3 ms·

What about using it to share information with people for them to use in an emergency. Data is stored in multiple locations, but only someone with access to 3 of

What about using it to share information with people for them to use in an emergency. Data is stored in multiple locations, but only someone with access to 3 of them would be able to read the data. The existing physical access controls would be the actual safety mechanism. A thief would have to break into 3 locations in order to get the data. We could just encrypt the data and then split the password into three pieces and store those in different locations, but then you would have to store both the data and the password.

mjevans 3y ago
Step 1 : Create a compressed (must not 'store') archive split into small-ish sections of size N/K. Step 2 : Run par2 against the archive sections and create as much parity as possible. Step 3 : Distribute any middle (not the start of the archive, and not the incomplete end piece) segments of the archive and a 'correct' number of parity / recovery packets. If a complete count of the archive and parity pieces are brought together, par2 can recover the remaining pieces of the archive and extraction will be possible. The hashes only (no recovery data) par2 file should be distributed with all copies.
- hgomersall 3y ago
  This is what Shamir's secret sharing algorithm does, just that that has the benefit of being information-theoretically secure.
crazygringo 3y ago
Except that there are problems with the emergency scenario on both sides: - In an actual urgent emergency, getting in touch with the 3 people and getting the data might be difficult and take days/weeks. One is on vacation, another is going to take a couple of days to try to remember where they stored the USB key... - And nothing limits it to emergencies. The 3 people can just get together immediately and examine the valuable information inside, whether it's account numbers, crypto keys, a will, etc. So the only value here is in not having to remember a separate password. But I expect it's just as likely for people to lose the files entirely as much as it is for them to lose passwords. If you share a password-encrypted file with 5 friends, I wouldn't be surprised if 10 years later, only 1 of them still had it. In that case, better to store file+password per-person, rather than require 3 of them to keep it.
- UncleMeat 3y ago
  Worse than that. "Oh fuck, I lost that thing" is going to be a common occurrence in these scenarios. Data lost forever. You can then go to K-of-N schemes or whatever, but the truth is that if you don't have a professional obligation to keep some data safe and accessible, people will simply lose it (and this will still happen in plenty of cases where you do have a professional obligation).

mjevans 3y ago

Step 1 : Create a compressed (must not 'store') archive split into small-ish sections of size N/K. Step 2 : Run par2 against the archive sections and create as much parity as possible. Step 3 : Distribute any middle (not the start of the archive, and not the incomplete end piece) segments of the archive and a 'correct' number of parity / recovery packets. If a complete count of the archive and parity pieces are brought together, par2 can recover the remaining pieces of the archive and extraction will be possible. The hashes only (no recovery data) par2 file should be distributed with all copies.

hgomersall 3y ago
This is what Shamir's secret sharing algorithm does, just that that has the benefit of being information-theoretically secure.

crazygringo 3y ago

Except that there are problems with the emergency scenario on both sides: - In an actual urgent emergency, getting in touch with the 3 people and getting the data might be difficult and take days/weeks. One is on vacation, another is going to take a couple of days to try to remember where they stored the USB key... - And nothing limits it to emergencies. The 3 people can just get together immediately and examine the valuable information inside, whether it's account numbers, crypto keys, a will, etc. So the only value here is in not having to remember a separate password. But I expect it's just as likely for people to lose the files entirely as much as it is for them to lose passwords. If you share a password-encrypted file with 5 friends, I wouldn't be surprised if 10 years later, only 1 of them still had it. In that case, better to store file+password per-person, rather than require 3 of them to keep it.

UncleMeat 3y ago
Worse than that. "Oh fuck, I lost that thing" is going to be a common occurrence in these scenarios. Data lost forever. You can then go to K-of-N schemes or whatever, but the truth is that if you don't have a professional obligation to keep some data safe and accessible, people will simply lose it (and this will still happen in plenty of cases where you do have a professional obligation).