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 hash a list of multiple items?

In some protocols, a key is derived from a hash of many parameters (K=H(param1,param2,param3)) Is there a hash function that takes many parameters as input ? Or we can simply use a function like ...
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72 views

Is size Q equal to size SHA(Q)? [closed]

Assume d is a 128 bit random integer and P is base point of an elliptic curve and Q = dP is a point on the elliptic curve and SHA is a hash function with 128 bit output, my question is: Is size Q ...
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1answer
281 views

Does CBC encryption of a hash provide authenticity?

Given a message $M$ and a cryptographic hash function $H$, let $f(M) = E_K(M || H(M))$ where $E_K$ is AES-128-CBC encryption with PKCS#5 padding. Take $H = \textrm{SHA-256}$ if it matters. In other ...
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268 views

Why have hashes when you have MACs?

It would seem to a naive eye that if you have a MAC, you have a hash function: use a key that all the parties know (such as all-bits-zero). A potential application would be a resource-constrained ...
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1answer
162 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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146 views

Multiple parties must encrypt and get the same result

Hopefully this question is not too simple - I did some research but with encryption I really don't want to make a mistake. Our scenario is that multiple groups need to encrypt a number and arrive at ...
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5answers
752 views

Is it theoretically possible to construct a string that contain its own hash value?

After saw the xkcd comic self-description, I wonder is it theoretically possible to construct a self-descriptive string that contains its own hash value? Let's say the string's md5 value is ...
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2k views

what kind of hash function can provide a short hash and be collision resistant?

When you try to connect via SSH, you see a signature which is short but I heard it is even stronger than sha256. It is perhaps stronger because it uses more rounds. Is there a hash function or a ...
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Is HMAC-DRBG or Hash-DRBG stronger?

Out of the two deterministic random bit generators defined in section 10.1 of NIST SP 800-90A (i.e. based on hash functions), which one is cryptographically stronger? Hash-DRBG (Section 10.1.1) ...
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Pre-image resistant but not 2nd pre-image resistant?

Are there any cryptographic hash functions for which there is a known pre-image attack, or a known second pre-image attack, but not both? The attack doesn't have to be practical - just anything that ...
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246 views

Allowing the user to choose the hashing formula at the registration

I was thinking of a potential new way to increase someone's account security. The idea was allowing the user to choose one of the hash formulas available in the software (example: "MD5", "SHA512" and ...
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197 views

Why are there $ signs in my passwd file?

I am trying to get access to my eReader and I managed to get the passwd file. ...
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615 views

What is the purpose of using different hash functions for the leaves and internals of a hash tree?

I just learned that the THEX hash tree specification which is widely used in P2P requires that two different hash functions be used: one for the leaf nodes (hashes of input data) and one for the ...
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1answer
329 views

Why is feed-forward mechanism used in hash functions?

The compression function of SHA-1 when used in Davies-Meyer mode adds its input to the chaining values at the final step. For the first message block, the IV is used as the input and in the next step, ...
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1answer
224 views

Did Merkle invent cryptographic hashing?

Chapter II of Merkle's 1979 PhD thesis is titled "One Way Hash Functions." The chapter appears to be the first reference to cryptographic hashing. The chapter has no references. Is there an earlier ...
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1answer
1k views

Is a second preimage attack on MD5 feasible?

What's the practical status of MD5 w.r.t. second-preimage? Integrity of a piece of data is protected by an MD5 hash, itself assumed genuine. The data (and thus the hash) is known to the adversary. ...
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1answer
539 views

Why is H(message||secret_key) not vulnerable to length-extension attack?

Given a Merkle-Damgård hash function $H$, I know that an attacker can forge a message protected by a MAC computed as $H(\textrm{secret_key}||\textrm{message})$. Why can't he perform the same ...
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2answers
579 views

How did LinkedIn “salt” all their passwords?

First, just to make sure I understand "salting" correctly: You randomly generate a string to append to the password before hashing it, so as to increase its length and make precomputed tables much ...
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1answer
181 views

split up sha256 hash and compare indiv block results

We have a h/w accelerator in our SoC and it can do sha256. The restrictions are it's input descriptors (which defines the input packet and len) must not straddle 64K boundary. When it does we can ...
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4answers
636 views

Compare two hashes with different salt

I'm storing the salted hash of a credit card number in a database. What I'd like to be able to do is determine if two different entries in the same database correspond to the same credit card. ...
10
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1answer
580 views

Is it possible to actually verify a “sponge function” security claim?

When using a “sponge function” to create a cryptographic hash, we can look at the flat sponge claim, which flattens the claimed success probabilities of all attacks using a single parameter: the ...
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1answer
213 views

why hash(hash(str)) is bad?

Why do people say that using hash twice or more is bad? yes there is key derivation that do that job, but in a low bandwidth network countries, the solution i see is to use a simple hashing system on ...
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228 views

Parallel-resistant proof-of-work scheme?

I am looking for a proof-of-work scheme which cannot be effectively parallelized. For example, in hashcash (and by extension bitcoin) you have some collision-resistant hash function $f()$, a target ...
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1answer
457 views

Hash function from narrower block cipher operated in CBC-encryption mode?

I am trying to build a public hash function (thus collision-resistant and preimage-resistant, and more generally behaving like a random oracle), with input a message $M$ of fixed size $|M|=m\cdot b$ ...
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2answers
124 views

What prevents continued hashing of a key from being used as a cipher when xored with plaintext? [duplicate]

This is just an idea I had while looking through some threads so take it as you will. Given a plaintext of any length and a key that a specific hash function is capable of taking as input(I mention ...
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233 views

Length of data to hash for PGP

I have finally managed to verify some simple PGP signed message blocks. However, I discovered that for some reason, my implementation limits me to verifying data that is 9-16 bytes long. no less. no ...
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1answer
93 views

Best hash size for hash trees

I want to know if having a 8-byte hash value is better than 16-byte hash value for use within hash trees. My mind tells me that the shorter the hash value, the better. But doesn't a smaller hash ...
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1answer
229 views

Difference between actual attacks and theoretical attacks on SHA cryptographic series

Could anyone tell me what the difference is between a THEORETICAL ATTACK (Like the one done on SHA-1) and an actual attack (Like the one done on SHA-0). Is a theoretical attack a proposed method of ...
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164 views

Hash Family Example

I am reading my lecture and I found this definition: Let be $F$ be a family of hash functions, that is, a parameterized set $$F=\{g_k:\{0,1\}^{*}\rightarrow\{0,1\}^{n}|k\in K\},$$ where $n\in ...
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1answer
179 views

Tor's integrity verification system?

I am trying to understand the design of Tor(onion router). I am reading the original paper on the 2nd generation onion routing system. Where, under integrity checking on streams, they say, "When Alice ...
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1answer
303 views

md5: is reverse length-extension attack possible?

If I know H = md5( SECRET_KEY | DATA ) then I can calculate H' = md5( SECRET_KEY | DATA | DATA' ) That's length-extension ...
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186 views

Digital Signature Scheme Count

My question is How I will be able to count digital signature Scheme that can sign many documents with one private key. There are signature scheme as long as exists private keys in the keys spaces? or ...
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1answer
357 views

Which MACs can be converted into a secure unkeyed hash function?

It is known that setting the secret key to a fixed, public value does not make MACs like CBC-MAC or GMAC into secure unkeyed cryptographic hash functions that could be used - for instance - for ...
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Difference between “one-way function” and “cryptographic hash function”

What's the difference between a one-way function and a cryptographic hash function?
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154 views

Hash function with values in a multiplicative group of prime order [closed]

I have to implement a cryptographic protocol which involves a cryptographic hash function $H: \{0,1\}^* \to G$. It is viewed as random oracle. $G$ is a multiplicative group of prime order. I want to ...
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understanding a length extension attack

I have been trying to understand exactly how a length extension attack works on SHA-1. I'll detail below what I've understood so far, so that I can convey my understanding of the same and hopefully ...
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1answer
241 views

Is there a problem with constructing a CSPRNG using MD5 or SHA1?

Is there any security concerns with building a CSPRNG using a broken hash function like MD5 or SHA1? The design is such that a CRC-like function is used for mixing entropy and MD5 is used as the ...
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Why does HOTP use such a complex truncate function?

In the HOTP protocol after calculating a 20 byte hash it is truncated to 4 bytes. For this first an offset is calculated (low-order 4 bits of the last byte) which determines the four bytes to be ...
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9k views

Why use an Initialization Vector (IV)?

Why use an Initialization Vector (IV)? How are IV's used? What are the advantages/disadvantages of using an IV? Why use an IV instead of a longer key in which some section of the key is pubic? What ...
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1answer
226 views

Preimage resistance hash in digital signature

I'm studying about preimage resistance property of the hash functions. In particularly I'm reading as the missing of this property can be fatal in digital signatures that use RSA. Further details: ...
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1answer
515 views

length extension attack on an MD5 hash of a text file of about 10K Bytes?

How much computing time on a typical desktop computer would it take to find a new length and new data to extend a text file of about 10K Bytes with a given MD5 hash?
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When using HMAC, does key encoding matter?

Given: H is a good hash function with block size L. K is a key of length >= L (recommended by RFC 2104). Khex and Kbase64 are ASCII encodings of K. In the HMAC algorithm, is there a good reason to ...
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1answer
80 views

“proof of access” schemes

What is the state of the art way when implementing a scheme challenging a party to prove they have access to certain data? What I'm looking for something along the lines of Give them ...
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154 views

How to compare two datasets „anonymously”?

Ok, I hope this question makes some sense because I am not so sure how to word it any differently… Imagine the following situation: There are 10 defined colors (blue, orange, yellow etc.) There are ...
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2answers
503 views

What does “message schedule” mean in SHA-256?

I am trying to understand the sha-256 algorithm from FIPS 180-2. I understood the padding and parsing of the message string. However after that it states (page 15): For $i = 1$ to $N$: { ...
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163 views

Does collision resistance stay when extending a hash function to a set domain?

Given a Cryptographic hash function $h$ for element $x$, let's extend it to sets via $H(S)=\prod_{x\in{S}}{h(x)}$. I am asking if the new hash $H$ (in domain of set) is still collision resistant? To ...
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1answer
462 views

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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Distributing blocks with validation and non-dependant list generation

Problem Suppose I have a system of nodes that can communicate with a parent node, but not among each other. Suppose then a file on the parent node is split up into blocks and divided among the ...
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HMAC and assumptions on the cryptographic hash

According to Wikipedia, a cryptographic hash function has the following properties: Pre-image resistance: Given $h$, it's difficult to find any message $m$ such that $h = H(m)$. Second pre-image ...
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Why crypto hash functions must be collision resistant and how to find resistant?

Why cryptographic hash functions must be collision-free and is there any methods to evaluate whether a function is not resistant to collision? Thanks,