I made a short video explaining what nothing at stake means with proof of stake cryptocurrencies as well as what can be done about it and how much it effects the currency as a whole.

https://www.youtube.com/watch?v=pzIl3vmEytY

In this video I discuss what is generally called a short range nothing at stake double spend attempt. Nothing at stake could mean a few other potential issues, but this is the most interesting to study and the one that is potentially feasible in most Proof of stake systems.

thank you to kushti and the consensus research team (http://consensusresearch.org/) for their work on this subject.

I've been in the cryptocurrency space as a developer for a little over a year and a half now, and I have realized that there are so many cool ideas that have yet to come to the surface with this technology.

Personally I use Nxt as a platform because it has so many features that make it incredibly interesting to develop on. I decided that the best way to get some new ideas off of the ground was to have a hackathon centered around the API of Nxt, and with some help I have been able to do this.

Some information - http://jnxt.org/nxthacks

Date: 11:59PM (GMT+0) July 31st to 11:59PM (GMT-0) August 2nd (48 hours)

Prizes:
1st Place - 40'000 NXT (~$500)
2nd Place - 20'000 NXT (~$250)
3rd Place - 10'000 NXT (~$125)
The winners will be decided through a vote of all competitors and contributors to the hackathon.

Rules:
- Must be completed in the allotted 48 hours
- Must utilize one or more featurs of the Nxt API (http://jnxt.org:7876/test)
- Only solo entries are considered for prizes, teams can compete, but don't qualify for prizes.

You can use any programming language you would like, though js, node.js, python, or php are most common.

More information:
The sign up and information page http://jnxt.org/nxthacks

Introduction video at https://www.youtube.com/watch?v=BrL3WcReJyo
The Nxtforum thread https://nxtforum.org/general-discussion/testing-the-waters-an-nxt-hackathon/

And for the most up to date information and the chat that we will use for the competition is the #nxthacks channel on supernet slack (http://slackinvite.supernet.org to gain entry)
There will be many people, including myself, to answer any questions and help with problems during the hackathon.


* an in advance answer to the 'nxt is a scam' people:

No matter what you believe nxt to be, a scam, or a useless alt coin, it does have a very large API with many cool features that can be used to build cool little applications. I believe it is worth a try for a developer no matter what your skill level or language is.

If you don't want to go through the trouble of installing the Nxt client or figuring out which lite wallet is best for the new Nxt 1.5.10 release, then try out the features online with this demo.

http://jnxt.org:6876 (top level page at http://nxt.org/demo/)

Just click the start demo button and you will arrive at an account funded with 200'000 Nxt.
This new version has the ability to create and vote in blockchain based polls, as well as make transactions that are only accepted into the chain when certain conditions are met (phased transactions).
If the account you arrive at is empty, just refresh the page and try again, you will enter a new account.

Sample screenshot:


Have fun

The Jay Framework is a revolutionized way of dealing with web wallets.
Instead of giving all of your information to a web wallet service, you hold all of your password data locally.

Jay uses interfacing between your small html local client that holds all your private keys encrypted on your computer, and 3rd party wallets hosted online that don't have to worry about security.

http://jnxt.org/jay

Introductory video:
https://www.youtube.com/watch?v=UKKkLBsJBK8


Thus far version 1 has been released with jay.js and documentation(http://jnxt.org/docs)
as well as the Jay Client with most Nxt transaction types implemented

Next version should include encrypted messaging as well as the rest of the MS transaction types (crowdfunding/currencies)

I will try to keep this thread up to date if anyone wants to follow progress here, but main talk happens on SuperNET slack channel #jay and nxtforum (http://nxtforum.org/jay-framework)

Lets say there is a currency with 100 units.
I define the consensus group as anyone currently holding a positive number of units. (PoS)
because there is a block chain type ledger, I know the public keys of all of the accounts with positive balance.
lets say that for each block the code:
1. generates a list of all nonzero account balances and public keys
2. Takes that list and makes a sha256 has of each public key along with the hash of the previous block.
3. Takes the first 8 bytes of this sha256 to make a big number for each account.
4. Divides the number by the current balance in the account.
5. Now it makes a list of the accounts in order by the number generated earlier, smaller numbers first
6. We want a block every two minutes, and we will allow for thirty second of clock varience. (fifteen on each side)
7. Starting 1 minute 45 seconds to 2 minutes 15 seconds, we accept blocks from the number 1 on the list.
8. If the block is revieves and hood, this is started over, if not, keep going.
9. If there's no block, or a bad block, then the account is blacklisted
(blacklisted accounts cant generate blocks for a day and their block generating power is given to everyone else)
10. Keep waiting/blacklisting until an account steps up

the careful observer is now yelling WAIT, the black list makes any chain have the ability to create blocks with all of the stake, how will we know which is the correct chain.
- thanks for asking, we can resolve these disputes quite simply by just looking where more of the accounts are not skipping their turns, (will have a higher difficulty)

now the very careful observer is almost falling out of their seat, the normal nothing at stake argument PDF in hand, ready to derail this possible idea "Why doesn't everyone generate blocks on every chain, there's not reason not to"
- another great question, the reason why they wouldn't stems from economics, all of the people generating blocks have a n investment in the system and want to protect that investment, in this system, there are no fees (spam is dealt with differently) so there's no incentive to generate blocks on any chain besides to protect investments.
the only punishment for using a malicious chain is not being able to use your currency with anyone else. Lets say you buy coffee on the block chain every day, the coffee seller includes a block from the chain their on with every transaction they make to show what chain they are on, if I start a different chain, and people begin to adopt it, because why not generate blocks on as many branches as possible, then its down to the people to decide which chain to use.
in this case I would choose the same one my coffee seller is on, because I want coffee.
if a big enough representation of business is on one branch, it wouldn't make sense to ever switch to another one.

thoughts?