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Horcrux: Split your file into encrypted fragments

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Re: Horcrux: Split your file into encrypted fragments

#131

Post by coppsilgold »

coppsilgold wrote: post #126

According to the FAQ it uses a Shamir Secret Sharing Scheme to split an encryption key. But you can actually use a Reed-Solomon scheme[1] and have no encryption key to achieve this objective. First, you process the input data with an all-or-nothing transform (AONT)[2]. Then you split it into Reed-Solomon shares. AONT is required due to Reed-Solomon being vulnerable to a distinguisher[3] and it will most likely leak i…

I was able to find a project which appears to do exactly this: https://github.com/atbarker/AONT-RS>

Paper: https://www.usenix.org/legacy/event/fast11/tech/full_papers/...>

Re: Horcrux: Split your file into encrypted fragments

#132

Post by shaklee3 »

scubbo wrote: post #75
chongli wrote: post #41

Earlier quoted context omitted.

I’m not an extreme Harry Potter fan or anything. It just bothers me when people ride the coattails of some popular term/phrase but then get it wrong. Another one is “isomorphic” as in “isomorphic JavaScript” which abuses the term from mathematics to mean something completely unrelated.

I had a coworker try to use "isomorphic" to mean "when given the same inputs and environment, always produces the same outputs", then accused me of pedantry for pointing out that misusing a word with a very clear definition was likely to cause confusion.

I think they mean idempotent

Re: Horcrux: Split your file into encrypted fragments

#135

Post by wilg »

mmastrac wrote: post #8

There's a cool paper-based backup tool that also uses Shamir Secret Sharing to let you distribute a bunch of paper copies to your friends to restore a file optically: https://github.com/cyphar/paperback

This is very neat! Feels a bit too early to rely on it, but could be very cool for lots of people if it was a bit more mature and easy to use.

Re: Horcrux: Split your file into encrypted fragments

#136

Post by scubbo »

shaklee3 wrote: post #132
scubbo wrote: post #75

Earlier quoted context omitted.

I had a coworker try to use "isomorphic" to mean "when given the same inputs and environment, always produces the same outputs", then accused me of pedantry for pointing out that misusing a word with a very clear definition was likely to cause confusion.

I think they mean idempotent

Whoops, you're right, I brain farted the wrong word.

To be clear, though, they were still wrong. `f(x)=2x` has the property they described of consistently giving the same input for a given input (if you pass in 1, it will always output 2), but it is not idempotent because f(f(x)) does not, in general, equal f(x).

Re: Horcrux: Split your file into encrypted fragments

#138

Post by EE84M3i »

mmastrac wrote: post #8

There's a cool paper-based backup tool that also uses Shamir Secret Sharing to let you distribute a bunch of paper copies to your friends to restore a file optically: https://github.com/cyphar/paperback

Does SSS work well for large inputs, or do you need to AEAD the plaintext and then SSS the key?

Re: Horcrux: Split your file into encrypted fragments

#140

Post by manbitesdog »

Maybe it's too naïve of a question, but why not just using XORs?

Let's say we have a file that we want to split into 4 encrypted shards. We could just generate 3 random files, and make the fourth one be a bitwise XOR of the 3 files plus the original one. Then, doing a bitwise XOR of the 4 encrypted shards will return the original file.

Assuming the PRNGs are unbiased, how would this method not be safe enough?

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