Subject: Re: [Bitcoin-development] Time

From: Aaron Voisine <[email-masked]>
Date: Fri, 25 Jul 2014 07:45:40 -0700

The problem is if someone moves system time forward between app launches.
The lockout period doesn't have to be all that precise, it just makes you
wait for the next block, then 5, then 25, and so on. Using a well
known time server over https would also be a good option, but the wallet
app already has the chain height anyway.

On Friday, July 25, 2014, Mike Hearn <[email-masked]> wrote:

> Given that the speed at which the block chain advances is kind of
> unpredictable, I'd think it might be better to just record the time to disk
> when a PIN attempt is made and if you observe time going backwards, refuse
> to allow more attempts until it's advanced past the previous attempt.
>
>
> On Fri, Jul 25, 2014 at 7:56 AM, Aaron Voisine <[email-masked]
> <javascript:_e(%7B%7D,'cvml',[email-masked]');>> wrote:
>
>> It's based on the block height, not the block's timestamp. If you have
>> access to the device and the phone itself is not pin locked, then you
>> can jailbreak it and get access to the wallet seed that way. A pin
>> locked device however is reasonably secure as the filesystem is
>> hardware aes encrypted to a combination of pin+uuid. This was just an
>> easy way to prevent multiple pin guesses by changing system time in
>> settings, so that isn't the weakest part of the security model.
>>
>> Aaron Voisine
>> breadwallet.com
>>
>>
>> On Thu, Jul 24, 2014 at 8:21 PM, William Yager <[email-masked]
>> <javascript:_e(%7B%7D,'cvml',[email-masked]');>> wrote:
>> > On Thu, Jul 24, 2014 at 10:39 PM, Gregory Maxwell <[email-masked]
>> <javascript:_e(%7B%7D,'cvml',[email-masked]');>>
>> > wrote:
>> >>
>> >>
>> >> Is breadwallet tamper resistant & zero on tamper hardware? otherwise
>> >> this sounds like security theater.... I attach a debugger to the
>> >> process (or modify the program) and ignore the block sourced time.
>> >>
>> >
>> > It's an iOS application. I would imagine it is substantially more
>> difficult
>> > to attach to a process (which, at the very least, requires root, and
>> perhaps
>> > other things on iOS) than to convince the device to change its system
>> time.
>> >
>> > That said, the security benefits might not be too substantial.
>> >
>> >
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>>
>>
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>
>

-- 

Aaron Voisine
breadwallet.com