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When I'm at work, I connect my iPhone to my computer over USB to keep it charged during the day.

When I do so, the phone appears in iTunes. I don't remember my phone prompting me if I wanted to trust my work computer (or I don't remember choosing Yes), but I'd rather not have this connection. All I need is the precious, precious voltage.

Is there any way to remove or un-trust a particular computer?

(My specifics: iPhone 5, iOS 7.0.2, Windows 7, iTunes 11.1)

10 Answers 10

18

With iOS 7

You cannot untrust with iOS 7. Once you respond with "Trust", you cannot change it. If it's not prompting you now when you connect, it means you have chosen to trust it before.

Snippet from the end of this Apple support article titled "iOS: 'Trust This Computer' alert":

Additional Information

Note: If you select Trust, the computer will be trusted indefinitely. If you select Don't Trust, you will be asked if you want to trust that computer each time you connect your device to that computer.

Last Modified: Sep 18, 2013

With iOS 8

With iOS 8, Apple has provided ways to untrust all previously trusted computers (there is no way to untrust computers selectively). Depending on how you do it, this will result in losing your location and privacy settings or losing your network settings or losing everything with the "erase device" option. The 'Trust This Computer' alert on iPhone, iPad, or iPod touch KB article referenced above has been updated as follows:

If you tap Trust, the computer will be trusted until you untrust all computers or you erase the device. If you tap Don't Trust, you'll see this alert each time you connect your device to that computer.

If you're using iOS 8 or later: To untrust all computers, tap Settings > General > Reset > Reset Location & Privacy. This will also reset your location and privacy settings. You can also untrust all computers by tapping Settings > General > Reset > Reset Network Settings. This will also reset your network settings.

Last Modified: Sep 17, 2014

  • Interesting. I wonder what mechanism iOS uses to uniquely identify a particular computer? – Brant Bobby Oct 4 '13 at 20:31
  • All USB devices provide a Vendor ID and Product ID. Beyond that, a serial number may also be provided. While this can be used to uniquely identify devices, it's not reliable (rogue devices can spoof these). – M K Oct 4 '13 at 20:58
  • I think those exist for peripherals but not USB hosts. And until I've entered the FileVault password on my Mac, the iPhone apparently considers it a different computer. – nschum Oct 24 '13 at 14:20
  • 1
    Further to this line of discussion, I would expect that (though I may be entirely wrong!) iTunes and an iOS device undergo some sort of key exchange. If you can defeat this PC-side—possibly by uninstalling iTunes or clearing its configuration somehow—you may be able to achieve your goal. – zigg Oct 31 '13 at 10:16
  • If it were just a key exchange, then Apple would be able to provide an easy way to un-trust a computer (somewhat similar to how it allows the ability to deauthorize computers for specific iTunes store accounts). – M K Oct 31 '13 at 14:04
23

Here is how to do this on a Mac: Go to /var/db/lockdown in Terminal, as Apple instructs in http://support.apple.com/kb/TS5335 . You can remove everything in this folder, which will remove trust from every device -- you can then re-trust those devices you still want to trust. Or you can remove trust for the specific device; this is a little trickier:

First, find out the "Wi-Fi Address" of your device. For an iPhone/iPad, go to Settings->General->About, and scroll down. You'll see a set of numbers and letters that look like "D0:23:DB:6C:B9:13". You'll need this.

Now, on your Mac, fire up Terminal and type:

cd /var/db/lockdown

(Don't forget to press return.) Take that Wi-Fi Address you just found and very carefully search for it like this:

grep -i D0:23:DB:6C:B9:13 *

Instead of my example, use your Wi-Fi Address. You'll see something like this:

39c1082da11b4920c2298dca702ca3795efbf0cc.plist: <string>d0:23:db:6c:b9:13</string>

The long string of numbers and letters ending in .plist (not including the colon) is the file you need to remove! (If you don't see anything, check very carefully that you typed the Wi-Fi Address correctly. If you still don't see anything, then your device likely wasn't trusted in the first place. Be very careful to use zero and not the letter O when you type this string!)

How to remove the file? Well, type:

sudo rm xx...xx.plist

where "xx...xx.plist" is the file that you want to remove ("39c1082da11b4920c2298dca702ca3795efbf0cc.plist" in the example). You can use copy and paste for the file name, or type the first few letters of the name and hit tab. You'll have to type your password (and you need to be set up as an administrator on your Mac), but this will nuke the file and untrust the device with that Wi-Fi address.

(My appologies to the CLI-adept at this long explanation, but even highly adept Mac users don't necessarily grok the Unix command line. And, yeah, I know what a MAC address is, but imagine the confusion!)

  • Wouldn't it be easier to replace the manual search in the third paragraph with grep MACAdress *.plist (might be easier to do even for people not grokking bash)? And welcome to the site! – nohillside Jul 17 '14 at 5:14
  • That's a great idea! But the problem with using <b>grep</b> is that it is the line following "WiFiMACAddress" that has the actual address. However, here is a line using <b>egrep</b> that looks for any MAC address pattern and (in my test) provides a clean list of file and address: egrep -i '[0-9a-f]{2}(:[0-9a-f]{2}){5}' *.plist – Ed Hall Jul 17 '14 at 19:15
  • The goal is to find the file containing the MAC address, right? The chance of having something looking like a MAC address (and even the same one) for a different key is, let's say, very small. So grep MAC *.plist gives you the name of the plist you want to delete :-) – nohillside Jul 17 '14 at 20:07
  • 2
    Ah, so you mean grep for the specific address. Yup, that will work great. Example: grep -i "D0:23:DB:6C:B9:13" *.plist. (You'll probably need the -i since, at least in my test, the iPhone used uppercase while the lockdown dir uses lowercase.) I'll edit the original answer to reflect this solution (assuming SE lets me). – Ed Hall Jul 17 '14 at 21:02
  • This should be the accepted answer. Thanks for the help. The -i was important... I'm pretty comfortable with command line so I didn't read that closely and was wondering why mine didn't come up. – user43892 Mar 18 '15 at 16:34
11

Delete the contents inside the Lockdown Folder on your PC leaving the folder itself in place.

This worked for me, both iTunes and all the iOS devices asked me again for authorization the next time they connected.

you may need to pinpoint the correct file if you want to delete only one authorization.

see http://support.apple.com/kb/TS5335

2

Reset your Privacy settings. This worked for me. Settings > General > Reset > Reset Location & Privacy

2

I know this is old but for those who come across it, the above answers especially the chosen one are not completely correct or not specific to the askers setup (Windows 7).

It is possible to "untrust" a computer from the computers side, simply navigate to C:\ProgramData\Apple\Lockdown (start, type in %ProgramData%\Apple\Lockdown )

There there are .plist files that contain the device and host certificates used to pair (trust) and they are named using the iOS devices UDID. Delete the file that pertains to the device you want to unpair (remove trust). Deleting all but SystemConfiguration.plist would work but would also cause all others to have to retrust. You can get the UDID of your device several ways, one of which, since asker said iTunes pops up, is on the main "Summary" page for the device, on top has "Serial Number:" Click once on that and it will toggle to UDID.

The other methods suggested even by apple are not ideal as they also remove the trust from all the devices and also defaults other key settings causing you to have to change them back to how you want them.

This is a serious security issue that I am amazed is not addressed better by Apple. I say serious because it allows bypassing any and all passcodes (current or changed ones in future) needing to be entered in order to have iTunes/Computer access to the device and collect all sorts of data from it. If one has not set a password on encrypt backups (sticks to device not computer) then one could create one and backup the more sensitive data as well. iTunes should have an "untrust" method implemented but they don't. It's literally like a setup where one can sign in (like by using a username password as commonly used instead of entering passcode to unlock and choosing "Trust") and not having a sign out and having the login perpetual, even if you change your password!!

1

Find your WiFi MAC address on the iOS device : Settings > General > About > "Wi-Fi Address"

eg. 40:98:aa:01:02:03

Then on the Mac you wish to remove trust from :

sudo find /var/db/lockdown -name '*.plist' -exec fgrep -i '40:98:aa:01:02:03' {} \; -delete 
0

Settings > General > Reset > Reset All Settings should do this if you really need to un-trust.

  • Factory reset doesn't remove the trust. – user59171 Oct 9 '13 at 15:58
  • @Chicago How would you be able to tell? And where/how would the "trust" information be stored so that it could survive a reset? More to point, why on earth would Apple want it to work this way? All questions I think it would help us to have answers to. – irrational John Feb 9 '14 at 23:04
0

One straight forward solution I found (Easy if you remember Trust'ed Date)-
1. Open folder on path "/var/db/lockdown" with the help of "Go to Folder" under "Go" menu in Finder
2. Short items by Date Created
3. Search .plist if you have idea about date it was created. Mine was under today ;) Or simply open each .plist files and match WiFiMACAddress with your device's MAC Address
4. Delete that file
Hurrey! You have done!

-1

Go in Device Manager, find the device and delete the driver for the iPhone. Right Click "Apple Iphone" > Properties > Hardware > Properties > Disable > [OK].

Voila!!!

  • 1
    It would be useful if you provide detailed instructions. A single sentence answer like this does not help much. – M K Oct 31 '13 at 15:02
  • Doesn't removing the driver prevent charging on PC? Does this also mean that no iPhones can sync with that iTunes? – bmike Mar 11 '14 at 23:13
-2

if you open itunes on the computer that you wish not to trust... there is a bar that has File, Edit, Veiw, Controls, Store, Help

click on "Store" Scroll down and click on "Deauthorize Computer"

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