[freehaven-cvs] three questions that need more attention, possibly c...

[arma@xxxxxxxx]

Update of /home/freehaven/cvsroot/doc/alpha-mixing
In directory moria:/home/arma/work/freehaven/doc/alpha-mixing

Modified Files:
	alpha-mixing.tex 
Log Message:
three questions that need more attention, possibly controversial.


Index: alpha-mixing.tex
===================================================================
RCS file: /home/freehaven/cvsroot/doc/alpha-mixing/alpha-mixing.tex,v
retrieving revision 1.39
retrieving revision 1.40
diff -u -d -r1.39 -r1.40
--- alpha-mixing.tex	8 Jul 2006 19:27:28 -0000	1.39
+++ alpha-mixing.tex	8 Jul 2006 19:39:51 -0000	1.40
@@ -205,6 +205,12 @@
 steady-state (i.e., messages arrive with various alphas at a regular rate, and
 the mix fires at regular intervals). In this case the threshold mix is
 indistinguishable by a local observer from a timed mix.
+%% XXX Actually, we need another assumption if we want steady-state to
+%% still mean that we fire at regular intervals. It seems this assumption
+%% is that the alphas we receive are uniformly distributed? -RD
+
+%% XXX Is it the case that assuming some fixed distribution of incoming
+%% alphas, timed and threshold alpha mixes are still indistinguishable? -RD
 
 We assume the adversary does not know the specific alpha of any
 message entering the mix, e.g., that this is provided to the mix
@@ -244,7 +250,12 @@
 If the adversary does know the strategy (although still not the actual
 $\alpha$) for each incoming message, then the anonymity of $M$ is
 unaffected by the strategy that other messages use for choosing $\alpha$
-in a steady-state network. However, if the strategies are not known,
+in a steady-state network.
+%% XXX I'm not sure I buy this. Compare the situation when other users
+%% use high-variance strategies or low-variance strategies. Doesn't Alice
+%% get different anonymity in these cases, even if the adversary does know
+%% the strategy of alpha distribution for each incoming message? -RD
+However, if the strategies are not known,
 then choosing $\alpha$ from a broader range increases the anonymity
 for other messages in the mix as well, although it is difficult to say
 by how much. If the distribution of strategies across all

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