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26 votes
Accepted

How do you derive the private key from two signatures that share the same k value?

ECDSA signatures are pairs (r,s) where r=(kG).x mod n, and s = (m + rx)/k mod n, where x is the secret key, k is the random nonce, and m is the message. If you have two s values s1 and s2 for the same ...
Pieter Wuille's user avatar
7 votes

What's stopping someone from taking over all the bitcoin addresses?

There are about 2^256 private keys, 2^256 public keys, and 2^160 (simple) addresses. There are other addresses (multisig) that have more than one corresponding public key and thus more than one ...
Andrey Dzhukov's user avatar
7 votes

How (un)safe is it to use non-random seed words?

There is a lot to unwrap here. I'll go over the points that need addressing, most important first: Don't try to invent your own cryptographic scheme If you read the manual to your wallet, it most ...
Vojtěch Strnad's user avatar
5 votes
Accepted

Is the 'real barrier' to attack bitcoin's consensus 33.34%, rather than 51%?

In this proposed attack, you need more than just hash power. However, if you assume that you can partition the network as this attack imagines, you need no hashing power at all. If I can split the ...
David Schwartz's user avatar
5 votes
Accepted

Can a signed raw transaction's locktime be changed?

A transaction's locktime is part of the data committed to by the transaction's signatures. If you change it, the signatures become invalid, and so the transaction becomes invalid. If the locktime ...
Vojtěch Strnad's user avatar
5 votes

Can a clever hacker still steal everyone's money from the blockchain.info wallet?

They anticipated this type of attack and they are monitoring their JavaScript files, check this website of theirs http://blockchain-status.com/javascript_verifier Also, CloudFlare (the reverse proxy ...
Onur Yapar's user avatar
4 votes

What was the timeline of the Bitcoin Unlimited Hack as of 2017-March and where was it in the code?

The commit implementing the fix was issued Mar 14, 2017, 3:16 PM GMT. A Github release was made at 7:39 PM GMT. It was announced on Reddit at 7:59 PM GMT. The vulnerability was discovered sometime ...
Nick ODell's user avatar
  • 29.4k
4 votes

Am I being hacked, can I prevent it?

You are not being hacked. These are not two separate transactions; it is one transaction with two outputs. The second output was automatically created by your wallet client and sends back to a new ...
Nate Eldredge's user avatar
3 votes

Can malicious peer hack freshly installed bitcoin-core node

Does freshly installed bitcoin-core node have genesis block included in the installation? Yes. This fresh node contacts some peer for downloading blockchain. Can malicious peer give node wrong ...
David Schwartz's user avatar
2 votes

Pictures and non-transaction data in block chain

Yes, it's absolutely still possible; nothing has changed to prevent it. It's not clear how you even could if you wanted to; because of the consensus requirement, you would need some universally ...
Nate Eldredge's user avatar
2 votes

Pictures and non-transaction data in block chain

It is still possible to embed data into the blockchain, and it is actually fairly trivial. But don't do it. It is rude and detrimental to the network as it takes up resources to host your random data ...
Ava Chow's user avatar
  • 70.8k
2 votes

What happens if a network “splits”

The chain would split and when the networks re-connected the longer chain would take precedence. All transactions on the orphaned chain from the time of the split would be invalidated. Good if you ...
sipsorcery's user avatar
2 votes

What's stopping someone from taking over all the bitcoin addresses?

Based on Andrey's 2^160 addresses, I did a thought experiment. Let's say Dr. Evil wants to occupy all the bitcoin addresses, because of something Satoshi once said about his ears. He thinks of using ...
joeytwiddle's user avatar
2 votes

If the nodes are what keep Bitcoin decentralized, what if some big internet company spun up 60%+ majority nodes?

Block verifiers don't manipulate the block chain. What matters is the economical weight of those verifiers, not the number of node processes they run.
Antoine Poinsot's user avatar
2 votes

If the nodes are what keep Bitcoin decentralized, what if some big internet company spun up 60%+ majority nodes?

Each Bitcoin transaction is signed using the private key(s) of the sender(s). The cryptographic signatures both provide authorization of the payments and ensure integrity of the transaction. The ...
Murch's user avatar
  • 75.7k
2 votes

How can someone get my private data (such as email, name, IP ...) from bitcoin transaction?

IP addresses are not private information. As for email and name no one can get that information based on the blockchain data alone unless you go out of your way to publicly associate your identity ...
Abdussamad's user avatar
  • 2,699
1 vote

How (un)safe is it to use non-random seed words?

Very bad idea. Relying on a number that 'seems quite large to me' is insecure. There were several recent cases of brute forcing vanity addresses, or mnemonics that were generated using a insecure ...
OptOut's user avatar
  • 344
1 vote

If the nodes are what keep Bitcoin decentralized, what if some big internet company spun up 60%+ majority nodes?

If the nodes are what keep Bitcoin decentralized, what if some big internet company spun up 60%+ majority nodes? Nothing. There is nothing special about the number of nodes. What’s stopping them ...
David Schwartz's user avatar
1 vote
Accepted

Security of online Electrum wallet after deleting wallet file

Are there any risks that my bitcoin will be stolen if the computer is hacked? Yes. Uninstalling software or deleting files will not remove actual data in disk blocks that have been deallocated. ...
RedGrittyBrick's user avatar
1 vote
Accepted

How Crypto Payment Processors Handle Wallet Balance Privacy?

TL;DR: your question is a valid one; there is no easy solution but CoinJoin and XMR swaps will help. The 3rd party payment processors use wallet that is shared for all customers so this specific ...
CypherpunkDev's user avatar
1 vote
Accepted

What's relationship to each address other in Bitcoin Core?

Is there any relationship to each address? Like based on seedphase? or Just literally making 'random' address? It depends. In old versions of Bitcoin Core, addresses were just randomly generated and ...
Matthew Smith's user avatar
1 vote

Can hackers behind the ransomware WannaCry be traced through bitcoin transactions?

Can hackers behind the ransomware WannaCry be traced through bitcoin transactions? no, if they are smart enough Is there is central server of bitcoin no where all transactions can be looked ...
amaclin's user avatar
  • 6,780
1 vote

How do Blockchain.info recovery mnemonics encrypt wallet data and what prevents hacking of the algorithm?

Edit: Blockchain.info is open source, the algorithm is public. The mnemonic that they use stores information about your wallet id and your password only. Previous answer: You should read into BIP 39 ...
Mark S.'s user avatar
  • 2,730

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