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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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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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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What is the starting point of Hellman's TMTO method?

I understand what is happening and how the endpoint is computed but I'm still a bit unsure of where "SP" (Staring Point) came from. Are the starting points, randomly selected keys from the key-space ...
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40 views

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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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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35 views

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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101 views

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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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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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. ...
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51 views

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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24 views

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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Calculation of the avalanche effect coefficient

Given a strict avalanche criterion matrix/dependence matrix for a hash function,how do I calculate the avalanche coefficient for it. I want to calculate a single parameter(value) which represents the ...
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48 views

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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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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29 views

Partial-Message Collisions on Iterated Hash Functions

In Cryptography Engineering by Ferguson et al it says the following is a problem with iterated hash functions: Because hashing $m$ and $m'$ leads to the same value, $h(m||X) = h(m'||X)$... for all ...
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154 views

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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44 views

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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71 views

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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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 ...
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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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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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87 views

How to choose the reduction function in rainbow tables?

I have a question regarding Reduction Functions in Rainbow Tables. If the hashing function is MD5 or SHA-1 etc then should the reduction functions also be MD5 or SHA-1? That is, should the Reduction ...
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72 views

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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97 views

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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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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464 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 ...
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Padding password before SHA-512 hashing to avoid info leak via timing

I've noticed that SHA-512 password hashing leaks some information about the password length. There's a weak correlation between password length and time to hash. It's roughly linear, but in steps of ...
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Why is Pearson hash not used as a cryptographic hash?

The original algorithm produces 1 byte long hash and is (of course) not suitable for cryptography use. But according to wikipedia, it is possible and easy to produce Pearson hash of any length, ...
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Difference between MAC and Authenticated Encryption?

I am currently studying authenticated encryption and I was wondering if there was a difference between using a MAC and authenticated encryption. It seemed like authenticated encryption schemes use ...
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78 views

Weak and Strong Collision Resistance, again

Weak collision resistance (CR), or second-preimage resistance, is the property that given $x$ and $h(x)$ ($h$ a hash function) it's difficult to find $x' \neq x$ such that $h(x') = h(x)$. Strong CR, ...
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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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80 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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Distribution of hash values

I was wondering if the uniform distribution of hash values is a generally required criteria for cryptographic hash functions. The english wikipedia article only mentions four main properties. But it ...
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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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Does encrypting with MGF1/SHA-512/1024-bit seed equal to a 1024-bit key block cipher?

Suppose: Alice uses SHA-512 with MGF1(as in PKCS#1 V2) and a 1024-bit random seed to generate a mask, XORs the mask with a message(M), gets a cipher text (CT), and sends the CT to her old friend ...
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Why is the compression function in Miyaguchi-Preneel scheme secure?

I was reading about the Miyaguchi-Preneel scheme and had difficulty in understanding why the compression function, $h(H,m)=E(H, H \oplus M) \oplus M \oplus H$ can be called secure. The only resource I ...
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Is there an algorithm that allows verification that 2 encrypted or hashed bits of data are the same, given that I may only know half of the key/ salt?

We have an interesting problem. Currently, we store a salted hash of some secret key known only to the clients of our clients to allow us (and our clients) to find other records that were generated ...
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What is the threat to a PKI when the root CA certificate is generated using SHA1?

We have thousands of servers that have been issued certificates signed by our CA using SHA256 but the our root CAs own certificate was generated using SHA1. Assuming SHA1 is no longer secure for our ...
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Store hashed password using Digest authentication

Digest Authentication is something like this: Server sends client a nonce. Client hashes username and password with nonce. Client sends hashed value back to server. Server validates hash. However, ...
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Decrypting SHA-256 with SHA-256 as input?

Is there a way to somewhat decrypt a SHA-256 hash, provided that the initial string was also a SHA-256 hash? If not, could anyone link me to a rainbow table containing some of the $16^{64}$ possible ...
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3 digit code at the end of a changing magstripe (maybe hash?) [closed]

Myself and some fellow students are doing some "Independent Security Research" on campus and trying to crack the campus paid parking system to better understand how it might work. The system works ...
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Can a list of hashes with property $X_{n+1} = \operatorname{SHA-256}(X_n)$ loop?

This is the situation: I have a list of hashes where each hash is always the SHA-256 of the one above it. If I keep going down the list it must at some point loop since there can only be $16^{64}$ ...
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Hash + Salt v. Hash + Encryption

I was wondering if using a salt with a hash is more effective than hashing and encrypting your hash.
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Implementing hmac+bcrypt in bash script

I was recently reading Mozilla's Secure Coding guidelines and found their password storage method interesting. They combine an hmac hash of the password with bcrypt which allows for added security ...
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Differential Cryptanalysis for Hash functions

How is differential cryptanalysis used to attack hash functions? I've been struggling through a couple academic papers and thesis's on the subject but they all sound like greek to me. Does anyone know ...
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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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Is it secure to send the hash along the message without encryption?

Lets suppose Alice send to Bob a message $M$ along with its hash value say $H$ which is calculated using SHA3 algorithm. It is sent on the network where it got read by Eve and she does not make any ...
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Are checksums essentially non-secure versions of cryptographic hashes?

Are checksums basically toned-down versions of cryptographic hashes? As in: they are supposed to detect errors that occur naturally/randomly as opposed to being designed to prevent a knowledgeable ...
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Misuse-resistant authenticated encryption based on SHA-3/Blake2b and AES-CTR/ChaCha20

I am wondering if the following is a useful misuse-resistant authenticated encryption scheme: Parameters (shared by many users): Choose a hash function $H$, such as Blake2 or Keccak. SHA2 could ...
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Negative lookup table concept

Interested in password cracking, I thought of a concept for lookup tables that can tell if a hash can be created using a dictionary in about O(log n) time. A simple overview of the idea is a follows: ...