Is it Possible to Guess a Private key of Bitcoin Paper Wallet?

[nagoarif]

I was wondering about, how a paper wallet works and found a shocking reality that javascript-based generators can be used to create paper wallet addresses. My question is: is it possible to guess the private keys of the BTC paper wallet? is there any clue in the public key to guess the private key?
For just knowledge purpose, I have created two paper wallets by using the same website btc-paper-wallet.com twice in one minute. The first letters of both wallet's private keys were the same. You can see this in the screenshot below.
I'm confused about the storage of my BTC that I'm going to buy from coinbase. Should I use a paper wallet? is it still safe? Can people or machines guess my private keys?

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[HCP]

No... it is impossible to "guess" a private key based on a public key... if that were possible, Bitcoin would be worthless... anyone could spend any coins they liked.

Javascript-based generators are not necessarily the greatest (poor RNG etc)... and some were found to be giving out "used" keys and/or pre-generated keys which caused coins to get stolen (there was a high profile, popular paperwallet site that got sold and turned "bad").

You also should not use "online" generators... Paper wallets should be securely generated offline... otherwise you're defeating the entire purpose of a paper wallet (which is to make sure that the private key never touches an online computer until you are trying to spend the contents of the wallet).

Also, the first letters of the private keys being the same is not that unusual... they should all start with a "K" or "L" (or a "5" if for some weird reason it was generating uncompressed keys)...


Personally, unless you've very familiar with Bitcoin and paper wallets... I would not recommend them. It is very easy to mess up and either lose your coins via theft... or via misplacing keys... or via not unstanding how "change" works and losing coins if only partial spending the contents of a paper wallet.

[Quickseller]

For just knowledge purpose, I have created two paper wallets by using the same website btc-paper-wallet.com twice in one minute.

Don't use this website. It appears this website will not generate private keys on the client side (on your computer), but will rather generate the private keys on their server. Your private key will also be known to the owner of api.qrserver.com, if different from the owner of the website you are using.

[pooya87]

Should I use a paper wallet? is it still safe? Can people or machines guess my private keys?

A paper wallet is simply a "secret" that is written on a physical medium including but not limited to paper.
That secret can be your private key, your mnemonic or your password,... and the security of it depends on (1) how it was created (2) how it was printed and (3) how it is stored.

Obviously if you create the paper wallet using a website and do it on a possibly compromised computer and store it recklessly then it is going to be the least safe thing to do!
But you could generate it on an airgap computer using a safe software such as an open source and trusted desktop wallet (eg. Electrum) and store the key encrypted and create multiple backups of it. This way it can be the safest option.

[nagoarif]

For just knowledge purpose, I have created two paper wallets by using the same website btc-paper-wallet.com twice in one minute.

Don't use this website. It appears this website will not generate private keys on the client side (on your computer), but will rather generate the private keys on their server. Your private key will also be known to the owner of api.qrserver.com, if different from the owner of the website you are using.

So, can you please suggest a safe and secure site that is 100% trusted?

[Quickseller]

For just knowledge purpose, I have created two paper wallets by using the same website btc-paper-wallet.com twice in one minute.

Don't use this website. It appears this website will not generate private keys on the client side (on your computer), but will rather generate the private keys on their server. Your private key will also be known to the owner of api.qrserver.com, if different from the owner of the website you are using.

So, can you please suggest a safe and secure site that is 100% trusted?

You can consider using bitaddress. You can generate a paper wallet offline while using the site offline.

I would suggest that you not use a paper wallet until you have some experience using bitcoin, and you are confident that you have a solid understanding of how bitcoin works, including things such as private keys, importing private keys, and the importance of backups.

[Charles-Tim]

My question is: is it possible to guess the private keys of the BTC paper wallet? is there any clue in the public key to guess the private key?

It is not possible to guess the private key from the generated public key, private key is made up of characters that are long and not guessable.

But, if you mean 'is it possible to calculate the private key from public key' because public is generated from the private key. Still not possible because it is an asymmetric calculation in which what is generated from multiplying private key with a constant point called generated point to give public key is using one way function elliptic curve multiplication, dividing the public key with the constant point can not result to private key generation, it is not possible as it is one way-function.

Also, if you mean if the private key can be brute-forced from the public key, it is also not possible with the modern days computer. The private key space size is a very large number (2^256) which is approximately 10^77, while the visible universe is estimated to contain 10^80 atoms, so brute-forcing a private key just still remain impossible.
It is better you use bitaddress.org to generate the paper wallet as suggested by Quickseller or using using wallets like electrum offline to generate it as pooya87 implied. During generating it from recommended means, also still make sure you generate it safely in an offline environment.

[DireWolfM14]

So, can you please suggest a safe and secure site that is 100% trusted?

You can safely generate a "paper wallet" by finding a site that allows you to download the source and run it on an off-line.  There are a couple out there, but I won't link to any because I don't recommend that method.

You can also use a light-client desktop wallet to do the same thing, but better.  I recommend Electrum, which will allow you to create a wallet with many addresses that backed up by a 12-word long seed phrase.  You can create a wallet on an on-line computer to use as a "hot wallet" or you can create a "cold wallet" on a off-line computer and have a "watch only" version to access on your on-line computer.

Electrum home page: https://electrum.org/#home
Verify authenticity: https://bitcointalk.org/index.php?topic=5240594.msg54223763#msg54223763

[nagoarif]

Thank you buddies for your support and help 

[ranochigo]

You shouldn't visit the site directly to run it offline. Rather, you should download the codes in its entirety from Github, validate it and run the html files. Directly downloading the webpage alone is not enough, it can easily be modified with a MITM attack and compromise your security.

But yeah, AFAICT, the fact that it salts your entropy with some mouse movement and various factors should mitigate the ramifications of the browser's CSPRNG not working as intended to a certain extent. JS is certainly not suitable to be used for paper wallet generation.