Subject: Re: [Bitcoin-development] BIP70: why Google Protocol Buffers for encoding?

From: Mike Hearn <[email-masked]>
Date: Wed, 28 Jan 2015 18:14:07 +0100

I think we'll just have to agree to disagree on this one. I've implemented
BIP70 a couple of times now and didn't find it to be difficult. I know you
had odd problems with the C# protobuf implementation you were using but
library bugs can happen for any kind of programming.

I forgot to mention the other reason it's done this way. One of the driving
goals of BIP70 was to support the TREZOR and similar devices. For hardware
wallets, it's critical to keep the amount of code they need to run as small
as possible. Any bugs in the code there can cause security holes and lead
to the device being hacked.

Doing it the way you suggest would mean the secure code would have to
contain complex and bug-prone text parsing logic as well as a full blown
HTTP and SSL stack, that requires not only X.509 handling but also lots of
other stuff on top. It'd increase cost, complexity and decrease security
quite a bit.

Whilst I appreciate if your platform provides a scripting-like API and
nothing low level it might seem easier to use JSON+HTTPS, that isn't the
case for one of the primary design targets.

On Wed, Jan 28, 2015 at 6:04 PM, Nicolas Dorier <[email-masked]>
wrote:

> Mike, I am not denying it is impossible to do all of that.
> Just that it is not a trivial stuff to do to make it works everywhere, and
> I think that it is not a good thing for a client side technology.
> BIP70 has its use, and I understand why there is case where it is good to
> ship the certs in the message and not depends on the transport.
>
> But a standard that just use JSON and HTTPS, even if less flexible that
> BIP70, would make it easier and sufficient for today's use case.
>
> On Wed, Jan 28, 2015 at 5:55 PM, Mike Hearn <[email-masked]> wrote:
>
>> My point is not that there is a limitation in BIP70. My point is that you
>>> put the burden of certificate verification on developer's shoulder when we
>>> can just leverage built in HTTPS support of the platform.
>>>
>>
>> Platforms that support HTTPS but not certificate handling are rare - I
>> know HTML5 is such a platform but such apps are inherently dependent on the
>> server anyway and the server can just do the parsing and validation work
>> itself. If WinRT is such a platform, OK, too bad.
>>
>> The embedding of the certificates is not arbitrary or pointless, by the
>> way. It's there for a very good reason - it makes the signed payment
>> request verifiable by third parties. Effectively you can store the signed
>> message and present it later to someone else, it's undeniable. Combined
>> with the transactions and merkle branches linking them to the block chain,
>> what you have is a form of digital receipt ... a proof of purchase that can
>> be automatically verified as legitimate. This has all kinds of use cases.
>>
>> Because of how HTTPS works, you can't easily prove to a third party that
>> a server gave you a piece of data. Doing so requires staggeringly complex
>> hacks (see tls notary) and when we designed BIP70, those hacks didn't even
>> exist. So we'd lose the benefit of having a digitally signed request.
>>
>> Additionally, doing things this way means BIP70 requests can be signed by
>> things which are not HTTPS servers. For example you can sign with an email
>> address cert, an EV certificate i.e. a company, a certificate issued by
>> some user forum, whatever else we end up wanting. Not every payment
>> recipient can be identified by a domain name + dynamic session.
>>
>>
>>> However, if you want to use your plateform's store, then you are toasted
>>>
>>
>> That's a bit melodramatic. BitcoinJ is able to use the Android, JRE,
>> Windows and Mac certificate stores all using the same code or very minor
>> variants on it (e.g. on Mac you have to specify you want the system store
>> but it's a one-liner).
>>
>> Yes, that's not *every* platform. Some will require custom binding glue
>> and it depends what abstractions and languages you are using.
>>
>>
>>> Have you tried to do that on windows RT and IOS ? I tried, and I quickly
>>> stopped doing that since it is not worth the effort. (Frankly I am not even
>>> sure you can on win rt, since the API is a stripped down version of windows)
>>>
>>
>> There is code to do iOS using the Apple APIs here:
>>
>>
>> https://github.com/voisine/breadwallet/blob/master/BreadWallet/BRPaymentProtocol.m#L391
>>
>>
>>> Why have you not heard about the problem ? (until now, because I have
>>> this problem because I need to have the same codebase on
>>> winrt/win/android/ios/tablets)
>>>
>>
>> WinRT is a minority platform in the extreme, and all the other platforms
>> you mentioned have the necessary APIs. Java abstracts you from them. So I
>> think you are encountering this problem because you desire to target WinRT
>> and other platforms with a single codebase. That's an unusual constraint.
>>
>> AFAIK the only other people who encountered this are BitPay, because they
>> want to do everything in Javascript which doesn't really provide any major
>> APIs.
>>
>>
>>> Also, you bundle mozilla's store in bitcoinj, what happen when the store
>>> change and your customer have not intent to use bitcoinj new version ? by
>>> leveraging the plateform you benefit from automatic updates.
>>>
>>
>> Yes, there are pros and cons to bundling a custom root store.
>>
>>
>>> Also, does java stores deals with certificate revocations ? sure you can
>>> theorically code that too... or just let the plateform deals with it.
>>>
>>
>> It can do OCSP checks, yes, although I believe no wallets currently do
>> so. A better solution would be to implement an OCSP stapling extension to
>> BIP70 though.
>>
>
>