Satoshi Nakamoto - Timestamp Server
http://www.paymentobserver.com/tag/block-chain
A Bitcoin transaction consists of the senders address, the receivers address, and of course the amount of Bitcoins. The sending party signs the transaction with its private key. The transaction is then broadcast to all nodes of the Bitcoin Network. Due to the asymmetric encryption every Bitcoin client can easily verify the transaction but only the user that has access to the private part of the key can create a valid transaction for that Bitcoin address.