I understand Bitcoin but

[venomdog]

I still have few doubts so I thought to create this thread and get some answers from you guys.
I bought few Bitcoins (well at wrong time on 3rd Jan  ) and since then all I seen is how bitcoin goes down, but still I have trust in it.
My questions are as follows :

1. I have a wallet at blockchain and I am not storing my private keys online as I printed them out. So does that mean if someone crack my wallet password he can take all my bicoins or he still need my private keys ? Because seriously I am not using my private keys, may be blockchain does when I send some bitcoins to other address, is that understanding true ?

2. From Question 1 if it really is true then Blockchain does have my private key so if someone hacks my account he/she gets both then ? (key and coin).

3. What are cold storage and/or what is secure way to store your coins then ?

4. Online wallets are trust worthy ?

5. A while ago I bought a VIP account of nzb indexer through bitcoin (my first purchase) but that site was waiting for me to transfer the requested bitcoin by giving their wallet address and starting a counter (10 min before that transaction will cancel automatically), but what I don't understand is how on earth that site knew that the coin it got is from me, it could have been anyone doing transaction on that moment. I was anonymous user and happens to be transferring bitcoin to that site. But how on earth they knew that I paid them.

If I have anymore question that will come up during this discussion I will add them.

Thanks.

[odolvlobo]

1. A wallet does not actually hold bitcoins. It holds private keys. The private key is used to send bitcoins stored at an address. If the blockchain.info wallet does not hold the private keys that you printed out, then the wallet's password won't help he hacker get those private keys.

2. Blockchain.info stores an encrypted copy of your wallet. When you access your wallet, the site sends you the encrypted copy and you decrypt it with your password. If someone steals your password, they can log into your account and access the wallet, too.

3. Cold storage is a wallet that is not accessible from the internet. It can be stored on paper, or a USB flash drive, or a computer -- as long as it is not connected to the internet. A "hot wallet" is a wallet on a machine connected to the internet.

4. The term "online wallet" is ambiguous. A site that holds your bitcoins for you (e.g. an exchange or Coinbase) has full control over your bitcoins. You have to trust that they will give you your bitcoins when you want them. All sites accessible using a browser have some security risks (primarily phishing).

5. They know who you are by giving you a unique address. Every order gets a different address. They know you paid when the see the transaction sending bitcoins to that address.

[findftp]

I still have few doubts so I thought to create this thread and get some answers from you guys.
I bought few Bitcoins (well at wrong time on 3rd Jan  ) and since then all I seen is how bitcoin goes down, but still I have trust in it.
My questions are as follows :

1. I have a wallet at blockchain and I am not storing my private keys online as I printed them out. So does that mean if someone crack my wallet password he can take all my bicoins or he still need my private keys ? Because seriously I am not using my private keys, may be blockchain does when I send some bitcoins to other address, is that understanding true ?

I don't understand. Do you have an account at blockchain.info? Or do you mean you have an address on the blockchain?

2. From Question 1 if it really is true then Blockchain does have my private key so if someone hacks my account he/she gets both then ? (key and coin).

Your wallet contains the private keys, no matter where you store the wallet. You can encrypt the wallet to protect them for others.

3. What are cold storage and/or what is secure way to store your coins then ?

Cold storage is a wallet which is not connected to the internet. For example a computer disconnected from the internet, or a paper wallet.

4. Online wallets are trust worthy ?

Not if you have to trust someone else to protect the private keys.
Usually online wallets are a bit more vulrnable than offline wallets.
Put only pocket change in online (hot) wallets.

5. A while ago I bought a VIP account of nzb indexer through bitcoin (my first purchase) but that site was waiting for me to transfer the requested bitcoin by giving their wallet address and starting a counter (10 min before that transaction will cancel automatically), but what I don't understand is how on earth that site knew that the coin it got is from me, it could have been anyone doing transaction on that moment. I was anonymous user and happens to be transferring bitcoin to that site. But how on earth they knew that I paid them.

Because nobody else knows that address you were sending the coins to.
Every address is very unique and rare.
If there were no transactions made from that address in the past, nobody knows the address.
The address becomes known to the rest of the world when there is a transaction made, then it's a part of the blockchain.

If I have anymore question that will come up during this discussion I will add them.

bring it on.

[venomdog]

Thanks @odolvlobo and @findftp, trust me it cleared a lot of stuff for me.
I summarize my understanding based upon your answer :
Blockchain.info (where I have an account) stores my encrypted wallet and that address has some coins associated (the one I purchased) so when I am hacked hackers can get access to this wallet and in turn my private keys. So to be safe I should probably use cold storage.

Questions :
But I read on this forum that one of the guys wallet was hacked but users were asking if he still has private keys (not known to hacker) how does that help, because if someone get access to my blockchain account then that means he got everything nope ?

Secondly, can I duplicate my wallet at multiple sites, meaning can I create multiple accounts at different wallet sites with "same coins" (if it make sense), because one of your answer made me believe that a unique address is associated to transaction so its not possible to associate same "coins" to multiple address.

Thirdly about this

Because nobody else knows that address you were sending the coins to.
Every address is very unique and rare.
If there were no transactions made from that address in the past, nobody knows the address.
The address becomes known to the rest of the world when there is a transaction made, then it's a part of the blockchain.
----------------
They know who you are by giving you a unique address. Every order gets a different address. They know you paid when the see the transaction sending bitcoins to that address.

so it means the receiver sends you address which they generate for your transaction and once they receive coins on it, they can discard it or may be transfer the coins to their main wallet, yeah ?

[findftp]

Thanks @odolvlobo and @findftp, trust me it cleared a lot of stuff for me.
I summarize my understanding based upon your answer :
Blockchain.info (where I have an account) stores my encrypted wallet and that address has some coins associated (the one I purchased) so when I am hacked hackers can get access to this wallet and in turn my private keys. So to be safe I should probably use cold storage.

More or less, yeah. But it does not make sense to put your currency completely out of sight. A currency need to be spent. Large amounts you can better put in a safe (cold storage)

Questions :
But I read on this forum that one of the guys wallet was hacked but users were asking if he still has private keys (not known to hacker) how does that help, because if someone get access to my blockchain account then that means he got everything nope ?

Yes, once someone has the private keys they are able to spend the coins, that's the whole point of bitcoin. Bitcoin doesn't care about the rightfull owner, it only care about the one who knows the private key. If you keep the key secret, you must be the owner.

Secondly, can I duplicate my wallet at multiple sites, meaning can I create multiple accounts at different wallet sites with "same coins" (if it make sense), because one of your answer made me believe that a unique address is associated to transaction so its not possible to associate same "coins" to multiple address.

It does not really make sense what you say (you should change the subject )
The private key does not "contain" coins, it points to an address at the blockchain were an amount of coins is stored.
You can copy the private key thousand times, but they all point to the same public address which is stored at the blockchain (which every node has a copy of)

Thirdly about this

Because nobody else knows that address you were sending the coins to.
Every address is very unique and rare.
If there were no transactions made from that address in the past, nobody knows the address.
The address becomes known to the rest of the world when there is a transaction made, then it's a part of the blockchain.
----------------
They know who you are by giving you a unique address. Every order gets a different address. They know you paid when the see the transaction sending bitcoins to that address.

so it means the receiver sends you address which they generate for your transaction and once they receive coins on it, they can discard it or may be transfer the coins to their main wallet, yeah ?

Yes, that is true. They can also reuse the address only for you or generate a new address for every transaction.
Addresses are free to create, so why not.