Let's say I've written a blog post, and I've dated my hypothetical blog post to August 21, 2008. How can anyone be certain that I actually wrote it at that date and time?
If I store the raw message and the raw date in a plain old text file, no one may know for sure.
If I sign the message and the date with my private key, it's not any more certain, since I could have signed an identical counterfeit message just yesterday.
Now, if we had a block chain, which is essentially a peer to peer synchronized clock, I could prove that I supplied the signature of a given piece of text (signed with my private key) to the network at a given date and time (plus or minus ten minutes). The signature of the text would reside in the chain and the proof of work would ensure it happened at one (or more) points in the chain. The earliest point for a given text would be the date of origin.
Why would such a system be valuable? I think it's obvious, but just to spell it out:
Patents are a burden on the development of software (in my opinion) and patents are usually invalidated by showing prior art. However, prior art may also be useful in enforcing patents if you own both the patent and the prior art. (IANAL)
Another use might be in preventing fraud or enforcing contracts.
Essentially, this would be a distributed notary bearing witness to the date of digital document creation.
One downside of the genesis of such a block chain might be everyone scrambling (or patiently waiting) to submit any pre-existing idea as their own. I've not thought of a way to prevent this attack and it may make such a system infeasible due to false ownership of old documents popping up at any time. However, you may be able to tweak the incentives, similar to what Namecoin has done for early adopters.
Also, such a system may incentivize the physical (or digital) pillaging of private keys. I think this may be unlikely given only the signatures of texts would be stored in the block chain rather than the texts themselves, but you never know.
Also, what would stop people (or bots) from generating random texts and signing them in the chain as a sort of denial of service attack to strain the system?
What do you think?