
Tarsnap now accepts Bitcoin - cperciva
http://www.daemonology.net/blog/2014-03-27-tarsnap-bitcoin.html
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minimax
_I tell them I want to get paid X dollars in bitcoins, and they tell me how
many bitcoins I should ask for and what address they should be sent to. Stripe
then gives me the dollars I asked for (minus a small processing fee, of
course)._

How much is the fee? Is it a fixed amount or proportional to the transaction
value? How does Stripe set the dollar denominated bitcoin price? One easy way
to make a bitcoin payment look cheap is to offer a low fee but offer a
slightly inflated exchange rate and take a profit out of the difference
between the rate used for payment and the rate you can get in the market
(exchanges or dealers). It's hard to compare the economic value of dollar
denominated bitcoin payments (relative to credit cards) without knowing these
details.

~~~
pc
We actually haven't figured out how the pricing will work yet. (We want to
make sure we have the product right first.)

~~~
waffle_ss
Will you be easing up on the "prohibited businesses"[0] restrictions for these
Bitcoin transfers, since you aren't beholden to the credit card networks for
these transactions? I've got a business that falls under category #2 that I'd
like to use Stripe for but can't.

[0]:
[https://stripe.com/prohibited_businesses](https://stripe.com/prohibited_businesses)

~~~
driverdan
Why bother with Stripe if you just want to accept BTC? Use BitPay, Coinbase,
or someone else.

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fpgaminer
@cperciva, slightly off-topic: I had a curious question this past week about
one aspect of the scrypt algorithm. If I recall correctly, it sandwiches the
memory hard function between PBKDF2, and uses Salsa20 as the mixing function
internally. In the spirit of reducing code, I'm wondering if it makes sense to
replace Salsa20 with HMAC, SHA256, or just SHA256's mixing function? It would
reduce the number of crypto primitives in the implementation. Not that it
really matters much, but just curious (and partially curious if Salsa20 had
specific properties that are useful in scrypt's design). Sorry if this is a
dumb question; I was going to read back through your scrypt paper, but have
been busy all week.

~~~
cperciva
Salsa20 could be replaced by almost anything -- the requirements for the
mixing function are very very weak (basically just that there's no short-cut
to iterating). But Salsa20 has an advantage in throughput, which matters for
maximizing the amount of memory you can use in a given amount of time.

Asymptotically speaking the best function there is the one which maximizes
[B/s software output]^2 / [B/s hardware output].

~~~
gburt
Can you elaborate a little on how you got to that maximization? I am not sure
I understand why you're squaring the software level.

~~~
cperciva
ASIC cost ~ memory * time = (time_software * bandwidth_software) *
(time_software * (bandwidth_software/bandwidth_hardware)) = (time_software)^2
* (bandwidth_software)^2 / bandwidth_hardware.

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gregimba
Stripe seems to be the default payment processor for tech startups. Especially
now they are going to support Bitcoin.

~~~
cperciva
Absolutely. Stripe understands how to build clean and easily usable APIs.

~~~
aroch
After setting up Paypal and Google Wallet payment forms and being left wanting
to shoot myself, Stripe was a fantastic breath of fresh air.

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Scaevolus
It's strange that Stripe doesn't support paymentiframe.com's feature
directly-- I'm sure many have similar concerns about embedding arbitrary JS
into their domain.

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mitchellh
Hopefully it is a temporary thing but the iframe is not loading for me in any
browser. "Server refused the connection"

~~~
cperciva
Accidentally ran paymentiframe.com out of swap space. Should be back now.

~~~
cperciva
And now I'm moving it to a heftier EC2 instance type.

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stuhood
Because it got slammed? Unlikely, but would be a nice surprise!

~~~
cperciva
Yes, because it got slammed. It doesn't take very much to slam a t1.micro when
you're forking a CGI script on every page load...

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datr
Is Tarsnap going to drop prices in response to the AWS S3 drop?

~~~
cperciva
I've been busy with bitcoin for the past few days -- I need to crunch some
numbers on my AWS bills to see how much money this saves me; it's not as
obvious as it sounds once GET/PUT costs and EC2 costs (which are mostly
reserved instances, thus not affected by this price cut) are factored in.

But my first guess is that a price cut is very likely to be coming. ;-)

~~~
icelancer
Please don't. Just pocket the margin. The prices should have gone up, anyway.

~~~
wheels
This is something that's repeated here, but I have a feeling mostly by folks
that are backing up small amounts of mostly static data.

Even after de-duplication and compression, my company stores about 400 GB of
data with Tarsnap. Tarsnap is a double digit percentage of our monthly
infrastructure costs.

I think, perhaps, it's rather that the value that a business backing up a 30
MB database every day gets isn't radically different from the value that we
get backing up several orders of magnitude more than that.

The question really is if straight utility pricing makes sense. I could
imagine that a floor on the pricing, or a non-linear curve would probably do
better than simply keeping the same model and raising the prices. There's also
a question of distribution of total revenue -- if the revenue for the small
accounts was increased by 10x, would it balance out a 50% loss of large
accounts?

~~~
runeks
> The question really is if straight utility pricing makes sense. I could
> imagine that a floor on the pricing, or a non-linear curve would probably do
> better than simply keeping the same model and raising the prices.

The question is if the costs of running tarsnap correlate exactly with the
amount of data that is stored, or if the number of users also have to be
factored into the equation, ie. if each additional user has an added cost. I
would say that in a business like this, with a low barrier to entry, the price
should reflect the costs as close as possible. So if there's a constant setup
cost for each user, the price shouldn't be $ _X_ /GB, but $ _X_ /GB + $Y.

Ideally, Tarsnap should make the same amount of money from a single user
storing 100 TB and 100×10^12 users store a single byte. If this is not the
case, the pricing structure is suboptimal.

~~~
computer
Suboptimal in what way? I doubt that would be optimal for profit.

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mhartl
This is great news. One quick suggestion: I recommend dropping the material on
Bitcoin's unsuitability as a store of value or unit of account, or at least
softening the language to sound less certain. It's possible that these views,
which are shared by most mainstream economists, will prove to be true, but
Bitcoin's design is a _test_ of the contrary position. It seems reasonable to
concede that there's some uncertainty in the matter.

~~~
gburt
For what it's worth, my opinion on that is the exact opposite. Colin's blog
post was enlightening and clearly just his own opinion.

~~~
cperciva
Thanks! I do my best to put the "news" at the top of posts and the "rambling
thoughts" later in case people aren't interested in my opinions.

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akama
I wonder how Stripe is going to handle the tax implications of Bitcoins. It
may not have an impact because they shouldn't be holding them, but it could be
complicated.

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prirun
The IRS just ruled that Bitcoins are property, not currency, and are subject
to capital gains taxes when they are spent. IOW, you have to keep track of
your basis every time you buy and spend Bitcoins, just like stock.

[http://www.bloomberg.com/news/2014-03-25/bitcoin-is-
property...](http://www.bloomberg.com/news/2014-03-25/bitcoin-is-property-not-
currency-in-tax-system-irs-says.html)

~~~
cperciva
Fortunately, I'm neither buying nor selling Bitcoins, so this doesn't apply to
me.

