A cryptographic hash algorithm is a function which takes a variable size input and produces a fixed size output. The algorithm makes it difficult to predict the output for a given input, find two inputs with the same output, or reconstruct the input from the output.

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How to construct Hash function of type $H:\{0,1\}^x \times G \mapsto Z_p^*$?

In many cryptographic protocols design, I have seen the statement 'Choose a Hash function $H:\{0,1\}^x \times G \mapsto Z_p^*$ i.e a hash function which takes as input a binary string of finite ...
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138 views

Questions about a SHA3 cipher stream encryption scheme

I have written an encryption implementation using a hash as a cipherstream for demonstration purposes. I know it is slower than more sensible options such as AES but I am interested in several things, ...
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comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
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Does including the size of the hashed data improve security over just the hash

Trying to settle a discussion at work. We are mostly concerned with pre-image resistance. Suppose we have a common secure hash function $H$ (e.g. SHA-1/SHA-2) and some message $M$ we want to hash. ...
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64 views

Cryptographic hash with ability to ignore specific bits based on a hidden pattern?

I'm looking to use password-style hashing to validate an environment, where some parts may be irrelevant. For example: ...
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49 views

How to detect changes in data while preserving confidentiality (under constraints)?

Suppose party $A$ has two pieces of data, $X$ and $Y$, either of which may change separately, or they may change together. Given the following constraints: $A$ knows its current $X$ and $Y$ but has ...
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268 views

Testing hash functions for collision resistance

I was hoping to implement a software that allows testing a user-defined hash function for cryptographic properties (Meant to pique interest in cryptographic hash function for a school showcase), as ...
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92 views

Converting a pre-image resistant hash to second pre-image resistant

I am looking for some standard conversion from any hash function $f$, which has pre-image resistance, to another hash function with second preimage resistance. Is there such a standard conversion?
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68 views

Salting in asp.net?

I have spent the past hour reading up on salting and still don't understand how it is achieved. Forgive me if im wrong, but the way I am thinking of salting is, storing an ArrayList of random strings ...
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69 views

Question about keyed hash functions

Maybe the answer to my question is obvious, but I have doubt... I have noticed that hash functions are studied in two forms, keyed hash functions or unkeyed. In general, lecture notes present hash ...
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Is it safe to use a secret salted hash of a public id for client to prove ownership of id to a server that knows salt but does not store ids?

I am writing a peering server - the server assigns randomly generated public IDs to users, and I want users to be able to reclaim their ids in the future, but only to be able to claim ids that they ...
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133 views

Generate hash value using public key along with message

I was trying to understand one way signature chaining on message by Saxena and Soh. As the message is passed from one user to other, every user can combine their signature to create one single ...
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142 views

Crypto hash function vs encryption algorithms

Why is a cryptographic hash function generally faster to execute in software than conventional encryption algorithms such as DES?
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58 views

Can a tree hash with leaf-size of 1 byte support verification of content with elided ranges, at a cost of at most 2 supplied internal-node hashes?

Perhaps someone can confirm my intuition: A tree hash with leaves of size 1 (for example Blake2 in a tree-hash mode) would of course not be very efficient. But it seems that it might be a suitable ...
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252 views

Large file validation on an embedded system through hash and encryption

As a preface, I have to say that I am a noob in this area. Having said that, I will ask the question. I have a situation where I need to validate and protect against tampering a handful of large ...
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137 views

Help to understand the chameleon hash function?

Recently, I'm reading Non-Interactive Key Exchange, in the section 4.2(Towards a factoring-based scheme in the standard model,Page 10), the authors uses $$t\gets ChamH_{hk}(Z||ID;r);\\ Y\gets ...
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280 views

How can I map arbitrary group elements to unique integers without using Hash functions?

Let's say, I have a group $G$ of large prime order $p$. A set $S$ consists of $n$ random elements chosen from $G$. Without using a collision resistant hash function $H$, how can I map elements of $G$ ...
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120 views

Cryptanalysis of Nonlinear Table Lookup

I am trying to derive a symmetric key based on a master key, combined with a simple string. Based on my limited knowledge, it seems that something like PBKDF2 would do that for me in a well-defined ...
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113 views

Is it possible to deduce the value of a string when given its hash and multiples hashes of the string + other known strings?

To be clear, I have access to $H(S)$ and as many $H(S||K)$ as I want. Every string $K$ is known. Can I use the extra information to my advantage and try to deduce $S$, without requiring bruteforce? Or ...
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Is a collision attack possible on MD5 if message is known partially

Is it possible to find $m'$ such that $\operatorname{MD5}(m'||m_1)=\operatorname{MD5}(m_1||m_2)$ if I know $m_2$ and $\operatorname{MD5}(m_1||m_2)$? Is this a collision or a preimage attack? Also in ...
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231 views

Building a stream-cipher out of a hash function?

I've already read this: Is it feasible to build a stream cipher from a cryptographic hash function? However, my proposed construction differs… Suppose the hash generates N bits. These bits are split ...
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100 views

Simplified Key Wrapping to Achieve Only Confidentiality?

I'm looking for help in understanding why the algorithm described here would not deliver adequate protection of confidentiality. We don't care about other criteria such as authenticity or integrity. ...
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Questions about hash functions

Let $H$ be a secure hash function (e.g. SHA256), is it possibile to find $H(M1)$ given $H(M1||M2)$ if the length of $M1$ and/or $M2$ is exact the block size of the hash (that is, 64 bytes for SHA ...
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334 views

Are there attacks that break collision resistance but not preimage resistance?

Are there any examples of attacks on hash functions which: break collision resistance and second preimage resistant, or break collision resistance and preimage resistant? I have looked at Rogaway'...
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325 views

2 comparable hashes generated from one string

Assume a website where people log in with their password. The password is now stored in sql database as: md5(password + random_salt) We are adding the ...
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193 views

SHA256 Round Equivalence

I have calculated the average number of operations in 1 round of SHA256 as follows: Additions: 9.25 Bitwise Rotations: 9 Bitwise Shifts: 1.5 Bitwise AND: 5 Bitwise XOR: 10 I have certain ...
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When making public key fingerprints - is a sha1 hash still a good idea?

I'm thinking about trying to save some space (and readability) when referencing 2k and 4k public keys (millions of them) by storing the fingerprint in some places instead of the full public key. ...
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Is it safe to hold key file's hash in application

Title says all; Is it safe to hold key file's hash (MD5 or SHA1) in application (hard-coded)? Thanks
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HASH Algorithm for 8 bits MCU

I need to implement the HASH algorithm (MD5 & SHA-1) on an 8 bit MCU. I hear it can only be implemented on 32bit and sometimes 16bits MCU. Is that possible? I will appreciate link where possible. ...
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289 views

How does the energy consumption of the SHA-3 finalists compare?

I am curious, is there any paper where SHA-3 competitors are compared in terms of energy efficiency?
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What is perfect collision-resistence in probability terms?

update: removed lots of stupidity... sorry. I didn't know I can be this stupid but I achieved it. 1. Goal Let $\mathcal{D}$ be the universal space of our plain data. Our goal is to find a function $...
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how to verify subset of hashes from hash list

I need to verify a couple hashed (SHA256) integers from a list of approximately 50 hashed integers in a message. The list can be divided into groups. The (plain) integer data is not in the message, ...
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Why do we need Merkle–Damgård strengthening [duplicate]

Reading through some manuals, wikis and other documentation I'm learning about Merkle–Damgård construction. I understand why padding beginning with '1', followed by '0's is needed, but I can't ...
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Cyclic group collision resistant keyed cryptographic hash function

I am self-studying cryptography from a book and have come across a really difficult question that's doing my head in. I would be very grateful if somebody can help me out here with this difficult ...
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Probability approximation of no collisions

I am comparing the actual probability of no collisions to the probability approximation formula of no collisions from the Understanding Cryptography text. The approximation is as follows: $$P(\text{...
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Signing integers and UUIDs and restoring them from a third party server without tampering

I'm educating myself about cryptography. I know this is a long one, but please, bear with me. :) Now I have a scenario in my mind and I'd like to ask if what I've thought is sound (enough), what more ...
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Discrete logarithms: large prime modulus vs. large semi prime modulus

I have a cryptography homework question, in the question it says a cryptographic hash function in the form of $f(x) = g^x \bmod n$ , where $n$ is a very large prime (1024bits and more), $g$ is a ...
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Bobcat hash, trying to find a 48-bit hash collision for x

I am trying to find a collision with the Bobcat hash of the 48-bit hash. I am a beginner coder so please point out any flaws in my modification of the bobcat program. It does find a truncated 12-bit ...
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Is there a way to slow down collision attacks using iteration?

The simple way to iterate a hash function $H(H(m))$ only makes brute force preimage finding slower, but leaves collision attacks as fast since a collision in the inner hash function is a collision in ...
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Determine safety of exercise hash functions [duplicate]

There have been several attacks against hash functions such as $h_{sha1}$ and $h_{md5}$. Professor A suggests a new function $h_{666}$ with an output length of 666 bits. Professor B suggests ...
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SHA3 Keccak, absorbing data to the state

I'm working on implementation of keccak algorithm and have one problem. Tell me please, takeing an example "test": will state (before block permutations, but after padding - pad10*1) look like this: {...
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How to map a handful of numbers in a large range to a much smaller range deterministically without collissions

I want to map a set of long integers (say around 100 different values) that can span the entire 64 bit integer range to a much smaller range such as from 0 to 25000 deterministically with almost zero ...
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159 views

Security of basic SHA256 MAC in an authenticate-then-encrypt scheme

I know the following construct is insecure if the MAC as defined below is appended to the encrypted message in an Encrypt then Authenticate (EtA) scheme. $k_1$: encryption key $k_2$: authentication ...
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Formal proof of theorem concerning the Random Oracle Model

Reading a book on cryptography by Douglas R. Stinson I've met the following theorem, which is stated without proof (see here). Thereby, $\mathcal{F^{X,Y}}$ denotes the set of all functions from $\...
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Does this guarantee a unique 32 bit Hash?

I came across some source code that loosely does the below in order to achieve a 32 bit hash. The input string is passed through MD5 to get 16 bytes Hash (as usual). Then the 16 bytes are split into ...
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Cipher built from GPU primitives [closed]

Is it feasible to build a cipher (or hash) out of GPU or DSP primitives (e.g. big matrix multiplication, Fast Fourier Transform, big block SIMD, or hardware H.264/AVC codec)? Preferably those are slow ...
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Implementation Attacks on Hashes

So I am familiar with attacking implementations of block ciphers via side channel attacks, cache-timing attacks, etc. What implementation attacks are there against hashes or hashed based functions (...
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implementing a cryptographic hash with a block cipher [duplicate]

How can a cryptographic hash function be implemented/created using the block cipher? I was wondering if we can use AES in cipher block chaining mode to implement it.
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Design requirements for a keyed hash function?

I am actually preparing for a cryptography exam, and I found a question asked by the professor in the class, below are the lines that I copied from the slide : Example: Let $Ek$ be the encryption ...
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How does use of HMAC affect hash function combiners?

In the comments of this question, Ricky Demer proposes a function $HMAX$ to combine two $HMAC$s based on different hash functions: $HMAX_{H0,H1}(⟨k_0,k_1⟩,m) = HMAC_{H0}(k_0,m) \oplus HMAC_{H1}(k_1,m)...