I have an iPhone 8 with iOS 12.4.1 and a MacBookPro 15" (mid 2012) with MacOS 10.12.6 “Sierra” and nearly every day I connect the iPhone via the USB-to-Lightning cable in order to download photos to the Mac.
Every time, the iPhone asks “Trust This Computer?” and I answer “Trust”.
Why does the Mac (or the iPhone) not remember this?
My guess would be that exchanging enough data to know it’s a familiar computer would require more trust than iOS is willing to grant without your consent.
That is—at the point your phone asks you to trust the computer, all it knows is that there’s a machine trying to talk to it, and it wants your permission to listen. But without listening it can’t know that it has seen the machine before. So the only options are to allow it to start listening before you give permission or to be unable to recognize familiar computers. And Apple has chosen option #2, which is the more secure choice.
Dave Scocca
but to @jimp 's point, I sync my iPhone X to my desktop Mac every couple of days or so, and rarely get the “Trust This Computer” prompt. If I sync my iPad, which I do less frequently (maybe every month or if there is a major iOS update), I get the prompt.
Edit:
In other words, you being prompted so frequently is a sign that something is awry.
Like @seth I do not get this prompt every time I sync my iPhone to my Mac through USB. I do get it when I sync a brand new iPhone setup to the Mac, but not on subsequent syncs.
I do however have to make sure my iPhone is unlocked IIRC. I find that a bit odd because that’s AFAIK not required when you do wifi syncing.
My guess is that this is a security practice. Chances are good that at one time or another most people will be hooking into a computer it might not be in their best interest to share data with. Though the possibly might be minuscule that your Mac in your home could have been tampered with or infected with a virus, or that your iPhone might have picked something, I think it is a good idea that Macs will ask someone to confirm that you are safe with sharing. I’ll bet that a good % of people don’t even consider the possibilities of what could happen to the iPhone they plug into someone’s Mac, or visa versa.
I do use wifi on my iPhone at Starbucks, the local libraries, hotels, etc., so I’m fine with this reminder.
If you haven’t already, maybe try backing up that phone/iPad to the Mac using iTunes (it is good practice anyway). There might be more chance of the iOS device remembering the computer this way.
I use iTunes to backup the iPhone to this computer a couple of times a month; the last backup was 16 days ago.
I connected the iPhone just now (answering “Trust” and entering the 6-digit passcode) and used iTunes to back up the iPhone.
Then I disconnected and re-connected the iPhone to the Mac three times in a row, with the iPhone unlocked each time, and each time it asked “Trust This Computer?”.
My iPhone5 and my Mac Pro did not do this. But I suppose security concerns have changed a lot since iOS 8 and OS-X 10.6. and newer systems may be more demanding.
Very frustrating. There seems to be an “issue” with Apple security features at present. I did get a “Trust this computer?” message when I plugged the iPhone into my Macbook, when it has trusted the Macbook previously. I also find that unlocking the iMac or Macbook with my Apple Watch is intermittent and I sometimes have to open settings and re-enable it.
The first sign of recent troubles (after iOS 13 release) was 3rd Generation Apple TV users unable to get Homesharing to work. Maybe it is getting all too complex for every combination of hardware and software to be reliable? Grrr
You could try resetting your trust settings on the iPhone. See
Your device remembers the computers you’ve chosen to trust.
If you don’t want to trust a computer or other device anymore, change the privacy settings on your iPhone, iPad, or iPod touch. Go to Settings > General > Reset > Reset Location & Privacy. Now when you connect to formerly trusted computers, the Trust alert will ask you whether you trust that computer.
See also the section under “Get Help” on that page - resetting the privacy and location settings is number 4 on that list.
This will, of course, reset all of the privacy and location application prompts on your phone, so you’ll be asked again to confirm things like whether an app can access your location, access Bluetooth, access photos and the camera, etc. Just be aware of that before you try that.
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Appears to be a problem with Personal Hotspot. Make sure that is off and see if the Trust issue goes away.