Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [sha-2]

SHA-2 is a family of cryptographic hash functions designed by the NSA and published by NIST in 2001. The family includes various output lengths (224, 256, 384, and 512 bits).

SHA-2 is a family of cryptographic hash functions , the de facto standard for current developments. It was originally published by NIST in 2001. It is based on a construction. It is replacing the older SHA-1 hash function and the even older MD5 .

The family comprises 6 functions with different output lengths.

  • SHA-256 and SHA-512 are the most commonly used hash functions. Their internal state and output size are both 256 for SHA-256 and both 512 for SHA-512. The algorithms are similar, but SHA-256 is expressed in terms of computations on 32-bit words while SHA-512 uses 64-bit words. SHA-512 has more rounds (80) than SHA-256 (64).
  • SHA-224 and SHA-384 are very similar to SHA-256 and SHA-512 respectively, but with output truncated to a smaller size, and different constants.
  • SHA-512/224 and SHA-512/256 (added in 2012) are truncated versions of SHA-512, also with different constants.

In 2012, NIST selected proposal for a SHA-3 algorithm. Although SHA-3 was initially intended as a replacement for SHA-2, it is now planned that SHA-2 and SHA-3 will coexist.

External links

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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…
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Are there any known collisions for the SHA (1 & 2) family of hash functions?

Are there any known collisions for the hash functions SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512? By that, I mean are there known values of $a$ and $b$ where $F(a) = F(b)$ and $a ≠ b$?
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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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Are common cryptographic hashes bijective when hashing a single block of the same size as the output?

It's been said that CRC-64 is bijective for a 64-bit block. It the corresponding statement true for typical cryptographic hashes, like MD5, SHA-1, SHA-2 or SHA-3? For example, would SHA-512 be bijective when hashing a single 512 bit block?
SDL
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Assuming a 1024qb quantum computer, how long to brute force 1024bit RSA, 256bit AES and 512bit SHA512

Assuming in the future there was a functioning 1024 qubit quantum supercomputer and it could run Shor's algorithm or Grover's algorithm to crack encryption very quickly. I'm interested in how the number of qubits translates to performance…
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How are the functions used in cryptographic hash functions chosen?

I'm learning about cryptographic hash functions and I have some questions about the functions used in the compression function. MD5 uses the following functions: $f_{1}(B,C,D)=(B\wedge C)\lor(D\wedge \lnot B)$ $f_{2}(B,C,D)=(B\wedge…
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Is calculating a hash code for a large file in parallel less secure than doing it sequentially?

I would like to improve the performance of hashing large files, say for example in the tens of gigabytes in size. Normally, you sequentially hash the bytes of the files using a hash function (say, for example SHA-256, although I will most likely use…
Michael Goldshteyn
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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 performing a SHA256 hash on the public key, and then…
Timur Lemeshko
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What's the difference between PBKDF and SHA and why use them together?

I've been reading a little bit about hashing lately and according to AgileBits, they use "SHA512 within PBKDF2" in their new vault file. I've looked in Wikipedia for both names and I know PBKDF2 is a key derivation function and SHA is a…
Danowsky
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Why does the padding in Merkle–Damgård hash functions like MD5 contain the message length?

I understand the need for padding in MD5 and other hash algorithms such as SHA-1, SHA-256, SHA-384 and SHA-512. But why do we append the message length to the padding? I heard it strengthens the hash but how? Please provide an example if possible…
Ibrahim Najjar
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Are there any well-known examples of SHA-256 collisions?

The popularity of SHA-256 as a hashing algorithm, along with the fact that it has 2256 buckets to choose from leads me to believe that collisions do exist but are quite rare. Are there any well-documented SHA-256 collisions? Or any well-known…
Ari Sweedler
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Does SHA-1024 hash exist?

Does SHA-1024 cryptographic hash function exist similarly to SHA-512? If not, what's the reason for that? Links: SHA-2 at Wikipedia SHA-3 at Wikipedia
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Does the SHA hash function always generate a fixed length hash?

I'm using the SHA1/2 family of algorithms for a particular project. I was wondering if all the SHA algorithms return a fixed length hash regardless of the length of the data.
Robin Rodricks
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Is SHA-256 secure as a CTR block cipher?

Generate a 256-bit random nonce. XOR it with a 256-bit reusable symmetric key. This is x. We represent numbers in simple binary instead of a counting function. 0 in dec = [256 zeros] in binary, 1 = [255 zeros]1, 23092348 = [241…
Jordan
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SHA-224 Purpose

One of the new features of Java 8 is the SHA-224 message digest. What is the use case for having a 224-bit-length hash?
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