Before selling: erase iPad and iPhone - but do it right!

Wondershare SafeEraser

There have been several embarrassing moments when iPhone owners have sold their old device and the new owner finds intimate photos, still receives messages from the previous owner via the messaging app or finds other sensitive data on the device. Most smartphone users now know that they should delete their personal data before selling their used iPhone so that they do not experience any nasty surprises.

What many people are not aware of, however, is the fact that experienced people are capable of restoring the supposedly deleted data from many smartphones. This is possible because during normal deletion the data is not actually overwritten, but only the administrative entries in the index file of the file system are removed. The data itself remains on the hard drive or in the flash memory until the file system needs the space and the corresponding locations in the memory are overwritten. Until this happens, however, you can use special software to restore the photos, messages, documents and even emails and do all sorts of things with sensitive data that the previous owner certainly does not want. Here is just a brief reference to an article on heise.de that deals with "identity theft" on the Internet.

Correctly delete by overwriting the memory several times

The data can only be classified as technically irretrievable if they have been overwritten three times with random new data. This procedure prevents old information from being restored somehow and this is how you proceed when you use the US security standard US DoD 5220.22-M want to meet.

Reset iPhone via iOS

Although Apple offers the option of resetting personal data and settings via iOS in order to restore the iPhone to the delivery state, the memory is not overwritten several times here. This is also due to the fact that every iOS device encrypts its data itself. If the device is reset via the settings, the key is “thrown away” and the data on the device can no longer be restored without the key. However, this is theoretically still possible if you run a [brute force attack -> brute force] with a lot of computing power and automatically try out many keys until you get recognizable data. For private individuals, however, this should be less of a question, because which private person is so interested that he plows through his previous owner's cell phone with a computer for months and years in order to find out any intimate details.

The brute force attack is more likely to correspond to the approach of the NSA or BND. Whereby you have to say that with the iPhone 6 too NSA and Co no longer have a chancebecause the encryption is so strong it would take over 5 years to crack the code. However, a jailbroken iPhone is a security flaw, because here a large part of the encryption is bypassed and the data is stored in clear text on the device. Here it is indeed advisable to overwrite the data several times.

Here are the instructions for iOS in brief: If you want to delete it using iOS tools, go to “Settings” -> “General” -> “Reset” (at the bottom!) -> “Delete content and settings”. If you pass the device on to friends and trust them, deleting the iPhone in this way is completely sufficient. However, if you offer your device on eBay or other used trading platforms, you might be better off using software to reset the iPhone.

App to securely erase iPhone

There used to be one for iOS App called iShredder, which overwrote the free memory of the smartphone several times. Unfortunately, the iOS app is no longer available in the AppStore as Apple has removed the application. I couldn't find why, but maybe you'll find them again shortly via the manufacturer's website.

Wondershare SafeEraser
Wondershare SafeEraser to erase iOS devices.

However, the Mac app Wondershare SafeEraser is definitely available and can be used to erase iOS devices according to the military standard mentioned above. I tested the software to erase my old iPhone 5 and can only say that it is very easy to use and has obviously overwritten the data, because if you select triple overwrite on a 5 GB iPhone 64, the software is busy for several hours writing useless data to the flash memory. I have included a few screenshots.

SafeEraser High security level
I selected the highest security level in my test with the iPhone 5.
SafeEraser progress bar
With 64 GB of storage you have to plan a good 4 hours to have everything overwritten 3 times.

My conclusion

In most cases, throwing away the key is probably enough to render the data on the Apple iOS device unusable. This can be done via the "Reset" path in the iOS settings. If you want to be on the safe side or have operated your iOS device with a jailbreak, you are well advised to erase the device's memory with a Mac app like SafeEraser before selling it. So you can be sure that no one can recover any personal data.

Update - Query about the Mac app SafeEraser

A reader wrote me a few questions today that I would like to answer publicly in the article, because I think they will also be of interest to other readers:

Can you really trust Wondershare's SafeEraser software? For Mac, the program costs more than 30 €. And I don't want to spend so much money on a program that may not be serious or not really work.
I would also like to know whether the data on your iPhone 5 64 GB has actually been overwritten? Have you been able to recover the data with a recovery program?
And what about the initial setup wizard on the iPhone, was it available as normal so that the person I want to sell the iPhone to only has to set it up after the wizard and can then use it normally?

My answers are probably a bit unsatisfactory, because you can actually only trust software 100% if you can keep an eye on the “source code”. However, Wondershare is a software company that has been around for a long time and has not released any shady products. I personally have no doubts that the company can be trusted.

My tip: If you don't want to spend the 30 EUR, then I would simply advise you to follow the instructions above. With it you can also erase your iPhone quite securely, there is no software running on it that you cannot trust and as mentioned: When you reset your key, your key is deleted and all data is encrypted and cannot be restored without immense expenditure of time and technology.

After I treated my iPhone 5 with the software, the normal setup wizard came, which is also started with every new (deleted) iPhone. In this respect, the software has definitely done something. It does not delete so much that you can no longer start the iPhone afterwards, but only the personal data - not the operating system.

I have not tried restoring the data. There is no software for this on the market either, because it would have to senselessly try out all possible keys on your iPhone using a brute force attack and see whether it can recognize meaningful data with a key somewhere and then hope that it is the right key. This is not something normal people want or can do. The effort is far too high. What is still possible is the recovery of deleted photos, but this is only possible if you have not erased all of your data and reset the iPhone. Once that has happened, accidentally deleted files can no longer be repeated.

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11 Responses to “Before selling: delete iPad and iPhone – but do it right!”

  1. Hi Jens,

    You write in your post that there is no software that can restore the iPhone. Wondershare offers a program of its own.

    Do you think that you can also safely erase the iPhone by repeatedly recording music on the free flash memory? Or with photos? Videos?

    1. Hello Emilia! Ah, does Wondershare have such a program? That probably didn't exist when I wrote the article. To your question: Yes, you can of course overwrite the data by playing new data such as music and videos over it. But then you have to fill the iPhone completely so that you are sure that every storage area is filled. And if you want to be absolutely sure, you would have to delete all data again and copy new ones onto it and do that several times. It would also work, but it takes a lot of time.

  2. Hi all,
    Some time ago I bought the Safe Eraser program from Wondershare and have used it several times.
    The great disillusionment: After "erasing" the data with Wondershare SafeEraser in the highest security level 3, it is easily possible to use the software from the same provider, namely Wondershare Dr.Fone for iOS, to find and restore some of the files again.
    The only way to rid an iPhone of its old data is to do a factory reset, remove the SIM card and then completely reinstall the iOS operating system.
    Only after this procedure does Dr.Fone no longer find any data on the device.

    1. Hello Lucky! Thank you for your comment. Normally the Safe Eraser should overwrite the data several times. That should make recovery impossible. I can't say why it still worked for you... you might have to inform or ask Wondershare support. In any case, resetting the iPhone is effective because it removes the key for encrypting the data. Without the key, you're just left with "junk" data on the iPhone... a simple but effective method of wiping data, although technically it's not actually a wipe.

  3. Hi
    I have iShredder and the description there states that you can only overwrite empty memory areas. So reset the iPhone completely, put the program on it and only then let it run. It is not possible to overwrite any storage space that is still in use.

    1. Yes that's true. In the FAQ it says there:

      Why can't ProtectStar ™ iShredder ™ directly delete data securely?

      In order to be able to securely delete files directly, the app would need access to the file system of your Apple ™ iPhone®, iPad® or iPod®. Unfortunately, Apple ™ has protected its iOS operating system so that access is not possible in order to be able to safely delete individual files.

      The only way to carry out the secure deletion process and still securely delete the data, photos, contacts, apps, etc., is to do this manually and then let the ProtectStar ™ iShredder securely delete the free space on your Apple ™ device.

      and below:

      Preparing iPhone / iPad / iPod touch for sale or transfer: What steps do I have to follow in order to be able to sell my Apple device using iShredder ™?

      To prepare your Apple device for sale with the help of iShredder ™, please follow the five steps below:

      (If necessary, please make a data backup of your device using Apple iTunes).

      Go to Settings -> General -> Reset on your device in the main screen of iOS and select “Erase All Content and Settings”. If necessary, please confirm the process by entering your pin code.
      This now ensures that your device is deleted and reset to the factory settings.

      After your device has been reset, please reconfigure the AppStore (use your Apple ID and password). Then buy or download 'ProtectStar ™ iShredder ™ Pro' and let iShredder ™ install.

      Start iShredder ™ and select a secure deletion method. Start the deletion process and please wait until the deletion process is 100% complete.

      If the deletion process by iShredder ™ was successful, please repeat step # 2 (see above).

  4. Hello everyone, I have another question on the subject. I want to sell my i phone 4s to friends, if I reset the phone now, the messages, photos and e-mails on my i pad will also be lost ??? !!!! I get messages and emails on both devices. Of course, I don't want to lose anything on the i pad. Thanks for your help. Carmen

    1. Hello Carmen!
      I can reassure you that if you reset your iPhone, the emails, photos and other content on the iPad or Mac will not be affected. The process only deletes the local storage of the iPhone and not the iCloud or the data on other devices such as Mac or iPad. Your emails are probably in an IMAP mailbox so that they are synchronized on all devices. If you delete a device, the mails in the IMAP account are not deleted. So do not worry. Nothing will happen. :)

  5. I found a link in your mail about a subscription management. Did I misunderstand something? I just wanted an answer and not one !!! Subscription. Carmen

    1. Hello Carmen! The "subscription" is your link to the administration, whether you want to be informed about new comments on this post. It has nothing to do with the usual subscription traps that cost something. :-) So here too: don't panic. Everything's ok! :)

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