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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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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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 this a correct understanding of Universal Hash Functions?

I'm studying universal hash functions and have been reading several papers but now i'm focusing on Wegman and Carters original paper from 1979 (Universal classes of hash functions) and the H1 class. ...
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Is it safe to derive ephmeral keys by hashing a curve25519 key and a sequential number?

My understanding of curve25519 is that a key is derived solely from Alice's private key and Bob's public key and that curve25519 will always yield the same shared secret $K_s$ for the same keys. Now, ...
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Client puzzle using hash

When a server is under attack, it send the client the following data: Nonce - a byte array of Y length Hash - the hash digest of the puzzle solution The client has to find X such as ...
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How is HMAC(message,key) more secure than Hash(key1+message+key2)

I understand how for hash functions which are vulnerable to length extension attacks (such as SHA1 and SHA2) it is safer to use a HMAC construction. What I don't understand is, how or why is ...
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45 views

What is the idea behind hashing the QueryString in OAuth?

In OAuth 1.0a and 2.0 using MAC Authorization, I need to generate a hash of all the QueryString Parameters, which requires normalization (alphabetical ordering) of them. I'm trying to understand what ...
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77 views

File Encryption (EFS method)

I'm implementing (for learning purposes) a file encryptor, which uses the following method (from http://en.wikipedia.org/wiki/Encrypting_File_System). I have 3 kind of keys: RSA public/private, AES ...
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141 views

Example of second preimage attack [closed]

Please, I'm trying to understand second-preimage attacks on cryptographic hash functions. I understand the definition well: given a message and it's hash, an attacker finds another message which ...
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Hash function that is efficient on GPU and poorly suited to ASIC

I have such requirements to the hash function in my project: operating on 32-bit data, not mathematically breakable (built on existing hashes known to be secure), free of branching, as much as ...
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120 views

A fast non-cryptographic hash function that is “strong enough”?

I'm designing a simple one-time-password mechanism for authentication against a possibly-insecure server - i.e. I don't want to use symmetric shared secrets. The first idea that came into mind was ...
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55 views

Binary simmilarity function [closed]

I've been reading about hash functions, but found nothing close to solve this problem - I'm looking for a function with could be used for binary comparison of multiple files / streams of bytes etc. ...
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TCR hash functions from MD5

I'm reading Collision-Resistant Hashing: Towards Making UOWHFs Practical (pag. 10 and 11) and here say The most direct way to construct a TCR hash function is to key a function like MD5 or SHA-1. ...
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108 views

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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119 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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118 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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Is there a way to analyse xxHash and tell, either by human analysis, or with an automated tool, that this hash function is or is not cryptographic? [duplicate]

After reading some excellent papers on SipHash, I understood that good non-cryptographic hashes such as MurmurHash and CityHash are not secure for Internet usage, due to a certain type of DDos attack ...
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School exercise on untrusted channel comunication [duplicate]

Possible Duplicate: Why is H(k||x) not a secure MAC construction? I've the following problem: two parties, A and B, share a secret key Kab. M is a plaintext message, H an unkeyed hash ...
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P-Complete hashes, hashing to a larger set

Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits). Also, hash functions that are P-complete have no known parallel algorithm; they must be computed ...
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76 views

Why do we always append padding bits in SHA-512? [duplicate]

Possible Duplicate: In the SHA hash algorithm, why is the message always padded? I'm reading the book Network Security Essentials written by William Stallings. To create a message digest ...
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69 views

Applying multiple hash functions to improve security? [duplicate]

Possible Duplicate: Guarding against cryptanalytic breakthroughs: combining multiple hash functions I'm a total newb to cryptography but after reading what I've read about it, I had a ...
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Using one-way hash functions as the encryption method

Suppose two parties want to communicate securely with each other (Bob and Alice) using a simple messaging system in English. There are approximately 180,000 currently used words in the English ...
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Is the One Time Pad (OTP) considered a cryptographic hash function?

As the title states, would the One Time Pad (OTP) be considered a cryptographic hash function?
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Construct an encryption algorithm using hash function [duplicate]

We know that Cryptographic hash function is generally a one-way function where we can't retrieve the original message. On the other hand, encryption is a two a function where we get the original ...
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194 views

Can a salt for a password hash be public?

For my understanding salts in password hashes are used to prevent the precompuation of plaintext$\to$hashvalues (rainbow tables). I know from different threads, it is not necessary to keep the salt ...
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Should an AES byte key generated with OpenSSL be converted to hex?

I am generating a key & iv with Ruby's OpenSSL wrapper for an AES CBC 256 setup: ...
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Why is the hashing (SHA256) specification symbol for rotate S and vice versa? [closed]

In the specification for SHA hashes, such as SHA-256, the symbol for a rotation is S and the symbol for a shift is R. Is this an attempt to be deliberately confusing, or some kind of in joke, or ...
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Idea for user/pass hashing to prevent rainbow tables, would it work?

I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
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95 views

Convert SpookyHash to semi-secure 192bit hash [closed]

What do you think of converting SpookyHash into semi-secure 192bit hash function by this way: increase security by using 8 * 8byte = 512bit blocks instead of 8 * 12byte blocks, but remaining 8 * ...
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Generating a number using SHA512 that users can later verify (once I publish secret seed)

I've wrote following C# method that basically takes 3 seeds and gives you number in 0-100 range. I then use that number for variety of purposes but for this question the most important one is the ...
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Ensuring that an operation takes a relatively specific amount of time, but easily verify the result

I want an algorithm of some sort that can ensure that an operation takes a fairly specific amount of time, but proof that this operation was done can be completed relatively inexpensively. For ...
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101 views

No Birthday Attack to TCR

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” , which compared TCR (Target Collision Resistant) and ACR (Any collision Resistant). It says we wish to stress ...
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382 views

HMAC vs Encrypted Hash

What is best to use (for message integrity) between… AES(Data) + HMAC(Data) AES(Data + HMAC(Data)) AES(Data + Hash(Data)) …and why?
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Is stretching hash several times basically the same as bcrypt?

As I understand it, the main advantage of bcrypt is stretching so it becomes slower to crack overtime. But, is using a "good enough" algorithm (e.g., SHA-2 family) then stretching until it's slow ...
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Should I use md5 for my new application?

MD5 is a very fast hash and its output is short and easy to store. Should I use it for my non-security-sensitive application? I don't think so, but I can't seem to convince anyone else that this is ...
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Thoughts on secure hashing and the “mds” algorithm

Almost a decade ago Raymond Chen blogged [1] about the "hash reset attack" cautioning developers to record the content length in addition to the message digest. Recently I came up with a variation on ...
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Changing a bit Changes Hash

I am very curious on the fact that SHA,MD5 and all related Hash Functions change the output even by changing one bit in input Message.Why is that?
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Help in understanding exactly how lattices used as one way functions for hashing

I am doing a cryptography course via long distance and we have been given an assignment which is based on lattice-based cryptography. I have spent the majority of the past week sifting through papers ...
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175 views

Convert a number to sha-1

I have a task to find a the message for which the SHA-1 hash's last 11 symbols in hexadecimal presentation corresponds to an 11-digit number. I have been given the following example solution: For ...
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90 views

Explicit Key SHA-1

I'm reading “Collision-Resistant Hashing? Towards Making UOWHFs Practical” and in the Section 2 it says: Hash functions like MD5 or SHA-1 have no explicit key. But no notion of ...
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552 views

How is input message for SHA-2 padded?

I read about how is an input message prepared to be hashed by MD4,MD5 or SHA-1: Step1 Append padding bits The input message is "padded" (extended) so that its length (in bits) equals to 448 ...
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Do I need to keep a 64-bit version number secret?

Assume the following structure: version | iv | ciphertext | HMAC(version | iv | ciphertext | ..., key) The version starts out ...
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What key length is required to keep simple keyed “hash” secure?

In a previous question, I described a particular keyed "hash" that mapped a 5-digit input code into a 5-digit output code. It used a 8-bit key which is very insecure - more than 99% of the time, you ...
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143 views

Physical Level Encryption

What types of algorithms that are capable of signing a message are out there that run on a physical level, e.g. lacking the infrastructure of a standard PC, no memory, processor or motherboard in the ...
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How to hash a structure that needs to include that hash's outcome?

so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
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161 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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488 views

How to implement order preserving encryption or order preserving hashing [closed]

Does anybody know any free implementation of either order preserving encryption or order preserving hashing? I've found some codes like CMPH but I need to dynamically add new DATA and that's why most ...
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Hash function and outputs of arbitrary length

I know that Skein can output a digest of arbitrary size, with a kind of counter mode. Blocks of the resulting digest can be computed in parallel. What about Keccak ? I know that a sponge function can ...
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Hash Function to get same value for different messages

I am studying a function where I found the some hash properties. Hash functions: Given a code c is computationally infeasible to find m such that ...
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51 views

Bicliques for permutations

So I'm trying to understand the complexity of the biclique attack on Grostl and I have some questions: 1) The paper introduces sliced bicliques where on Grostl one constructs a biclique of dimension ...