All Questions
Tagged with z-cash or cryptocurrency
290 questions
61
votes
3
answers
13k
views
Hashing or encrypting twice to increase security?
Over on the bitcoin forums I asked why the bitcoin client computes SHA-256(SHA-256(x)) as its cryptographic hash for a variety of purposes. The leading theory--since the bitcoin author has disappeared-...
- 711
57
votes
4
answers
58k
views
Is secp256r1 more secure than secp256k1?
Curves secp256r1 and secp256k1 are both examples of two elliptic curves used in various asymmetric cryptography.
Googling for these shows most of the top results are Bitcoin related. I've heard the ...
- 1,047
40
votes
2
answers
13k
views
How does hashing twice protect against birthday attacks?
The bitcoin wiki says:
Bitcoin is using two hash iterations (denoted SHA256^2 ie "SHA256 function squared") and the reason for this relates to a partial attack on the smaller but related SHA1 hash. ...
- 503
32
votes
2
answers
3k
views
Prevent double-spending with decentralized digital currencies without all transactions being public?
A recent approach to creating a decentralized online currency, called Bitcoin, has been generating some interest. The goal is to have a way to transfer currency without a central authority and without ...
27
votes
1
answer
10k
views
Why hashing twice?
I'm trying to understand the Bitcoin protocol, and sometimes see instructions like this:
The TransactionId is defined by SHA256(SHA256(txbytes))
or
The hash of the public key is generated by ...
- 373
21
votes
4
answers
2k
views
How secure is the Bitcoin protocol?
Are there any evidence (other than not being cracked so far) that the Bitcoin protocol is secure? "How secure" is it?
(I realize that this might not qualify as a meaningful question - feel free to ...
- 1,047
21
votes
1
answer
986
views
How to provide secure "vanity" bitcoin address service?
Bitcoin addresses are RIPEMD-160 hashes of the public portion of a public/private ECDSA keypair (along with an abbreviated hash of the hash to provide a check code, as @pulpspy notes in a comment). ...
- 580
20
votes
1
answer
6k
views
Will IBM's Condor quantum processor run Shor's Algorithm to crack a 256-bit Elliptic Curve key?
Yesterday IBM announced that they have a 433 bit quantum computer, called Osprey. There is nothing in the press releases I can find that says whether it can or cannot run Shor's Algorithm.
They also ...
- 353
19
votes
2
answers
9k
views
SHA-256: (Probabilistic?) partial preimage possible?
Currently busying myself with the Bitcoin "mining" algorithm, I am wondering if the process really cannot be simplified.
For reference, the algorithm is basically SHA-256d:
$$\mathit{success} := \...
- 312
15
votes
4
answers
16k
views
How to deal with collisions in Bitcoin addresses?
When creating a Bitcoin account, you need to issue a couple of private/public ECDSA keys. Then, you derive your account address by taking a 160-bit hash (through SHA-256 and RIPEMD) of the public key ...
- 605
14
votes
1
answer
5k
views
Why "1" in 51% attack on Blockchain network
In many sources, included Wikipedia, we read:
Any pool that achieves 51% hashing power can effectively overturn network transactions, resulting in double-spending.
My question is: Why do we talk ...
- 243
13
votes
2
answers
8k
views
Does secp256k1 have any known weaknesses?
I am wondering whether there are any properties of the curve which would technically make it easier to attack than any other curves of 256 bits in size.
I have heard that being a Koblitz curve, it ...
- 245
11
votes
3
answers
6k
views
Is double SHA-256 the best choice for Bitcoin?
So I was just curious.
I really look up to Blockchain technology and I have read that Bitcoin uses double SHA-256 for hashing.
( from what I understood, double sha256 is essentially $\operatorname{SHA-...
11
votes
1
answer
1k
views
HD (Hierarchical Deterministic) Keys using Safe Curves?
Bitcoin's HD (Hierarchical Deterministic) Keys as described in BIP32 allow for a master key to be created (a private key and a chain code) such that a tree of both public and private keys can be ...
10
votes
3
answers
928
views
Bitcoin Research
I have recently been assigned to advise a student on a senior thesis in math. She has taken linear algebra, introductory real analysis, basic cryptography, and abstract algebra. Her interest is in ...
- 227
10
votes
3
answers
3k
views
Why don't crypto-currencies use the Lamport signature scheme?
The Lamport signature scheme is faster, less complex and considerably safer than ECDSA. It's only downside - being only usable once - isn't really a downside when signing transactions, since you could ...
- 1,365
10
votes
1
answer
224
views
A general definition for cryptocurrencies
I am trying to find the definitions to several terms related to digital currencies. Unfortunately, I am always ending up on Bitcoin-oriented pages and websites which only take Bitcoin itself into ...
- 605
9
votes
2
answers
895
views
Is there a guarantee that for each possible hash y there exists a number x such that with hash function H, H(x) = y?
Specifically talking about SHA-256 here and its involvement in Bitcoin, this was a question someone asked me which I didn't know the answer to. Yes, I am aware that SHA-256 can only have a hash from $...
- 93
9
votes
1
answer
2k
views
Simple digital signature example that one could compute without a computer?
I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms.
There is a great question ...
- 207
8
votes
1
answer
467
views
What are the characteristics of a quantum secure protocol?
What are the characteristics of quantum secure protocol, and does it always need to be information theoretic to be called as quantum secure? Are the current techniques used in bitcoins quantum secure?
- 563
8
votes
1
answer
3k
views
How can uniformity of hash functions (e.g. SHA-256) be proved?
In reading about the Bitcoin protocol I noticed how much its proofs-of-work apparently depend on uniformity of the SHA-256 hash function. And so presumably do many other applications.
How do ...
- 243
8
votes
1
answer
689
views
Is the 'nonce' in bitcoin really a nonce?
Is the 'nonce' in bitcoin really a nonce? Reading definitions of nonce and salt it seems the number is used as a salt but the same value can occur in multiple blocks; there's no requirement or indeed ...
- 81
7
votes
1
answer
2k
views
Elliptic curve cryptography related key attacks [closed]
This question is an extension of Families of public/private keys in elliptic curve cryptography
As described above, bitcoin "type 2" deterministic wallets use a root private/public key pair, where ...
- 95
6
votes
2
answers
191
views
Is there a signature scheme which doesn't rely on the difficulty of factoring/dlp which generates short signatures?
The Lamport signature scheme, for example, doesn't rely on the difficulty of any problem and it only depends on the existence of one-way functions.
Is there an alternative scheme which also doesn't ...
- 1,365
6
votes
2
answers
355
views
Ways to make a "doomsday" cryptocurrency which becomes untradable
As a social experiment (not a money-making scheme), I'm interested in developing a crazy cryptocurrency which, by its very design, will become worthless and untradable after a certain point. Ideally, ...
- 61
6
votes
3
answers
1k
views
How are objects sold as NFT's ("non-fungible tokens")?
I'm familiar with "blockchain" and the theory and technology behind cryptocurrencies, tokens, and the economics behind why such things are capable of having monetary value, however I've ...
- 163
6
votes
1
answer
1k
views
Any use for now-defunct Mt Gox Yubikey? [closed]
As everyone is now aware, Mt Gox has declared bankruptcy. As what appears to be the very last thing they did, Mt Gox accepted my $35 and fulfilled my special Mt Gox Yubikey. Having just arrived in the ...
- 61
6
votes
1
answer
864
views
Can a digital money system exist, that's secure, anonymous and allows offline transactions?
I just read Offline anonymous electronic money systems and their cryptographical base , which asks for anonymous offline systems. The OP claims eCash is such a system, and the answer claims that ...
- 25.1k
6
votes
1
answer
3k
views
How are new coins minted in Proof of Stake systems
I've been trying to understand Proof Of Stake cryptocurrency systems, but I don't see how new coins are made using the Proof Of Stake system.
My current understanding of Proof Of Stake
People put up ...
- 191
5
votes
1
answer
2k
views
In Bitcoin, given half the 52-character private key in WIF format, is it possible to reconstruct the whole private key?
Given the following two preconditions:
It is almost impossible to reconstruct a bitcoin private key if an attacker only has one half of the private key as well as the public key.
It is almost ...
- 151
5
votes
3
answers
18k
views
How can i check if a public key match with a private key
Is there a way to check, (with openssl command for example), if a given public key match with a private key ?
Thanks
- 151
5
votes
1
answer
891
views
Is there a flaw in this ECC blind signature scheme?
Recently I've found the following work on the internet: An ECC-Based Blind Signature Scheme
The paper claims to be an ECDSA blind signature however it seems that their scheme has a flaw in it.
The ...
- 185
4
votes
3
answers
1k
views
Why do people criticize and mistrust the e-voting based block chain?
I am planning to implement an e-voting system based on hyperledger fabric blockchain, however, I came across many criticisms from well-known security experts like Josh Benaloh and others. The problem ...
- 65
4
votes
2
answers
2k
views
Modulo p in Elliptic Curve Cryptography
To carry out Elliptic Curve Cryptography between parties, are all elliptic curve equations considered to be in the form $\bmod p$?
For example, the $secp256k1$ Bitcoin curve of the equation $y^2=x^3+7$...
- 43
4
votes
2
answers
19k
views
How insecure is AES-128-CTR to encrypt any kind of data using the Ethereum keystore file format?
I am using the Ethereum keystore file format to encrypt any other data such a plain text or JSON.
Here is an example of pseudocode of the implementation:
...
- 151
4
votes
3
answers
498
views
Why won't a BFT protocol using simple signing/voting work?
PBFT and most consensus algorithms are more complicated than a simple voting scheme. By simple voting I mean the following: we require all nodes to sign their local copy of the state and send this ...
- 101
4
votes
1
answer
590
views
Can keys from Bitcoin's Hierarchical Deterministic Wallets be correlated (reducing privacy)?
I'm trying to understand if the feature "Hierarchical Deterministic Wallets" in Bitcoin allows for complete privacy of all derived keys, and if any of those keys can be associated with each other ...
- 2,631
4
votes
1
answer
242
views
ECDSA (ecrecover) - How an attacker can construct a hash and signature that look valid
I found information, that it is possible to construct a hash and signature that look valid if the hash is not computed within the contract itself (we are talking about ECDSA/ecrecover here).
So, the ...
- 143
4
votes
1
answer
1k
views
SECP256K1 Jacobian algorithms
I am working on a bitcoin related project and I am trying to speedup the ecc calculation. I started with double-and-add and sliding window.
I would like to go move over to the jacobian coordinates. ...
- 395
4
votes
1
answer
131
views
Time locked cryptography using Bitcoin difficulty param and/or smart contract?
Outcome: Create a message with a count down timer. Once a top level password is entered, a countdown timer starts. Once timer expires, the message is decrypted.
Known methods: Proof of work. ...
- 151
4
votes
1
answer
351
views
Could the multisignature scheme in bitcoin alternatively also be implemented by means of a Shamir Secret Sharing Scheme?
When I first came across the Bitcoin multisignature scheme, I wondered that it remarkably looked similar to what Shamir Secret Sharing does (SSS), but then by using facilities in the bitcoin scripting ...
- 111
4
votes
1
answer
135
views
Is there any serious discussion about using blinding intermediaries in digital currency scenarios?
A digital currency system like Lucre (OpenTransaction) creates a coin by a mint blind signing the output of a hash function, which the payer then unblinds and pairs with the input to the has function.
...
- 1,136
4
votes
1
answer
212
views
Can you elaborate on pBFT for dBFT in relation to PoW and PoS consensus algorithms in layman's terms?
I've read all other related answers and googled this extensively. My intention and background in asking this question is that I am delving into cryptocurrency and blockchain technology in general. ...
- 41
4
votes
1
answer
289
views
Post-quantum aggregate / multi signatures
Are there any practical post-quantum aggregate / multi signatures?
Currently, the aggregate / multi signature schemes seem to be limited to pre-quantum elliptic curve assumptions only, e.g., [BDN18], [...
- 438
4
votes
3
answers
2k
views
What's the difference between a hash chain, transaction chain and a blockchain?
Can anyone explain to me what the difference is between a hash chain, transaction chain and a blockchain?
- 41
4
votes
1
answer
399
views
Complexity class of an idealised version of Bitcoin's proof-of-work (hashcash)? [closed]
To formulate this question precisely, I will define an idealized hypothetical "perfect" hash function $H(n)$ which has nice scalability properties, and will formulate a problem PERFECT HASHCASH in ...
- 149
3
votes
1
answer
1k
views
Has a SHA256 output ever been found consisting entirely of the same character?
Is it possible to have an output consisting purely of one character and does this change the entropy of that output? (If that's even possible to ascertain.)
As an example, the Bitcoin cryptocurrency ...
- 149
3
votes
2
answers
3k
views
Would SHA-256(SHA-256(x)) produce collisions?
Was reviewing some Bitcoin public-key hash literature and the use of RIPEMD-160 and the SHA-256 as below:
RIPEMD160(SHA256(ECDSA_publicKey))
The Proof-of-work ...
3
votes
2
answers
2k
views
Can you tell me why doing scalar multiplication of a point on a Elliptic curve over a finite field gets to a point at infinity?
I am reading Programming Bitcoin. The author said:
Another property of scalar multiplication is that at a certain multiple, we get to the point at infinity (remember, the point at infinity is the ...
- 139
3
votes
1
answer
748
views
Is AES a group?
The question I'm wondering is whether the AES cipher is a closed cipher (which is equivalent to AES being a group). And this question interests me due to the lack of understanding of whether it is ...
- 53