It's one of the key use cases discussed for blockchain technology, yet I haven't found a tutorial or example of this for Ethereum. Granted I'm a newbie, but could anyone explain the big picture of how to achieve this.
In PKC, what I'd do is I'd sign some piece of data which I want to prove as "mine" with my private key, envelope the signed content using e.g. pkcs7, send that along with the original data to the person/authority whom I want to sign it and let them sign the envelope with their private key. Using the mine and the signer's public key I can prove at any time that the original content was signed by me and the signer.
How would I achieve this using Ethereum?