionality I'd like to add to em73xx, for example I only grab longitude/latitude from the GPS data and I'd like to be able to reset or power-cycle the modem in case of problems, however it's in pretty good shape overall.

As for xsms, it's the second Tkinter application I've put together, and while I'm finding it easier each time I write something (with fewer cut-paste lines from effbot.org's Tkinter docs) it's starting to be a little unwieldy. For example the ttk module allows you to add widgets to your application with a unified theme, but it's missing a multi-line text entry widget - which is something I use for inputting and displaying the SMS messages. This meant that I had to either decide to put off styling xsms or add some hacks to customise the Tkinter.Text widget that I ultimately used. In addition programatically constructing the UI using the grid() and pack() layout managers feels a little like creating a webpage laid out using nested <table> elements in the late 90's. Ultimately if I find myself writing a Python desktop app in future I'll spend a little more time investigating the frameworks available and weighing them up against using Tkinter, now that I'm broadly familiar with it.

Useful Links

Thinkpad X250 - SmartCards and GPG

This post describes setup and example usages of Smartcard with a Thinkpad's onboard reader and OpenPGP to handle keys for authentication and encryption. 

Your master key will be stored (securely I hope) on a USB drive and rarely used, with your Smart Card containing a couple of subkeys which will be used to sign and authenticate day-to-day.

At the end of the guide you should have a master key securely stored on a USB key, a hard-copy of revocation certificate,  some sub-keys stored on your Smart Card and some knowledge about how to use it to emails, and authenticate via ssh:

There are already very technical guides on how to set this up like the one on jclement.ca which steps 1-5 heavily lean on but even if you're pretty tech-savvy you may end up not 100% understanding exactly what you've actually done. 

I got my Smart Card by becoming a member of the EFSF fellowship or by picking up another OpenPGP smartcard (or a YubiKey if you don't have a reader, here).

Step 1. Securely create and boot from a Debian Live USB image

Download and verify a Debian live image per my previous guide here. We can now flash the USB key we're going to boot from:

    $ sudo dd bs=4M if=./debian-live-8.3.0-amd64-xfce-desktop+nonfree.iso of=/dev/sdb && sync
    272+0 records in
    272+0 records out
    1140850688 bytes (1.1 GB) copied, 214.052 s, 5.3 MB/s
Yes I used a very slow USB flash drive and it was rather painful.

Step 2. Setup the packages

Next couple of sections are pretty much the same steps as the jclement.ca guide - install gnupg2 and libraries we'll use:
    $ sudo apt-get install haveged gnupg2 gnupg-agent libpth20 pinentry-curses libccid pcscd scdaemon libksba8 paperkey opensc jpegoptim xloadimage
Change the configuration file for GnuPG so that it uses a different, stronger set of ciphers by default:
    $ mkdir ~/.gnupg
    $ cat > ~/.gnupg/gpg.conf << !
    no-emit-version
    no-comments
    keyid-format 0xlong
    with-fingerprint
    use-agent
    personal-cipher-preferences AES256 AES192 AES CAST5
    personal-digest-preferences SHA512 SHA384 SHA256 SHA224
    cert-digest-algo SHA512
    default-preference-list SHA512 SHA384 SHA256 SHA224 AES256 AES192 AES CAST5 ZLIB BZIP2 ZIP Uncompressed
    !

At this point jclement.ca advise that you disconnect from the network - which is probably a good idea since we're about to generate a handful of keys and we don't want anything to leak. 

What we're going to do is create a Master Key - which will be stored on a USB drive - and then use it to create a handful of Sub Keys which will be stored on the Smart Card for day-to-day use. Since the Sub Keys could conceivably be compromised we'll generate a revocation certificate which we can use to notify everyone that they should no longer be trusted - at this point we'd generate a new set of Sub Keys and load them onto our card.

Since there are a number of utilities and technologies you may not be familiar with I'm going to show a diagram at the end of each step in the key-creation process to help visualise what exactly is going on where. Here's a little diagram showing what symbols I'll be using.

Step 3. Creating the Master Key

    $ gpg2 --gen-key
    gpg (GnuPG) 2.0.26; Copyright (C) 2013 Free Software Foundation, Inc.
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.
    
    gpg: keyring `/home/sean/.gnupg/secring.gpg' created
    gpg: keyring `/home/sean/.gnupg/pubring.gpg' created
    Please select what kind of key you want:
       (1) RSA and RSA (default)
       (2) DSA and Elgamal
       (3) DSA (sign only)
       (4) RSA (sign only)
    Your selection? 4
    RSA keys may be between 1024 and 4096 bits long.
    What keysize do you want? (2048) 4096
    Requested keysize is 4096 bits
    Please specify how long the key should be valid.
             0 = key does not expire
            = key expires in n days
          w = key expires in n weeks
          m = key expires in n months
          y = key expires in n years
    Key is valid for? (0) 0
    Key does not expire at all
    Is this correct? (y/N) y
    
    GnuPG needs to construct a user ID to identify your key.
    
    Real name: Sean McLemon
    Email address: sean.mclemon@gmail.com
    Comment: 
    You selected this USER-ID:
        "Sean McLemon "
    
    Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O
    You need a Passphrase to protect your secret key.
    
    We need to generate a lot of random bytes. It is a good idea to perform
    some other action (type on the keyboard, move the mouse, utilize the
    disks) during the prime generation; this gives the random number
    generator a better chance to gain enough entropy.
    gpg: /home/sean/.gnupg/trustdb.gpg: trustdb created
    gpg: key 0xC87419541EAC16A8 marked as ultimately trusted
    public and secret key created and signed.
    
    gpg: checking the trustdb
    gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
    gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
    pub   4096R/0xC87419541EAC16A8 2016-04-01
          Key fingerprint = D90B 2575 6FD3 D781 A856  9AE3 C874 1954 1EAC 16A8
    uid                 [ultimate] Sean McLemon 
    
    Note that this key cannot be used for encryption.  You may want to use
    the command "--edit-key" to generate a subkey for this purpose.

And add a pic:

    $ gpg2 --edit-key 0xC87419541EAC16A8
    gpg (GnuPG) 2.0.26; Copyright (C) 2013 Free Software Foundation, Inc.
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.
    
    Secret key is available.
    
    pub  4096R/0xC87419541EAC16A8  created: 2016-04-01  expires: never       usage: SC  
                                   trust: ultimate      validity: ultimate
    [ultimate] (1). Sean McLemon 
    
    gpg> addphoto
    
    Pick an image to use for your photo ID.  The image must be a JPEG file.
    Remember that the image is stored within your public key.  If you use a
    very large picture, your key will become very large as well!
    Keeping the image close to 240x288 is a good size to use.
    
    Enter JPEG filename for photo ID: test.jpg
    Is this photo correct (y/N/q)? y
    
    You need a passphrase to unlock the secret key for
    user: "Sean McLemon "
    4096-bit RSA key, ID 0xC87419541EAC16A8, created 2016-04-01
    
    
    pub  4096R/0xC87419541EAC16A8  created: 2016-04-01  expires: never       usage: SC  
                                   trust: ultimate      validity: ultimate
    [ultimate] (1). Sean McLemon 
    [ unknown] (2)  [jpeg image of size 746]
    
    gpg> save
So now we've got a Master Key our live distro's temporary filesystem. As I mentioned before this should only ever live on a USB key - to do anything useful we'll need to generate some Sub Keys.

Step 4. Creating the Sub Keys

A bit of a better explanation of Sub Keys is at https://wiki.debian.org/Subkeys. Remember, these are the keys we'll be using day-to-day and will be stored on our Smart Card.

    $ gpg2 --expert --edit-key 0xC87419541EAC16A8
    gpg (GnuPG) 2.0.26; Copyright (C) 2013 Free Software Foundation, Inc.
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.
    
    Secret key is available.
    
    gpg: checking the trustdb
    gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
    gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
    pub  4096R/0xC87419541EAC16A8  created: 2016-04-01  expires: never       usage: SC  
                                   trust: ultimate      validity: ultimate
    [ultimate] (1). Sean McLemon 
    [ultimate] (2)  [jpeg image of size 746]
    
    gpg> addkey
    Key is protected.
    
    You need a passphrase to unlock the secret key for
    user: "Sean McLemon "
    4096-bit RSA key, ID 0xC87419541EAC16A8, created 2016-04-01
    
    Please select what kind of key you want:
       (3) DSA (sign only)
       (4) RSA (sign only)
       (5) Elgamal (encrypt only)
       (6) RSA (encrypt only)
       (7) DSA (set your own capabilities)
       (8) RSA (set your own capabilities)
    Your selection? 4
    RSA keys may be between 1024 and 4096 bits long.
    What keysize do you want? (2048) 2048
    Requested keysize is 2048 bits
    Please specify how long the key should be valid.
             0 = key does not expire
            = key expires in n days
          w = key expires in n weeks
          m = key expires in n months
          y = key expires in n years
    Key is valid for? (0) 6m
    Key expires at Wed 28 Sep 2016 21:41:58 CEST
    Is this correct? (y/N) y
    Really create? (y/N) y
    We need to generate a lot of random bytes. It is a good idea to perform
    some other action (type on the keyboard, move the mouse, utilize the
    disks) during the prime generation; this gives the random number
    generator a better chance to gain enough entropy.
    
    pub  4096R/0xC87419541EAC16A8  created: 2016-04-01  expires: never       usage: SC  
                                   trust: ultimate      validity: ultimate
    sub  2048R/0x191900DBF062921B  created: 2016-04-01  expires: 2016-09-28  usage: S   
    [ultimate] (1). Sean McLemon 
    [ultimate] (2)  [jpeg image of size 746]
    
    gpg> addkey
    Key is protected.
    
    You need a passphrase to unlock the secret key for
    user: "Sean McLemon "
    4096-bit RSA key, ID 0xC87419541EAC16A8, created 2016-04-01
    
    Please select what kind of key you want:
       (3) DSA (sign only)
       (4) RSA (sign only)
       (5) Elgamal (encrypt only)
       (6) RSA (encrypt only)
       (7) DSA (set your own capabilities)
       (8) RSA (set your own capabilities)
    Your selection? 6
    RSA keys may be between 1024 and 4096 bits long.
    What keysize do you want? (2048) 2048
    Requested keysize is 2048 bits
    Please specify how long the key should be valid.
             0 = key does not expire
            = key expires in n days
          w = key expires in n weeks
          m = key expires in n months
          y = key expires in n years
    Key is valid for? (0) 6m
    Key expires at Wed 28 Sep 2016 21:42:14 CEST
    Is this correct? (y/N) y
    Really create? (y/N) y
    We need to generate a lot of random bytes. It is a good idea to perform
    some other action (type on the keyboard, move the mouse, utilize the
    disks) during the prime generation; this gives the random number
    generator a better chance to gain enough entropy.
    
    pub  4096R/0xC87419541EAC16A8  created: 2016-04-01  expires: never       usage: SC  
                                   trust: ultimate      validity: ultimate
    sub  2048R/0x191900DBF062921B  created: 2016-04-01  expires: 2016-09-28  usage: S   
    sub  2048R/0x46BDB50E980A2B9B  created: 2016-04-01  expires: 2016-09-28  usage: E   
    [ultimate] (1). Sean McLemon 
    [ultimate] (2)  [jpeg image of size 746]
    
    gpg> addkey
    Key is protected.
    
    You need a passphrase to unlock the secret key for
    user: "Sean McLemon "
    4096-bit RSA key, ID 0xC87419541EAC16A8, created 2016-04-01
    
    Please select what kind of key you want:
       (3) DSA (sign only)
       (4) RSA (sign only)
       (5) Elgamal (encrypt only)
       (6) RSA (encrypt only)
       (7) DSA (set your own capabilities)
       (8) RSA (set your own capabilities)
    Your selection? 8
    
    Possible actions for a RSA key: Sign Encrypt Authenticate 
    Current allowed actions: Sign Encrypt 
    
       (S) Toggle the sign capability
       (E) Toggle the encrypt capability
       (A) Toggle the authenticate capability
       (Q) Finished
    
    Your selection? s
    
    Possible actions for a RSA key: Sign Encrypt Authenticate 
    Current allowed actions: Encrypt 
    
       (S) Toggle the sign capability
       (E) Toggle the encrypt capability
       (A) Toggle the authenticate capability
       (Q) Finished
    
    Your selection? e
    
    Possible actions for a RSA key: Sign Encrypt Authenticate 
    Current allowed actions: 
    
       (S) Toggle the sign capability
       (E) Toggle the encrypt capability
       (A) Toggle the authenticate capability
       (Q) Finished
    
    Your selection? a
    
    Possible actions for a RSA key: Sign Encrypt Authenticate 
    Current allowed actions: Authenticate 
    
       (S) Toggle the sign capability
       (E) Toggle the encrypt capability
       (A) Toggle the authenticate capability
       (Q) Finished
    
    Your selection? q
    RSA keys may be between 1024 and 4096 bits long.
    What keysize do you want? (2048) 
    Requested keysize is 2048 bits
    Please specify how long the key should be valid.
             0 = key does not expire
            = key expires in n days
          w = key expires in n weeks
          m = key expires in n months
          y = key expires in n years
    Key is valid for? (0) 6m
    Key expires at Wed 28 Sep 2016 21:42:43 CEST
    Is this correct? (y/N) y
    Really create? (y/N) y
    We need to generate a lot of random bytes. It is a good idea to perform
    some other action (type on the keyboard, move the mouse, utilize the
    disks) during the prime generation; this gives the random number
    generator a better chance to gain enough entropy.
    
    pub  4096R/0xC87419541EAC16A8  created: 2016-04-01  expires: never       usage: SC  
                                   trust: ultimate      validity: ultimate
    sub  2048R/0x191900DBF062921B  created: 2016-04-01  expires: 2016-09-28  usage: S   
    sub  2048R/0x46BDB50E980A2B9B  created: 2016-04-01  expires: 2016-09-28  usage: E   
    sub  2048R/0xF1D25AD8AC008AA1  created: 2016-04-01  expires: 2016-09-28  usage: A   
    [ultimate] (1). Sean McLemon 
    [ultimate] (2)  [jpeg image of size 746]
    
    gpg> save

Now we've got the newly created Master and Sub-keys on the local filesystem. 

Step 5. Generate a revocation certificate

    $ gpg2 --gen-revoke 0xC87419541EAC16A8
    
    sec  4096R/0xC87419541EAC16A8 2016-04-01 Sean McLemon 
    
    Create a revocation certificate for this key? (y/N) y
    Please select the reason for the revocation:
      0 = No reason specified
      1 = Key has been compromised
      2 = Key is superseded
      3 = Key is no longer used
      Q = Cancel
    (Probably you want to select 1 here)
    Your decision? 1
    Enter an optional description; end it with an empty line:
    > FSB got hold of my private key
    > 
    Reason for revocation: Key has been compromised
    y
    Is this okay? (y/N) y
    
    You need a passphrase to unlock the secret key for
    user: "Sean McLemon "
    4096-bit RSA key, ID 0xC87419541EAC16A8, created 2016-04-01
    
    ASCII armored output forced.
    Revocation certificate created.
    
    Please move it to a medium which you can hide away; if Mallory gets
    access to this certificate he can use it to make your key unusable.
    It is smart to print this certificate and store it away, just in case
    your media become unreadable.  But have some caution:  The print system of
    your machine might store the data and make it available to others!
    -----BEGIN PGP PUBLIC KEY BLOCK-----
    Comment: A revocation certificate should follow
    
    iQIgBCABCgAKBQJW/s+XAx0CeQAKCRDIdBlUHqwWqEsbEACFj7ZDRgwcvG99F1Hb
    PHzqGPXh5X04nnjpPbnWaKviycvdCQtFT3N3Hg0c1fmgBBDMXHXKcP8dBwrsgmU0
    x1vEFUSmzvaW+s/EZXh8xwfXhGVmBG+H+i5JqfiPXelaKH12/pDPqIIE+jlwFx5O
    a+I3TMg5x5pBzpSWmCNmFgxU4jEJ6SBwsYYDCwGjStS3C8Dojk7RfJug/+wZAhk2
    nuGbHKeL48TmLwVsoqlbut57yUzqJ16wC9u46oOwKUeUnluEhOm8eT8fvQsHwM11
    THx8UshfjY1/2p5oA4e7GOyB93u7mS5+u57dkKiHwDbNKVq++rMnJH5nesgOT3f6
    D/5quHjQNUXwGJsxu3H+ZSxAmmj2q8ooaPZfDxeAqSgjLSu3vTQGK8HtsnJ3Cgu5
    tANW4SrDrqqvmpNzutGkmfLRgN/stSLi+MJz78h87nCDPQkMUmp6fEk2kEnVmj1B
    BEMY5SSrJrIDGwf4CGn4kzHDb9/GlS47x33LcE8g7F1lM1LQ7eNvRNpDU36dmiwj
    luJLtl0tKVW4YBz4Yo7AxmT0QYSCgXHWStt9XB1devps1CJ45dlbPNzAE8rJH2+1
    3YjZfFAgiSFFHMsq0C1M2+mQaqrAyGUVT/lR42Tok0GgwaZK48VWeP+cRZu07NDr
    pxodVfJ7TjcVUF04AEtSxayfbg==
    =ck5O
    -----END PGP PUBLIC KEY BLOCK-----
    
JClement suggests printing this out - if you do so it might want to create a QR code to make it easier to digitize. You might want avoid QR code generator sites since we're aiming for security, but you can generate one easily enough using python qrcode module:
    $ pip install qrcode
    Downloading/unpacking qrcode
      Downloading qrcode-5.2.2-py2.py3-none-any.whl (89kB): 89kB downloaded
    Requirement already satisfied (use --upgrade to upgrade): colorama in /usr/lib/python2.7/dist-packages (from qrcode)
    Requirement already satisfied (use --upgrade to upgrade): six in /usr/lib/python2.7/dist-packages (from qrcode)
    Installing collected packages: qrcode
    Successfully installed qrcode
    Cleaning up...
    $ python
    Python 2.7.9 (default, Mar  1 2015, 12:57:24) 
    [GCC 4.9.2] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import qrcode
    >>> cert = open("revoke_cert.asc")
    >>> cert_text = cert.read()
    >>> cert_qr = qrcode.make(cert_text)
    >>> cert_qr.save("revoke_cert.png")
The certificate itself is pretty sizeable, so the resulting QR code is pretty dense and you'll need a reasonable camera to successfully scan it (my iPhone 6S worked nicely). Using the lines above the resulting image will look a little like this - it's a little huge so I didn't want to include it in-line.

So assuming we've printed out revoke_cert.png and discarded the .asc file, at this point we should have created:

Step 6. Backup GPG and store keys on SD/USB

Now we've generated our keys we can copy them somewhere safe (an SD card, or USB)
    $ tar -czf gnupg.tgz ~/.gnupg
    tar: Removing leading `/' from member names
    $ gpg2 -a --export-secret-key 0xC87419541EAC16A8 >> 0xC87419541EAC16A8.master.key
    $ gpg2 -a --export-secret-subkeys 0xC87419541EAC16A8 >> 0xC87419541EAC16A8.subkeys.key
    $ gpg2 -a --export 0xC87419541EAC16A8 > 0xC87419541EAC16A8.public.key.asc
    $ sudo cp gnupg.tgz 0xC87419541EAC16A8.master.key 0xC87419541EAC16A8.subkeys.key 0xC87419541EAC16A8.public.key.asc /media/SDCARD/

Note - it is important to do this. Once we restart the filesystem of the live CD will no longer exist, and we'll lose all of our keys. then load the subkeys to the card.

Now we can distribute the key:

    $ gpg2 --keyserver hkp://pool.sks-keyservers.net --send-keys 0xC87419541EAC16A8
    gpg: sending key 0xC87419541EAC16A8 to hkp server pool.sks-keyservers.net

Now we can reboot, upload our public key to the internet and here's what we have - a master key stored offline/disconnected, a set of sub-keys on the smartcard we can use for everyday tasks, a printed certificate we can use to revoke our subkeys, and a public key somewhere on the net we can share with anyone we need to communicate securely with.

Step 7. Boot into usual OS + load keys

When you're sufficiently certain you've got a nice backup of the .gnupg directory, and the subkeys loaded to the card we can boot into our normal OS and remove the live USB card. 

We'll need to 

    $ gpg2 --import 0xC87419541EAC16A8.public.key.asc
    gpg: /home/sean/.gnupg/trustdb.gpg: trustdb created
    gpg: key C3969A6B: public key "Sean McLemon " imported
    gpg: Total number processed: 1
    gpg:               imported: 1  (RSA: 1)
Now everything is set - we explore a few situations where you might want to use a smart card.

Example 1. Signing/Encrypting a text file using your card

There's a very good guide produced by the Free Software Foundation @ https://emailselfdefense.fsf.org which you can follow if you want to use EnigMail and Thunderbird - if you want an easy way to sign/encrypt emails you should follow that. However if we just want to sign a message in a text file from the command line, we could do something like the below

    $ echo > msg << EOF
    > paddy schwartz party time
    > EOF
    $ gpg2 --output msg.sig --sign msg

Example 2. Decrypting a file using your card

If someone's sent you a file they'll encrypt it using your public key. You can use the keys stored on your card to decrypt it.

To set this up we'll first encrypt a simple text file using our own public key:

    $ echo "a funky test message" > plaintext.asc
    $ gpg2 --out cyphertext --recipient 0x2F3F79CDC3969A6B --encrypt plaintext.asc
    gpg: 720D24AD: There is no assurance this key belongs to the named user
    
    pub  2048R/720D24AD 2016-03-24 Sean McLemon 
     Primary key fingerprint: 63EB 6DF3 C42E 1AB3 92B5  BF02 2F3F 79CD C396 9A6B
          Subkey fingerprint: 3E3C 084E 622A BB06 EEFB  A739 A3FE 2BC1 720D 24AD

    It is NOT certain that the key belongs to the person named
    in the user ID.  If you *really* know what you are doing,
    you may answer the next question with yes.

    Use this key anyway? (y/N) y

OK now we'll verify that the card isn't connected, and that we cannot decrypt it without the card

    $ gpg2 --card-status
    gpg: selecting openpgp failed: Card not present
    gpg: OpenPGP card not available: Card not present
    $ gpg2 --out plaintext-decrypted.asc --decrypt cyphertext 
    gpg: selecting openpgp failed: Card not present
    gpg: encrypted with 2048-bit RSA key, ID 720D24AD, created 2016-03-24
          "Sean McLemon "
    gpg: public key decryption failed: Operation cancelled
    gpg: decryption failed: No secret key

Now if we insert the smart card and try to decrypt again we'll be prompted for our PIN, and the file will be decrypted successfully:

    $ gpg2 --out plaintext-decrypted.asc --decrypt cyphertext
    gpg: encrypted with 2048-bit RSA key, ID 720D24AD, created 2016-03-24
          "Sean McLemon "
    $ cat plaintext-decrypted.asc 
    a funky test message

Example 3. Authenticating with a remote machine using your card

    $ echo enable-ssh-support >> ~/.gnupg/gpg-agent.conf
    $ sudo emacs /etc/X11/Xsession.options # and comment/remove the line "use-ssh-agent"

Now we'll add our public key to the computer we want to connect to using ssh - in my case it's mokpo.local

    $ ssh-add -L | ssh mokpo.local 'cat >> ~/.ssh/authorized_keys'
and we can now test logging in

Example 4. Revoking your keys using the QR code

If our key is ever compromised and we'd like to revoke we will need to issue a revocation certificate to say that this key shouldn't ever be trusted. We can use the QR code we previously generated + printed out - first scan the QR code and save the results into a file revoke-certificate-qr.txt, and perform the following steps:

$ gpg2 --import revoke-certificate-qr.txt
$ gpg2 --keyserver hkp://pool.sks-keyservers.net --send-keys 0xC87419541EAC16A8

Now the world should know not to trust our old keypair, and we can go back to the start of this article and generate a completely new one - this time being extra careful to keep it safe!

Debian - verifying a downloaded ISO image

Part of something I'm doing involved flashing a Debian live image to a USB thumb drive, which is a pretty straightforward process. However this time I realised that I always ignore the little checksum and signature files that sit alongside them and that if I wanted to use them to verify the integrity/security of the image I had no idea how. So here's a quick HOWTO describing the process I followed.

I needed to use a Debian non-free live image since the Thinkpad X250 has an intel wifi device which requires a closed source firmware blob:

    $ wget -c http://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/8.3.0-live+nonfree/amd64/iso-hybrid/debian-live-8.3.0-amd64-xfce-desktop+nonfree.iso
    $ wget http://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/8.3.0-live+nonfree/amd64/iso-hybrid/SHA512SUMS.sign
    $ wget http://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/8.3.0-live+nonfree/amd64/iso-hybrid/SHA512SUMS

Firslty we need to check that the signature of the sha512sum file was created by someone we trust

    $ gpg2 --verify SHA512SUMS.sign SHA512SUMS
    gpg: Signature made Thu 28 Jan 2016 02:07:24 CET
    gpg:                using RSA key 0xDA87E80D6294BE9B
    gpg: Can't check signature: No public key

In this case gpg2 doesn't have any knowledge of the key used to sign this image - 0xDA87E80D6294BE9B. We'll need to retrieve it from the official Debian key server:

    $ gpg2 --keyserver keyring.debian.org --recv-keys 0xDA87E80D6294BE9B
    gpg: requesting key 0xDA87E80D6294BE9B from hkp server keyring.debian.org
    gpg: key 0xDA87E80D6294BE9B: public key "Debian CD signing key " imported
    gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
    gpg: depth: 0  valid:   1  signed:   0  trust: 0-, 0q, 0n, 0m, 0f, 1u
    gpg: Total number processed: 1
    gpg:               imported: 1  (RSA: 1)

Now we have the key we can check the signature, checksums match the key:

    $ gpg2 --verify SHA512SUMS.sign SHA512SUMS
    gpg: Signature made Thu 28 Jan 2016 02:07:24 CET
    gpg:                using RSA key 0xDA87E80D6294BE9B
    gpg: Good signature from "Debian CD signing key " [unknown]
    gpg: WARNING: This key is not certified with a trusted signature!
    gpg:          There is no indication that the signature belongs to the owner.
    Primary key fingerprint: DF9B 9C49 EAA9 2984 3258  9D76 DA87 E80D 6294 BE9B

So the signature is fine, but since we haven't explicitly trusted this key yet we're getting a warning. I'm about 99% sure this is sufficiently secure. Now that is out of the way we can check the ISO using sha512sum:

    $ sha512sum -c <(grep "debian-live-8.3.0-amd64-xfce-desktop+nonfree.iso$" SHA512SUMS)
    debian-live-8.3.0-amd64-xfce-desktop+nonfree.iso: OK

So everything semes to check out and we can be confident the NSA haven't sneakily compromised the image somehow. Just to quickly summarise - here's what we've done:

  1. downloaded a Debian 8.3 live image, checksums and signature
  2. verified the signature was produced by the Debian organisation, and the signature represents the sha512sum 
  3. verified the ISO matches the sha512sum. 


Thinkpad X250 - Debian, XFCE and X.org config

My trusty 2011 Macbook Air started to die recently, and since I'm getting more and more frustrated with OS X (neutering root in El Capitan, for example) I bit the bullet and picked up a Thinkpad X250 on a nice deal and switched to linux full-time. My distro of choice is Debian 8.3 ("Jessie") which is very nice under the hood,but the out-of-the-box UI is a little bit unpolished. Over the last week or so I spent some time bashing it into shape, and since it wasn't so simple I thought I'd share the main steps with anyone else out there.

Display/DPI and Fonts

The first thing is that the X250's screen is 1920x1080 but only 12.5 inches and when you first boot up the text appears to be scaled at 96dpi - and it's pretty tiny. Annoyingly the screen is not high-res enough for the standard HiDPI/Retina approach - scaling everything 2x - to work, everything looks a little too big. Getting something halfway is involves fiddling around with a lot of settings, and this is compounded by the fact that various apps and desktops have different ways of handling it. 

Note that this is mostly for XFCE - some of the other environments look and behave semi-OK (for example Cinnamon is reasonably usable but it eats my battery for breakfast) but I prefer the look and feel of XFCE even if I have to jump through a couple of hoops to get it to play nice.

First thing's first - my display's DPI setting was being incorrectly detected and I didn't have an xorg.conf to modify, so needed to generate one. Logout, switch to a terminal prompt, kill the lightdm process and use Xorg to generate the file:

    $ sudo service lightdm stop
    $ sudo Xorg --configure
    $ sudo cp /root/xorg.conf.new /etc/X11/xorg.conf # or from wherever Xorg created it

Then open up /etc/X11/xorg.conf and edit the Monitor section's DisplaySize - the ThinkPad X250's size in millimetres, so since the X250's screen is 276mm x 155mm we can set it to the following:

    Section "Monitor"
        Identifier "Monitor0"
        VendorName "Monitor Vendor"
        ModelName "Monitor Model"
        DisplaySize 276 155
        Option "DPMS"
    EndSection

After you reboot X11 will have loaded with the correct DPI setting. Things will still look a little wonky - but we're on the right track so sit tight and keep going.

Fixing the XFCE UI element fonts is pretty simple, go to Settings -> Appearance, select the Fonts tab, check the "Custom DPI Setting" box and input 150. 

If you have Chrome or Chromium installed you'll notice that the UI elements and fonts are pretty huge - this is because it's detected that you have a high DPI and has defaulted to scaling things by 2x. You'll need to edit the launcher so that it uses the --force-device-scale-factor to use 1.3 (a number I reached by pure trial-and-error):

Change the following line in /usr/share/applications/google-chrome.desktop:
    Exec=/usr/bin/google-chrome-stable  %U

to 

    Exec=/usr/bin/google-chrome-stable  --force-device-scale-factor=1.3 %U

If you use Chromium you can make a similar change to /usr/share/applications/chromium.desktop. So now Chrome will look a little saner - I also copied over the Times and Helvetica Neue fonts from my Mac and downloaded  Source Code Pro to make things look even better.

Next the login window - we fixed XFCE's DPI but the login window is still using 177, to alter it we need to fix up /etc/lightdm/lightdm-gtk-greeter.conf:

    font-name=Helvetica Neue 8
    xft-antialias=true
    xft-dpi=150
    xft-hintstyle=hintslight
    xft-rgba=rgb
After all this here's what Chrome running with the updated fonts looks like:

Qt fonts

Qt uses some slightly different settings - you need to ensure that ~/.fonts.conf is as appears below:

$ cat ~/.fonts.conf
<!DOCTYPE fontconfig SYSTEM 'fonts.dtd'>
<fontconfig>
    <match target="font" >
        <edit mode="assign" name="hinting" >
            <bool>true</bool>
        </edit>
    </match>
    <match target="font" >
      <edit mode="assign" name="hintstyle" >
	<const>hintslight</const>
      </edit>
    </match>
    <match target="font" >
        <edit mode="assign" name="antialias" >
            <bool>true</bool>
        </edit>
    </match>
</fontconfig>

To keep the layout consistent I opened up Settings -> Qt 4 Settings, went to the fonts tab and set it as follows:

Video Playback

I found that video playback was pretty choppy - to resolve it I had to just uncomment out a single option in xorg.conf:

    Section "Device"
        # ... lots of commented out options
        Option     "TearFree"           "true" # <-- uncomment or add this one
        Identifier  "Card0"
        Driver      "intel"
        BusID       "PCI:0:2:0"
    EndSection

Trackpad

Now that things look a little better we can fix the next couple of things that bothered me. By default there's a little area in the corner with counts as a "right" click that personally I don't use. Disabling it was as simple as commenting out the SoftButtonAreas and SecondarySoftButtonAreas in /etc/X11/xorg.conf.d/50-synaptics.conf

    Section "InputClass"
        Identifier "Default clickpad buttons"
        MatchDriver "synaptics"
        #Option "SoftButtonAreas" "50% 0 82% 0 0 0 0 0"
        #Option "SecondarySoftButtonAreas" "58% 0 0 15% 42% 58% 0 15%"
    EndSection

There's another couple of problems - the trackpad is extremely fast and sensitive by default, and additionally scrolling is too fast and has a sort of inertia that irritates me (I found I'd end up accidentally zooming in/out a lot). Scrolling can be tamed by adding the VertScrollDelta, CoastingSpeed and CoastingFriction sections to the same 50-synaptics.conf file as above, under the Driver "synaptics" section:

    Section "InputClass"
            Identifier "touchpad catchall"
            Driver "synaptics"
            MatchIsTouchpad "on"
    # This option is recommend on all Linux systems using evdev, but cannot be
    # enabled by default. See the following link for details:
    # http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
    #       MatchDevicePath "/dev/input/event*"
    	Option "VertScrollDelta" "200"
    	Option "CoastingSpeed" "1"
    	Option "CoastingFriction" "200"
    EndSection

For me adding the MaxSpeed option (which controls pointer sensitivity/speed) to 50-synaptics.conf didn't work, so I added the following to my ~/.xinitrc:

    synclient MaxSpeed=1.0 # it is 2.5 by default

The final touchpad tweak is to prevent it from registering touches as clicks while you're typing. XFCE has a setting that looks like it should work, but it leaves an agonising 2 second delay after you type before it enables the touchpad again. There's a handy utility to alter this which is syndaemon.

    syndaemon -i .2 -K -t -R -d

This can also go  into .xinitrc.

Power Management

By default the power management settings are a bit of a farce - my battery was exhausted after a handful of hours use even though it's pretty hefty. Strangely it seems that power management is still a bit of a ridiculous scene, I'd last operated a Linux laptop back in 2007 - a Thinkpad T40 - and sadly the out-of-the-box power management is pretty dire. There's a handful of useful applications which can help with individually tweaking things - like powertop - but thankfully there's a useful utility called tlp which appears to improve things significantly with only a little config required.

First you need to add the correct depot to your /etc/apt/sources.list - so add the following line to the end

    deb http://repo.linrunner.de/debian DIST main

And install the tlp and thinkpad packages:

    $ sudo apt-key adv --keyserver pool.sks-keyservers.net --recv-keys CD4E8809
    $ sudo apt-get update
    $ sudo apt-get install tlp tlp-rdw acpi-call-dkms

I still find power management a little unreliable - when closing the lid the system doesn't always sleep/suspend, the battery charge is sometimes reported incorrectly (it was stuck at "52%" for a while, which I didn't notice before it died on me). In addition XScreenSaver appears to mess things up too - when I enabled its power management settings it would kill performance after resuming from sleep (with the xorg process consuming >100% of the cpu). Disabling this altogether was fine.

Sound

Sound through the built-in speakers worked out of the box for me. However I have a little Bose Soundlink II bluetooth speaker which I like to use that's a little bit tricky. After pairing in blueman (which weirdly was a little bit trial-and-error) I wasn't sure how to get sound to play out of it. The solution was to install PulseAudio Volume Control, a utility that provides a nice graphical interface to controlling PulseAudio:

    $ sudo apt-get install pavucontrol

Then start the process that's playing the sound - so for me it's Chrome as I was watching Netflix. Open up pavucontrol, switch to the Playback tab find your application and select the bluetooth speaker from the dropdown. 

This being manual is a little bit frustrating but it's actually a minor step-up from OS X - where sometimes some apps wouldn't output sound to the speaker.

Conclusion

After the above tweaks my experience on Debian as a user is roughly on par with OS X (as a developer, it's far better of course). However there are still a number of things I am missing which would make my life a lot better.

  • Expose style window switcher. I know that there's skippy-xd but it is pretty buggy. There's an xfce bounty for this, so if anyone fancies picking up a whopping $70 then go nuts: https://www.bountysource.com/issues/3327306-expose-like-task-switcher-for-xfce
  • Trackpad gestures. I was quite fond of multi-touch gestures in OS X to switch workspaces, I haven't got this working in Linux/X.org just yet and I'm not sure if it's available.
  • AirDrop-style file sharing from iPhone

Hopefully I can pick away at those.