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Questions tagged [security]

This tag should be used for questions regarding security issues with the design or implementation of Bitcoin and related cryptocurrencies.

7
votes
3answers
5k views

How do I know that my bitcoins are real

I have bought some bitcoins off local bitcoins and stored them in an Electra wallet in my computer. Given that I have now paid hard cash, how am I to determine that these are real?
9
votes
2answers
6k views

The length of the Bitcoin's private keys

I read here: In Bitcoin, a private key is usually a 256-bit number ... Although it is a silly question, is this length safe? Based on this site, Elliptic Curve 256 bit keys are safe until 2040. ...
2
votes
1answer
104 views

Is transaction malleability the only consensus issue that needs fix to allow lightning network?

Is transaction malleability the only thing needs fix in the bitcoin consensus code to enable lightning network to be implemented? Of course, lightning network itself would need to be implemented, but ...
4
votes
1answer
261 views

Would quantum computing be able to deanonymize CoinJoin transactions?

Using the worst case scenario of this question, namely: Bitcoin ECDSA algorithm would be broken. Because quantum computers can easily decrypt the private key using the public key, anyone with a ...
1
vote
1answer
98 views

MtGox's secondary market?

I remember back in the day when MtGox halted its BTC withdrawals, someone put together a secondary market exchange for trading MtGoxBTC for actual BTC. You could deposit MtGox BTC to it since the ...
1
vote
1answer
358 views

The randomness of vanitygen is secure enough?

If two people running vanitygen 1abcdefg What is the chance that both of the person will get the same public key & private key? I hope that the answer is less than 0.0000001. But for this ...
1
vote
0answers
41 views

How can I find out if a mining pool has been leaking user information?

To my surprise, I have received spam to an email address which I exclusively used with a mining pool that seems to be generally considered trustworthy and reliable. The spam is bitcoin related and ...
1
vote
1answer
85 views

Noob questions about transfering and offline security

I created a wallet on a USB and one with coinbase. I bought a bunch of bitcoin on coinbase and transferred .01 bitcoin to my USB wallet to make sure I transferred it right before I transfer ...
0
votes
0answers
505 views

Does multibit HD still work offline and is it safe to connect to transfer funds?

I am new to the whole bitcoin situation and have some super noob questions. I watched this tutorial for creating a multibit coin wallet on a USB stick https://www.youtube.com/watch?v=2qmOM567BF4 . I ...
4
votes
1answer
496 views

Lightning network and lightweight clients

How will the lightning network handle lightweight clients? Do I understand it correctly that opening a payment channel require writing on the blockchain to protect against double-spend? The integrity ...
1
vote
1answer
315 views

How do you make a coin resistant to soft forking?

Soft forks are probably worse than hard forks, since it is hard for a client to reject a soft fork (indeed, that is the point of soft forks). The only way to do so is either to gain 51% of the hash ...
11
votes
1answer
1k views

The incident with 92 billion bitcoins

There is a documented case from 2010 when a block with 92 billion bitcoins was discovered. The bug was found and software was patched within 5 hours and everyone had to "hit the load button" to an ...
5
votes
4answers
480 views

Why can malicious miners not award themselves with any number of bitcoins?

Why can malicious miners not award themselves any number of bitcoins? Is that because the award itself is a transaction which has to be confirmed by a random miner? And if so, what if the miner ...
2
votes
2answers
1k views

Why DARPA wants blockchain based secure messaging system

DARPA (US Defense Advanced Research Projects Agency) has released a Request for Proposal for a Secure Messaging Platform using a blockchain framework. The following is the Objective paragraph from ...
8
votes
3answers
470 views

Could cryptocurrency “insurance” slow Bitcoin adoption?

Does the concept of cryptocurrency "insurance" undermine the purpose of "being your own bank"? Recently I have seen more Bitcoin related companies offer some sort of insurance for Bitcoins stored in ...
4
votes
2answers
281 views

Can bitcoin node startup be secure without validating the entire blockchain?

One of the largest hurdles in my mind to increasing the number of full nodes operating is the startup cost related to downloading the blockchain. A similar but less important (in my mind) issue is ...
4
votes
2answers
1k views

Is there a possibility that the whole blockchain system will be DOWN?

I want to know if there is a possibility that all of our hard-earned bitcoins will turn to dust if the Blockchain system will get shut down or stop. Is this possible? I really have a big question mark ...
5
votes
1answer
365 views

Bitcoin safe if ECDSA is broken?

I've read that one reason to use a new address for each transaction is because it hides the pubkey behind a hash, so that even if ECDSA is broken and someone is able to derive my privkey from my ...
2
votes
2answers
234 views

How multi-signature wallets comunicate with each other?

I wonder how multi-signature wallets communicate with each other? My favorite wallet is copay. How do they communicate with each other before payment is done? How is privacy handled between each ...
18
votes
2answers
2k views

What security weaknesses result from using off chain solutions?

What type of security weaknesses are potentially created by using off chain solutions (such as the lightning network) for a portion of Bitcoin network traffic?
2
votes
1answer
472 views

Does the private key have special mathematical properties?

[I read that there are private keys with lengths other than 256 bit. I only talk about 256 bit private keys here. Are other lengths even common and supported by popular wallets like Electrum?] Let's ...
0
votes
1answer
723 views

Double Spend Attack [duplicate]

What's to prevent someone from sending bitcoins back to themselves using the same transaction id before any confirmations? So if I go into a deli and pay with Bitcoin and send those bitcoins back to ...
2
votes
2answers
829 views

can man in the middle change transaction before its broadcast?

i'm very new to bitcoins (started learning it today). i hope i get the question right: i understand when a transaction is created, using my private key i sign the transaction, but i also provide the ...
-1
votes
1answer
204 views

How many confirmations do bitcoin escrow websites wait on average?

To me it seems very dangerous not to wait for 6 confirmations when running an escrow. The scenario I'm thinking of: a miner deposits a large sum of bitcoins the escrow waits for one or two ...
1
vote
4answers
1k views

Trezor Custom Mnemonic

How do I go about using words I pick in a trezor seed? I only want words that I select and in an order I select. I'm not worried about this being a less secure way to generate a seed. I will be doing ...
0
votes
1answer
177 views

Bitcoin adresses seem not to be collision resistant. Please tell me I am wrong [duplicate]

I am trying to understand Bitcoin addresses, but it does not seem to be easy at all. As far as I know, a Transaction uses one or more addresses as input and one or more addresses as output. Is this ...
1
vote
2answers
130 views

Bitcoin adress security questions

I am trying to understand Bitcoin addresses, but it does not seem to be easy at all. As far as I know, a transaction uses one or more addresses as input and one or more addresses as output. Is this ...
6
votes
2answers
447 views

Capturing IP address of transactions submitted to Bitcoin

Dan Kaminsky has pointed out that it would be possible to build a service that tries to infer the source IP address of each Bitcoin transaction. His idea, which he calls Blitcoin, works by ...
1
vote
1answer
74 views

Displaying the bitcoin wallet on the internet

I was wondering, is it a security risk if you display your bitcoin wallet on the internet? Let's say my bitcoin address is 123abc. This is linked to my wallet which stores several bitcoins. It is ...
5
votes
2answers
1k views

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

Blockchain.info claims: We cannot (and don't want to): View your balance View your address book Make transactions on your behalf Confiscate your wallet Lock you into our service. ...
12
votes
2answers
2k views

Who mined the infamous block 364422?

Block 364422 contains a transaction that takes a long time to verify. This transaction design demonstrates a way a denial of service attack could be executed. This prompted Gavin Andresen to propose ...
4
votes
5answers
540 views

How one checks which customer made a payment

One question I'm not able to properly answer when asked is How exactly the blockchain can verify the identity of the user without a centralized trusted party such as VeriSign? I know this is done ...
3
votes
2answers
154 views

Is there any wallet that allows safely storing private keys in an offline computer?

I have a computer that is 100% disconnected from the internet. I'd like to: Generate my own private keys by dice rolls; Import them on the offline computer wallet; Send coins to their addresses; ...
2
votes
2answers
104 views

Should you be able to insure Bitcoin the way banks insure bank accounts?

If insurance for Bitcoin were available for Bitcoin losses what kind of losses would the insurance cover?
2
votes
1answer
692 views

Can we make Sybil attacks virtually impossible?

I suspect that we CAN make them virtually impossible, but that we have not yet done so. We operate on the assumption that computing a private key from the public key is virtually impossible. We also ...
2
votes
1answer
4k views

Is it safe to authorize Coinbase to withdraw cash directly from my bank account?

I wanted to buy Bitcoin. Coinbase said that they could transfer money directly from my U.S. bank account and convert it to Bitcoin, and then I'd have a Bitcoin address and could give people Bitcoin or ...
3
votes
2answers
81 views

Is it computationally feasible to find two transaction IDs with the same first 20 bytes?

Transaction hashes uses sha256, so they are 32 bytes long. If I have to store a very large database of transaction hashes, only for the purpose of checking existence later on, is it really necessary ...
2
votes
2answers
339 views

Can google steal my Bitcoins if I store the private key in Google Keep note

A while ago I put all my addresses with private keys (although they did not have that much money in them) onto a google keep note. I put it on a password protected notepad on my phone now, but could ...
3
votes
6answers
2k views

Why are brain wallets not secure? People keep saying it, but explain to me why?

Everyone keeps saying brain wallets are insecure. Can someone explain to me WHY? What if I had a brain wallet that is 200 characters long which is the concatenation of all of my family members names ...
4
votes
1answer
249 views

Why is a chain code needed for entropy in HD wallets?

In the documents and articles I have read, it is stated that the "chain code" in HD wallets exists to provide entropy to the derivation of child public/private keys. If I understand the process ...
2
votes
3answers
355 views

Could someone solve for your private keys by sending many transactions to the same address?

I've read that it's never safe to use the same bitcoin address more than once because there is a small chance that someone could solve for your private keys (though I don't have a solid-enough ...
6
votes
1answer
1k views

Why can't bitcoin miners modify transaction outputs?

I am learning the Bitcoin protocol by reading the bitcoin developer reference documentation. As far as I know, a raw transaction consists of: Version (which is always 1) Inputs. Each input contains: ...
3
votes
1answer
219 views

What's the maximum possible utxo growth rate now? Can that be turned into an attack?

Now bitcoin unspent transaction output growth rate (not total size) can be, 260k utxo/day (3×60×60×24). With 8MB blocks, that's 2.8 million. Single 1 bitcoin output can be split into 1000 x 1 mBTC ...
3
votes
2answers
111 views

Can contracts programmed in bitcoins be used to scam merchants?

I've been learning a lot about bitcoin over the past couple of weeks because I have some interesting ideas for websites and I would like to accept bitcoin as payment. One of my concerns centers ...
3
votes
1answer
2k views

How to secure my Electrum wallet?

What I did is put a password on word document and put the seed words in there and then put the file in google drive. I can't think of any way I can lose it. I can't think of anyone stealing the money ...
4
votes
1answer
116 views

Would it be wise and extra secure to use non-ascii characters in a brain wallet?

What are some pitfalls if you use non-standard ascii characters in your brainwallet? Say if you were to use asian language characters? Or even extended ascii characters (http://www.theasciicode.com.ar/...
2
votes
1answer
442 views

getnewaddress (RPC) on encrypted bitcoin wallet without wallet password?

Say for example an encrypted wallet has 5000 addresses already pre-generated in the keypool. Can getnewaddress be called via RPC command without knowing the actual wallet password? I envisage a ...
2
votes
1answer
236 views

BIP 38 Implementions for Altcoins?

Trying to identify implementations for creating BIP 38 encrypted private keys for alternative coins to spark collaborative open source discussions to standardize BIP 38 to support altcoins. Please ...
3
votes
2answers
1k views

How do on-line wallet or bitcoin exchanges usually secure their private keys?

I suppose they're kept encrypted as not to do so would be the equivalent as saving plaintext passwords. I heard most of them keep a percentage of the funds in cold storage, but then isn't it ...
8
votes
2answers
537 views

How can importprivkey compromise wallet security when importing a publicly known private key?

A question was asked on reddit over here which I gave a reply: https://www.reddit.com/r/Bitcoin/comments/3khrvm/how_do_i_use_private_keys_to_receive_bitcoin/ However, luke-jr replies with: Don't ...