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For a full-disk encryption setup, with a physical disk X and the induced logical volume X_crypt, there are several ways to initially fill the disk:

  • (A): Fill X with zeros;
  • (B): Fill X with random data;
  • (C): Fill X_crypt with zeros;
  • (D): Fill X_crypt with random data.

All theses methods have advantages and disadvantages:

  • (i): (B), (C) and (D) allow you to hide which parts of the disk are used, while (A) does not.
  • (ii): (A) and (C) allow you to prove that you have fully decrypted the disk, which (B) and (D) do not.
  • (iii): (C) would be slightly easier to attack if a known plaintext attack was discovered for your cypher.

It looks to me like (ii) is necessary if you ever plan on traveling to countries that value security a lot more than they value privacy, which only leaves (A) and (C). Then, since I don't really see any danger to (i), and with (iii) in mind, I would be tempted to choose (A). However, most tutorial seem to recommend either (C) or (D).

Is there something I'm missing?

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  • $\begingroup$ It looks to me like (ii) is necessary if you ever plan on traveling to countries that value security a lot more than they value privacy, which only leaves (A) and (C). Could you elaborate what you mean with this? I don't understand what the problem is there... $\endgroup$ – AleksanderRas Apr 29 '19 at 13:43
  • $\begingroup$ @AleksanderRas My understanding is that when entering (at least) some countries, people at the customs can ask you for your encryption keys. And if you used for example (D), they could be more suspicious (because of things like hidden volumes existing, for example with truecrypt) whereas with (A) and (C), there is no more room for suspicion once you gave them the encryption keys. $\endgroup$ – xavierm02 Apr 29 '19 at 14:07
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    $\begingroup$ "allow you to prove that you have fully decrypted the disk"; typically, you can't prove it, as disk encryption typically doesn't provide any integrity checking (due to concerns as to where to keep, and how to update, the integrity tags); hence any bit pattern on the disk will decrypt to something, and there's no way anyone can say it is invalid $\endgroup$ – poncho Apr 29 '19 at 14:31
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    $\begingroup$ I would suggest that you review why the tutorials suggest what they do. Are they based on real world experience? Have they travelled to the US? Remember that this isn't a cryptography question at all. This is a question of how not to be sent to Gitmo by an over zealous minimum wage TSA agent. There's probably not much point discussing with them the algorithmic indifferentiability of encrypted data from random. $\endgroup$ – Paul Uszak Apr 29 '19 at 22:58
  • $\begingroup$ I'm not exactly sure what the question is. Are you asking what you should do if you visit a country that may demand that you disclose your password? Or are you asking about the cryptographic security? $\endgroup$ – forest Sep 8 '19 at 7:03

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