I have a used KNC Saturn miner for sale. Currently mining at 340 GH/s, and making 0.09 BTC/day. Payment accepted in BTC or cash.

If you're interested please PM me with a price you would be willing to pay for it. Pickup from North-West London, or buyer to pay shipping.

http://bitcoinwisdom.com/bitcoin/calculator

Doesn't have the knc neptune, but seems to have most of the others.

Can you just keep escrowers honest based on a reputation system? In order to build reputation an individual uses the same address for all their transactions in the market. Based on signed feedback from the addresses of counterparties they trade with they build a track record of being trustworthy, and you can make a judgement based on the amount of business they have done already as to what their reputation is worth to them and therefore how much they can be trusted with in escrow.

A way to build initial trust to start up would be to use a public address on the network that was expensive to generate, and that you are less likely to want to throw away in order to defraud someone. Two ways to do this: either use a vanity address starting with for example a string of 1s as a proof of work, or make a couple of transactions from your address with large mining fees which is then the cost of that address to you.


Is this necessary for all trades though? It helps to have some instant trades, but there is no reason that p2p localbitcoins type transactions couldn't exist within the same system. A seller of bitcoins could advertise a fiat payment method along with the price. A trade would be entered on the p2p network as "agreed" when an agreement is made, as "paid" when the buyer confirms they have dispatched fiat payment, and as "settled" when the fiat payment settles and the BTC are sent.

The settlement date could be anything from a few minutes later for a wire transfer, to several days later when cash arrives in the mail, but the prices can still be broadcast to the market to help determine a market price. It is up to the buyer/seller to decide what risks they wish to take in the trade based on each others reputation and the risks of the payment method (cash vs paypal vs wire transfer etc).

bitcoin-qt keeps the private keys for any change accounts it makes, even if the corresponding public key is not shown in your address book. You should therefore have full control over this change address. If someone sends coins to it they will show up in your bitcoin-qt wallet, you can spend them, and you can use bitcoin-qt to sign a message using the key (just put in the associated public address).

I've bought bitcoins in the UK from blockchain in the past, but their UK bank account funding option has been closed, and so has their pingit account. The same has happened to other exchanges offering bitcoins by UK bank transfer, and I'm not aware of any currently operating.


I bought a few on localbitcoins. It works, and you simply do a bank transfer from your online banking to their account, so the person you trade with will not have your account details.

The cheapest way of buying bitcoins from the UK at the moment seems to be using transferwise (http://transferwise.com/) and one of the online exchanges (Bitstamp or MtGox). Transferwise do cheap bank transfers from the UK to the EU - they have a UK bank account to which you can transfer money, and will convert to Euros at a decent rate and send it as something called a "SEPA" transfer. Bitstamp and MtGox will both accept SEPA transfers in.

What you do is setup a Bitstamp (or MtGox, but I've not tested that) account, go to "Deposit", and then "EU Bank(SEPA)". Setup the deposit and you will be given a whole load of bank details. Then go to transferwise and set up a transfer, entering the bank details Bitstamp gave you as the recipient. Finally you pay transferwise, either by debit card or bank transfer. Funds have arrived within 36h when I've done it, but it apparently can take up to 3 days.

How do you know they don't touch your private keys? They say they don't, but unless you read the javascript source code every time you access their website, you are taking that on trust. If their website is hacked, the hacker could edit the javascript to leak your private keys/password back to them and steal your bitcoins.

This is a much lower risk than an old style web wallet that stores your private keys. In the blockchain.info case you would only be at risk if you tried to access your webwallet in the window between the site being hacked and someone noticing and taking it offline.

Best to think up your own four word passphrase though.

correct horse battery staple
5KJvsngHeMpm884wtkJNzQGaCErckhHJBGFsvd3VyK5qMZXj3hS
https://blockchain.info/address/1JwSSubhmg6iPtRjtyqhUYYH7bZg3Lfy1T

OK, maybe not the best suggestion for the original poster, but it did answer the question in his first post - the number of characters required to make a brain wallet difficult to crack directly relates to the speed of the brain wallet algorithm. If there is only one existing brain wallet algorithm available online then that's not that helpful for him I agree. If there is more than one, then choose the slowest.


I meant the algorithm for converting a password into an address. The expensive bit of any brainwallet is going to be generating the keys from the wallet. If everyone using a brainwallet uses the same algorithm then a cracker who brute-forces possible passwords can check the generated public keys for each trial password against all existing public keys with significant funds in them very cheaply (eg. using a bloom filter). If the trial password matches anyone's brain wallet then he has a hit.

It seemed to be six when I did it yesterday. Until 6 confirmations the transfer doesn't show up at all in your account.

How difficult is really difficult? It depends on how much in the way of computer resources someone is willing to expend on the attack, which depends on how much money you have stored in your brain wallet.

You need to test how many passphrases your computer can create brain wallets from per second. If your computer is old then multiply this up to a decent high end computer available now. How long will it take them to crack your password? (there are 3 x 10^7 seconds in a year).

Now work out the number of possible passphrases according to the scheme you are using. If you go with printable ascii characters then there are 95^x =~ 10 ^ (x * 2) possiblities, where x is the length of your password. If with a randomly chosen word from the most common 10000 words in english then 10 ^ (x * 4) possiblities where x is the number of words. eg.
   
    8 characters =~  4 words = 10 ^ 16 possibilities
    12 characters =~  6 words = 10 ^ 24 possibilities

I've just generated a sample 10 ^ 24 possiblity password for each of these so you can decide which type is easier to remember.
     Lj0Z4c|==i5CJ<pT
     heroin swallowed goddamn hustle serge imitating

If you assume the crackers top end hardware will depreciate to near nothing over 5 years, it is only worth them trying to crack your password if:
     value_of_bitcoins_in_brain_wallets >  cost_of_hardware * password_possibilities / (passphrases_per_second * 5 * 3 * 10^7)

Note that if many brain wallets use the same generation code then a hacker can test all of them at the same time, so the important value is that stored in brain wallets using the same generation code as you, not that stored in your wallet.

The best defence is probably to make brain wallets slow to generate.  If the cracker can crack brain wallets at 350billion per second then you need a long passphrase. If the first step of the brain wallet is to sha hash the passphrase 80 billion times, it might take you 80000 seconds to create your brain wallet (just under a day) on your 1MH/s CPU, but even a cracker with a 80GH/s ASIC is only going to be able to try crack passphrases at one per second. A 3 word (or 6 random character) passphrase now takes them 100000 years to crack...

Ivanol

blockchain.info for everyday spending. An offline wallet for savings.

If these are coins that you sent to a blockchain.info wallet address then you should be able to send them directly using their web interface.

If they are coins you sent to an address that you have the private key for elsewhere then you can import this into blockchain.info through their web interface, and then send the coins on from there.

Some methods of private key import are fussy as to the format of the private key. If so then www.bitaddress.org is a great tool - the Wallet Details tab allows you to enter any format of private key, and does the conversions (all in Javascript on the client side, so you can run it offline in a disconnected computer).

Hi. I'm Ivanol.

I've been lurking for a while, run a node, and have a few bitcoins that I bought (and a few satoshis I CPU mined before realising it was pointless).

From a few months of lurking on the main forums, it's obvious that these restrictions don't actually prevent the trolling, but are a pain for those who now want to unlurk.

Although if you're thinking of buying an ASIC make sure you do your research first (Custom Mining board probably a good place to start). You might find you're waiting longer than the vendor's website implies...