[Cryptography] Crptographic ticket tape (fake news)

[John Denker]

On 6/3/19 4:22 AM, Danny Muizebelt wrote:

> In securing original footage from tampering would a ticker tape in the
> background be viable? The tape would be timestamps encrypted with the
> producer's private key.

That's not good enough.
Nothing in that general category will ever be good enough,
because the information required to verify the assertion
is exactly the same as the information required to construct
a forgery.  And the work-factor is nearly the same.

To say the same thing another way:  If today I send you
a signed copy of tomorrow's ticker tape, that is (for the
moment!) evidence that I have a time-travel machine.
HOWEVER the validity of the evidence expires tomorrow!
I can't wait until tomorrow to send the message.

Again: In such schemes, the prover and the verifier do not
enjoy any information-based advantage over the forger.  They
might enjoy some slight work-factor advantage, namely the
work required to construct a good-quality forgery ... but
given the state-of-the-art in image editing software, this
is insignificant.  Maybe 80 years ago a movie of somebody
holding a newspaper might have been nontrivial evidence,
but not anymore.