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A lot of data wipe algorithms have the final wiping pass with random characters. They discuss about verification after the wipe. An example of this is from this link:

https://www.datanumen.com/blogs/8-effective-algorithms-wipe-erase-data-permanently/

That brings up this question:

When you view the dump in the first few sectors, you see a lot of non-sensical characters but how do you know that it's truly random or may contain potential information? How does the verification process work? I don't see how you can verify when every byte is random, it has to be a consistent pattern where you can establish verification, right?

  • This article seems to describe it. It sounds like they're just verifying that the write-over worked, not if the data is "truly random" or anything like that (which isn't a real thing anyway). So, the verification process is probably just to try to read back the data to make sure that it matches what the secure-erase function tried to write. – Nat Sep 30 '18 at 18:17
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There's no reason that random data needs to be non-deterministic. You could easily use a stream cipher keyed with a random key and overwrite the block device with the keystream it outputs. It would then be trivial to verify that it was all written correctly by comparing the contents of the drive with the keystream generated by the cipher. Without access to the key (which vanishes when the program closes), it would not be possible to distinguish the drive contents from truly random data.

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