generating and guessing BTC-adresses - page 2.

shorena

copper member

Activity: 1498

Merit: 1528

No I dont escrow anymore.

Quote from: ?? on ??

-snip-
edit: a further questions:
i generated an address. then I encrypted my wallet. nobody can spent my coins even though this address will be generated in the future. right?

No, a private key is nothing more than a number. You encrypt it locally so no one can look at it. If however someone should guess the same number as you, their version is not encrypted and they can use it without the password.

shorena

copper member

Activity: 1498

Merit: 1528

No I dont escrow anymore.

Quote from: ?? on ??

@shorena: thank you. do you have a link/source?

-> https://bitcoin.org/en/alert/2013-08-11-android

achow101

staff

Activity: 3458

Merit: 6793

Just writing some code

Quote from: ?? on ??

Quote

Most wallets are not designed to check for the address collision as it is impossible....

why is this impossible?

It would need to rescan the blockchain and every transaction to see if that address has been used before. It takes a lot of time to do that so that every time you want a new address, it would take hours for it to finish rescanning.

Quote from: ?? on ??

and how do i know that my newly generated address is really new? i never checked that. so possibly i generate an address and someone else had already generated this one. then you send me some coins. and uups a few weeks later this coins are gone because someone else received them to - by hazard - and spent them.

It is assumed. With a good random number generator, the likelihood of a collision is next to nothing. There have been cases where addresses have been generated multiple times on different devices but that was due to poorly written random number generators. You can check yourself if an address has been used before by just looking it up on a block explorer. However, to do this in a wallet is considered poor practice since it requires using an outside API, which may not be reliable and most good wallets don't want to rely on someone else to do the work.

shorena

copper member

Activity: 1498

Merit: 1528

No I dont escrow anymore.

Quote from: ?? on ??

Quote from: shorena on November 08, 2015, 07:54:36 AM

Quote from: vlom on November 08, 2015, 07:47:23 AM

Hi

i have some questions concerning BTC-addresses.

when i generate a new address e.g. with multiunit HD.

Multibit HD?

i uses this wallet:

https://multibit.org

Quote

If two persons generated the same address they share the funds. Each of them can spend everything.

anybody know if this already happened?

It did, but only because the wallets did not use the whole range of possible private keys. Due to a bug on android devices the range was limited to 2³² or 4294967296 which is quite small compared to 2¹⁶⁰ or 1.4615016373309029182036848327163 * 10⁴⁸ which is a number with 49 decimal digits.

iram66680

hero member

Activity: 630

Merit: 502

Quote from: Crypt0Ninja on November 08, 2015, 08:07:19 AM

Quote from: vlom on November 08, 2015, 07:47:23 AM

Hi

i have some questions concerning BTC-addresses.

when i generate a new address e.g. with multiunit HD.
- my wallets knows all the addresses that have been generated yet?
- are theses addresses saved in the blockchain?
- as far as i know the address is saved in the blockchain when it was used. you can generate an address offline, right?
- if two persons generate the same address offline and then start to use it. what will happen?
- is it possible to guess a specific address? and when my guess is correct and this wallet is not encrypted.

thanks for answers.

I'm pretty sure you wont hit any dublicates, since the system will not allow it.

Most wallets are not designed to check for the address collision as it is impossible. A weak random number generator can make private keys guessable or if the random number generator is bugged and it can generate the same address everytime. See the most recent incident in blockchain.info android app.

Crypt0Ninja

member

Activity: 122

Merit: 10

Bitcoin Investor & Programmer

Quote from: vlom on November 08, 2015, 07:47:23 AM

Hi

i have some questions concerning BTC-addresses.

when i generate a new address e.g. with multiunit HD.
- my wallets knows all the addresses that have been generated yet?
- are theses addresses saved in the blockchain?
- as far as i know the address is saved in the blockchain when it was used. you can generate an address offline, right?
- if two persons generate the same address offline and then start to use it. what will happen?
- is it possible to guess a specific address? and when my guess is correct and this wallet is not encrypted.

thanks for answers.

I'm pretty sure you wont hit any dublicates, since the system will not allow it.

shorena

copper member

Activity: 1498

Merit: 1528

No I dont escrow anymore.

Quote from: vlom on November 08, 2015, 07:47:23 AM

Hi

i have some questions concerning BTC-addresses.

when i generate a new address e.g. with multiunit HD.

Multibit HD?

Quote from: vlom on November 08, 2015, 07:47:23 AM

- my wallets knows all the addresses that have been generated yet?

No.

Quote from: vlom on November 08, 2015, 07:47:23 AM

- are theses addresses saved in the blockchain?

No.

Quote from: vlom on November 08, 2015, 07:47:23 AM

- as far as i know the address is saved in the blockchain when it was used. you can generate an address offline, right?

Yes, used addresses are stored in the blockchain (to some extend) and yes you can generate an address offline. In fact thats the normal way to do it.

Quote from: vlom on November 08, 2015, 07:47:23 AM

- if two persons generate the same address offline and then start to use it. what will happen?

If two persons generated the same address they share the funds. Each of them can spend everything.

Quote from: vlom on November 08, 2015, 07:47:23 AM

- is it possible to guess a specific address? and when my guess is correct and this wallet is not encrypted.

thanks for answers.

Yes, is possible to "guess" a private key to an address and be able to spend someone elses funds. But its in the realm humans usually call impossible. Its the same realm where all the air molecules collect into a corner of your room and you die.

I think you assume somehow that its checked whether or not an address was already generated. Thats not the case. There are so many possible private keys (2²⁵⁶) for so many possible different addresses (2¹⁶⁰) that I can sit at home generating a 36 million private keys and addresses per second and still cant find one that has funds on them. Everyone on earth could do this and the chances are still so small you are more likely to hit the lotto jackpot several weeks in a row.

vlom

legendary

Activity: 1498

Merit: 1117

Hi

i have some questions concerning BTC-addresses.

when i generate a new address e.g. with multiunit HD.
- my wallets knows all the addresses that have been generated yet?
- are theses addresses saved in the blockchain?
- as far as i know the address is saved in the blockchain when it was used. you can generate an address offline, right?
- if two persons generate the same address offline and then start to use it. what will happen?
- is it possible to guess a specific address? and when my guess is correct and this wallet is not encrypted.

thanks for answers.

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