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Comment by urda | Hacker News Reader

Browsing through the website I came across this:

> VeraCrypt runs on Windows, Linux and Mac, and is believed to be a secure encryption tool to encrypt your files locally. It keeps your files confidential, but does not protect the integrity, i.e. a hacker can't read your files, but they could modify them without you noticing. [1]

Veracrypt encrypts an entire container. I would love to know what they mean by a hacker being able to modify my container's files without being able to read them. Encrypted is encrypted, so this is either PR fluff or the maintainers truly do not understand how encryption works, which is concerning when they are shipping a security app themselves.

  [1] https://www.cryfs.org/comparison

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I believe they talk about authenticated encryption (AEAD schemes, like GCM which CryFS uses).

VeraCrypt uses XTS, which is not authenticated. AFAIK, if attacker messes with some bytes of your encrypted disk, you'll get some garbage but you won't know it's not the correct data.

But that doesn't really give the attacker much, if they just scramble an encrypted container no? They can't really do much by doing that.

Well, there was a problem with CBC, where an attack exists that malicious party may flip specific bits by somehow XORing inputs (I'm not a cryptographer and haven't grokked the details properly). If attacker has a good idea what the plaintext is, they may alter it, like, replace my ~/.ssh/authorized_keys with theirs - and that would be really bad. Such attacks is AFAIK not possible with XTS, though, so irrelevant to VeraCrypt. Just an example.

All I've got is that this stuff is not as simple as "it's either encrypted and safe or not". There are tons of different algorithms (cipher modes etc) with different properties, assumptions about their use and possible attack scenarios.

While this may not give much, I still don't want anyone to mess with my files without me (or, better say, my software) noticing until it's too late and backups are also corrupt. And remote storage knows exactly where I'm writing to (with block-level granularity), so the encrypted blob isn't completely opaque.

> Encrypted is Encrypted

This is very much not the case as their are numerous side channel attacks against unauthenticated symmetric ciphers with regards to padding

   [1] http://www.cs.colorado.edu/~jrblack/papers/padding.pdf

That's not what my comment, or the article is about at all though. There are a number of attacks, my question was in regards to some of the copy on their site.

We would spend our entire day here if we had to discuss attack surfaces and different encryption trade offs if that was the original topic I was discussing.

I understand, but your first comment was criticizing how the comparison was misleading and their are valid concerns that people who are using veracrypt on the cloud might have if their data was unauthenticated; which cryfs addresses.

I still think it is misleading. Once you have a veracrypt container created, an attacker can't just modify a file inside of it without you noticing because it'll just be garbage data at that point.

That is, unless they have your container password / key then it's all over anyway so that point is moot regardless.

Actually I think, the misunderstanding is on your side. Unauthenticated DOES mean that the attacker can modify anything without you noticing. You might only notice because you are getting a file that looks like random junk but you wanted it to be a picture. But that is not something you should rely on for security.

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