Re: Is it possible to transfer data by using light
Re: Is it possible to transfer data by using light
- Subject: Re: Is it possible to transfer data by using light
- From: Jens Alfke <email@hidden>
- Date: Sun, 20 Sep 2015 21:55:57 -0700
I don't think the ambient light sensor would be sensitive enough for this anyway, so the camera is the right thing to use.
Look into the AVFoundation framework; it has some classes for setting up a video feed from the camera and receiving frames. I believe there's sample code.
But honestly, if you're going this route, it will be much faster to transmit QR codes, since each code contains thousands of bits.
—Jens
> On Sep 20, 2015, at 7:21 PM, ico <email@hidden> wrote:
>
> After reading all of the replies, no one mentioned how to use iPhone to
> detect the light changes (bright and dark) in codes, I just have no clue
> how to make it works as long as I remember developers have no right to
> access the light sensor, so I guess we have to use camera to achieve this,
> but I just don't know how. Can anyone point me to something to read so I
> can start digging into this and make the whole thing start to work?
>
> Thank you all.
>
> On Fri, 18 Sep 2015 at 20:38 Michael David Crawford <email@hidden>
> wrote:
>
>> Do iOS devices support Trusted Computing in hardware? If so is it
>> accessible to userspace apps?
>>
>> If so, you could store your phones secret in a write-only register.
>> For the profoundly paranoid, even the duplication of your storage
>> would not yield your phone's secret, The Bad Guy would need your
>> personal phone.
>>
>> Modern Macs - to the best of my knowledge - provide trusted computing
>> chips, on can access them from userspace with a modest bit of code.
>> Michael David Crawford P.E., Consulting Process Architect
>> email@hidden
>> http://mike.soggywizard.com/
>>
>> One Must Not Trifle With Wizards For It Makes Us Soggy And Hard To
>> Light.
>>
>>
>>> On Fri, Sep 18, 2015 at 3:12 AM, Maxthon Chan <email@hidden> wrote:
>>> The "over-the-shoulder" issue can be avoided using what is effectively a
>> Diffie-Hellman on top of QR codes. This can be done using front-facing
>> cameras on two devices placed face-to-face.
>>>
>>> Sent from my iPhone
>>>
>>>> On Sep 18, 2015, at 00:46, Pascal J. Bourguignon <email@hidden>
>> wrote:
>>>>
>>>>
>>>>
>>>>> On 17/09/15 17:32, Michael David Crawford wrote:
>>>>> And what the man said: I myself experience seizures in which I lose
>>>>> consciousness for as long as three weeks. Before they were diagnosed
>>>>> I would experience seizures while driving my car then suddenly find
>>>>> myself in unfamiliar places without any clue how I got there.
>>>>>
>>>>> I don't know for sure but strongly suspect that modern computer user
>>>>> interfaces caused my seizure disorder as well as that of my cousin.
>>>>> Seizures are not otherwise found among any of our blood relatives.
>>>>
>>>> But then if you don't use the whole screen, but only the area that
>>>> should be in front of the camera of the superposed phone, then users
>>>> shouldn't be subjected to much stroboscopic light.
>>>>
>>>> Having the objective so close from the light source does not allow
>>>> the camera to distinguish pixels; for example, a black to white
>>>> transition takes about 1/10 of the height of the camera view.
>>>> But this means that you might still able to transmit about ten pixels
>> at once,
>>>> and you can multiply that by a number of color that you can detect
>> reliably
>>>> being that out of focus. Basically, I would expect 8 colors to be
>> clearly
>>>> distinguishable. Actually, probably more colors should be
>> distinguishable,
>>>> if you can filter out the interferences due to the grid of the camera
>> vs.
>>>> the grid of the screen. So assume 4 bits for the color, and 9 areas,
>>>> that's 36 bit/moment, and you should be able to do 30 moment/second,
>>>> for a total of 1080 bit/second. A little less for ECC, about 1 KB/s
>>>> is not too bad. It's good enough to transmit a good private key, and
>> then
>>>> transfer the data thru wifi.
>>>>
>>>>
>>>> Of course, if you move the camera out to focus on the screen, then
>>>> you can transmit at a higher speed things like QR codes, but they
>>>> could also be seen over the shoulder by high resolution cameras.
>>>>
>>>> --
>>>> __Pascal J. Bourguignon__
>>>> http://www.informatimago.com/
>>>>
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