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Thread: Disembodied fingers & touch ID

  1. #1
    we're gonna make it out of the fire The_Ink_Goddess's Avatar
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    Disembodied fingers & touch ID

    I had a (pretty embarrassing) plot point in my WIP that someone cuts off a finger in order to access the touch ID on a cell phone, in order to access the information therein. I have googled this question, so I know the common answer is no, the iPhone uses the electric charge and the live tissue below the fingerprint. However, if the finger is hacked off immediately after death (not by the police), does all of this still apply? I assume, therefore, that the phone can't use a fingerprint alone (which would be relatively easy to get to and possibly even simulate)? The hacker - both literal and metaphorical! - is technically versed and used to computers/technology, but no world-ending genius in this regard.

    Also, the phone in my WIP is never specified as being a particular iPhone because I'm sure at some point they will be replaced by something even scarier and more technical, but this phone basically is an iPhone (well, it works like an iPhone and acts like an iPhone, so therefore, it's probably an iPhone). I wondered if anyone particularly versed in technology or the science of disembodying dead fingers could help me think if there could be a way to tweak this plot point without having to throw the baby out with the bathwater, so to speak?

    Thank you!
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  2. #2
    practical experience, FTW
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    you could connect finger to a battery like frog legs, or rub it for static guessin here.

  3. #3
    Stakhanovite Helix's Avatar
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    A freshly severed finger would have the same resistance as living tissue, so go for it.

  4. #4
    Rewriting My Destiny Cyia's Avatar
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    If it's somehow registering the bloodflow through the tissue, then no - it won't work. Otherwise, you should be okay.

    You can always hand-wave an applique by taking an imprint of the dead dude's fingerprint (with glue or other simple, quick-drying material) and overlaying it on a live hand. Maybe stick it into one of those touchscreen gloves that allows you to use touch screens when it's cold.

    If you've got the phone on hand, then why take the finger instead of pressing it to the screen still attached? Rigor won't set in immediately to the point that you can't move the hand.




  5. #5
    Just Another Lazy Perfectionist Brightdreamer's Avatar
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    Off-topic, but this thread has me flashing back to a Red Dwarf episode ("The Inquisitor"), where a severed hand was used to unlock a door - and for the show's closing lines.

    Kryten: "I believe that this would be an appropriate juncture for you to give me five, sir."
    Lister: "Give you five? I can do better than that. I can give you fifteen."
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  6. #6
    practical experience, FTW stephenf's Avatar
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    hi
    I can't give you any links , but I have seen/read versions of your idea before. I think it was an early episode of Mission Impossible that used false finger tips to access something. Away, if originality is important , you may need something different. But if it is just a technique question . It sounds convincing to me , and how many people would know it was impossible . Because they have tried it and it did not work?

  7. #7
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    I've heard that forensic investigators and people doing autopsies have to cut the skin off of the decedent and slide it over their own finger (a smaller one) in order to get accurate fingerprints. This would supposedly work for any heat or electrical sensitive sensors, I suppose. And it's yucky.

  8. #8
    Have pen, will travel Cindyt's Avatar
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    Quote Originally Posted by Fabio_of_Mullets View Post
    I've heard that forensic investigators and people doing autopsies have to cut the skin off of the decedent and slide it over their own finger (a smaller one) in order to get accurate fingerprints. This would supposedly work for any heat or electrical sensitive sensors, I suppose. And it's yucky.
    They do that when the skin is too loose to press the finger into the ink and card.
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  9. #9
    I aim to misbehave Myrealana's Avatar
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    Quote Originally Posted by The_Ink_Goddess View Post
    I had a (pretty embarrassing) plot point in my WIP that someone cuts off a finger in order to access the touch ID on a cell phone, in order to access the information therein. I have googled this question, so I know the common answer is no, the iPhone uses the electric charge and the live tissue below the fingerprint. However, if the finger is hacked off immediately after death (not by the police), does all of this still apply? I assume, therefore, that the phone can't use a fingerprint alone (which would be relatively easy to get to and possibly even simulate)? The hacker - both literal and metaphorical! - is technically versed and used to computers/technology, but no world-ending genius in this regard.

    Also, the phone in my WIP is never specified as being a particular iPhone because I'm sure at some point they will be replaced by something even scarier and more technical, but this phone basically is an iPhone (well, it works like an iPhone and acts like an iPhone, so therefore, it's probably an iPhone). I wondered if anyone particularly versed in technology or the science of disembodying dead fingers could help me think if there could be a way to tweak this plot point without having to throw the baby out with the bathwater, so to speak?

    Thank you!
    According to these hackers, it can be done with a photograph of the fingerprint.
    http://www.ccc.de/en/updates/2013/cc...-apple-touchid
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  10. #10
    Benefactor Member WeaselFire's Avatar
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    Quote Originally Posted by The_Ink_Goddess View Post
    I have googled this question, so I know the common answer is no, the iPhone uses the electric charge and the live tissue below the fingerprint.
    Well, sort of. The iPhone reads the fingerprint conventionally but the screen is resistance conductive, which means it reacts to the resistance of the finger in order to activate. At least as far as I understand the mechanics. Resistance continues after death, but does diminish. How long after death the effect would last is a science experiment I don't want to get my fingers into.

    That said, it can be hacked with a scan of the fingerprint pressed with a live finger. Don't know the actual mechanics but I've seen it done. Of course, you could just change your story to unlocking the phone a different way.

    Jeff

  11. #11
    practical experience, FTW neandermagnon's Avatar
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    If the fingerprint sensor on my phone (and various other fingerprint devices I've used before) is anything to go by, it's not just a question of touching the thing with the right finger, but with just the right part of the finger at just the right angle. Someone could chop the correct digit off (my phone's only programmed to respond to one of them and I have ten) but still not be able to access my phone because the wrong part of the digit's used. Then bear in mind that they won't know whether it's not working because they're holding it at the wrong angle, or they've got the wrong digit. So I think it would take a lot of messing around with the severed hand/finger for it to work. Not saying that I wouldn't find it plausible in a story, but if it worked first time I think it would be stretching plausibility somewhat.

    Even with my completely alive and non-severed digit, it still takes 2-3 attempts. And my phone's one that's supposed to be really good.
    Last edited by neandermagnon; 05-20-2017 at 01:38 AM.
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  12. #12
    Ideas bounce around in my head Jason's Avatar
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    Sadly, no forensic detective work or disembodied fingers needed to bypass the fingerprint technology built into most "smart" phones:

    https://www.theverge.com/2016/5/2/11...-hack-security

    https://www.youtube.com/watch?v=2u4ZLGsw1zo

    https://www.macrumors.com/2014/09/24...gerprint-hack/

    There's tons more...(Google is your friend )
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