[Taler] anonymity set thoughts

[Jeff Burdges]

I'd propose this initial approach for dealing with anonymity set
concerns :

Taller wallet should display an icon that's either red, yellow, or
green on both the payment dialog, and the coin issuing screen.  If you
mouse over this icon, it gives you an explanation for the color.

Coin issuing screen:
Red : "You have a Taler payment dialog open in another tab.  We
recommend that you withdraw Taler coins in advance of spending."
Yellow : n/a
Green : "We believe that withdrawing coins at this time should not be
linkable you with your previous purchase activity."

Red is simply controlled by what the user is doing in another tab.

Payment screen:
Red : "You have a Taler withdrawal dialog open in another tab.  We
recommend that you withdraw Taler coins before visiting the site where
you plan to spend them."
Yellow : "You have withdrawn taller coins quite
recently.  You'll be more anonymous if you wait a couple minutes before
visiting any sites where you plan to spend them."
Green : "We believe
that spending at this time should not be linkable you with your
previous withdraws activity."

Again red is controlled solely by what Taler sees you doing in another tab.  
Yellow is activated when you withdraw coins, every minute there after it has a 
50% chance of switching to green, and definitively switches to green after 10 
minutes.  

I've no argument that this average 1.999 minute probabilistic delay really 
helps the user's probability that much, except for the fact that other users 
take out coins according to an exponential distribution.  Two minutes should 
however be long enough that user's eventually notices it and read the text.

Jeff

p.s.  We could optionally replace the word "wait" with funny phrases like "look 
at cute cat pictures for", etc.


p.s.  This might be relevant to our interests : 
https://hacks.mozilla.org/2015/09/subresource-integrity-in-firefox-43/

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