All Questions
Tagged with cryptocurrency sha-256
22 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
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
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
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
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-...
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
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
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
3
answers
2k
views
Question regarding multiple SHA-256 rounds on a Bitcoin Brain Wallet passphrase…
I am attempting to come up with a way of memorizing a seed that could lead to any number of brain wallets for bitcoin. I need multiple wallets because a) I don't want all my eggs in one basket, and b)...
- 33
2
votes
1
answer
1k
views
How difficult is it to crack sha256(sha256(pin)) with a 6 digit pin and no salt?
My friend forgot the password to his electrum wallet but knows that it's a 6 digit pin. I looked into it and from what I can find electrum uses the sha256(sha256(pin)) to generate the key used to ...
- 41
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 ...
2
votes
1
answer
457
views
Hash function and Digital Encryption Algorithm
I am familiar with the fundamentals of cryptography as well as Digital Signatures. I understand how DSA like RSA works and the fundamentals of mathematics behind digital signing and verification. I ...
- 21
2
votes
1
answer
458
views
Sane implementations of Bitcoin cryptography routines w.r.t. side-channel attacks
Bitcoin uses SHA-256, Base58Check, ECDSA (Sep256k1) and RIPEMD-160 as the basis of its encryption (see this article for a short guide on how addresses are created).
I would like to create an iOS-...
- 131
1
vote
1
answer
255
views
Is this simple Proof of Work algorithm based on SHA256 susceptible to length extension attack?
Each block's contents are hashed into 32 bytes using $\operatorname{SHA-256}$ (call this string $a$). In order for the block to be accepted, there must be a 256bit nonce (call this string $b$) ...
- 123
1
vote
1
answer
383
views
Near preimages, applicable to Bitcoin?
Bitcoin mining relies on generating a smaller hash than the so-called target (a function of the so-called difficultly), thus is vulnerable to a truncated preimage attack (you just need to obtain a ...
- 711
0
votes
2
answers
2k
views
Probability last character sha256 hash
A quick question. I want to use the last character of a SHA256 hash (blockhash of a bitcoin block) as my random source. Is 100 /16(amount of different chars) = 6.25% true for all characters or are ...
- 3
0
votes
1
answer
788
views
Bitcoin mining nonce and birthday attack
Having read the basics of mining and this about SHA256 (probabilistic?) partial preimage possible? and SAT solving - An alternative to brute force bitcoin mining, I have the following question:
...
- 103
0
votes
0
answers
44
views
i want to verify the following p2pkh transaction
I know to veify the p2pkh transaction we have to place the unlocking script and locking script in a stack and than evalute the stack. In such cases the the scriptpubkey_asm is of the form <OP_DUP ...
- 1
-1
votes
1
answer
982
views
Is it possible for a hash in SHA-256 to have more than 8 digits? [closed]
Is it ever possible for a hash to have more than 8 digits in SHA-256?
user69001
-1
votes
1
answer
263
views
How to pad in the SHA256 Algorithm (an example using Bitcoin Header)?
For any bitcoin block we combine various Header fields to create a string which is an input to a 2 pass SHA algorithm. The resultant hash must match with the Hash in the Block header for the Block to ...
- 151