Future-proofing a deflationary currency from future counterfeiting Say someone locks away a wallet in durable storage for 100 years and BitCoins are still actively used.

Are those BitCoins still going to be valid if they haven't been traded in/upgraded to the newer protocols?

I've seen other answers on this site that suggest either that 1) BitCoins will need to be upgraded by a certain block (at the switching of the hash function and protocol, for example, to adapt to any discovered weaknesses) OR 2) that they will forever be valid but that future equipment might be able to steal away those bitcoins (or even generate never-before-seen ones under the older protocols).

1) Would be awful, it seems to me.  What if you miss the deadline because you're in a coma and nobody knows to keep your wallet updated?

2) Seems like a danger for a deflationary currency where the older money is easier to counterfeit AND is worth more.

Perhaps I'm just confusing matters of BitCoin, Blocks, and Wallets?

As I understand it, if the first BitCoin ever made had been squirreled away and the currency takes off as a success, the novel and deflationary nature of the currency will make the exchange value of that first BitCoin very high compared to it's initial exchange value.

Over time, weaknesses in the original hash functions may be found and counterfeiting early BitCoin may become practical.  And the reward for doing so seems to me that it would be higher than counterfeiting BitCoin of the future-present!

In the physical world, finding a buried treasure of gold or a sack of US dollars has a lot of protections against counterfeiting.  I don't know how old of a design of US dollars banks would accept, but I guess that as long as you can do a convincing show of where you found it and forgery experts examine it all different ways and it checks out, they you're entitled to trade up.  Gold is pretty easy - can't fool people for too long.

Authenticity of BitCoin is all in the math, so if the technology to forge the math is practical at any point in the assumed infinite future of technological advancements then the forgery would be undetectable.

Due to inflation, an old $20 would get you a lot more than it did today.  But then again, I'm assuming that the old $20 and the new $20 are equivalent, once the old $20's authenticity is established.  And due to deflation, a BitCoin today will get you a lot less than the equivalent BitCoin in the future.

With inflation, the standard denomination of the future might be $100s or $1,000 or $10,000 ...  so a recovered or counterfeit old $20 isn't worth much, and a sack of $10,000 bills from 1960 would be hard to explain!

With deflation, the standard denominations get smaller, so a counterfeit old BitCoin would be easy to explain and forge.

So we could require that people keep their wallets updated.  You mean if I don't keep up with my BitCoin Updates every Tuesday that my bank accounts would be wiped clean?  But that seems unacceptable to me - seems that a powerful group could do a lot of damage to a person or a population by somehow disrupting or disallowing access to their wallets.  I don't know how that would play out, but it seems plausible that a scheme could be devised if money expires like that.
There are a few things one needs to consider:


Bitcoin software is bound to change. It will be adapted to new systems, hardware, and so forth. Expecting a program from now to work 100 years from now is probably not going to happen.
Bitcoin protocol probably will change, but the change will be less drastic. For example, block size might get changed. If a protocol changes, it makes software that uses old protocol not able to properly communicate with the network.
The last part that needs to be addressed, is whether or not the way bitcoins are "stored" will change. At the moment, everything is handled using secp256k1 ECDSA algorithm. In order to spend bitcoins, one needs to sign a transaction with their private key. The exact specific of what such a transaction might look like is likely to change, but the algorithm itself is very unlikely to change unless some serious threat appears for Bitcoin. At the moment, quantum computers are a thing that might or might not brake that algorithm in the future. If that was to happen, the algorithm would be changed.


In order to be able to access one's bitcoins 100 years from now, one would need to get their hands on a piece of software from that time (pretty easy), that works with the protocol at that time (very easy), and the Bitcoin protocol must still accept ECDSA signatures or at least private keys (unknown).

Provided secp256k1 is still secure in the future, your coins will be yours to claim (unless someone adds an unlikely exception of "coins older than X years cannot be spent").