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Ask HN: Why do laptop chargers have data wires?

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Re: Ask HN: Why do laptop chargers have data wires?

#51

Post by dragonwriter »

PrimaryAlibi wrote: post #5
gnabgib wrote: post #3

The USB standard only allows 7.5W (5V @ 1.5A) of power. By negotiating over the data lines, the supplier and consumer can agree to higher amperage and voltage (up to 100W in USB3, 240W in USB3.1) - but you need data lines for this feature. Some USB condoms include a chip to do this negotiation (with the other device) for you - but you still have to trust the chip. You may very well have experienced this with a very b…

So the charger won't work without the data wire and it could destroy the laptop. It's so crazy because I've seen in these tech communities people saying it's recommended to cut the data wires and everyone is upvoting it. I guess that's another popular misconception going around that it's generally fine to cut a data wire.

No, the charger will work fine – and at full power. GP is incorrect, the data lines are not used in power negotiation.

Re: Ask HN: Why do laptop chargers have data wires?

#52

Post by dragonwriter »

acdha wrote: post #33

There are two things to remember: one is that “juice jacking” is an urban legend hyped up by gullible police departments since the 2000s which just doesn’t happen in real life. Making computing clunkier for everyone doesn’t make any more sense than it does to put roofs over the keyboards in your server room to stop Tom Cruise from rappelling down from the ceiling. Second, the same risk applies to every other device.…

> There are two things to remember: one is that “juice jacking” is an urban legend hyped up by gullible police departments since the 2000s which just doesn’t happen in real life.

Its kind of like the magic aura-of-intoxication of fentanyl, only juice jacking is a technically possible and demonstrated capability that approximately never happens in the wild, while magic fentanyl actually is sheer fantasy. But both propagate as ideas by the same mechanism.

Re: Ask HN: Why do laptop chargers have data wires?

#53

Post by dragonwriter »

nonrandomstring wrote: post #4

> It creates an unnecessary security risk by having the data wires. What are your opinions on this? That you are correct. It creates no small security risk (as does the overly-chatty relation between batteries and function boards nowadays) (I am not sure you could produce a battery bomb without a separate back-signal to detonate it) USB was never a very far sighted show, It's undergone so many revisions to squeeze mo…

> You can even encode data as a side channel on the power lines themselves.

USB-C PD standard basically does this (well, on a side channel compared to the main data lines, at any rate.)

> But that would be more expensive and since the separate data lines were already there few designers thought to prioritise security over simplicity and cost.

Pretty sure that the reason the pre-USB-C quick charging non-standard implementations that used existing data lines didn’t do so because it was cheaper to build but because it was more useful for users to not have to have special, incompatible cables for charging.

Re: Ask HN: Why do laptop chargers have data wires?

#54

Post by dragonwriter »

Someone wrote: post #9
nonrandomstring wrote: post #4

> It creates an unnecessary security risk by having the data wires. What are your opinions on this? That you are correct. It creates no small security risk (as does the overly-chatty relation between batteries and function boards nowadays) (I am not sure you could produce a battery bomb without a separate back-signal to detonate it) USB was never a very far sighted show, It's undergone so many revisions to squeeze mo…

> You can even encode data as a side channel on the power lines themselves. But that would be more expensive and since the separate data lines were already there few designers thought to prioritise security over simplicity and cost. The security issue isn’t that there are separate data lines, it’s that there’s a data communication channel between charger and device. So, encoding data as a side channel won’t fix the s…

> The security issue isn’t that there are separate data lines, it’s that there’s a data communication channel between charger and device.

Yes, you can only eliminate the security issue by eliminate the functionality requiring communication.

You can, however, mitigate the security issue and narrow the range of potential attacks by having a dedicated-purpose channel that only is connected to capabilities related to the functionality for which it exists. Security is always a balancing act of how to mitigate the risk associated with desired functionality; shedding functionality is only the optimal solution where the risk outweighs the benefits of the functionality.

Re: Ask HN: Why do laptop chargers have data wires?

#55

Post by DanielHB »

thedanbob wrote: post #36
DanielHB wrote: post #31

Earlier quoted context omitted.

My inlaws were trying to transfer files to a PC from their phones with one of these non-data cables. Even my somewhat tech-savy partner didn't know non-data cables. I taught them the trick about feeling the cable stiffness, I showed them a type-c cable without data vs one with data vs thunderbolt3 type-c. They just couldn't understand why it wasn't working until I showed them there was a physical and tactile differen…

Wild that the best way to tell what kind of USB cable you've got is the equivalent of knocking on a melon to see if it's ripe.

Why? When electronics don't work the first thing I do is hit it kinda hard, same as the old days.

Re: Ask HN: Why do laptop chargers have data wires?

#56

Post by thedanbob »

DanielHB wrote: post #55
thedanbob wrote: post #36

Earlier quoted context omitted.

Wild that the best way to tell what kind of USB cable you've got is the equivalent of knocking on a melon to see if it's ripe.

Why? When electronics don't work the first thing I do is hit it kinda hard, same as the old days.

Relevant SMBC: https://www.smbc-comics.com/comic/halting
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