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.

learn more… | top users | synonyms (2)

-2
votes
1answer
25 views

How to find HEXA value of String [closed]

This may be very easy thing, but i am just unable to understand this. I have a string "Hi", and in HEXA its written like this ...
0
votes
0answers
11 views

Rotate values in predefined manner

I want to create a Server S1, that publish a different value every 10 minutes on the internet. The value looks something like f7826da6-4fa2-4e98-8024-bc5b71e0893e. ...
1
vote
1answer
56 views

Safe MD5 digest

So I've heard that MD5 is broken because it's possible to engineer collisions. So instead we should use, say, SHA256. The problem which SHA256 digests is that they are long. So I've come up with this: ...
0
votes
1answer
50 views

Given a hash function how to find all/some inputs that hash to 0? [duplicate]

Say I have a simple hash function where $x$ is a sequence of integers: $$h(x)=(a_1\cdot x_1+...+ a_n\cdot x_n) \bmod N=\sum_i a_i\cdot x_i \bmod N$$ where $a_1,a_2,a_3,...,a_n$ is the coefficient ...
2
votes
1answer
59 views

How to find collisions in a hash function knowing its coefficent?

Say I have a simple hash function where $x$ is a sequence of integers: $$h(x)=(a_1\cdot x_1+...+ a_n\cdot x_n) \bmod N=\sum_i a_i\cdot x_i \bmod N$$ where $a_1,a_2,a_3,...,a_n$ is the coefficient ...
6
votes
2answers
139 views

Why do cryptographic hashing and symmetric encryption use different functions?

Something about encryption and hashing has always bothered me. Given a cryptographically secure hash function $H$, I can produce an arbitrarily long key from any seed $s$ by recursively applying $H$ ...
2
votes
1answer
63 views

SipHash's (non-)collision resistance

I'm very new to cryptography, and I need help understanding the security claims made in Aumasson and Bernstein's paper on the SipHash. In particular, I'm trying to understand the following statement ...
0
votes
0answers
28 views

PHP Apple News HASH HHMAC

I am having a problem generating the signature key in PHP as describred in the Apple nes API documentation found here: https://developer.apple.com/library/ios/documentation/General/Conceptual/...
1
vote
1answer
44 views

Is it safe to use fast/small hash for key identity?

I have to roll database access keys often, but it's important to know which key each system is using in order to avoid unavailability. I want the systems to report that without exposing the key itself,...
4
votes
2answers
73 views

Strength of $H(k\|H(m))$ as a MAC algorithm

What is the strength of $H(k \| H(m))$ compared to HMAC? Compared to $H(m \| k)$? What is the strength in bits of a given key/output size?
5
votes
1answer
116 views

Why do we use hex output for hash functions?

Why do we use hex representation as default for the output of a hash functions result? For example the sha256 hash function: the output of sha256 in hex representation uses 64 characters, while ...
1
vote
1answer
49 views

Can I get successful signature verification with just altering message and signature?

Assuming I can modify a message and also modify the verification signature, and I also have the public-key but not the private-key. Can I create a message that can be verified with a signature that I ...
0
votes
0answers
16 views

What are the advatages or disadvatages of using seperate chaining over linear or quadratic probing?

I was looking through different hash methods the other day and was curious as to what the advantages or disadvantages of using separate chaining over linear or quadratic probing. I know that with ...
2
votes
1answer
80 views

Is it possible to combine two hash functions in such a way that cracking the constructed hash would require cracking the constituent hashes? [duplicate]

Suppose A is some arbitrary hash function, for example BCrypt or MD5. And B be some other arbitrary hash function, maybe SHA256 or SCrypt. Let ...
0
votes
0answers
80 views

Why are hash functions like SpookyHash and MurmurHash so highly collision resistant?

Why are hash functions like SpookyHash and MurmurHash so highly collision resistant? I tried to test these hash functions using a few billion input messages and I found that there is no hash value ...
0
votes
1answer
62 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]. ...
2
votes
1answer
53 views

Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
4
votes
1answer
115 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.
0
votes
0answers
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 ...
3
votes
1answer
78 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....
1
vote
1answer
48 views

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 ...
0
votes
0answers
50 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 ...
2
votes
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 ...
1
vote
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 ...
0
votes
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 ...
4
votes
4answers
132 views

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?
3
votes
2answers
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 ...
1
vote
1answer
31 views

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 $p$ ...
0
votes
3answers
151 views

Is it possible to brute-force a hash algorithm of 32 bits

I have a 30000 user passwords and usernames stored in a table on a database in which the passwords are stored as hash where ,I need to guess the passwords for all users and I have the hash function ...
1
vote
0answers
32 views

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?
-2
votes
3answers
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 ...
3
votes
3answers
73 views

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.
1
vote
2answers
114 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 ...
0
votes
1answer
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 ...
1
vote
1answer
37 views

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 n?...
1
vote
1answer
47 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 ...
0
votes
0answers
27 views

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 $H'$ ...
4
votes
1answer
36 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 ...
0
votes
1answer
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 ...
6
votes
2answers
167 views

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 ...
6
votes
2answers
94 views

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\}...
0
votes
1answer
54 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 ...
0
votes
0answers
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?
4
votes
1answer
111 views

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 ...
3
votes
1answer
50 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 ...
9
votes
1answer
273 views

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: ...
0
votes
1answer
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 ...
3
votes
1answer
207 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 ...
-1
votes
1answer
49 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.
-1
votes
1answer
77 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 $\...