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).

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Change initial hash value of SHA512/t

Fips 180-4 defines under 5.3.6 how to calculate initial hash values for SHA512/t for a given value t. Can someone explain me how the t actually affects the outcome of the procedure (which, as far as I ...
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56 views

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 ...
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56 views

How are the IVs of SHA512/256 and SHA512/224 calculated?

This seems odd to me, because there are a lot of resources out there saying that the initializer values of SHA512 and SHA384 are the first 64 bits of the fractional parts of the square roots of prime ...
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81 views

Is Schannel supposed to use SHA1 for (EC)DHE params?

I captured a TLS 1.2 handshake on my server (WIN2012.R2/IIS 8.5) and noticed that SHA1 is being used to hash ECDHE parameters despite both the server and client(s) supporting SHA2 signatures. ...
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22 views

Randomness and reversibility of a sequence generated by taking sha256 hashes of an predictably-changing input?

Let's say we generate a sentence in a way like for example this: Fix an initial seed. Attach '1' at the end of the seed and compute sha256 of such a string. This hash is our first number. Now attach 2 ...
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240 views

Can the SHA256 hashes of consecutive integers be attacked?

Suppose that the attacker knows the SHA256 values of integers $n, n+1, n+2 ... n+k$. $n$ is sufficiently big, so we do not expect to be able to brute force $n$ just by $\operatorname{SHA256}(n)$ ...
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83 views

“Security” of SHA functions (Wikipedia), what does it mean?

Wikepedia's table Comparison of SHA functions mentions "Security(bits)" for some SHA functions. From the ratio (Output size (bits): Security(bits)), I feel it is something like "collision resistance". ...
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61 views

Difficulty to find any preimages $a$ and $b$ for given $V$ so that $H(a) \oplus H(b) = V$?

Suppose I have the values $a$, $b$, and $V = H(a) \oplus H(b)$ with inputs $a \neq b$ and $H$ being SHA-224. None of these values are a secret. How secure is it to assume that no other possible values ...
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253 views

What is the difference between SHA-3(Keccak) and previous generation SHA algorithms?

SHA-1 and SHA-2 share the same structure and mathematical operation as their predecessors - SHA-0 and MD5. Both SHA-0 and MD5 have been broken. This is one of the main reasons why SHA-1 is considered ...
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688 views

Which bitwise operations are used in SHA-256?

From the wikipedia entry on SHA-256 I'm a bit confused about which operations actually go into the algorithm. From the pseudo code it appears the operations are $\texttt{xor}$, $\texttt{and}$, rotate, ...
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117 views

Transforming SHA-512 into SHA-512/256?

Based on my skimming over FIPS 180-4 it looks like the only difference between SHA-512 and SHA-512/256 is the initial hash value and the fact that the final output is truncated to 256 bits. My ...
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108 views

Would SHA-1 be safe for certificates with short validity?

There are articles floating around the topic of SHA-1 deprecation. The gist of it is that in (mostly) developing countries, people are still using mobile/computing devices that are 5 years old (or ...
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99 views

Unconditionally Secure Authentication

I'm trying to add the authentication for my One-Time Pad implementation. I know that to provide Unconditionally Secure Authentication I need to use the One-Time MAC authentication. But I don't ...
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2answers
573 views

Algorithm for generating OAuth tokens

I'm trying to find a good algorithm for generating authorization codes, access tokens and refresh tokens in an API. Currently, I am looking into the following setup: Tokens are generated using the <...
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394 views

Is base64 the best two-way hash function to encrypt and trasmit a set of integer numbers via Internet?

I am writing a mobile game and I need to save my game data on my game server, So crackers can not find and access the saved files(data) on their mobile, the game data can be expressed by numbers, So, ...
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146 views

SHA512 vs HKDF key expansion

I'm working on a secure file storage server. This server allows users to upload and download files based on a "seed". This "seed" is a 128-bit value. From this 128-bit seed, we run SHA512 to derive a ...
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122 views

Same 64-bit preimage resistance security for SipHash and SHA-512/64?

If I have to chose a 64 bit preimage resistant hash function; will there be any difference in security between SipHash and SHA-512/64 (SHA-512 truncated to 64 bits)? How long will it take an ...
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104 views

Is modular Barrett reduction usable for Ed25519?

I currently try to implement Ed25519 following this draft. I have implemented every field operation except the reduction by the group order $q$ (in chapter 5). I looked for a reduction algorithm and ...
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129 views

How can I generate a good password from a SHA512 hash?

I have to change local administrator passwords on machines. I don't want to store password in a database. I have to generate a password that I can find later to connect to the machine again. So I ...
2
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1answer
82 views

Is “Bit Independence” of SHA-2 hashes secure?

I know bit independence is good in SHA2 function output, but is it truly 100% secure? For example: Y = SHA512(secretKeyNonce256bit) A = first 32ytes / 256bits of Y, used as message encryption key B ...
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134 views

Rationale for use of right-shift (rather than rotate) in SHA-2?

The SHA-2 hashes in FIPS 180 define $\Sigma$ and $\sigma$ bijections of words, with $\Sigma$ used in the round function, and $\sigma$ used in preparing 48 words of message schedule from 16 words of a ...
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342 views

What makes SHA-2 and SHA-3 have security levels half their output hash length?

The tag wiki for sha-256 says, in part: SHA-256 ... processes the input in 512-bit block and has a 256-bit output, for a 128-bit security level. I'm not a cryptographer, just an interested ...
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158 views

What is SHA-256 in Conjunctive Normal Form?

What is the conjunctive normal form (CNF) representation of $\text{SHA-256}(m)=h$, where $m$ is of fixed (or bounded) size and $h$ is 256 bit?
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870 views

What is the best hash for HMAC?

Long question but I am starting to lose sight of all the HASH algo's there are. I know SHAKE128 and 256 are part of the SHA-3 standard but is the SHA3 standard officially released yet? i can only ...
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2k views

What is the length field in SHA-512 padding?

If I am using SHA-512 on a message and need to determine the padding field and length field, how do I determine the length field? I think I understand the padding, but not the length field. For ...
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169 views

FIPS-Compliant SHA2

I want to use SHA-512 for hashing in a system that must be FIPS-compliant. When I look at the FIPS 140 list of approved providers, I don't see SHA from any provider as being an approved algorithm, I ...
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65 views

what does rsaSha512Sign do?

I have the following function: ...
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3k views

SHA1 no longer considered secure for SSL Certificates — what about Cipher Suites?

Many browsers and Internet companies have recently claimed that SSL Certificates with a signature algorithm of SHA1 will imminently no longer be considered secure. Most notably, Google and Google ...
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3k views

Is SHA related to AES or TLS in any way

I have been reading about SHA-2 family and I found a lot of in depth details, but I am confused about how it is related to TLS and AES. TLS encrypts data between server and client, but does it make ...
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176 views

Is hashing a list of hashes safe?

I have an arbitrary long list of hashes (e.g. git tree hashes), and I'm wondering by how much I am increasing the risk of hash collisions by condensing them into a single hash, like so: ...
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5k views

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
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289 views

Where do I truncate the bits in SHA 256 hash algorithm?

I'm implementing SHA-256 in PHP using strings. Where do you truncate in the algorithm? There are a lot of places where there's binary addition happening so the number of bits in $W(i)$ keep ...
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492 views

Encryption and HMAC key derivation

I'm deriving keys from a user-supplied passphrase for symmetric encryption using AES-256 in CBC mode with a HMAC for authenticity/integrity. My key derivation function currently looks like this: ...
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614 views

Understanding how SHA-512 achieves its design goals

The Wikipedia entry on SHA-2 contains a usable pseudocode recipe. In the hope of some deeper understanding, I implemented SHA-256 and SHA-512 from it. This was helpful, but I still don't think I have ...
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85 views

Does displaying HMAC hashes of user inputs compromise the HMAC validation?

Here is the scenario: "SECRET" is a secret key that is kept private and only used in this one application. The application allows users to enter in any "VALUE" (within various open-ended limits such ...
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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 ...
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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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83 views

Using cryptographic hash to match AES key size

I am making a tool for myself where I intend to store cipher text. I wish to use AES together with arbitrary sized keys to create these cipher text strings. The idea is to use a cryptographic hash ...
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675 views

Why are the initial states of hashes functions (like SHA-1) often non-zero?

There is already a question asking "Why initialize SHA1 with specific buffer?" and my question follows on from this: Why are the initial states of hash functions often non-zero? For most, I have ...
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Timing Attacks on ECDSA, ECDHE, AES and SHA2

Are there any known timing attacks (both practical and theoretical) on any implementations of the following? ECDSA (I'm aware of this one - are there any applicable to prime fields?), ECDHE (again, ...
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12k views

Decrypting the password from SHA-512 hash value

I am currently studying AES algorithm and writing a Code using Python. I am trying to add 'Salt' into the user input password, Here is what I am doing, ...
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2k views

HMAC-SHA1 input size

I know that the HMAC is a message authentication code that uses a cryptographic key in conjunction with a hash function (SHA1 , MD5, etc.). The HMAC output is 160 bits for HMAC-SHA160 and 256 bits for ...
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4k views

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 ...
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1answer
981 views

Digital Signature size requirement

What is an approximate length for a digital signature (SHA) given the following? Using RFID tags, size ranging from 100 to 2000 bytes (8000 bits), our project is setting aside a portion for a digital ...
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1answer
4k views

How is input message for SHA-2 padded?

I read about how is an input message prepared to be hashed by MD4,MD5 or SHA-1: Step1 Append padding bits The input message is "padded" (extended) so that its length (in bits) equals to 448 ...
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836 views

Is Wikipedia's table about SHA-2 collisions correct?

I was looking a Wikipedia article on SHA-2, and the "Comparison of SHA functions" table seems to indicate that SHA-2 is less secure than SHA-1. Is this true, or is the table wrong / misleading? ...
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What does Maj and Ch mean in SHA-256 algorithm?

I'm guessing they're some kind of standard function but what do they do and what do the names mean? A little explaination or link me to an article would be great.
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830 views

Why are these specific values used to initialise the hash buffer in SHA-512?

I'm reading the book Network Security Essentials written by William Stallings. To create a message digest with SHA-512, we have to go through some steps: append padding bits. append length ...
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95 views

Why do we always append padding bits in SHA-512? [duplicate]

Possible Duplicate: In the SHA hash algorithm, why is the message always padded? I'm reading the book Network Security Essentials written by William Stallings. To create a message digest with ...
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1k views

Using SHA-256 with different initial hash value

FIPS 180-3 defines the initial hash value for SHA-256 as the first 32 bits of the fractional parts of the square roots of the first 8 primes 2..19. What would be the risks of using a different value (...