Here is Ente's implementation: ( https://2of3.ente.com/ )
There's an implementation packaged up for most Linux distros: http://point-at-infinity.org/ssss
How Shamir's Secret Sharing Works
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Re: How Shamir's Secret Sharing Works
#12Do the people who hold the root DNS keys do anything like this? Or is that too much complexity when a safe in a secure room works as an effective backup?
Re: How Shamir's Secret Sharing Works
#13something tangentially i am interested in is computing following the 'two person rule' for things like sudo. Yes I am logged into server X at terinal Y, and so is my co-worker and we both sign off on running command X
That sounds like you might want to look into digital signatures.
Re: How Shamir's Secret Sharing Works
#14before I learned of shamir secret sharing, I wondered why one couldn't do the same exact thing with a par2 like system (albiet with smaller pieces than a par2 system would traditionally have). i.e. you have X bits of data, you create Y*X/N sized recovery blocks (where Y > N). You hand each recovery block to individual users. and any N users can get together to recover the key and decrypt the contents.
Well in theory the base math is indeed the same; unfortunately though the "randomly chosen" part of shamir's secret sharing is fairly important to the security because information theoretic security of the scheme requires each fragment to be as large as the original secret by way of essentially including a desired count of random data blocks to the original before applying the reed-solomon-like erasure coding to it where now enough fragments to reconstruct the secret plus all random blocks have to be combined.
Also the way of usage of the erasure code has to be selected to not be leaking information but that's more of an issue of not picking a bad way of how to implement the basic concept here. Basically just a case of "do follow the instructions to shamir's secret sharing, don't do something different just because it's a popular way of implementing reed-Solomon".
Yes, you can just GF(256), but if you're worried I'd also just use a prime field instead.
Re: How Shamir's Secret Sharing Works
#15See also a story about an implementation from Max Levchin: https://max.levch.in/post/724289457144070144/shamir-secret-s...
Re: How Shamir's Secret Sharing Works
#16ente means mine in Malayalam language. it's said to be one of the toughest Indian language to learn. FYI.
Re: How Shamir's Secret Sharing Works
#17something tangentially i am interested in is computing following the 'two person rule' for things like sudo. Yes I am logged into server X at terinal Y, and so is my co-worker and we both sign off on running command X
Had something like this at Google. There's a service running as root (or equivalent) which receives your desired command to run, and it has to get authorization from another user for the specific command to run, then runs it. That makes sense at Google, because those are production machines and have access to LDAP and who is allowed to run a command on a machine is defined by an LDAP group and you would need two of them (or more?) and there's already existing management website this can be shoe-horned into.
Your environment is unlikely to have all of that already, so you'll need to figure out equivalents for all those. But I think you're going to need a local service running as root and it's going to need to be able to tell the difference between distinct human users, if you want secure. Just typos is way easier.
Re: How Shamir's Secret Sharing Works
#18It's an incredible technique, when I came across it, it just changed the way I thought of solving giving out keys without "truly" giving them out.
This gave me confidence for eternalvault.app, a project of mine.
Re: How Shamir's Secret Sharing Works
#19Bruce Schneier described this in his seminal book Applied Cryptography, and HashiCorp Vault used to have an implementation in Go. On the practical side, I always wondered how large - in bits - the shares should be. One answer I got on a news group was "1 bit more than the actual key length". Nowadays, I wonder how the quantum computing threat would inform 1) share size choice and 2) pro/con Secret Sharing in general. Does anyone know?
Re: How Shamir's Secret Sharing Works
#20I also had written an article on the subject a while ago if you want to dig a bit deeper: https://petal.cafe/posts/shamir/