Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [sha-256]

SHA-256 is part of the SHA-2 family of hash functions with a 256-bit output and a 128-bit security level.

SHA-256 is one of the algorithms in the SHA-2 family of cryptographic hash functions defined by NIST. It processes the input in 512-bit block and has a 256-bit output, for a 128-bit security level. It is defined in terms of operations on 32-bit words.

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Why haven't any SHA-256 collisions been found yet?

I've been thinking about this for a few days, a SHA-256 algorithm outputs 64 characters which can either be a lowercase letter or a number from 0-9. Which should mean that there are 64^36 distinct SHA-256 results. How has a collision never been…
ninesalt
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Has SHA256 been broken by Treadwell Stanton DuPont?

In a recent press release issued by Treadwell Stanton DuPont, the claim is made that their research laboratories have successfully broken all 64 rounds of the SHA256 hashing algorithm. They further claim that they achieved this milestone a year ago…
Gary
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SHA-512 faster than SHA-256?

I'm getting this strange result that SHA-512 is around 50% faster than SHA-256. I'm using .net's SHA512Managed and SHA256Managed classes. The code is similar to the one posted here but I'm referring to tests taking caching into account (from the…
ispiro
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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--seems to be that from a security standpoint it…
maaku
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"SHA-256" vs "any 256 bits of SHA-512", which is more secure?

In terms of security strength, Is there any difference in using the SHA-256 algorithm vs using any random 256 bits of the output of the SHA-512 algorithm? Similarly, what is the security difference between using SHA-224 and using any random 224 bits…
Pacerier
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How do hashes really ensure uniqueness?

This might seem an impractical and unnecessary conversation, but I feel it's something I need to clarify. Especially, as I just got my first developer job in a blockchain startup. So hashes are said to generate the same thing for any information it…
James Kumar
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What is the difference between SHA-3 and SHA-256?

I am new about cryptography, I learned that SHA-3 (Secure Hash Algorithm 3) is the latest member of the Secure Hash Algorithm family of standards, released by NIST. But I recently saw SHA-256 but I don't get what is it in comparison to SHA-3 ?
Ced
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Cryptography algorithms that take longer to solve on a GPU than a CPU

I know that Graphics cards are faster at solving algorithms like SHA-256 because of the many builtin processors, but are there Algorithms that take actually longer on a Graphics card than on a modern consumer CPU (Amd/intel)?
user51749
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Best way to reduce chance of hash collisions: Multiple hashes, or larger hash?

I would like to maintain a list of unique data blocks (up to 1MiB in size), using the SHA-256 hash of the block as the key in the index. Obviously there is a chance of hash collisions, so what is the best way of reducing that risk? If I also…
Theodor Kleynhans
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How can hashes be unique if they are limited in number?

I'm curious, how can for example SHA-256 be unique if there are only a limited number of them?! For clarification: how many MD5 hashes are there? $16^{32}$ MD5 hashes can be produced. $16^{64}$ SHA-256 hashes can be produced. while there are…
M D P
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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. SHA1's resistance to birthday attacks has been…
4nt
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HMAC-SHA1 vs HMAC-SHA256

I have three questions: Would you use HMAC-SHA1 or HMAC-SHA256 for message authentication? How much HMAC-SHA256 is slower than HMAC-SHA1? Are the security improvements of SHA256 (over SHA1) enough to justify its usage?
Mario
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Should I use the first or last bits from a SHA-256 hash?

I have the need for a hexadecimal token that is smaller than the normal length of the hexadecimal representation of a SHA-256 hash. Should I take the first bits or the last bits? Which of them contain the most entropy?
Peter Smit
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Key size for HMAC-SHA256

After reading a bunch of past stack exchange posts like this one and RFCs 5869, 2104, and 4868 I felt comfortable that a 32-byte key was sufficient for HMAC-SHA256. However, I am implementing my code in C# and someone pointed out to me that the…
Ralph P
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Fixed point of the SHA-256 compression function

SHA256 Free Start Self Collision (Full 64 rounds) IVec: 72BF9EF1 27B82DFB F298F3B7 22B6C32C 18A54860 4C032D91 ADD7B85B 7ED1A4AC Block: 0000004D 0000006F 00000075 00000073 00000065 00000054 00000072 00000061 00000070 00000000 00000000 00000000…
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