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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Collision-Resistance Hash Function PRF

I am trying to solve the following question with an example/proof. The question is from Introduction to Modern Cryptography by Katz and Lindell. Any help would be appreciated.
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How to construct a collision resistant hash function that is not a one-way function?

How to construct a CRHF (collision resistant hash function) that is not a OWF (one-way function)? Not sure but I think it probably needs another CRHF?
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Fast forwarding hash functions

We know that a good hash function is a one way/trapdoor function. Easy to calculate one way, harder to work out a previous state. I was wondering if anyone knew a good hashing system that allowed you ...
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Is there a simple hash function that one can compute without a computer?

I am looking for a hash function that is computable by hand (in reasonable time). The function should be at least a little bit secure: There should be no trivial way to find a collision (by hand). For ...
2
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0answers
61 views

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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131 views

Example describing Baek and Zheng’s threshold identity-based decryption scheme

I am trying to work through an example of Baek and Zheng’s “threshold identity-based decryption scheme” and I tried a lot to solve this, but somewhere I’m doing something wrong. I hope someone can ...
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61 views

Give a simple hash chain example in Java [closed]

I am looking for a very simple example of cryptography hash chain source code. Could you forward me some examples or link, guys? For example, https://en.wikipedia.org/wiki/Hash_chain [1]. ...
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113 views

Is there any function that does not suffers birthday problem?

I am eager to know that if there is any function that does not suffer birthday problem and how to prove it formally that the function is not suffering the birthday problem.
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27 views

MAC is constructed by hashing and then encrypting

Suppose the MAC is constructed by hashing and then encrypting, that is $MAC(m, k2)=E_{k2}(H(m))$ where H is a public hash function. There can be several alternatives in how the transmitted message is ...
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1answer
39 views

What implementation properties of a hash function prevent safe truncation? [duplicate]

Truncating a hash function's output should, in theory, not increase the likelihood of a collision more than you would expect based on the truncated output size. This makes sense when thinking about ...
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76 views

What are the time considerations with regard to security against birthday attack?

When designing security for a physical safe, one of the critical specifications is how long will the safe resist attack, this tells you how quickly you must detect and respond to an attack on the safe....
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Are collision-resistant hash functions even possible? [see description] [duplicate]

Surely there can be no real collision resistant Hash function since hash values are of finite size which means there are finitely many of them, but there are an infinite number of messages we could ...
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What are preimage resistance and collision resistance, and how can the lack thereof be exploited?

What is "preimage resistance", and how can the lack thereof be exploited? How is this different from collision resistance, and are there any known preimage attacks that would be considered feasible?
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49 views

signature, hashing schemes

I have 20 friends. we create message(s) (1...i) and tar them up with a file messages.hashes(1..i). We sign these tars with our ...
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1answer
73 views

SHA256(RsaPrivateKey) == AES key?

I have an RSA private key (more specifically, an SSH key in Putty format, 4096bit) and want to use its SHA256 hash as an AES256 key, instead of using an independent newly generated AES key. Are ...
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1answer
41 views

Why hash function are used in digital signatures? [duplicate]

In the lectures I see, hash functions are always used when we want to sign a document $d$. My question is why they are used in digital signatures? Maybe, because it is more easy and fast to calculate ...
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Possible problems in using a hash algorithm to construct a stream cipher

I'll define an example hash-based stream cipher as such: $H: \{0,1\}^* \rightarrow \{0,1\}^{256}$ is the hash function. $K=\{0,1\}^{256}$ is the secret key. $N=\{0,1\}^{128}$ is the nonce. $C=\{0,1\}...
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63 views

A bijective hash function

Suppose: $H: \{0,1\}^{n} \rightarrow \{0,1\}^{n}$. $H$ is bijective. It is difficult to derive $x$ from $H(x)$. Is this type of function possible? What would the strength of it be? I realize that ...
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76 views

Reducing the probability that a password will be guessed

In a file users' password hashes are stored. There are 2 approaches to reduce the probability that the password is guessed. Increase the size of the salt from 12 bits to 24 bits. Increase the length ...
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Encryption strength when using a PBKDF

Suppose: $m$ is a positive integer. $n=2 \times m$. $H: \{0,1\}^{*} \rightarrow \{0,1\}^n$. $p$ is a password. $s$ is a salt. $K=\{0,1\}^n$ is the derived key. $PBKDF(p,s)$ derives a key from $p$ ...
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544 views

How to reverse this hash function?

I have a function that takes an $m$ byte inputs $x_i$ and maps it a 32 byte outputs $y_j$. The hash function is defined as: $$y_j = \sum_{i=1}^{m} (x_i)^{i-1} \pmod {127}$$ The input is restricted ...
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113 views

Understanding Hash function notations

I am implementing a Certificateless Cryptography Algorithm by referencing the paper An Efficient Certificateless Encryption for Secure Data Sharing in Public Clouds. In this paper on page no. 4 during ...
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Does salt size affect password hash security?

I use PBKDF2-SHA512 with an iteration count of 128,000 to hash my passwords. I use a CSPRNG to generate a salt per password. However, I am unsure about the ideal size of the salt. I have read a lot of ...
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Increase in security with increase in size of salt [duplicate]

Does increasing or doubling the size of salt result in improved security? It will require some extra time to brute force the passwords, but any added advantage?
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Are there any hash functions that use integers of arbitrary bit size (e.g., int63)?

More precisely, I am looking for hash functions where the internal state can be decomposed as a vector of integers of size 63. That is, machine integers where one of the bits is fixed and unusable.
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What may be causing conflicts in Whirlpool implementation versions?

I see by layman articles (e.g. at Wikipedia) that the Whirlpool hash function has seemingly three current versions. That is to say, they are referenced as ...
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Non-iterative cryptographic hash functions

Consider the following cryptographic hash function $H$ which maps a message $m$ of variable size to $b$ bits: $$H:\{0,1\}^{*} \mapsto \{0,1\}^b$$ $$y = H(m) = SPRP(IV||m||padding)\mid_{b}$$ , where: ...
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Large Volumes of Asymmetric Encryption

First of all, I apologize in advance if I use any incorrect terminology. I am just getting my feet wet when it comes to cryptography and there is a lot to learn. For the past 12 months we have been ...
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Do I need to use null bytes and \x80 in hash length extension attack?

Say I want to perform a hash length extension attack. All the tools I have used use \x00 and \x80 to pad hashes (hlextend and hashpump). But is it necessary to use these bytes? Based on my ...
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Inserting a backdoor into a cryptographic hash function

I'm curious as to how a backdoor can be built into a hash function. What might it take the form of? What's probability of getting one that can be backdoored in a way that can actually undermine its ...
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Composing hash functions

Suppose there is a cryptographic hash function $H : \{0,1\}^* \to \mathbb G$. Now, we want to define a hash function $H' : \{0,1\}^* \to \mathbb G \times \mathbb G $. My first idea is to define $H'$ ...
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Rainbow Table - Number of Chains and Chain Length

Is there a difference between having 10,000 of chains (with 1,000 chain length) and 10,000 chain length (with 1,000 of chains)? How does it affect the success rate of the rainbow table? I understand ...
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can anyone explain inversion per byte?

I am designing the truncating block of SHA3 algorithm , there its given that first we need to do the inversion per byte of the 1600 bit output and then truncating it to give 512 bits output. Can any ...
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Filling in MD5 input variables

I have a majority of an input string(as well as the total length) and the output for an MD5 hash. Is there a way to calculate the remaining input bytes that I am missing?
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Is $H'(M) = 5M + 9H(M) \pmod{2^n}$ a secure hash function?

theorem: For arbitrary $i≥0$ there exists $m,n≥0$ such that $35+i=5m+9n$. We can use this theorem for constructing simple hash function. Let $M$ be message and $H(M)$ be its hashed value with hash ...
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How can I figure out a hash algorithm?

This may be trivial, and may be impossible... this is outside my field but willing to learn. I have a hardware device that accepts a network MAC address (6 bytes of data) like this: 38-60-77-EC-1D-33 ...
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What are fixed points and length extension attack in hash functions?

I was recently reading about hash functions, and I came across fixed points (one or more fixed points, interested in both) and length extensions, but I didn't exactly understand how these work. If ...
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174 views

Provable security of cryptographic hash functions

I am working on the following exercise question: Consider the following construction of a “keyed” hash function from Katz & Lindell (ex. 7.22 (1st ed.)/ 8.21(2nd ed.)). Gen : On input $1^...
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Are hash functions chaotic?

I'm looking into "bitcoin like" mining processes. Say a security process uses a hash of data as proof that the data was known at some point in time. From what I understand, hash functions are ...
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About MAC and HMAC

I'm studying mechanisms of integrity and authentication in symmetric encryption scenarios. I want to propose some examples to see whether I got the point here: Let $m$ be the message, $c$ the ...
3
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What's the safest TrueCrypt algorithm and hash?

I have an encrypted file container inside my NTFS pendrive. The root folder Write permission is blocked for everyone. A folder inside it has all permissions unblocked. The dummy file of TrueCrypt is ...
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Associative standard cryptographic hash function

I am looking for a standard hash function which satisfies the following property: A hash function $H(a,b) = F(h(a),h(b))$ with $h$ (within $F$) any standard cryptographic hash function and $F$ an ...
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What are the applications of sha3 algorithm? [closed]

I know it is used for digitally signing any data or message. It can be used for sending any message securely, but where is it applied in industries? Can anyone tell the practical applications of $\...
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How to invert a linear hash function?

My friend is trying to convince me that his linear hash function (with a few bit operations) is secure. Is there a way to disprove this? (Or prove this, but I've read from multiple sources that this ...
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59 views

Proof of Knowledge/Data Integrity using Hash Function

Objective: A verifier wants to ensure that a block of data M is also known to a prover. The protocol should exchange little information and should not leak information about the value of M. Proposed ...
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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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Given the first half of a SHA-1 hash, can you predict the second half?

I know this applies to secure ciphers, but does this also apply to hashes?
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Parallel hashing function that always gives the same hash despite a variable number of cpus

The title pretty much sums it up :) I'm looking for a hashing algorithm that does not need to be cryptographically secure beyond reducing the number of accidental collisions. There is no need to ...
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Reversing a hash of known hashing algorithm

I am sure this is a very easy thing to do but I am not sure how to go about solving a problem like this, So there is this hash function which operates on a message which is in the form of a byte array ...
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465 views

How is the message digest related to Signatures and Encryption?

I was studying about 'Data Security' and I found out this one thing confusing. What is an message digest? I got it is the hash of the message. Is the message here referring to the plaintext or ...