When will the public key of an address used in the network?

Question

On block explorer there are some address with public key available, and some without.

(e.g. this one has public key:

http://blockexplorer.com/address/1HBheYzvX7NDtcwVrMS7gxReNRVezYS7w2 ,

and this one doesn't:

http://blockexplorer.com/address/1111111111111111111114oLvT2)

Why is that?

Is it because one has money sent out and one doesn't?

If I understand correctly then the public key is included in the transaction out of an address, is that right?

Answer 1

The 1111111111111111111114oLvT2 hasn't been spent yet whereas 1HBheYzvX7NDtcwVrMS7gxReNRVezYS7w2 has.

To spend, the public key is part of the INPUT's ScriptSig:

• http://en.bitcoin.it/wiki/Transactions#Explanation

So until there is a spend transaction, the public key isn't known to the network, just the Bitcoin address.

Related: Why is it impossible to derive public key from address?

Answer 2

(Those two links are the same...)

In short, there are two common ways to send money:

1. Include the public key. The sender will need to prove that he has the matching private key.
2. Include a hash of the public key. The sender will need to provide the public key matching that hash and also the the proof of owning the private key.

Most people use the second way because the hash of a public key (the address) is shorter.