Are there any places to do this?

And more importantly - is this viable? Could margin trading be offered in the world of cryptocurrencies? I don't mean established pairs like BTC/LTC but small altcoins.

Naturally this could be difficult due to the immaturity of altcoins. Theres little liquidity, little volume and I assume other unfavourable factors. Although, suppose its your own exchange (and you're not a meta exchange like Bitfinex once were) and you can post a stop loss at exactly the right level and guarantee it executes - as long as you can satisfy every margin call then everything is dandy - surely?

Originally BitFinex would act as a meta-exchange and place orders at bitstamp and other exchanges. This explains the necessity of them having creditors on the site from which to borrow money.
Today they trade on their own exchange only meaning that they don't need to borrow money to open positions. I suppose it makes sense to actually borrow money from someone interested in lending it - but is it necessary?

It is my understanding that the practice of an exchange opening positions without the asset backing is a naked call. How common are naked calls in the real world? Would it be a good idea for a cryptocurrency exchange to offer uncovered positions? What are the possible implications of doing it this way?

Can anyone offer any thoughts and ideas?

I was looking at http://dustcoin.com/ and noticed that mining some scrypt coins can be twice as profitable as mining litecoin.

Suppose that a litecoin pool operator actually gets his users to mine dogecoins or bbqcoins. He then uses the proceeds to purchase litecoins and pays them out to his miners. The end effect is that the pool operator is way better off than he would be otherwise.

Is it possible for this to be happening seamlessly without the miners not realising? When a scrypt pool miner is issued a work unit would it be possible to have them mine on a different coin than the user assumes?

Given blockchain difficulty and primerate how does one calculate the expected interval between mined blocks?

How is block reward calculated?

I recall seeing an image that represented bitcoin as a single pixel on a canvas of circles proportional in size to the value of what they represent. I think gold, silver, various stocks and the M1 of a bunch of countries were displayed.

I can no longer find this image, any ideas where to find it?

I've been trading BTC in the UK via bank transfer for a while now and may begin doing cash purchases soon. I've realised that it is critical I document the cash withdrawal as an expense so that I get taxed only on the profit and not the entire turnover of the bitcoin sale. Usually this is done via the means of keeping receipts - so I guess I could have some sort of receipt that documents the exchange but I'm not sure where to begin.

What kind of information do I put on it? Do I want the sellers signature on it? How much information on the seller do I want, bearing in mind that he may not want to disclose any?

I'm not really sure what I'm asking for here so I'll just word my thoughts and then hopefully I can get some ideas back.

I'm looking to work on a site that will handle bitcoin that will obviously need to receive bitcoins from users. No bitcoins will be sent automatically so no private keys have to be known.

The first thought that came into my head is to use armory's specification of bitcoin wallets. I could generate a wallet on an offline machine and then derive the public-only seed. Then I'd use this seed on the website server to get public keys at a specific index of the key chain, for example based on the user's ID.

What I'm wondering is - what approach do other bitcoin services take to this issue? Do they also use some form of deterministic key creation. As far as I know generating an address on the spot completely from random implies that you're also having to store the private key on the same site. I don't need to do this so I don't see why take the risk.

I'll probably be using AppEngine with Java. Is there any java deterministic wallet APIs? How challenging would it be to write one based on armory's python code?

More importantly - what is the logic behind creating a chain of private keys from a seed but also being able to generate a chain of public keys from the public part of the seed?

I'm looking for a simple library to handle basic bitcoin related calculations such as
- generating private keys
- calculating public keys
- calculating bitcoin addresses

I'm not looking for any actual bitcoin network interaction. I'm looking at bitcoinj opened but before I slim it down to the classes that are relevant to me I figured I'd ask and see if this is something that's already available.

This afternoon I worked on a little mining sim sorta deal that's a bit better than what's available currently. It was mainly an excuse to get familiar with AppEngine and then implementing Lua for a bit of fun.

http://bitcoineering.appspot.com/simulator

- Left column concerns the network situation. The last retarget field atm is hardcoded and won't update dynamically - couldn't find a good source on that.
- Right column concerns your own mining efforts and finances involved.
- Logs the status after simulating each day so you can see exactly what's happening day by day.
- Simulates difficulty adjustments.
- 25 BTC reward upon block #210,000 onwards.

The script area allows you to use Lua to write your own functions to be used in the simulation. So far only a hashrate prediction function works. The function takes a parameter of time which is a UNIX timestamp in milliseconds. The Lua environment also has some helper functions for interpolating between dates and the likes.

I'd appreciate if the mining savvy ran some checks on my calculations. I did and it all seems to check out but you never know.