You can send a single satoshi* to an address that cannot spend said satoshi with the cryptographic signature of a document as the notation on it. Once the transaction is validated in the blockchain, you can prove mathematically that the document (while keeping secret the contents of the document) was published (created) on a given datetime.
*1 satoshi = 5.8e-6 USD @ current coinbase exchange, Sat Dec 07 2013 02:59:12 GMT-0500
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You can send a single satoshi* to an address that cannot spend said satoshi with the cryptographic signature of a document as the notation on it. Once the transaction is validated in the blockchain, you can prove mathematically that the document (while keeping secret the contents of the document) was published (created) on a given datetime.
*1 satoshi = 5.8e-6 USD @ current coinbase exchange, Sat Dec 07 2013 02:59:12 GMT-0500