Sorry for the late reply, I am busy these days. Thank you @bojack for the split topic.
I tested the procedure a lot and there is no reason for this procedure not to work any more because it is mathematical. As noted by @agniles, there is the Shamir Secret Sharing algorithm that let you have n out of m seeds to recover a wallet, which is implemented within the latest Trezor. You can also use Electrum to create a multisig wallet. You can use the public key to check that the money is there at any time. There are risks but the procedure stopping working is not one of them.
Now, here are a few thoughts about holding cryptos in a secure way. Please, please, do not jump to a conclusion and then lose everything because of this post. Be careful, don’t follow blindly any method.
The first thing you should do is to assess the risks. I will list a few here:
- computer hacked
- device stolen (e.g. Trezor)
- physical seed stolen (e.g. piece of paper)
- threat to your life or someone close
- house burns down
- scam, social engineering
- your death
I consider that there are no perfect solutions, there is always a way to lose money. Thus, the safest is not to have all your eggs in the same basket. Split the money and use different methods to store it. Perhaps it is also practical to have more accessible methods but with less money at risk (“cold” vs “hot” wallet).
List of holding options
This list is not exhaustive of course. It is to give some ideas and illustrate how to assess them. I do it quick here, you can just skip it if it bores you.
- Simple, light-weight wallet
- Example(s) : Electrum, Coinomi, Metamask
- Trust placed in : wallet developers, device being safe, browser developers (metamask)
- Pros: Handy, in particular on the phone and in the browser.
- Cons: Many ways to lose your money. Many risks and much trust involved.
- HW wallet (multisig, pin)
- Example(s) : Trezor, Ledger, keepkey
- Trust placed in : the producer (sw & hw, honesty and competency), reseller, transporter, browser developers (trezor), + all the ones for a paper wallet due to the seed.
- Pros: Don’t trust your computer, possibility to hide the money with an extra keyword
- Cons: Less practical than a sw wallet, create a whole lot of new problems when you start wondering how to store the seed. See next item.
- Paper wallet
- Example(s) : just print the seed from your wallet or even just write down the private and public keys.
- Trust placed in : the sw developers of the wallet (if applicable) or the key generators, computer being safe, the paper being safe.
- Pros: little trust needed, in particular if you work on a fresh computer unconnected, you could even produce your own keys (beware mistakes!).
- Cons: Really impractical and error prone. In particular, always, always, move all the coins at once because you don’t know the return address. The paper must now be kept safe and secured. Home fire ? water disaster ? burglars ? amnesia ? death ? in a safe in a bank ? Multisig alleviates a number of these issues.
- Bank and exchanges
- Example(s) : Swissquote, Bitcoin Suisse, Kraken, MtGox
- Trust placed in : the bank or the exchange, your browser, your computer
- Pros: hopefully they are better than you to keep the coins safe, at least the well known, official ones, such as SQ (which uses Bitstamp).
- Cons: we have seen times and times again that many are worse than you at keeping the coins safe. Some were plain scams. It goes against what crypto is about, i.e. be your own bank. They take heavy fees.
A word about death
One risk that most people forget about is their own death. How convenient.
When you die, is/are your partner, children, parents able to recover the coins ?
You need to document, in details, where the coins are. But you don’t want the doc to be enough to steal from you. I do think that a notary is a good place to store these along with your will. Still don’t put private keys there, the notary could get robbed or lose it.
What I personally do
I don’t want to give too many details for obvious reasons. I use a bit of each methods, but in particular the multi-sig seeds and paper wallets. I like Metamask for quick purchases in ETH or tokens. I use Electrum as well. I don’t put coins on exchanges or in banks.