[messaging] Value of deniability
jacob at appelbaum.net
Wed Dec 10 20:03:09 PST 2014
On 12/11/14, Eleanor Saitta <ella at dymaxion.org> wrote:
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> On 2014.12.10 19.45, Jacob Appelbaum wrote:
>> On 12/10/14, Eleanor Saitta <ella at dymaxion.org> wrote:
>>> On 2014.12.10 17.00, Jacob Appelbaum wrote:
>>>> Why not have both options, legally and cryptographically?
>>> Because if you want to have both options, even if there was
>>> absolutely no cost in terms of protocol design, has a significant
>>> security planning overhead. Every security invariant that you
>>> intend to support must have a specific cost justification in
>>> terms of end-user outcomes. Adding a new one because it has no
>>> protocol cost ignores massive costs elsewhere, in a way that
>>> exactly parallels the complete usability failures of most
>>> encryption protocols. Usability and user requirements analysis
>>> must be part of cryptographic protocol design if there is any
>>> hope it will work.
>> It works in OTR and it works well enough, I think. I don't see any
>> obvious room for improvement. Though I admit, I like the
>> TextSecure design.
> Ending conversations in OTR is specifically a piece of user
> interaction that is only required due to the deniability component,
Not quite. I'd encourage you to look at the code and the specification
to understand the full process for refreshing or ending a
> So it's not true that there's no room for improvement. OTR
> is also, although far better than many alternatives, something I hear
> frequent usability complaints about. This is not what success looks
> like. This is at best what the absence of failure looks like. OTR
> does not in any meaningful way drive deniability as an invariant
> through the design process, nor do implementations clearly explain to
> users what invariants they can or cannot expect the system to maintain.
I never claimed that there wasn't room for improvement?
I like the design of TextSecure (and RedPhone/Signal) and I showed
that there is a legal context for this property, which is what was
requested in the first place. In any case, I don't think an
improvement would be removal of the denability properties from OTR.
All the best,
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