Since people need to prove, they are alive, this system will only be possible with a trusted third party to confirm without a doubt, that this DNA belongs to this very person, which always conflicts with point "3) decentralized , without a certifier authority"
There is no way out of this.
The rest is easy to achieve.
Birthday Paradox isn't it ? well at the present moment this <-?> reminds me that loads of 80's snooze alarms clock had 10 minutes default thing ...
hash target net convergence ;-)