Bitcoin Forum

after reading the book Digital Gold by Nathaniel Popper I learned this:
I quote:

ADDRESSES AND SECRET KEYS Anyone joining the Bitcoin network can generate his or her own Bitcoin address (generally a string of thirty- four letters and numbers), and a corresponding private key (generally a string of sixty- four characters).
As an example, one actual Bitcoin address is:
16R5PtokaUnXXXjQe4Hg5jZrfW69fNpAtF
The private key for this particular address is: 5JJ5rLKjyMmSxhauoa334cdZNCoVEw6oLfMpfL8H1w9pyDoPMf3
Unquote.
I assume Mr Popper is right and up to date because his book is a recent one.

I have two questions and I hope someone can help me.
1.) After I registred at a bitcoin exchange, I bought bitcoins (june 2015) I received a Bitcoin address and this contained the 34 characters as mentioned in the book.
I did not generate or receive a private key of 64 characters.
However I did get, a so called Identifyer. The Identifyer is 36 characters instead of the 64 mentioned by Mr Popper.

2.) If the identifyer is the equivalent to the private key, should I worry that this key was send to me via email by/via a third party.

Thanks for any input

1) You have an account at an exchange or other online bitcoin storage. It is not a wallet. The exchange controls the addresses and bitcoins and holds the private keys, not you.

2) I don't know what exchange you are using, so I don't know what the identifier is, but it is probably not a private key.

You can hold the bitcoins yourself if you download a wallet, such as Electrum, or Airbitz. In this case, the addresses and private keys are stored in the wallet.

On an exchange you dont actually own the address, unless you create a wallet on blockchain.info for example or download it.
The identifier is not the equivalent to the key :P

You'd actually need to use a wallet to own any kind of private key. Wallets essentially let you access your bitcoins by managing your private key. Also, by identifier, are you referring to your pubic address? Bringing the example from the quote up, the public address is this one: 16R5PtokaUnXXXjQe4Hg5jZrfW69fNpAtF

Everyone can see this address in the blockchain. However. it's ownes shouldn't really worry about that. He should only worry in the case that he losses access of his wallet (or private keys).

1) Exchangers would not give you any private key since they require you to send it to your own wallet. You can create it by using electrum, multibit or blockchain.info. The identifier is probably a transaction ID used by the exchange to identify your transaction.
2) Yes. Do not send unencrypted information over the internet. But in this case, you would probably have to withdraw it yourself. Even if a malicious party have your identifier, they can't do much.

I don't know of any exchanges that give you the private keys.   Most exchanges utilize cold storage methods so most of the funds aren't online at all times, just enough for estimated daily operations.   So they wouldn't be able to give you private keys to their addresses because your coins are usually mixed with other people's coins.   Your balance is essentially just a number in a database.

Mr. Popper's description is correct, addressed you create using a client such as bitcoin-qt or electrum or even blockchain.info have a public address and a corresponding private key.

However, as others have pointed out, your account at the exchange does not give you access to a private key.  As many old hands here like to say, "If you don't control your private key you don't own your bitcoins."

If you create a wallet in a client or online wallet like blockchain you can instruct the exchange to send your coins to one of those addresses, then you'll have the address and private key.

As long as your exchange is honest it is not functionally an issue, but they have your coins, you have a claim on them for your coins.

I would not worry too much about the identifyer as long as your exchange account is protected by another system, e.g. password, two factor authentication.

Good Luck!