-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 11/12/14 14:31, A. Johnson wrote:
Can you be more explicit with regard to privacy guarantees of the obfuscation schema that is currently implemented: 1) binning, 2) add Laplace noise, 3) no second binning.
I’ll discuss this in terms of attacks on the stats of the number of HS descriptors.
Binning: Suppose an adversary knows that the number of HS descriptors stays constant over a week. He knows when all descriptors are being published except for one. By binning he won’t know when that one is published unless the number of other descriptors exactly fills a bin.
Laplace noise: To provide cover in the case that all other descriptors exactly fill a bin, we add some noise so that sometimes an adjacent bin is reported instead, or (less likely) a bin two distant, etc. Then the adversary can’t immediately know whether an unknown descriptor is indeed published in any given period. However, he can eventually figure this out by making enough observations and looking at the resulting empirical distribution. But it’s better than not protecting it at all.
Sounds good. George, maybe these explanations should go into the proposal, too.
If you think 3) should be changed, can you explain why that leads to better privacy guarantees?
I don’t think that 3 should be changed, but if you removed it, it wouldn't affect the privacy argument.
I can see how the Laplace distribution doesn't add much noise to the second case. And your suggestion is to change the second delta_f to 8?
Yes.
Great. Changed the second delta_f to 8 in the code, and I think George will change it in the proposal. Thanks! All the best, Karsten -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: GPGTools - http://gpgtools.org iQEcBAEBAgAGBQJUia4mAAoJEJd5OEYhk8hImnYIAJD/TLsTRhL5UGYEMBoOnq+X gcOzVhrEg+fTHm1a6YSHPn0iPZvTDmg3w97XXl/IZg5L4Y84AAcHeuT6EXkmATT5 V52w5A1fdzOQ4Ef3f6wL0ZNPPG3qsFdv+nNRiiOuI1ASb0+5ML7hdU033up8l1zB 7CocU5rgACy2a6DMHPn4wPmXjlCPYcQ3ZUr/1xts63vxfQFes/D2ynUVEk6I/IUO YVz62WBg857RXWn8eIsdCF6TkRAJetyiIijPe5+Gs8r7XT+btINg7mS9SDynBWOB ee34vz/VqeczrAZZwq+yNTjENbsJCtyM5U8zHAiYarGnACmAYy50nnofhPjQ1/I= =3F1E -----END PGP SIGNATURE-----