That multisignature/blockchain commitment idea seems really solid, Peter.

Thanks very much indeed everyone, this is all very helpful. Much to research 
and think about.

Interestingly, a thread is presently raging on liberationtech about Tor Browser 
Bundle, and the subject of automatic updates has come up. Gregory Maxwell 
responded thusly (cross-posting for completeness):

> _please_ don't deploy automatic updates in a sensitive environment
> like this without at least quorum signatures (like gitian downloader)
> and timed quarantine with negative signatures (harder to make strong
> absent a jamming proof network).

-wendell | | gpg: 6C0C9411

On Aug 5, 2013, at 7:49 PM, Peter Todd wrote:

> Gregory Maxwell had some good ideas along these lines at the san jose 
> conference. Extending gitian with these kinds of features would be a good 
> approach.
> But I think its worth thinking about attack models. A huge danger with 
> auto-updating is that it is easy to target individuals; if I leave 
> auto-updates on I am essentially trusting the developers capable of signing 
> an update not to specifically try to attack me in the future, a much more 
> risky thing to do than simply  trusting them not to release a malicious 
> release.
> Sure you can try to implement anonymous downloads and similar mechanisms, but 
> they all tend to be fragile with regard to deanonymization attacks.
> A better way is to ensure that the act of making a release available for 
> download must be public, even if you can control what binaries are made 
> available to a particular target. You can do this by putting a commitment in 
> the blockchain itself. Each person on the signing list creates a transaction 
> with a special form from a specific pubkey that commits to the digest of the 
> binaries, and the auto-update code refuses to update unless it sees that 
> special transaction with a sufficient number of confirmations. The developers 
> now can't make a special release for a specific target without letting the 
> world know they did so, even under coercion.
> They developers could of course still make a release with code inside 
> targeting a specific individual, but in theory at least the public can check 
> if their builds are reproducible, and start asking questions why not?

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