[fprint] Writing a driver for138a:003c (VFS471)

[Vasily Khoruzhick]

On Mon, Oct 13, 2014 at 10:57 PM, Jonathan Daniel
<jonathandaniel at email.com> wrote:
>> Sent: Monday, October 13, 2014 at 9:21 PM
>> From: "Vasily Khoruzhick" <anarsoul at gmail.com>
>> To: "Jonathan Daniel" <jonathandaniel at email.com>
>> Cc: "fprint at lists.freedesktop.org" <fprint at lists.freedesktop.org>
>> Subject: Re: [fprint] Writing a driver for138a:003c (VFS471)
>>
>> Hi Jonathan,
>>
>> Firstly, please don't use HTML formatting in your messages to mail list.
>>
>
> Alright my bad, it should be fine now.

Please also keep mailing list in CC

>> Take a look at those bytes, it's very likely that sensor is 8bpp or
>> even 4bpp, so image pixels should contains similar values (at least at
>> the beginning and at the end of image). If they look like a random
>> data - then it's very likely that protocol is protect with encryption.
>
> To me it looks like random data, could I send you a few scans so you can determine if it's random or not?
> The other bulks look random too, I haven't scanned the initialisation yet though.

Send me whole dump in private email since it may contain your
fingerprints, and you definitely don't want to disclose them to wide
public.

>> There could be 2 options: whole protocol is encrypted or only image
>> payload is encrypted.
>>
>> If image is encrypted, you should analyze traffic and figure out (with
>> a lot of tries :)) which one command enables encryption. Usually, I'm
>> omitting a single transfer and then just capturing traffic again to
>> see if there're differences.
>> If whole traffic is encrypted, it's very likely that you won't be able
>> to replay whole sequence with a device, and it'll be close to
>> imposible to reverse engineer protocol without disassembling Windows
>> driver.
>
> Even if it's all encrypted there is still hope for this device, there is a closed source Linux driver available from HP:
>
> http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/public/psi/swdDetails/?sp4ts.oid=5071175&spf_p.tpst=swdMain&spf_p.prp_swdMain=wsrp-navigationalState%3Didx%253D%257CswItem%253Dob_97486_1%257CswEnvOID%253D2020%257CitemLocale%253D%257CswLang%253D%257Cmode%253D%257Caction%253DdriverDocument&javax.portlet.begCacheTok=com.vignette.cachetoken&javax.portlet.endCacheTok=com.vignette.cachetoken
>
> The problem with this driver is that its for Suse Linux and i'm using Debian, also it says it's made for the 2.28.3 kernel, is that a problem or should it work with other version too?
> I have tried making .deb's from the RPM's but without success. It should also work with libfprint, do you think there's a chance it will work on Debian?

When I looked at their driver last time it wasn't intergrated into
libfprint, they provided their own PAM module and an userspace daemon,
I don't remember much details, sorry. I don't know if it's possible to
get it working on Debian.

Regards,
Vasily