It's non trivial.

Key distribution is the hard part, because of MITM attack.

Decentralized approach: Web of trust works but is hard to use and
therefore hard to bootstrap. (Why no one uses pgp, and even fewer
people use WOT).

https://keybase.io/ is sort of half decentralized hybrid for pgp key
distribution.

If you're ok with centralized there are many approaches, but then you
have single point of failure.

Other interesting things to google/link:

bitid
http://bitcoinism.blogspot.com/2013/09/building-pgp-web-of-trust-that-people.html

various approaches to token authentication for kyc/aml using crypto
currencies (mastercoin/counterparty discussions)

truthcoin


On Wed, May 28, 2014 at 9:11 AM, Mats-Erik Pistol <meapistol@???> wrote:
> Dear all,
>
> There are many applications that need a reputation system.
> Would it not be handy to have a reputation server, probably connected with a
> public key server?
> Maybe this has been thought of before but I have not really read about it.
>
> --
> Cheers,
> Mats-Erik
>
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