What happens if PC is turned off when somebody sends you bitcoin?

[TonyT]

What happens if your PC is turned off when somebody sends you bitcoin?  I am using Armory, which resides on my hard drive of my PC.  So if somebody wants to send me bitcoin in the next 48 hours (but I don't know when), I have to keep the PC on for two days?  I think so.

Next question:  suppose the PC is turned off when the bitcoin is sent, then what?  Does it bounce back to the sender?  Probably not.  Does it stay somewhere in the blockchain as 'pending' (I am guessing so), until you turn your PC back on?  If nobody ever claims this bitcoin, say their PC is destroyed and they never rebuild it, does the pending bitcoin become what is termed 'orphaned bitcoin'? (I am not sure but I am guessing so).

[graves]

im sure you still receive the bitcoin.

but the wallet will need to catch up to the network?

[yatsey87]

Lol. Read up some more on btc. Your PC doesn't need to be on. Whenever you next turn it on and your wallet syncs you'll have the btc.

[TonyT]

Lol. Read up some more on btc. Your PC doesn't need to be on. Whenever you next turn it on and your wallet syncs you'll have the btc.

Good, I was right with my speculation.  But what about the other questions:  if the receiver dies and their PC is destroyed, what happens to the bitcoin?  Orphaned?

[MichaelBliss]

Lol. Read up some more on btc. Your PC doesn't need to be on. Whenever you next turn it on and your wallet syncs you'll have the btc.

Good, I was right with my speculation.  But what about the other questions:  if the receiver dies and their PC is destroyed, what happens to the bitcoin?  Orphaned?

Hopefully they have their wallet backed up somewhere or they'll lose their coins if they lose their wallet.   That's if they're running the core client that is.   If it's encrypted, I guess they'd have to write down the password somewhere, or tell someone or else they'll take their bitcoins to the grave.

[cp1]

The bitcoins aren't "sent" in the sense you're thinking.  The "sender" signs a message saying he is transferring the bitcoins from X to Y address.  That message goes in the blockchain that is distributed widely and anyone can view it.  So you never "receive" them.  If you have the private key to address Y then you can sign and broadcast a message saying you transfer those coins to address Z.

[bitsmichel]

You don't have to keep your pc on. I received BTC many times while my PC was off.  

Tech Explanation: What you store in your wallet are private keys to move the money. Money is not actually stored in the wallet. The transaction gets verified on the blockchain. If you lose all your private keys, you cannot move the money anymore and the money is forever stuck in that account. This has happened to a few users in the past.

[TonyT]

The bitcoins aren't "sent" in the sense you're thinking.  The "sender" signs a message saying he is transferring the bitcoins from X to Y address.  That message goes in the blockchain that is distributed widely and anyone can view it.  So you never "receive" them.  If you have the private key to address Y then you can sign and broadcast a message saying you transfer those coins to address Z.

Aha, this is very interesting. So the memory or state of the bitcoin system as a whole, for every transaction, is kept in the blockchain. The blockchain records each and every bitcoin, and who owns it now or can own it in the future (if you send it, you will be saying: 'in the future, this bitcoin belongs to somebody else').  But this raises an interesting question:  what if you make a typo in the "to:" field of the bitcoin address and put in a nonexistent address?  Probably your client will refuse to send it.  But let's say you type a legal bitcoin address, then what?  I bet the bitcoin just sits there until somebody 'claims' this address?  Perhaps even the original sender, if they realize they made a mistake?  Further, can you 'reverse' or cancel a bitcoin transaction *before* it is received by the receiver?   I bet that mechanism does not exist, though it probably should.  

Finally, consider this:  can two people have the same public key?  Yes, see here generally: http://learncryptography.com/bitcoin-addresses/   But can two people deliberately construct the same public / private key combination, in an attempt to fool the bitcoin block chain?  Of course they can.  But what will happen (I think) is that the first public/private key will win, meaning, the block chain will refuse to recognize the second pair.  So this is the thought experiment:  two researchers, A and B, deliberately create the same public/private key.  Then an assistant sends them bitcoin.  The first person, be it A or B, that logs onto the bitcoin peer-to-peer network first will 'win' or receive the bitcoin sent by the assistant.  First come, first served.

[TonyT]

You don't have to keep your pc on. I received BTC many times while my PC was off.  

Tech Explanation: What you store in your wallet are private keys to move the money. Money is not actually stored in the wallet. The transaction gets verified on the blockchain. If you lose all your private keys, you cannot move the money anymore and the money is forever stuck in that account. This has happened to a few users in the past.

Are you a techie?  So the private keys are in a dictionary: dictionary <private key, amount in BTC> ?  I think so, meaning each private key has a look-up table value (amount in BTC) associated with it.  So lose the keys, lose that value of BTC that is forever lost from the total number of bitcoin mined.  See also please my latest question.  Thanks for educating a noob!

[cp1]

Finally, consider this:  can two people have the same public key?  Yes, see here generally: http://learncryptography.com/bitcoin-addresses/   But can two people deliberately construct the same public / private key combination, in an attempt to fool the bitcoin block chain?  Of course they can.  But what will happen (I think) is that the first public/private key will win, meaning, the block chain will refuse to recognize the second pair.  So this is the thought experiment:  two researchers, A and B, deliberately create the same public/private key.  Then an assistant sends them bitcoin.  The first person, be it A or B, that logs onto the bitcoin peer-to-peer network first will 'win' or receive the bitcoin sent by the assistant.  First come, first served.

If two people have the same private key they can both sign a message "sending" it to another address.  You don't "receive" them in the sense you're thinking.  There's no logging in to the network.  Both people would have the ability to spend the bitcoins that were received at the address.  Just as two people can have a joint bank account, both can sign a check transferring funds to another account.

[TonyT]

Finally, consider this:  can two people have the same public key?  Yes, see here generally: http://learncryptography.com/bitcoin-addresses/   But can two people deliberately construct the same public / private key combination, in an attempt to fool the bitcoin block chain?  Of course they can.  But what will happen (I think) is that the first public/private key will win, meaning, the block chain will refuse to recognize the second pair.  So this is the thought experiment:  two researchers, A and B, deliberately create the same public/private key.  Then an assistant sends them bitcoin.  The first person, be it A or B, that logs onto the bitcoin peer-to-peer network first will 'win' or receive the bitcoin sent by the assistant.  First come, first served.

If two people have the same private key they can both sign a message "sending" it to another address.  You don't "receive" them in the sense you're thinking.  There's no logging in to the network.  Both people would have the ability to spend the bitcoins that were received at the address.  Just as two people can have a joint bank account, both can sign a check transferring funds to another account.

yes, I saw this feature of having two people send in Armory.  I also saw--either a proposal or implementation--of M-by-N I think it was called, meaning M people "sign" a bitcoin to be sent and N people can "receive" the bitcoin--does this sound familiar?  Meaning, two people can "sign" and three people can receive in their bitcoin address this jointly signed bitcoin and "spend" it (I guess any of the three can spend the jointly signed bitcoin, first come, first served)?

[TonyT]

Further, can you 'reverse' or cancel a bitcoin transaction *before* it is received by the receiver?   I bet that mechanism does not exist, though it probably should.  

Once the transaction is included in a block, it's basically written in stone.

Bitcoin transactions are, for all practical purposes, irreversible. This is a feature, not a flaw.

https://en.bitcoin.it/wiki/Transaction

Yes, thanks.  So if you send to a bitcoin address that belongs to a dead owner, who lost their keys and their estate does not have them, the money just sits there forever.  I saw a thread to this effect once, and the amount of bitcoin sitting in this dead address was pretty substantial.

[bitsmichel]

You don't have to keep your pc on. I received BTC many times while my PC was off.  

Tech Explanation: What you store in your wallet are private keys to move the money. Money is not actually stored in the wallet. The transaction gets verified on the blockchain. If you lose all your private keys, you cannot move the money anymore and the money is forever stuck in that account. This has happened to a few users in the past.

Are you a techie?  So the private keys are in a dictionary: dictionary <private key, amount in BTC> ?  I think so, meaning each private key has a look-up table value (amount in BTC) associated with it.  So lose the keys, lose that value of BTC that is forever lost from the total number of bitcoin mined.  See also please my latest question.  Thanks for educating a noob!

We are two young americans, my wife and me. 

If a key is lost the coins are stuck forever on the block chain (a database in all clients). All owners have a public and private key. If you are unfamiliar with public key cryptography this can get quite confusing, but it's a two key cryptographic system in which you need the private key to encrypt or sign. The private key gives you the power to authorize or authenticate.

An electronic coin is a chain of digital signatures which is stored inside the blockchain (the database). An illustration of a bitcoin:


If you press "send" a hash of the previous transaction is signed and the public key of the next owner and adding these to the end of the chain. If you are Owner 2, you'll see the transaction can only occur if it is signed with owner 2's private key (your private key).  The public key is commonly known in public key cryptography, but private key not. 

But let's say you type a legal bitcoin address, then what?  I bet the bitcoin just sits there until somebody 'claims' this address?

I do not know if this is possible or not.

Further, can you 'reverse' or cancel a bitcoin transaction *before* it is received by the receiver?

No, you cannot cancel a transaction. The only reason a transaction fails is if the other clients do not accept it.

Finally, consider this:  can two people have the same public key? 

Technically this is possible, but it is similar to the chance of winning one hundred lotteries in a row. 

[mezmerizer9]

What happens if your PC is turned off when somebody sends you bitcoin?  I am using Armory, which resides on my hard drive of my PC.  So if somebody wants to send me bitcoin in the next 48 hours (but I don't know when), I have to keep the PC on for two days?  I think so.

Next question:  suppose the PC is turned off when the bitcoin is sent, then what?  Does it bounce back to the sender?  Probably not.  Does it stay somewhere in the blockchain as 'pending' (I am guessing so), until you turn your PC back on?  If nobody ever claims this bitcoin, say their PC is destroyed and they never rebuild it, does the pending bitcoin become what is termed 'orphaned bitcoin'? (I am not sure but I am guessing so).

Bitocoin transaction doesn't depend on your pc is it on or off, it separated. You only need to keep your pc on for the wallet syncing.

[TonyT]

Next question:  suppose the PC is turned off when the bitcoin is sent, then what?  Does it bounce back to the sender?  Probably not.  Does it stay somewhere in the blockchain as 'pending' (I am guessing so), until you turn your PC back on?  If nobody ever claims this bitcoin, say their PC is destroyed and they never rebuild it, does the pending bitcoin become what is termed 'orphaned bitcoin'? (I am not sure but I am guessing so).

Bitocoin transaction doesn't depend on your pc is it on or off, it separated. You only need to keep your pc on for the wallet syncing.

Thanks, but in a way it does.  If the bitcoin address disappears, because the recipient's digital wallet was destroyed forever, for example, the bitcoin money can never be used again.  But I see your point and it is a good one:  I was confusing wallet syncing with receiving the bitcoin and spending it again.

[cp1]

Thanks, but in a way it does.  If the bitcoin address disappears, because the recipient's digital wallet was destroyed forever, for example, the bitcoin money can never be used again.  But I see your point and it is a good one:  I was confusing wallet syncing with receiving the bitcoin and spending it again.

If the wallet containing the private key is destroyed forever then the coins are unspendable.  But you don't require a computer being on 24/7 or even a computer at all.  You can print out your private key and put it in a safe, and then you just need to hold on to that piece of paper and your bitcoins will be spendable once you enter that key into a computer to sign a message.  Some wallet programs let you write down a string of words that when combined will map to a private key or group of private keys so that you only need to hang on to those words.

[M.Smith]

But let's say you type a legal bitcoin address, then what?  I bet the bitcoin just sits there until somebody 'claims' this address?

The bitcoins are lost forever. Remember the blockchain only records transactions. It does not know whether the address has a known private key or not or whether the intended recipient has the private key. It is only when you try to spend the bitcoins that you have to prove knowledge of the private key by signing over ownership to another address.

An example of bitcoins in limbo:

https://blockchain.info/address/1BitcoinEaterAddressDontSendf59kuE

Perhaps even the original sender, if they realize they made a mistake?  Further, can you 'reverse' or cancel a bitcoin transaction *before* it is received by the receiver?   I bet that mechanism does not exist, though it probably should.

Transactions can't be reversed although you can try to double spend them before they've confirmed. It's easy to try to double spend but much harder to succeed. To succeed you need a larger number of miners to agree to include your double spent transaction over the original one.

Finally, consider this:  can two people have the same public key?  Yes, see here generally: http://learncryptography.com/bitcoin-addresses/   But can two people deliberately construct the same public / private key combination, in an attempt to fool the bitcoin block chain?  Of course they can.  But what will happen (I think) is that the first public/private key will win, meaning, the block chain will refuse to recognize the second pair.  So this is the thought experiment:  two researchers, A and B, deliberately create the same public/private key.  Then an assistant sends them bitcoin.  The first person, be it A or B, that logs onto the bitcoin peer-to-peer network first will 'win' or receive the bitcoin sent by the assistant.  First come, first served.

An address is a hash of the public key. The hash is a 160bit number. Public keys are 256 bit numbers. So you have many public keys that will hash to the same address. Finding such hash collisions is impossible because the address space is so large.

If two people have the same private/public key pair then they both own the bitcoins until one of them spends the bitcoins. He may spend them by buying something with them or sending them to an address that only he controls. Either way it is only when you spend your bitcoins that your claims of ownership are tested.

[Simon8x]

Aha, this is very interesting. So the memory or state of the bitcoin system as a whole, for every transaction, is kept in the blockchain. The blockchain records each and every bitcoin, and who owns it now or can own it in the future (if you send it, you will be saying: 'in the future, this bitcoin belongs to somebody else').  But this raises an interesting question:  what if you make a typo in the "to:" field of the bitcoin address and put in a nonexistent address?  Probably your client will refuse to send it.  But let's say you type a legal bitcoin address, then what?  I bet the bitcoin just sits there until somebody 'claims' this address?  Perhaps even the original sender, if they realize they made a mistake?  Further, can you 'reverse' or cancel a bitcoin transaction *before* it is received by the receiver?   I bet that mechanism does not exist, though it probably should.

There is a checksum feature in bitcoin address, so typing a letter wrong would make the address invalid and your wallet will tell you it is wrong.
Also, you should copy and paste an address rather than typing the address yourself.

But if you copy and paste the wrong but valid address, there are 2 possible results:
1. The address is controlled by someone else. Say, you check my bitcointalk profile and somehow copy my address accidentally. Then you could contact me, and I may send you back your bitcoin or I may buy myself a meal with your bitcoin.
2. The address is controlled by no one. Say, you check the list of valid bitcoin addresses in alphabetical order and copy 1111111111111111111114oLvT2 accidentally. Then your bitcoin will stay there forever.

[mullerdan]

Its like a mail, you don't need to turn on your pc to receive your bitcoin.