Is it true you can't be certain who sent you coins ?

[MrKain]

Is it true that you can't tell for sure which bitcoin address
 sent you coins ?
 
 I asked about this when trying to understand how satoshi dice
 paid you your winnings to the bitcoin address you made your bet
 with.
 
 After some pondering and getting some help from this site, I'd
 like to ask this..
 
 Do sites like satoshi dice determine which address was used to
 send money, by generating a brand new bitcoin address which
 is displayed to the gambler to send coins to ?
 
 I don't think so - because satoshi dice use vanity addresses,
 and I would think it would be too difficult to generate this
 many of them..
 
 So the problem/question still remains - how do sites like satoshi
 dice, know who sent them coins ?
 

[1713630846]

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[1713630846]

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[Stephen Gornick]

So the problem/question still remains - how do sites like satoshi dice, know who sent them coins ?

They don't.  That's why if you send a wager from a hosted (shared) E-Wallet, you lost your bet.  (Or at least, the payout if you did win will go to someone else's wallet).

Since a Bitcoin transaction has INPUTs and OUTPUTs, SatoshiDICE looks at the INPUT (or chooses one of the INPUTs if there are more), and uses that for the payout address.

It works if you have your own wallet (Bitcoin-Qt, Blockchain.info/wallet, Coinbase even) but it doesn't work if you have a hosted (shared) E-Wallet.

Many coins have been lost by those wagering due to this.