Bitcoin Forum

How exactly btc transactions is reserved (only math task?)?? I don't think, that math task so high security for transactions with my money.

You're going to have to rephrase that because it makes little to no sense.

Every transaction involves math, not just Bitcoin. :P

I suspect your question is about the security of the cryptography used, which is designed to be as secure as possible. The network attempts to find hashes of blocks that start with a lot of zeros, with the amount depending on the difficulty, which is an extremely computationally expensive task. It is currently impossible to crack someone else's private key via brute force during the lifetime of the universe, and coins cannot be double-spent without gaining enough computational power to comprise 51% or more of the network, in which case mining normally remains far more profitable.

If you rephrase your question to make its intent clearer, it will be a lot easier for people to provide more helpful answers.

Well, it's certainly more trusteable than what you trust right now with banks and credit cards (basically a 3rd party doing the accounting with morals and ethics without any mistakes  ::))

Yes only the difficulty to reverse a (or better, find a specific) sha256 hash is protecting your transaction (TX). Think of it like this. To multiply 456 and 456 is easy. A child probably can do this. But to get the root of 207936 is very difficult. No calculator allowed! Sha256 is like this, only way more difficult.

If you want to find a new block to secure a TX (and get the reward for it) that gets accepted you have to calculate many many sha256 hashes. Not all are accepted only those that have enough 0 at the beginning. This can change and is called the target. Most of the time you will see "difficulty" which is related to the target. higher diffculty = must have more 0's to get accepted.

With the 1st block that has your TX in it you have 1 confirmation. Every block after that gives you one more confirmation. ~10 minutes for one.

If someone wants to undo your TX they have to make all blocks again and not only that, but faster than everyone mining for bitcoin. So after 6 confirmations an attacker has to find 7 valid blocks before all miners worlwide find one.

I read about problem with a lost of btc by transactions. What do you know about that??

Safety is backed by cryptography.

You can start by reading Satoshi's original paper, and take the Udacity's course introduction to cryptography, they explain cryptocurrency in some deep.

lost of btc by transactions? You mean double spending?
As shorena explained, if your tx has a few confirmations, it is extremely difficult to double spend it unless the attack has overwhelming hashrate (51% attack). But if your tx has no confirmation and has less than min fee, it is much easier to double spend it.

Not simple math task like 1million x2 billion. It is secured by cryptography, invented by NSA. Bitcoin basically is just your computer calculating billion and billion of hashes every second using hardwares. The hash of a block must start with a certain number of zeros. The probability of calculating a hash that starts with many zeros is very low, therefore many attempts must be made. Once you have reached six confirmation, it is fairly impossible to reverse the transaction unless you own 51% of the network. SHA256 currently have no weakness. Developers can always do a hardfork if any vulnerabilities is discovered.

There are a few things this question can mean.

1) Concern about lost btc due to theft

If you don't have good computer security and backup, you can lose your bitcoins by someone copying your private keys and sending the bitcoins to another address.  Also if your computer's data is lost and you don't have a backup, you'll never be able to get those private keys again and though you can still look at the bitcoins sitting on the blockchain, you'll never be able to move or spend them.

2) Concern about losing btc due to fees

Sometimes people have used rather high tech tools to make their own Bitcoin transactions. When using these tools (like brainwallet), if they don't understand how a transaction needs to be built not to lose money, they end up with big fees sent to the miners. The explanation on this is that each Bitcoin transaction takes a set of inputs and makes some number of outputs. The inputs are the money you have and the outputs are where the money is going. If the outputs don't add up to near the amount of the inputs, the rest goes to miners as transaction fees.

So typically when things went wrong, someone spent a 1 btc input and only made one 0.1 btc output for example. In this case, the other 0.9 btc have to be spent (since inputs must be spent completely) and they go to miners. In many of the higher profile cases, the mistake was remedied by contacting the pool that earned those fees but since miners may be anonymous, there is no guarantee that the coins will come back to you.