What could cause a paper wallet to become invalid?

[niko]

Just a thought: we don't know how Bitcoin will evolve in terms of block size, mining fees, and off-chain transactions. It seems likely that, if this experiment succeeds even more, most transactions will be performed off-chain, and "banks" and payment processors will use blockchain for occasional reconciliation of accounts. Proposals are already out there. If things unfold that way, blockchain transaction fees may be significant, to the point of rendering smaller savings from today uneconomical to spend.
If, on the other hand, developers manage to address scalability challenges (assuming they are willing to, which may not be the case for those who are also working on off-chain overlays), we might be able to use blockchain just fine.

[canton]

Has anyone tried spraying the paper after printing with acrylic or lacquer to protect it from water?

I got a suggestion in this regard from someone on YouTube. I'm going to order a can of Krylon "Preserve It" to see if that does the trick. That is, if the fumes don't kill me first. (Reviews say it's a good product but that it creates an unholy stink.)

If anyone has experience with specific spray-on waterproofing products I'd be very interested.

[dserrano5]

These bags may be "unprofessional" (?) but I believe that at the end of the day they keep the moisture outside.

[aantonop]

Great suggestion for plastic sleeves.

A bit of googling and I found several collector's sites selling archival sleeves to keep currency:

http://www.jpscorner.com/currency-sleeves.html

I am thinking of including a ring-binder and 3-note plastic holders (Pro Kit), or a pack of single note sleeves (Basic Kit).

I can add them to the basic kit for about USD0.05 (5 cents) each, or $2 for 40. Would you pay $2 to have 40 special sleeves included in a paper wallet kit?

[canton]

Would you pay $2 to have 40 special sleeves included in a paper wallet kit?

Definitely. I'd pay $.25 each in fact. Any wallet worth protecting long-term against moisture is worth protecting for an additional .25 cents.

I'm thinking about sleeves as an add-on to the order form at http://bitcoinpaperwallet.com as well since my initial experiments with waterproof inkjet paper haven't been going so well: The Krylon spray is so stinky that I have to work with it outdoors... and still the smell pollutes my work environment for days at a time. Yesterday I tried using polyester inkjet paper (Graytex brand) and while the front side printed fine, re-loading to print the backside caused a paper jam because the paper gets a little deformed during printing.

Low-tech sleeves seem like a great way to go. Good enough for baseball cards, good enough for me.

[canton]

A bit of googling and I found several collector's sites selling archival sleeves to keep currency

FWIW I think a better pick would be some kind of sealing sleeve. (I think those currency sleeves are open at the ends, so liquid would have an easier time finding its way inside.) Maybe something like this?

http://www.papermart.com/Product%20Pages/Product.aspx?GroupID=15037&SubGroupID=15038

[casascius]

My suggestion for long term secure storage of bitcoins:

Encrypted Paper Wallets

Make Two Copies

Store Them In Two Safety Deposit Boxes (two faraway cities preferably - makes theft by force more difficult)

Leave Passphrase with your attorney or estate planning professional

[SolarSilver]

If anyone has experience with specific spray-on waterproofing products I'd be very interested.

Why make things so complicated? Just use a laserprinter or photocopier and print direct onto plastic

Remember those transparency slides from the '90? Never thought I'd break open the box of blanks I still have here:



You basically print with black onto a transparent piece of plastic and if you store it well (put a white piece of paper on both sides) it lasts forever. It will not survive fire though.

In order to scan it in again to read the QR code, just put a new blank sheet of paper behind it and it looks just like a printed piece of paper (perhaps with some glare if the lighting is off)

The logic would be to print multiple copies of the same sheet, on quality thick white paper (that does not degrade due to acid from pollution), a transparency sheet and another style of your choice. Put a few of your choices through a laminator for the heck of it. Package them well into some presentation pockets with paper padding around them, avoid to write on them with permanent markers. Put them in sealed baggy. Put that into a thick envelope.

Keep fingers crossed...

[canton]

Just use a laserprinter or photocopier and print direct onto plastic

Folks with laserprinters are lucky because then they can print onto any one of the many polyester/tyvek type papers out there. Like this one, which according to the marketing sheet is used by the Navy for printing submarine manuals:

http://www.relyco.com/index.php/products/revlar-waterproof-paper

But what about people with inkjet printers, which are probably much more common?  Everyone knows someone with a laserprinter, but I don't want to recommend that people walk their laptop over to a friend's less secure network (or IT-managed/monitored work environment) to use their laserprinter. I'd love to find a reliable solution for making secure wallets at home with an inkjet printer.

[SolarSilver]

But what about people with inkjet printers, which are probably much more common?  Everyone knows someone with a laserprinter, but I don't want to recommend that people walk their laptop over to a friend's less secure network (or IT-managed/monitored work environment) to use their laserprinter. I'd love to find a reliable solution for making secure wallets at home with an inkjet printer.

You can buy a USB connected laser printer for less than $USD 100. Shop around.

Sure, don't get your hopes up to buy a new toner for that machine for less than $USD 100, but the default toner should last you a couple of hundred pages.

Inktjet prints always degrade. If you have to print with an inktjet, take it to a photo copy shop and make a 'hard' copy with toner of your page (and pray the photocopier does not store copies of your pages on the internal harddisk for later analysis ;-)

[kjj]

You can buy a USB connected laser printer for less than $USD 100. Shop around.

I think mine had a MSRP of like $65 when I got it a few years ago.  Cheap ass Samsung USB job.  Print density wasn't good enough for direct PCB toner transfer*, but it works great as a low volume home office printer.

*  For the iron method, the LaserJet 4+ is still king.  Absolutely no voids inside sold print areas, so you don't get random breaks in thin traces or pinholes in ground planes.

[kjj]

https://www.bitcoinstore.com/dell-b1160-laser-printer-monochrome-600-x-600-dpi-print-plain-paper-print-desktop.html

30 seconds of searching on bitcoinstore.com.  Currently 0.73 BTC.

[gmaxwell]

And if it did, the response would most likely be to add a new signature type, not to invalidate the old ones.

If sufficiently far in the future we were looking at a real break of ecdsa— not just a scary certificational weakness— I would be arguing to make the old transactions unspendable at such a time that any spending were very likely to be a theif rather than their real owner:  Reintroducing lost coins into circulation is a form of inflation, and the prospect of years of happy ecc mining justifies expenditures on cracking hardware— capping the upside should make users making the transition safer.  Regardless, from a personal perspective being unspendable is basically the same as being stolen, so in such an event action will be required no matter what the network does.

But short of such an issue, which I agree is unlikely, the "paper" wallet should still be spendable so long as adequate documentation is provided. I would personally include a copy of the complete source code used to generate the paper wallet.

Because of the (very small not non zero) risk of something like an ecdsa break, I'd discourage someone from putting a wallet where it would be completely inaccessible for decades.

we could see coins that haven't moved in 10 years from apparently inactive addresses being taken as mining fees, for example.

This would be an inflationary policy and it has a snowballs chance in hell. Insufficient granularity can be addressed by simply increasing precision.  Unmoved coins creating concern about the money supply are a different matter, however, but even correcting that seems unlikely (except maybe as a side effect of a crypto break).

[Welsh]

Yeah, seems like the only risks would be is physical damage.

[BitcoinBarrel]

Canines have a tendency to invalidate paper wallets

[DeathAndTaxes]

100% agreed. I think water damage is the biggest threat to a paper wallet. I've been doing some experiments to see what I can do to mitigate how water -- even just minuscule drops of condensation from a cold bottle of beer -- can turn an inkjet-printed wallet into squid-ink soup. Inkjet prints are alarmingly delicate.

If you are super paranoid you may want to look into thermal transfer barcode printers (not to be confused with thermal printers*).  They can use resin cartridges and tear resistant (tyvek) labels.  Once printed a resin wax label is not going to be affected by water, age, sunlight, moisture, and normal heat (excluding a fire).  The higher quality stuff (name brand Zebra ribbons) resists solvents, bleach, cleaner, gasoline, etc.  They routinely are used in warehouses and other dirty, hazardous areas and last ... forever.  Pretty routine for a 10 year old label to still scan with a barcode scanner.  

Thermal transfer printers aren't cheap (usually $300 to $400 or more) but if someone was looking to paper wallet say 1000 BTC I wouldn't use anything less.


*Slighly confusing but thermal printers have no ribbon they use a printhead which produces heat to cause a chemical change in paper.  Everyone has seen the faded receipts from a thermal printer.  The same technology however can be used to apply with high precision a layer of wax or resin onto a paper, or plastic card.  The later are called thermal transfer.  Most thermal transfer printers can do both (direct thermal or thermal transfer).