On a flight with no Internet. Sent my friend a few Satoshis worth of ecash and possibly set an altitude record doing so.
From phone to phone. We're both offline.
Try it out on Cashu.me
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Replies (77)
How did you open that website without internet ?
If both of those phones were destroyed then you didn't send the sats.
That's not ideal.
I'd say that's a great feature.
Awesome
PWA?
So where's the money transmitter here? @IRS
Your docs page is missing a nostr npub
Mile high club
Transaction is not settled until the receiver device comes online and contacts the mint. The mint is (illegal) money transmitter.
The mint doesn't transfer anything, it only keeps track of spent tokens.
awesome ⚡
That's 100% transfering in our book. The transaction would be impossible without the mint.
Saw your post the other day and thought 'that looks slick. Wonder what it is or what it does or how it works..?'
Got a page that covers that?
I've got some bitcoin, got cold storage, got a lightening wallet and got alby setup on nostr... but I still can't really tell what cashu is or what it does and why (compared to just a lightening wallet), but everybody seems excited about it so I want to figure it out.
Revolutionary. I wonder when the first one sent from space will be?
🫡🧡
A frying pan transfers heat therefore a mint transfers money
Paid to public key?
I like this :)
It makes the definitions of "mint" and "money transmitter" blurry as fuck!
Correct. Thanks for understanding. Now spread the good word
Hmm. How?
Thanks
Trust-based. You can do that with on-chain transactions, too. These, too are trust based. In both cases, if the sender decides to undo the payment, he can if he manages to get internet first.
super duper
Even with P2PK-locked receiving?
The new "mile high club"
good evening #nostr
On a flight with no Internet. Sent my friend a few Satoshis worth of ecash and possibly set an altitude record doing so.
From phone to phone. We're both offline.
Try it out on Cashu.me
View quoted note →
Just like cash wouldn’t you say
🤣
On a flight with no Internet. Sent my friend a few Satoshis worth of ecash and possibly set an altitude record doing so.
From phone to phone. We're both offline.
Try it out on Cashu.me
View quoted note →
It's basically sending someone the information need to claim funds from the mint. Since both the sender and reciever will have this information, they both can attempt to claim it once Internet is available.
Pretty cool, seems its locked to an address. I studied the base math behind ecash, but haven't read this detail. I wonder how this is achieved.
Just verified myself.
Sender (my laptop) can't clawback the payment because I went out of my way to lock the ecash to the public key of the recipient (my phone).
My phone (offline) has a "later" button when receiving offline.
It shows up in my offline phone's transaction history when press the receive "later" button. But you can see at the time how much the ecash token is worth and the fact that it is locked to your public key (can't be redeemed by anyone else before you can get to WiFi).
Offline instantaneous receiving of sats that are tied to your public key. Amazing.
So ISPs are money transmitters too then since I do online banking through them, and so is google since I use their devices, and so is Firefox, etc.
Cashu vs eNuts. One in the same?
Just accept that we will interpret the Law however we see fit to get what you want. If you don't like it, you can vOtE hArDeR 🤣
Excellent, Thank you.
Why would that be a feature?
who took the picture/ how many phones do you travel with @calle 🤓
I test it too. I works except if you lock the ecash to a key the sending phone needs to be online to bring up the barcode?
Wait, successful send without internet? Via QR/NFC?
Can the sender revoke it before the recipient has a chance to claim? As in, in an offline transaction. This is very interesting
Was just trying to replicate this. Looks like you can create the eCash token while offline and then send the token to the other offline cashu.me instance, but it’s not actually redeemed until the instance goes online. Seems reasonable to me.
It’s a bit like printing the eCash token string (or QR code) onto paper and then handing someone the paper. You “sent” them eCash, but the token hasn’t been redeemed yet.
Is there anything to prevent you from sharing the token multiple times? Then it becomes a race to be the first to redeem it. 🤔
Yeah, I didn't test that yet.
Just testing offline receiving to confirm that the sender couldn't pull back the funds if they got to internet first. (Which they could not. They couldn't claim the token to one of their own accounts since it was locked to the original recipient's public key).
I suppose if you knew that every Saturday you would pay the local rancher 100 sats for whatever, that you could make a stack of ready to go QR codes that ONLY that person could cash in.
You could print out a stack of QR codes that are like cash except locked to the recipient. (Who can melt them down and spend the sats anywhere they wanted) instead of locked to an establishment like a regular gift card.
It does not matter really unless the mint punishes the sender for double-spending afterwards but imagine:
Alice has a million bucks with a mint, represented as Chaumian tokens. She now clones her device and walks into the desert to meet Bob. Bob shares his public key with Alice. Alice signs the million bucks over to Bob's pubkey.
Now if Alice destroys her device and uses her pre-transaction-clone of it, to send the funds to a different receiver before Bob could talk to the mint, what magic other than later punishment for a provable double-spend could there be to prevent this claw-back?
The “rare stats” after the halvening sold for big $. You could be the “mile high sat club.” That was lame, but big thanks for sharing!!!I didn’t know cashu worked offline.
Likely not used in this case, but just fwiw: Briar chat messenger can work over local WiFi or Bluetooth. And so you can use it to chat with folks on airplane without internet...
True but why would it need an internet connection to lock it
you can thank me with sats
Just so we're on the same page: if both parties are offline the ecash can be double-spent.
CashuMe allows the sender to delete the token upon sending so that the receiver can have more confidence that it won't be double-spent while they're offline.
More: 
Gist
Cashu.me 0.1 – Release notes
Cashu.me 0.1 – Release notes. GitHub Gist: instantly share code, notes, and snippets.
Fun-fact in double-spending is, that the receivers don't trust the sender 😑
Yeah, for those cases one person has to be online (using P2PK for example).
I don't think so, it's like a race. So, it requires trust. But the method referred to in other comments seems ideal. That is, enforcing spend to particular address for situations where trust is not available.
Thank you with sats??? Sure thing, but why? For sharing a “Trader University now rebranded as Bitcoin University” video? I watch every video that Matthew Kratter posts on the day they come out.
Or were you trying to paste your lightening address and posted a video link instead?
ECB promises offline payment without a trace for the digital euro. I am curious how they avoid double spending 😁
Black box hw chips. Manufactured at 3nm scale. Nobodys gonna crack that to double spend 100 euros.
👀👀
So merchant and customer, both need ECB hardware? That's a stupid plan.
It's physically impossible to prevent the sender from clawing back the funds if the sender gets internet before the recipient does.
View quoted note →
🔥
Legend
👁️👄👁️
همون فدیمنت خودمونه که در موردش ویدئو دادم :)
Sat down or Sat up
😉 😜
On a flight with no Internet. Sent my friend a few Satoshis worth of ecash and possibly set an altitude record doing so.
From phone to phone. We're both offline.
Try it out on Cashu.me
View quoted note →
Mile high club?
You can triple spend those sats though until one of you goes back online
But profitable? 😂
Does this only work if you have the right sizes of ecash "bills" (😂) locally?
Correct! You could choose to overspend if the amount difference is only small, but essentially that's it.
Could it be possible, to use a mint offline? Like people who has ecash already from a mint could communicate with the mint, but noone would have internet?
If I understand correctly, when you use a mint, you anyway trust in it. If you do an offline transaction, you have to trust your peer too. If we can have offline mint usage, I still only have to trust the mint.
What do I miss?
You trust the mint but you do not need to trust other users. The receiver of a transaction needs to be online in order to refresh the token they received in order to prevent double spending. If there's no Internet, you need to trust the sender (or all previous senders) and the mint.
An app that facilitates offline transactions is a giant red flag. Scam waiting to happen. Leave offline transactions to people who understand the protocol well enough to do it themselves, don't encourage noobs to trust nonsense
This is the canned reply you should give every time anyone asks you anything
Wild
How is it possible to solve “the double spending problem” offline?
Never mind. This was answered here already:
View quoted note →