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It is generally recommended to safely erase the content of a disk before encrypting it, to avoid some forensic attacks.

But is it necessary when that disk was encrypted before ? Wouldn't the data left be "random" since it's all encrypted ?

  • are we speaking of Flash Storage (SSDs,etc.) or "real" HardDisks? – architekt Aug 24 '17 at 12:33
  • Well knowing for both case would be nice. What would be different with SSDs ? – user96649 Aug 24 '17 at 12:53
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Random bits of data can make up fragments or even whole files. While that doesn't happen too often, it depends on the importance of the data and will-power of individuals wanting to gain access to it. If the HDD/SSD was not wiped completely, it could contain traces of previous files/fragments/encrypted data that can be obtained. Erasing the HDD completely will remove traces of any potential files and is not considered a bad practice.

Not an expert, but I would assume that partial/broken encryption is irrecoverable even with an encryption key.

  • So I guess not wiping would not be as bad as if it was not encrypted before, but it would still be problematic if the attacker somehow found a way to break the old encryption ? – user96649 Aug 25 '17 at 8:36
  • If it weren't encrypted before, the files would be easier to access. Since it was encrypted, it is harder to access data mostly because not only of the file but also the potentially broken encryption. I say easier, but it would require quite a lot of time and dedication to piece fragmented information. – Josh Ross Aug 25 '17 at 8:41
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    Unless I'm very mistaken broken encryption wouldn't be a problem because data is overwritten by sectors, and each sector is encrypted individually. Fragmentation would cause difficulties with recovery, but the same is true for a filesystem on an unencrypted device. – AndrolGenhald Aug 25 '17 at 17:29

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