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Date: Mon, 05 Aug 2013 12:47:30 -0400
From: Alan Reiner <etotheipi@gmail.com>
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Subject: Re: [Bitcoin-development] Safe auto-updating
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Indeed.  You can hardcode a "distributor" public key in the software,
and client software will only trust signed data from that key.  Of
course, the private key for that data is not kept on the server
distributing the signed checksums.  Ideally it would be kept offline,
and the couple-times-per-year that you actually execute an upgrade, you
sign the new checksums offline and upload the signed checksum to the
distribution server.  Then even if the server is compromised, the
client-side software will not accept a bogus checksum because it won't
bear the right signature.

If you do this, it would be good to also have some kind of revocation
process that can be used in the event of the offline key being
compromised.  You won't be able to "switch" keys, as that would defeat
the purpose (the attacker who compromises the offline key could just
issue a replacement with his own).  Instead, it would be an irreversible
broadcast that would force clients to start rejecting updates from that
key.  If the key is compromised (and find out), you broadcast the
revocation and the users will stop auto-updating, and be given a warning
that they should manually upgrade the software through trusted
channels.  It's not failproof, but it's a decent way to minimize damage
if you discover compromise early enough.

-Alan


On 08/05/2013 11:54 AM, Daniel F wrote:
> If you want package authentication, you should at least throw in some
> digital signing, not just a checksum. With a compromised host, both the
> checksum and binaries can be changed undetectably, but if there's a
> signature made by a key that is not kept on the host, there's no way to
> fake a valid binary.
>
> There may be other issues people would want to bring up, but surely just
> a checksum is not sufficient.
>
> on 08/05/2013 10:39 AM Wendell said the following:
>> For usability purposes, we at Hive would like to have an
>> auto-updater
> in our wallet app.
>> What is a safe way to do this? I understand that Bitcoin-QT lacks
>> such
> an updater for security reasons... Has been thought out in more detail
> since that decision was made?
>> We have been toying around with the idea of placing one server
>> behind
> a Tor hidden service, whose only function is to output a checksum of the
> update package. The theory is that if it is well-secured, it will at
> least be immune to tampering at the physical hosting level.
>> Any thoughts or advice about any of this?
>> -wendell
>>
>> grabhive.com | twitter.com/grabhive | gpg: 6C0C9411
>>
>>
>>
>> ------------------------------------------------------------------------------
>> Get your SQL database under version control now!
>> Version control is standard for application code, but databases havent 
>> caught up. So what steps can you take to put your SQL databases under 
>> version control? Why should you start doing it? Read more to find out.
>> http://pubads.g.doubleclick.net/gampad/clk?id=49501711&iu=/4140/ostg.clktrk
>>
>>
>>
>> _______________________________________________
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>>
>
> ------------------------------------------------------------------------------
> Get your SQL database under version control now!
> Version control is standard for application code, but databases havent 
> caught up. So what steps can you take to put your SQL databases under 
> version control? Why should you start doing it? Read more to find out.
> http://pubads.g.doubleclick.net/gampad/clk?id=49501711&iu=/4140/ostg.clktrk
> _______________________________________________
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