Hi. I'm a newbie when it comes to the Lightning Network. So say I want to buy a cup of coffee with BTC while I am travelling to a different country. But I don't have any LN channels open yet. The coffee store accepts LN payment.

I want to buy a cup of coffee just this one time at this coffee shop because I am travelling. I will never buy coffee at this shop again after I leave the country. How much would the transaction fees cost me? Would I have to open a LN channel for the current transaction cost of $30 to send BTC just to buy a cup coffee? Do I pay another $30 to close the LN channel when I am done buying my cup of coffee?

My reply was to what ranochigo wrote:


I imported my private key to Electrum.  When I spend BTC, any remaining BTC gets sent back to my original address.  In effect, Electrum is reusing my BTC address as its default behavior for an imported private key.  To move my remaining BTC to a new address would require a second transaction, which would incur a transaction fee (about $25 USD to $30 USD based on today's rate?).

Thanks.  Switching to a new address after every transaction is not feasible because of the high transaction fees.  Not to mention the transaction time. 


Thanks.  I don't own thousands of BTC, lol.  At the end of all my transactions (after a few months), I'll probably move my BTC to a new address then.  Hopefully, the transaction costs will be equal or less than what it is now (but who really knows).

Yeah, I admit it's lazy.  I need to tinker with Electrum more.  I imported a private key into Electrum-LTC and spent some LTC.  For whatever reason, by default, after I spent a portion of the LTC, the Electrum-LTC wallet sent the leftover LTC back to the original address.  I'm assuming if Electrum-LTC is a fork of Electrum, they both work similarly for imported private keys.

Having said that though, I have my private key for my BTC address printed out.  I plan to spend some BTC over the next several weeks (or months).  At the very end of my spending, I then plan to move the remaining BTC to a new address so that it cannot be hacked.  But during the next few weeks and months, it's just a hassle to generate a new address each time, and then record the private key for each new address (hardware wallets are all sold out around the area I live).  As for the privacy of the destination address, it's a BTC address for my account on an exchange so I don't care too much about privacy.

That's why I was wondering what is the possibility that somebody can hack my address over the next several months if I reuse it.  If the probability is extremely low, I don't mind the risk I take over the next several months, provided that at the end of my spending at the end of the next few months, that I move my coins to a new address and don't spend from the new address.

In your opinion, do hackers even have the technology or has a weakness in ECDSA been found recently such that reusing the same address over the next few months is susceptible to being hacked?

Ok.  I'm not an expert in this, that's why I'm asking.  I read this reply in another thread (https://bitcointalk.org/index.php?topic=277097.msg2969391#msg2969391):


The author of this quote is implying that the more you reuse your public address, the easier it becomes to generate the private key from the public key.  The author seems to be implying there is a flaw with the RNG (I assume your reply assumes the RNG is not flawed).  Is there a flaw with the author's quote above?

If you have a public address and you reuse this address to send BTC from multiple times, my understanding is that your public address is more susceptible to being hacked (ie. easier for somebody to generate the private key from your public address).  From what I have read, if you send BTC from your public address and you keep any leftover coins in that public address, your public address is only protected by ECDSA.  I have also read that the more you reuse the same address to send BTC, the more your address is susceptible to being hacked.

So let's say I am using a public address.  I send a portion of my BTC from my public address to somebody else but the leftover BTC remains in my public address (doesn't Electrum keep your leftover BTC in the same address by default?).  I use this same public address to send BTC from over the next several weeks.  In total, I have sent from this address 4 or 5 times over several weeks.  Several weeks later, after I am done sending my BTC, I backup my wallet and my private key, uninstall Electrum and decide to let my leftover BTC sit there in my public address.

With today's technology, how long would it take to hack this public address?  Is this something I don't have to worry about for the next 10 years?  The next 5 years?  The next 1 year?