Looks easy for you, getting all the blocks now 

Difficulty up to the millions, block 26, average blocktime 555 seconds!

This coin is very similar to Beam. The same technology, often their price should be synchronous. Beam is already on Binance. Not waiting, but preparing.
[/quote]

Which  do you prefer, beam or grin?

More should read your blog Sergio, original thinking deserves a loud voice.  At least post the link next time!  I'll do it for you this time...

https://bitslog.wordpress.com/

A node of mine received these blocks at the following times

2015-05-02 12:29:45 height=354640

2015-05-02 13:06:01 height=354641
2015-05-02 13:09:46 height=354642
2015-05-02 13:12:59 height=354643
2015-05-02 13:17:45 height=354644

meh.

The size of the portion must matter since an even tinier portion could still mine all the free txes at 3x difficulty, but that much less frequently. 

This is a challenge for the distant future, if ever. It seems pretty likely the value of the currency at the next halving will be at least double its value at the last halving (which was only 12 USD), with 3 more doublings already provided for at today's price.

No, they can't.  They can only influence users' expectations of required fees in proportion to their hashrate, which you specified was small.

D&T, I agree with most everything you wrote, many thanks for the interesting research and composition effort.

After an infinite number of steps, an attacker with < 50% is guaranteed to be behind.

Satoshi calculates the probability that attacker ever gets ahead, at any point, since that is long enough to double spend.

You could say a "lucky streak" of some length is required at some point but in fact the success pattern could be arbitrarily complex (with arbitrarily low probability of any particular pattern occurring).

To simulate the process, you could use a recursive function.

Thanks to wumpus and everyone who contributed!

 

That site doesn't help author double-spends, but it will relay them, which OP originally asked for although he really wanted a friendly miner.

The site also has a record of the spends seen earlier (unlike blockchain)

http://respends.thinlink.com/tx/f34a12f0c153055ef8d9ca4c917861de9130651495c21b9eba792050a07bfa71
First seen in a block 12d after earlier tx 3d58d4417ce83003553c23c3c97cd942a6da8506864aa14af8dc963d618c1f9a

http://respends.thinlink.com/tx/604ff6cb6b605420139adfbf91fd31266cdafcb7ccd163cfbdbdf5a4fa7a1881
Seen on network 16h after earlier tx 333f27b77bea035e7e9a7a2551f55e395410945ebdc24d5c145b0cab0009d1cd.  Then confirmed.

The idea that third-party solutions will fix 0-conf... it completely throws the baby out with the bathwater.  Sure, it could work -- Visa works.

But it would no longer be bitcoin.  It would no longer be a global peer-to-peer currency.

There is a third option, aside from third party involvement and shorter block times.  The third option is innovation in the bitcoin consensus system itself.  Economic incentives keep miners following the rules today.  It may be possible to add incentives that lead to 0-conf transactions being very reliable in practice, on a time scale much shorter than 10 minutes.

0-conf respend attempts happen every day.  As was mentioned, the network actually tries to keep as nodes from seeing both.  This site tracks the ones it sees though: http://respends.thinlink.com

Any time you don't have the keys, you are trusting those who do.  I can't believe I have to remind anyone here about that.

Access to depositors' coins give market manipulators LEVERAGE.

It's simple folks. 

If you're concerned about naked short-selling, and short-selling in general causing price declines, do yourself and the rest of the community a favor.

TRANSFER your BTC to a wallet where only YOU have the keys.

Then they can't be lent to anybody.

Your successful double-spend shows up on this site that tracks them:

http://respends.thinlink.com

It's true that double-spending a 0-conf tx is easier than most people think, and it's true that you should be very careful *ever* trusting a payment with no confirmations.

The weird thing is the idea that no effort should be made to improve the situation, or at least let the victims know sooner.  The reason that comes up is "it won't work 100%, so don't even try."

Not a bad idea, but the bitcoin network is working against you.  It silently buries all evidence of double-spend attempts.  Here is data from one node that publishes the re-spend attempts that it sees though.

http://respends.thinlink.com

They pay Gavin.  That's reason enough to exist.

Good questions.  Everyone sees that the decentralized bitcoin system can't have complete, immediate protection from the effects of 0-conf double-spends, but that is totally different from saying that the situation cannot be improved immensely.  Some improvements that can be made are:

1 - Agree that 0-conf double spends should be made more difficult, not easier (there are actually people who disagree).
2 - Per inner quote above, wallets should immediately and loudly notify their users of double-spends.  Amazingly, I am not aware of a single wallet that does this!  Please post if I am missing one or more.  The reason you notify the user is that they may not yet have handed over the merchandise.
3 - Per outer quote above, the network should relay, and not drop, double-spends.  This makes #2 above much more effective.  The actual double-spend transaction is the best alert, because it is signed by the person double-spending.  Anything else would require a trusted 3rd party.
5 - Longer-term, before giving up on the bitcoin protocol, we should ask how to incentivize miners NOT to include second-spends in blocks.  For example, I have never seen a reason why this idea from 2011 could not reduce the unsafe period for 0-conf double spends to only seconds, instead of many minutes https://bitcointalk.org/index.php?topic=3441.msg48484#msg48484

You are endeavoring to reinvent money.  Money is not an enterprise.  There is no general name for what it actually is, but as just one of its many functions, it mediates interactions between ALL enterprises.  Therefore the solution needs to be far beyond enterprise-class, and far beyond sovereign-class.

Your plan is to explicitly co-opt bitcoin via a blockchain fork, using by your own words, rhetorical as they may be, only a large accumulation of (fiat) money as the tool.  You imply that the global cryptocurrency franchise is something that can be bought.  That is an uninspired enterprise-level business plan.  If it actually worked, you'd better watch out for the next guy's fork.  He might have an even bigger pile of fiat.

Have you considered that even fiat money issuers do not go so far as to pay dividends on cash?

As world-class institutions I offer 2 examples. One is the adversarial legal system.  Is presuming people innocent of criminal charges the most cost-effective approach?  Well, no, but only the adversarial system, where the state must confront and defeat every hare-brained defense, repeatedly ad nauseum, has left society feeling the remotest tinge of justice.

The adversarial system is also what works in nature.  In the open ocean, every creature has to ruthlessly protect and defend its genome.  There is almost no trust across genomes.  And yet, a beautiful, balanced ecosystem emerges.

In this context, I think you underestimate the design of the mining function.

Your project will have its chance in the wild, and I will be disappointed in the universe if you succeed.

I don't think you quite appreciate the irony of that statement.