User authentication
- From: raphfrk@xxxxxxxxxxxx
- Date: 25 Sep 2006 04:15:04 -0700
I was wondering if there was an easy way to extend Chaum's digital cash
so that it could be used for "single user" authentication.
Basically, the "bank" would be an agency that certifies that a given
user is a real person and issues only one "coin" to each RL person.
If websites didn't collude, the Chaum system would work. If someone
tries to create 2 accounts, they would be unable as the double spending
protection would allow the site to detect the double account attempt.
Otherwise, there would be no way to link the RL person to the account.
However, if they do collude, creating an account on 2 sites would allow
the encryption to be broken.
My understanding of the double spending protection is that the coin is
really N pairs of encrypted infomation. The user sends all N pairs and
then the merchant picks one of each pair and the user provides the
decryption for those. The blinding cannot be broken unless a merchant
has both parts to one pair. However, if the user tries to spend a
second time, there is a high probability that they will be asked to
decrypt the other half of a pair they gave to the first merchant, thus
allowing the bank to detect the double spend when the 2 merchants cash
in the coin.
Anyway, the desired features would be
- central agency that issues at most one coin to a given RL person
- web-sites can confirm that a given coin has not been used previously
on their site
- blinding is maintained as long as at most 1 account is created per
web-site
- web-sites cannot link 2 accounts created by the same person on 2
different web-sites
I guess each web-site would pick a random number as their ID and the
user's computer would make sure that it doesn't create an account on 2
web-sites which use the same ID. Also, the coin would likely have to
be renewed every year or something.
.
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