To request bitcoin from someone else you need to provide them with a "Bitcoin address". They look like this
1AhN6rPdrMuKBGFDKR1k9A8SCLYaNgXhty and you might want think of them as a unique address for a payment.
Anyone that you give this address to will be able to send you bitcoin from that moment on. Remember that they may keep this address for a long time so you should never abandon a wallet by throwing away the wallet words.
It's very unlikely you'll ever have to type a Bitcoin address by hand so don't worry about having to memorise them.
Bitcoin addresses are intended to be used just once since for technical reasons (see later) they become a little less secure after you have spent the bitcoin received by them. For this reason MultiBit always gives you a new address each time you click the "Request" button.
QR codes are a convenient way to transfer information from one machine to another. MultiBit will generate one for you by clicking the QR code icon near the Recipient box. This makes it easy for you to request payment from smartphones with Bitcoin wallets installed.
Once you have requested a payment it appears in the Payments screen with the status 'You requested'. At this point you are waiting to get paid, the general process is as follows:
The other person sends you bitcoin and the status moves to "Unconfirmed" to indicate that the Bitcoin network is processing it. You will also get a green alert bar with a message indicating that bitcoin is incoming.
You will see at the top of MultiBit the message "+ Unconfirmed: mBTC xyz", where "xyz" is the amount of bitcoin they sent you. You cannot spend unconfirmed transactions in MultiBit since they could fail to confirm for many reasons.
When your request has been paid and before it is confirmed the status of the transaction moves to "Receiving". If the other person only sends you part of the bitcoin you requested, the status is "Part paid" until they send you all that you requested.
Bitcoin miners process all the unconfirmed transactions and put them into blocks. Once this happens your transaction is confirmed and you can spend it. This normally takes between 10 minutes and an hour. Once your transaction is confirmed in a block its status changes to "Received".
You can view many details of a particular transaction as follows:
Use the Payments screen. select the payment request and click the Delete button. You can undo this if you select the wrong one.
This requires a technical explanation of how Bitcoin addresses are created. In short, a Bitcoin address is a hash of a hash of an elliptic curve public key (
RIPEMD160(SHA256(pubkey)) and some other integrity checking information. This process makes the address short so it doesn't take up much space in the block chain, and also makes it very hard to work back from the address through two different hashing algorithms to arrive at the original public key.
During the Bitcoin spending process the public key is exposed in the block chain for all to see. This is necessary to allow everyone to verify that the address matches the public key and that the private key was used to sign the transaction, but removes the hash of a hash protection. This weakens the security from that of an address to simply the mathematical relationship between a public and private key within elliptic curve cryptography. While this is immensely strong, it is still weaker than the additional hash of a hash which is why addresses should not be re-used.