user4070: Apologies if this question has been asked before, but when a bitcoin client wishes to send funds to an address, does the bitcoin protocol force the client to verify that the address has a corresponding private key? 
For example, I am given an address and I want to send a btc to this address, before I am allowed to authorize this transaction does the bitcoin protocol force me to verify that the address can decrypt a message encrypted from its public key?

user153: No, there is no enforcement that a private key exists. 
However, due to a Bitcoin address including a checksum, it is very unlikely for the client to create a transaction when for an address with a typo, paste error, or other erroneous data.  There are addresses that will pass the checksum test in which, presumably, no private key exists. 1BitcoinEaterAddressDontSendf59kuE is, in all likelihood, one such address.

4070: <p>Apologies if this question has been asked before, but when a bitcoin client wishes to send funds to an address, does the bitcoin protocol force the client to verify that the address has a corresponding private key? </p>

<p>For example, I am given an address and I want to send a btc to this address, before I am allowed to authorize this transaction does the bitcoin protocol force me to verify that the address can decrypt a message encrypted from its public key?</p>
 153: <p>No, there is no enforcement that a private key exists. </p>

<p>However, due to a Bitcoin address including a checksum, it is very unlikely for the client to create a transaction when for an address with a typo, paste error, or other erroneous data.  There are addresses that will pass the checksum test in which, presumably, no private key exists. <a href="http://blockexplorer.com/address/1BitcoinEaterAddressDontSendf59kuE" rel="nofollow">1BitcoinEaterAddressDontSendf59kuE</a> is, in all likelihood, one such address.</p>
