Questions tagged [cryptocurrency]

A cryptocurrency is a digital currency powered by cryptography. This tag is applicable only to Q&As about the CRYPTOGRAPHIC MECHANISMS used by a currency, not for questions about economy, usage, or acquisition of any particular currency. The latter kinds are unwelcome. Please note that Stackexchange has dedicated websites for Bitcoin, Ethereum, Monero, etc.

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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 ...
inherithandle's user avatar
10 votes
3 answers
5k 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-...
Pinkovai Krisztian's user avatar
8 votes
1 answer
2k 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 ...
Drux's user avatar
  • 243
60 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-...
maaku's user avatar
  • 701
1 vote
5 answers
4k views

Optimized modular multiplicative inverse for Bitcoin (secp256k1)

I have written an application to brute-force attack Bitcoin addresses for OpenCL. It implements a simple exhaustive search starting from public key G (private key 1) and point increment (addition of G)...
user3368561's user avatar
55 votes
4 answers
55k 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 ...
ripper234's user avatar
  • 1,027
18 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} := \...
JimmyB's user avatar
  • 302
19 votes
1 answer
5k 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 ...
Simon G.'s user avatar
  • 343
13 votes
2 answers
6k 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 ...
Matt's user avatar
  • 245
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 ...
user2006's user avatar
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 ...
Wingsuit's user avatar
  • 149
3 votes
1 answer
1k views

ECC partially blind signature scheme verification

Continued from Is there a flaw in this ECC blind signature scheme? The problem I needed a partially blind signature scheme for one of my projects, but couldn't find one on the internet, so I've made ...
Lu4's user avatar
  • 185
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 ...
Gopalakrishna Palem's user avatar
-2 votes
2 answers
906 views

How to find at least one private key from a large list of compressed public keys secp256k1

Not long ago I saw a discussion on the Bitcoin Talk forum: https://bitcointalk.org/index.php?topic=5060735.msg50736695#msg50736695 Please give advice and working methods? Is it possible to find at ...
BojarSONY's user avatar
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 ...
Christopher Allen's user avatar
9 votes
2 answers
798 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 $...
Styil's user avatar
  • 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 ...
Bob van Luijt's user avatar
6 votes
1 answer
851 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 ...
CodesInChaos's user avatar
  • 24.8k
5 votes
1 answer
866 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 ...
Lu4's user avatar
  • 185
4 votes
3 answers
14k 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
Bob5421's user avatar
  • 141
4 votes
1 answer
576 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 ...
makerofthings7's user avatar
4 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 ...
Ohumeronen's user avatar
3 votes
1 answer
800 views

Is it possible to combine digital signature to provide message addition?

Let's assume we are using the textbook RSA where $Sig(x)=x^d$. Alice has public key $(e,N)$, and private key $(d,p,q)$. Now, if Alice sends $Sig(5)$ and $Sig(10)$ to Bob, where $5$ and $10$ is just ...
NuminousName's user avatar
3 votes
2 answers
390 views

Cryptocurrency for quantum computers that is physically impossible to double-spend?

Could a cryptocurrency running (at least partially) on a quantum computer (and/or on a quantum network) be developed in which it is physically impossible to double-spend? In other words, a coin in ...
user1226313's user avatar
2 votes
0 answers
257 views

Are digital signatures a type of zero-knowledge proof?

Are the digital signatures used in cryptocurrencies such as Bitcoin a type of zero-knowledge proof?
CHONG ZHAO XIAN's user avatar
2 votes
1 answer
173 views

How to implement a "viewing key" for secrets proved by zero knowledge proofs?

In ZCash, Monero etc, the sender/receiver addresses as well as transaction details are hidden. However, with a viewing key, a third party can see the exact details of the transaction or all ...
toga's user avatar
  • 21
2 votes
1 answer
453 views

How Secure Is Splitting A Bitcoin Private Key?

NOTE: This question cannot be posted to Bitcoin SE because it will not render there due to the mathematical notation. Since the mathematical notation is part of the question, this is the more ...
Crypto L Plate's user avatar
2 votes
1 answer
3k views

Can someone give me an example of a Merkle–Damgård transformation?

I started reading "Bitcoin and Cryptocurrency Technologies - Princeton University" (coursera) and in the first chapter it talks about Merkle–Damgård transformations for SHA-256. I was trying to ...
Edward Mordechay's user avatar
2 votes
1 answer
1k views

Offline anonymous electronic money systems and their cryptographical base

What anonymous offline electronic money systems exist and what are they based on? I know only one currently - eCash, based on RSA blind signatures.
Vladislav Rastrusny's user avatar
1 vote
2 answers
386 views

How does this formula work $(aG + bG) = (a + b) G$ in ECDSA?

Please explain how does this formula $(aG + bG) = (a + b) G$ work in ECDSA? According to the source: $a$ and $b$ are different private keys Suppose $a = 3$ $b = 4$ then the public key is $Q = aG$...
Rozwrcd's user avatar
  • 19
1 vote
1 answer
2k views

anonymous signature implementation and usage?

This is one of the question asked in my class. Implement a anonymous digital signature. So it means hiding signers information. i could not find any article in anonymous digital signing. Also another ...
Bruce's user avatar
  • 111