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I used to make my own custom circuit boards. The process is simple:

 - You get a blank copper board from an electronic supply house(or ebay).
 - Then you print out a negative of your circuit design on a transparency.
 - You apply UV sensitive acid resistant ink to the whole board
 - You put the transparency over the board and bake it with bright UV light
 - Wherever the light goes through the transparency the ink will stay on, you wash the rest off with water
 - Then you expose the board to acid and everywhere you don't have acid resist ink dissolves away
 - You then wash off the acid and ink and have your design in copper

I just realized you could put a negative of your QR code and key strings on the board instead of a circuit and you would get a very resilient wallet.

Just an idea, have not actually tried it.

That's a cool idea.

Any pointers on where to get the ink and acid?

Both easily available at any electronics supplier. Even Radio Shack.
Also you can do this with laser printer output and ironing it onto the copper. It's not as crisp and clear but should work for QR codes as long as not too small.

I also think you can do the same with thin gauge steel. I remember reading a web article showing how to use the same idea that way.

Your local CNC sheet metal shop can also cut a design into steel real quick for a fee.

You can order 10 5cm x 5cm high quality PCBs from China on the web for $10 but they would have photo resist on them (the blue/green/red coating).

Here is a site that goes through the process: http://www.riccibitti.com/pcb/pcb.htm (http://www.riccibitti.com/pcb/pcb.htm)

You can get all the supplies off of ebay or radio shack/the source or any decent electronics store.

CR-80 size(credit card size) would be nice

I would never trust copper to keep etched pattern safe from corrosion. Just think green patina on the roofs and statues.

Copper lasts longer than:

• Paper (used in "paper wallets")
• Hard drives (used in "digital wallets")
• (arguably) Humans (used in "brain wallets")

That's all neat and scientific, but here is a typical state of copper coins (a copper-based alloy, that  is):
http://www.tc.umn.edu/~brams006/images/pennies/copper_pile.jpg
Many of them look shitty.

Again, there's no way I'll trust copper to keep etched pattern safe. Stainless steel, aluminum, gold of course.

PCBs get a nice brown layer on them if they aren't coated with a shellac. So that's a good idea. Dropping one into an acrylic resin block would be cool and even better.

But even so they last a long long time. And you're not likely to keep your PCB QR code out in the weather. More likely in a dry safety deposit box.

Yeah, it's not expected to last forever. But it'll outlast you inside a sealed box by a longshot.

The thing about those roofs and statues is that when they are new they pour horse piss all over them to create that nice green patina. This patina actually protects the copper underneath. Notice that those building roofs are often over 100 years old yet have no fallen apart? If they did not put ammonia(horse piss) all over them then they would have gone an ugly penny brown. You will also notice that 200 year old pennies are still intact and readable despite changing color. This is because unlike iron when copper reacts the new substance does not fall off but rather insulates what is under it.

I have printed circuit boards from the 50s that are just fine. As long as you do not leave it out in the rain it should be fine. Even if it does patina it will still retain its shape.

Generally you give it a layer of protective coating when you are done.

Really, I have never seen a printed circuit board that has had its traces decay away and I have handled a lot of vintage electronics.

The same technique could be used with other metals, you might need a different acid though.

Aluminum also reacts with the air and despite common belief otherwise stainless steel does too. Ever seen a stainless steel mixing bowl left out in the rain?

As for gold, I think I would prefer that too. However the only acid solution I know of that will dissolve gold is aqua regia which is a mixture of hydrochloric and nitric acid. I am not sure of the standard acid resist ink will resist this. Also, you will have to find a way to get your dissolved gold out of your acid when you are done. Platinum would be good too.

For very acid resistant metals like gold and platinum perhaps a selective electroplating method would produce a better image.

Check this site out

http://www.my-medical-id.com/product/Premium%20Medical%20ID%20Wallet%20Card (http://www.my-medical-id.com/product/Premium%20Medical%20ID%20Wallet%20Card)

Good deal I think!

Pretty nice. But I wouldn't want to send the private key info to them in plain text. It's 99.9% likely they have no idea what it is but maybe some day they will and have records.

You could send a long passphrase that seeds the actual key. That seems less likely to be figured out. In fact you could ask them to sell you one that was made with an error for someone else (cheap! because throwaway). Then use that data to seed a key. Not very personalized though.

I could see using one of those army "dog tags". Isn't there places that make those as well?

edit:
http://www.ebay.com/itm/2-Military-Dog-Tags-Custom-Embossed-Stainless-GI-Identification-w-Silencers-/320792157109?pt=LH_DefaultDomain_0&hash=item4ab0b3dbb5

Crikey! That guy's sold over 2800 tags on that listing!

I usually AES encrypt my private keys using a passphrase. Much better than a brain wallet in my opinion.

A brain wallet is never going to represent more than a tiny fraction of the available key space. If you want a key you can feel safe with for 20 years then you need a proper cryptographic random number based key and you need the "air gap" where the data never touched any hard drive or network adapter.

I create mine from an Ubuntu live CD on an old laptop that I have removed the wifi card and hard drive. I modified the live CD to have vanitygen and my printer drivers and a qrendcode and script that can create a wallet and print it.

The whole thing loads from the CD and is only stored in RAM.

I can be confident my code will not be guessed nor will it be discovered by some hacker. The problem is that paper does not last well, that is where the etched into metal came into my mind.

A brain wallet can in theory represent as much of the key space as a computer can deterministically compute, which is far larger than anything needed.

As long as you can find someone who will use mixed case... or possible find a vanity address generator that can enforce all caps?

No, a brain wallet can only represent as much keyspace as a human can come up with. While hashing will produce an evenly distributed random looking key it was chosen from a subset of keys that humans work with.

I think you will find that people have trouble remembering passwords that come anywhere close to the full keyspace available to private keys.

I got an M-disk drive from Amazon using spendbitcoins.com.This is supposed to use a high power laser to etch the data into special rock-like DVDs .It should last a long time. The DVDs are readable by any conventional drive.

http://www.amazon.com/LG-Electronics-WH12LS39K-Internal-Rewriter/dp/B00632U162/ref=pd_bxgy_e_text_b

Lasers are awesome!

I just came across brainwallet.org (http://brainwallet.org).
It has a convert tool that can output a key in RFC1751 format.
This is all upper case like this,

5JbrP892xZEXW9ZAyxaspYYW1qUYk4epi1E5qrVuyo18LET7Zgv equals
Unfortunately it's 112 chars and according to the dog tag offer they can do 5x15 = 75 char only.
So two tags would be needed, as offered for $4.99. Which isn't a bad idea anyway. Keep them in two places and bring them together when needed.

Or use hex - but upper case, only 64 chars =>

I would want to make it myself, you never know if they keep a copy of your work order somewhere.

You could just get an alphabet metal punch set and put the key in manually.

I just ordered one of these
http://www.my-medical-id.com/product/Premium%20Medical%20ID%20Wallet%20Card (http://www.my-medical-id.com/product/Premium%20Medical%20ID%20Wallet%20Card)

I order the Orange one. Will see what happens.

Card Color -:   Orange
1st Line:   Bitcoin Address
2nd Line:   1xxCGi9xxQ4xxSn5N
3rd Line:   FbxxQkSaxxDwFxxuM
4th Line:   ----- BEGIN AES ENCRYPTED BLOCK -----
5th Line:   U2FsdxxkX1/mDxxXLwA0xxk6WlZ/SNxxgF4xx3XB
6th Line:   6svfIvlxxaBNy2EJrtWxxVTNmxxNYd/xx+O8z82f
7th Line:   Xg79xxfdF/7xx/0xx9o/1jRUyCw=
8th Line:   ----- END AES ENCRYPTED BLOCK -----

i actually have the equipment to do this on hand. i personally prefer using brass to copper - but really i could use any electrically conductive metal. i use galvanic etching (salt water and electricity instead of acid) and then after removing the ink resist a blast of black spary paint really makes the design pop. a simple spray of clear varnish is excellent protection.

if there's enough interest i'd be more then happy to offer a service. i feel stupid for not thinking of this before, actually. :D

here's an example of the etching: this is about the size of half a sheet of regular (8.5x11 or A4) paper. all the "blemishes" you see are there for intentional artistic effect.
http://img.photobucket.com/albums/v21/Arklan/projects/smaugetch.jpg

I would be happy to help you design something. PM me if interested.

The image of all the "copper" coins looking "shitty" earlier is a joke. Firstly, those are not copper coins, they are Zinc coins with trace elements of copper. Also these are coins in circulation not a private wallet. Lastly, you allude to using Gold which is a softer metal typically made stronger by ADDING COPPER to it:


http://en.wikipedia.org/wiki/Gold

Bullshit. Pre-1983 pennies are 95% copper alloy. Post-1983 are copper-plated zinc coins. Plated with pure copper.
Other posts in this thread have actually convinced me that corrosion might not be a problem, but the post above only convinced me that Dunning-Kruger effect is endemic in this forum.

Hey Hal, good to see you are still around swinging for the fences with bitcoin :) ... thanks for the tip on the M-disk tech. also.

Store it in a vacuum chamber.