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comment by wasoxygen
wasoxygen  ·  390 days ago  ·  link  ·    ·  parent  ·  post: Pubski: May 24, 2017

On the way to packet pickup for the Devil Dog Double, I bought some bitcoin at a gas station ATM.

The machine by the door was dollar-based, so I hunted around and found a Satoshi1 machine in the back.

The process was quite painless. Enter a mobile number, receive a five-digit verification code via SMS from Austin number 512-233-6843.

The exchange rate was quoted as $1588 buy $2188 sell for up to $1000, a bid-ask spread of 27%, fairly high for a currency exchange. The spread was 16% ($1765 buy $2110 sell) for larger purchases, up to $10,000. (The price on BitStamp was between 1920 and 2010 that day.)

I fed a 20 in and elected to receive a new paper wallet rather than showing my own QR code. Out came a thermal-printed receipt with my new stash.

I tried a second transaction using a Google Voice number, but it was immediately rejected as a voice-over-IP number.

Smart money says you should not trust a wallet generated in a gas station, so I am trying to transfer the value out before I spill something on the receipt. This has been a learning process. Contray to my earlier dismissal, transaction fees are no longer less than a penny. My client software suggested that I include a fee worth more than a dollar, which struck me as pure frivolity. After insufficient research I offered 0.00025 BTC to the mining gods, still over fifty cents. Now I realize that my offer of 97 satoshis per byte is likely to leave my transaction unconfirmed indefinitely. Apparently the network will forget about my transaction in a few days and I'll be able to try again.

Bitcoin remains a stark example of the Subjective theory of value, that a thing is worth whatever someone is willing to exchange to get it.


At the race, I pushed hard to set a good PR at my first 5-miler, but did not even hit my conservative goal of 40 minutes. Then it was tough to find motivation to run the half marathon, and the lazy pace evident in my pace chart resulted in a finish almost half an hour slower than my best. Probably I should have walked up Hospital Hill.

mk  ·  390 days ago  ·  link  ·  

"Computer, enhance."

wasoxygen  ·  288 days ago  ·  link  ·  

    On Sep 3, 2017, at 15:02, qrguy wrote:

    Is this your posting?


    Your image gave enough away to steal your private key. I did that and took the remaining 0.0002424 BTC out of your account (+ 0.00005 BTC transaction fee). It was mostly just as a personal challenge but I will give it back if that bothers you. Just let me know.

    QR GUY

For the record, I figured US$20 would be a fair reward for anyone enterprising enough to salvage that QR code. I gave it a trial scan to confirm that it wouldn't be easy.

Now I've gone back and forth on whether QR guy is pranking me. First of all my transaction was eventually confirmed and I believe I still control the 0.00859833 BTC. The "remaining" 0.0002924 BTC was, I think, the transaction fee, and should have gone to a miner.

Yet I see a transaction today from that address, lending credibility to QR Guy's story.

Anyone have an insight? QR Guy, are you there? [How] did you manage to recover the private key?

qrguy  ·  285 days ago  ·  link  ·  

Your original transaction sent 0.00859833 BTC to your new address, paid 0.00025 BTC in miner fees, and sent the remaining 0.0002924 BTC in "change" back to the original paper wallet.

Of that remaining 0.0002924 BTC, I sent 0.0002424 BTC to myself, and paid the last 0.00005 in miner fees. The paper wallet now has nothing left. I probably could have used a lower fee, if I had been willing to wait longer. The transaction backlog isn't as bad as when you tried it.

I also stole your 0.0002924 in Bitcoin Cash from the same address.

I recovered the private key by filling in the blanks in your picture. The private key was on your receipt twice -- once as a barcode and once as text. You covered up part of each, but not the same parts -- QR codes actually start laying out the data from the bottom right. So I could reconstruct that corner using the beginning of the text.

This was how far I got before my phone could scan it (with a bit of difficulty):

Even if I hadn't been able to fill that much in, the combination of you showing most of the QR code, plus its built in redundancy, means that it would likely have been feasible to brute force the remaining bits of the key.

wasoxygen  ·  285 days ago  ·  link  ·  

Thanks for the clarification, and nice work!

I see now that the fee is listed separately from the input and outputs which have addresses. I assumed that the fees would be assigned to a bitcoin address, but the documentation is not quite clear, merely saying that "all transaction fees are collected by that user creating the block, who is free to assign those fees to himself."

So the only thing I don't understand is why I didn't transfer the entire amount of the ATM address, less the transaction fee, to my new address, instead leaving some leftover change. Rounding error? Sloppy copy/paste? I remember I wasn't too sure what I was doing and used the app for Android.

WanderingEng  ·  388 days ago  ·  link  ·  

Finally getting back to this. From the total elevation gain, I think Hospital Hill is quite a bit more impressive than anything I'll do this weekend. I'll have to go up Observatory Drive twice, and while no joke, it isn't a gain like that. I suspect I'll have about 650' ascent.

My main goal is always to survive, and clearly you did. Congratulations on running your fastest ever five mile race!

flagamuffin  ·  390 days ago  ·  link  ·  

    quoted as $1588 buy $2188 sell for up to $1000

(yikes? not really sure if it's fair to compare this to anything. but still)

wasoxygen  ·  390 days ago  ·  link  ·  

Maybe a Venezuelan shopping for USD?

When the exchange rate catches up to the money-changer's price in two or three days, it's hard to complain about the spread.