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 are not aware of, however, is the fact that savvy people are quite capable of restoring the supposedly deleted data from many smartphones. This is possible because the normal deletion does not actually overwrite the data, only the management 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 requires the space and the corresponding locations in the memory are overwritten. Until this is done, however, you can use special software to restore photos, messages, documents and emails and do all sorts of things with sensitive data that the previous owner certainly does not want. Here's just a quick reference to one Article on heise.de, which is about "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.

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Reset iPhone via iOS

Apple offers the option of resetting personal data and settings via iOS in order to restore the iPhone to the delivery state, but the memory is not overwritten multiple times. But this is also due to the fact that every iOS device itself encrypts its data. 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. Theoretically, however, this is still possible if you carry out 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 is unlikely to be an option, because which private person is already so interested that he plowed the cell phone of his previous owner with a computer for months and years in order to find out possibly 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 using the on-board tools of iOS, go to "Settings" -> "General" -> "Reset" (at the bottom!) -> "Delete content & settings". If you pass the device on to friends and trust the people, deleting the iPhone in this way is completely sufficient. However, if you sell your device on eBay or other used trading platforms, you might be better off using software to reset your 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.

But that is definitely available Wondershare SafeEraser Mac app, with which you can delete the iOS devices according to the military standard mentioned above. I tested the software to erase my old iPhone 5 and all I can say is that it is very easy to use and it has obviously overwritten the data too, because if you select triple overwrite on a 5GB iPhone 64, the Software occupied a few hours to write senseless data to the flash memory. I've added 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 enough to make the data on the Apple iOS device unusable. This is done via the "Reset" path in the iOS settings. If you want to be on the safe side or have jailbroken your iOS device, you would do well to clear the device's memory with a Mac app such as SafeEraser before selling it. So you can be sure that no one can restore 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 only trust 100% software that you can "keep an eye on" in the source code. However, Wondershare is a software company that has been around for a long time and has not released any shady products. Personally, I have no doubt 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 comments

  1. XY says:

    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?

    • sir appleot says:

      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. Lucky says:

    Hi all,
    Some time ago I bought the Safe Eraser program from Wondershare and have used it several times.
    The big disappointment: After "deleting" the data with Wondershare SafeEraser in the highest security level 3, it is easily possible to find and restore some of the files with the software from the same provider, namely Wondershare Dr.Fone for iOS.
    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.

    • sir appleot says:

      Hello Lucky! I thank you for your comment. Normally, the Safe Eraser should overwrite the data several times. Restoration should then be impossible. I can't say why it worked for you anyway ... you might have to inform or ask the support of Wondershare. Resetting the iPhone is effective in any case, as it removes the key for encrypting the data. Without the key you only have "junk data" on the iPhone ... a simple but effective method of data deletion, although technically it is not really deleting.

  3. Tenebrae says:

    Hallo,
    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.

    • sir appleot says:

      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).

      On your device, go to Settings -> General -> Reset on the main iOS screen and select "Erase content & settings" from there. 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. Carmen says:

    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

    • sir appleot says:

      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. Carmen says:

    Thank you very much for the quick and helpful answer ??? Carmen

  6. Carmen says:

    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

    • sir appleot says:

      Hello Carmen! The "subscription" is your link to manage 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. All good! :)

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