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I have a few TiB of data on machines that I control. For georedundant backup purposes I want to also have the data in the cloud. Obviously I don't want to give the provider (or any intelligence service that snoops around) access to the data, so I have to encrypt it.

But because of the long-term nature of that type of storage, I worry that AES-256 is not going to be enough. While is secure against Grover's algorithm, it may be broken in another way (NSA does research in Tau statistics to break it) in maybe 20 years.

I can use cascading ciphers, but I'm not sure what the security implications are and what cascade to use. There is Serpent/Twofish/AES, but I could also use something like AES/Twofish/Salsa20 because Salsa20 is a different type of cipher. I would obviously choose 3 independant IVs and 256bit keys. Is that a reasonable thing to do? What about the MACs?

  • While I certainly respect your desire for privacy, do you think that realistically the data you maintain is worth that much to someone? It seems to me as though you may be over complicating this, and as they say "Complexity is the enemy of security". – DKNUCKLES Jul 5 '16 at 16:09
  • to add to @DKNUCKLES comment - you are worried about data in 20 years. What kind of data from 1996 is so critical today? The kind which is (because there is some data like this) is not the kind maintained in a random cloud. In other words: good idea about the encryption but do not worry too much about it being cracked (because of technological / mathematical advances) – WoJ Jul 5 '16 at 18:01
  • @WoJ I'm primarily worried about something like what happend to RC4, while a full plaintext recovery attack is not possible using reasonable amounts of computing power, using active attacks you can get plaintext recovery in something like 2^23 tries. – Lorenz Jul 5 '16 at 22:11
  • @Aragon0: there is always a possibility of a breakthrough in cryptography. This would be quite literally the end of the world. This is what I meant in my comment - that there is data which is more valuable and that with the chaos following such discovery the criticity of your data would probably be minor compared to that. – WoJ Jul 6 '16 at 6:10

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