

Primecoin: The Cryptocurrency Whose Mining is Useful - gasull
http://bitcoinmagazine.com/primecoin-the-cryptocurrency-whose-mining-is-actually-useful/

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pongilu
"The underlying mathematics behind why six confirmations is a fairly safe
threshold is independent of block confirmation time, so the Primecoin
transaction at six confirmations is no less secure"

I think this is wrong. 6 conformations in Bitcoin means that 1 hours worth of
work has gone into sealing the transaction into the blockchain. To invalidate
these 6 blocks you would need, for example, twice the compute power of the
honest nodes for 2 hours. With primecoin you would only require this power for
12 minutes, which is 10 times less work.

Lowering the confirmation time only increases the granularity of the
confidence in a certain transaction over time.

~~~
makomk
This is actually a common misconception, and you're wrong. If you read
Satoshi's original paper, the probability of someone with substantially less
than 50% of the total compute power decreases exponentially as the number of
confirmations increases. The reason Bitcoin uses 6 confirmations is because
this was judged to give the best balance between time taken to confirm and
probability of a sub-50% attacker succeeding.

It has nothing to do with stopping attacks by someone with a majority of the
total compute power - realistically, if requring someone to dedicate that
amount of compute power for 12 minutes isn't enough to make an attack
infeasable, making them dedicate it for 2 hours is unlikely to do the job
either.

Edit: Also, requiring only one confirmation - which is what you'd have to do
to make Bitcoin as fast as 6 confirmations in Primecoin - is especially risky
because it allows any attacker capable of generating a block in a reasonable
amount of time to double-spend with very high probability at the cost of one
block's payout.

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Filligree
Well, no, primes aren't very useful, though this might have lead to a bit of
an arms race in probabilistic prime-finding algorithms - which would be good,
I suppose.

I wonder if you could make a proof-of-work algorithm based on, say, protein
folding?

~~~
jlcx
That (or any other useful work beyond just finding primes) would be great, and
it's mentioned in the article (as something that cryptocurrency "newbies"
commonly suggest), but the concern with all of that is efficient verification.

~~~
DennisP
Another issue is that the input to the calculation has to be, at least in
part, the transactions which you're verifying. That's not a problem if you're
just looking for hashes, and I imagine they have a similar process when
looking for primes, though I'm curious about exactly how they do it.

------
VMG
cache:
[http://webcache.googleusercontent.com/search?q=cache:r6c_Ul6...](http://webcache.googleusercontent.com/search?q=cache:r6c_Ul6H8hUJ:bitcoinmagazine.com/primecoin-
the-cryptocurrency-whose-mining-is-actually-useful/+&cd=1&hl=en&ct=clnk)

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javert
Claiming that finding prime numbers is _useful_ seems like a stretch to me.

~~~
reedlaw
Not necessarily. See [http://arstechnica.com/science/2013/02/ask-ars-why-
spend-tim...](http://arstechnica.com/science/2013/02/ask-ars-why-spend-time-
and-money-finding-new-prime-numbers/)

~~~
javert
I'm still not convinced. I did read the whole article, but the subhead sums it
up well:

> That new 17-million digit Mersenne prime number _might_ matter. _Someday._

(Emphasis mine, but that's not much of ringing endorsement of the usefulness
of prime numbers.)

------
VMG
This could become a new Proof-Of-Work function for Bitcoin itself.

Dan Kaminsky assigned 0% probability that the current proof-of-work function
will be used by the end of this year, due to problems with ASICs and the
centralization of hashing power: [http://bitcoinnews.io/dan-kaminsky-predicts-
the-end-of-the-c...](http://bitcoinnews.io/dan-kaminsky-predicts-the-end-of-
the-current-proof-of-work-function/)

~~~
nawitus
Zero probability? So will he pay out all his bitcoins to me if his prediction
fails? That's the meaning of _zero %_.

~~~
VMG
I'm not quite sure myself, it might have been hyperbole. He doesn't seem to
participate in this bet however:
[http://betsofbitco.in/item?id=1432](http://betsofbitco.in/item?id=1432)

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signalnine
This more or less addresses all of the major complaints I have about Bitcoin;
you know, minus the whole insane deflationary spiral which arguably is also
its' main feature.

~~~
icebraining
Pretty sure the "spiral" part is not lauded as a feature. Or accepted as an
inevitable outcome, for that matter.

~~~
Nursie
I'm not sure about the spiral, but the deflation aspect is definitely part of
the plan.

Those most in love with BTC seem basically to just want to sit on something
and get richer, because anything else is the government/other people/moochers
stealing their money through inflation.

------
swixmix
Does Primecoin cryptography depend on the difficulty of finding prime numbers
and then try to find them?

~~~
david4096
PrimeCoin searches for prime chains. For example 6 is at the center of a
bitwin prime chain of length 2.

6 - 1 = 5, prime 6 + 1 = 7, prime 6 * 2 - 1 = 11, prime 6 * 2 + 1 = 13, prime

The design paper is a light and interesting read:

[http://ppcoin.org/static/primecoin-
paper.pdf](http://ppcoin.org/static/primecoin-paper.pdf)

Also:

[http://en.wikipedia.org/wiki/Cunningham_chain](http://en.wikipedia.org/wiki/Cunningham_chain)

