If You’re Transferring Bitcoin, Be Careful With QR Codes

If You’re Transferring Bitcoin, Be Careful With QR Codes
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Here is a story that makes me want to vomit.

I recently experimented with buying Bitcoin, and bought a relatively small amount. Not a huge amount, but enough to be extremely upset if I lost it.

And guess what, I almost did. Because of QR codes.

For a bit of background, here’s how the Bitcoin buying process works. First you buy from an exchange. You’re welcome to hold your Bitcoin on that exchange after you buy, but for security you’ll almost certainly want to send it to a personal wallet for storage.

To do that you have to create a digital wallet with what’s called an ‘address’. You then plug that address into the exchange, send your Bitcoin to that address and voila – a day or so later it should arrive.

The only problem: wallet addresses are long, random and pretty scary to remember if you’re a human being. Also, if you put even one wrong digit in the address box when you send, ALL OF YOUR BITCOIN IS LOST IN THE ETHER.

And there’s no way of getting it back. Ever.

That’s why a lot of wallets come with QR codes that you can easily scan in order to get your address accurately and quickly. And this is where my cautionary tale begins.

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Last night I wanted to move my first Bitcoin purchase to my wallet. I was extremely nervous and worried and afraid I’d screw everything up and lose my money. In short, I was ultra cautious.

So I used the QR code. I took my mobile phone, opened up my wallet, scanned the QR code using my laptop and carefully copy/pasted the address into the ‘send’ box.

I had a look at the address – a jumble of letters and numbers. The first few were right. So far so good.


Since it was my first time and I was being ultra careful, I triple checked every single letter and number of my wallets address. And there it was…

The second last letter, on my QR scanned wallet address, was a ‘B’ instead of a ‘T’.

I was insanely confused. I thought QR codes were infallible. Apparently not. I stared at both addresses for like five minutes. Yep, the QR code had screwed up.

I found another way to copy and paste the address directly from my phone wallet to the exchange – I quadruple checked every single letter and digit and I hit send. Thankfully, this morning, the Bitcoin found its way into my digital wallet.

But yeah – lesson learned. Do not trust QR codes when transferring Bitcoin. And triple check everything.

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  • if you put even one wrong digit in the address box when you send, ALL OF YOUR BITCOIN IS LOST IN THE ETHER.

    This is patently false. Like credit card numbers, Bitcoin addresses include a checksum to ensure they are valid addresses. The chance of a corrupted address having a valid checksum is around 1 in 256^4 (1 in 4294967296). Your wallet software would not have accepted the address if you had hit send. It is however extremely concerning that a correctly implemented QR code reader would return a corrupted scan decode, given that a key property of the Reed–Solomon error correction algorithm is that it should fail closed in the event of severe corruption.

  • if you put even one wrong digit in the address box when you send, ALL OF YOUR BITCOIN IS LOST IN THE ETHER.

    Seriously mate? Is it that hard to do some research before posting public advise?

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