We are all familiar with the standard decentralized ID system, the web of trust, e.g. for PGP keys. However, normal web of trust systems are unable to guarantee uniqueness — there's no practical limit on the number of public keys I can register under aliases that appear to be seperate individuals. These systems are thus unsuited for applications like voting where uniqueness is paramount. My question is: are there any ID systems that are both decentralized, i.e. do not rely on trust in a single individual or group, and at the same time guarantee with high probability that any two given IDs belong to unique individuals?