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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Is a collision attack possible on MD5 if message is known partially

Is it possible to find $m'$ such that $\operatorname{MD5}(m'||m_1)=\operatorname{MD5}(m_1||m_2)$ if I know $m_2$ and $\operatorname{MD5}(m_1||m_2)$? Is this a collision or a preimage attack? Also in ...
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98 views

Simplified Key Wrapping to Achieve Only Confidentiality?

I'm looking for help in understanding why the algorithm described here would not deliver adequate protection of confidentiality. We don't care about other criteria such as authenticity or integrity. ...
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132 views

Questions about hash functions

Let $H$ be a secure hash function (e.g. SHA256), is it possibile to find $H(M1)$ given $H(M1||M2)$ if the length of $M1$ and/or $M2$ is exact the block size of the hash (that is, 64 bytes for SHA ...
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315 views

Are there attacks that break collision resistance but not preimage resistance?

Are there any examples of attacks on hash functions which: break collision resistance and second preimage resistant, or break collision resistance and preimage resistant? I have looked at ...
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286 views

2 comparable hashes generated from one string

Assume a website where people log in with their password. The password is now stored in sql database as: md5(password + random_salt) We are adding the ...
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183 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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119 views

Is it safe to hold key file's hash in application

Title says all; Is it safe to hold key file's hash (MD5 or SHA1) in application (hard-coded)? Thanks
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1answer
847 views

HASH Algorithm for 8 bits MCU

I need to implement the HASH algorithm (MD5 & SHA-1) on an 8 bit MCU. I hear it can only be implemented on 32bit and sometimes 16bits MCU. Is that possible? I will appreciate link where possible. ...
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289 views

How does the energy consumption of the SHA-3 finalists compare?

I am curious, is there any paper where SHA-3 competitors are compared in terms of energy efficiency?
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737 views

Hash or encryption function for challenge-response protocol?

Say I have an authentication protocol where the shared secret is never transmitted. The server passes a challenge to the client and the client calculates a response using an algorithm where the ...
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46 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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51 views

comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
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40 views

Signing integers and UUIDs and restoring them from a third party server without tampering

I'm educating myself about cryptography. I know this is a long one, but please, bear with me. :) Now I have a scenario in my mind and I'd like to ask if what I've thought is sound (enough), what more ...
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44 views

Discrete logarithms: large prime modulus vs. large semi prime modulus

I have a cryptography homework question, in the question it says a cryptographic hash function in the form of $f(x) = g^x \bmod n$ , where $n$ is a very large prime (1024bits and more), $g$ is a ...
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53 views

Secure and unlinkable identifiers

Let's say we have Alice and Bob sharing a symmetric key $k$. Alice wants to leave a number of messages for Bob on an untrusted server (honest-but-curious model) that is also used by many other people ...
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80 views

Bobcat hash, trying to find a 48-bit hash collision for x

I am trying to find a collision with the Bobcat hash of the 48-bit hash. I am a beginner coder so please point out any flaws in my modification of the bobcat program. It does find a truncated 12-bit ...
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88 views

Is there a way to slow down collision attacks using iteration?

The simple way to iterate a hash function $H(H(m))$ only makes brute force preimage finding slower, but leaves collision attacks as fast since a collision in the inner hash function is a collision in ...
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42 views

Determine safety of exercise hash functions

There have been several attacks against hash functions such as $h_{sha1}$ and $h_{md5}$. Professor A suggests a new function $h_{666}$ with an output length of 666 bits. Professor B suggests ...
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91 views

SHA3 Keccak, absorbing data to the state

I'm working on implementation of keccak algorithm and have one problem. Tell me please, takeing an example "test": will state (before block permutations, but after padding - pad10*1) look like this: ...
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110 views

Formal proof of theorem concerning the Random Oracle Model

Reading a book on cryptography by Douglas R. Stinson I've met the following theorem, which is stated without proof (see here). Thereby, $\mathcal{F^{X,Y}}$ denotes the set of all functions from ...
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233 views

Does this guarantee a unique 32 bit Hash?

I came across some source code that loosely does the below in order to achieve a 32 bit hash. The input string is passed through MD5 to get 16 bytes Hash (as usual). Then the 16 bytes are split into ...
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110 views

Cipher built from GPU primitives [closed]

Is it feasible to build a cipher (or hash) out of GPU or DSP primitives (e.g. big matrix multiplication, Fast Fourier Transform, big block SIMD, or hardware H.264/AVC codec)? Preferably those are slow ...
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83 views

Implementation Attacks on Hashes

So I am familiar with attacking implementations of block ciphers via side channel attacks, cache-timing attacks, etc. What implementation attacks are there against hashes or hashed based functions ...
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135 views

Convergent encryption has dictionary attack, but why hash function doesn't?

Convergent encryption (CE), $E_k(d)$, is a way to encrypt the data $d$, with the characteristic that the encryption key $k$ is $k=h(d)$, where $h(\cdot)$ is a cryptographic hash function. Consider a ...
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implementing a cryptographic hash with a block cipher [duplicate]

How can a cryptographic hash function be implemented/created using the block cipher? I was wondering if we can use AES in cipher block chaining mode to implement it.
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68 views

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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192 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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158 views

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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107 views

How does use of HMAC affect hash function combiners?

In the comments of this question, Ricky Demer proposes a function $HMAX$ to combine two $HMAC$s based on different hash functions: $HMAX_{H0,H1}(⟨k_0,k_1⟩,m) = HMAC_{H0}(k_0,m) \oplus ...
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Infinite depth BLAKE2b tree hashing

In the BLAKE2 paper, the authors define Maximal depth (1 byte): an integer in [1, 255] (set to 255 if unlimited, and to 1 only in sequential mode) Node depth (1 byte): an integer in [0, 255] ...
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502 views

Question about modifying the MD5 plain text to cause a collision

I was trying to understand MD5 and got stuck with this question, its from Michael sipser's book on Information security Principles and Practice, 2nd edition The MD5 collision in Problem 25 is said ...
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160 views

Precise meaning of various terms related to universal hash functions

I've been reading about universal hashing, but I'm confused by all these different terms and notations. Could someone help me understand the precise meaning or relation between the following terms: ...
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175 views

How can I prove that this encryption scheme from a random oracle is secure?

I am reading this example: A random oracle is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
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142 views

How hard is a known prefix hash preimage attack?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
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422 views

Openssl implementation of improved sha1 hashing [closed]

I want to use the improved sha1 hashing algorithm from the Intel blog described here Intel sha1 hashing. Currently I am using Openssl sha1 hashing in my application. I wanted to know if anybody has ...
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1answer
178 views

Hash function as secure as one-time pad?

We know that the one-time pad is provably secure as a cipher to encrypt some data. Is there an algorithm which does the same just as a hash function? Can we get a provably secure hash function? Maybe ...
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232 views

Are there cryptographic hash functions which do not have any collisions?

I've been studying digital signatures and hash functions recently, and I was wondering: Do hash functions exist which will never produce collisions?
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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,
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313 views

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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346 views

Different padding rules for Merkle–Damgård and Keccak/sponge function

We learned that length padding was used in Merkle–Damgård where after padding with zeros another block is added that contains the initial length of the input. This is supposed to prevent same hash ...
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341 views

Secure Hash Function based on AES

How secure would a hash function be which appends an extra block of 16 zeroed out bytes to the end of the message and then AES-encrypts it with a well-known password (say the first 128 bits of pi) ...
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160 views

Slow hash algorithm that does not require salt?

I usually choose bcrypt when hashing as I can set the work factor to slow down the calculations of the hash. However, I have to keep a copy of the hash in order to verify it (since it includes the ...
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189 views

Why can't we use a hash with no collision to compress data reliably?

According to wikipedia, a hash maps digital data of arbitrary size to digital data of fixed size. For all practical measures, a hash is a unique signature of a big chunk of data. But there is such a ...
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100 views

Is the hash function defined in this exercise collision-resistant?

I have this problem: "Let ${\rm Enc}_k(m)$ a safe block encryption system. We define a hash function $H(m)$ as follows: $m$ will be concatenated with $0$ until $|m|$ is a multiple of ...
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481 views

What are words in a HASH algorithms

From wikipedia: "They differ in the word size; SHA-256 uses 32-bit words where SHA-512 uses 64-bit words." In this context what do they mean with words? is it the same as a 32 bit (or 64 bit) block ...
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776 views

Comparing Files: Is it better to use multiple hash algorithms or just one?

I'm looking to compare (for byte-for-byte equality) two binary files. I already have the process down: Check for existence etc. Compare file lengths Use a hash or CRC of a sort (right now I use ...
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98 views

Preimage of SHA512 with a known suffix

Is it possible to figure out what $arg1 is if I know both $arg2 and $arg3 in addition to ...
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170 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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718 views

Real life collision when only using truncated hash

For MD5 two different inputs are known that produce the same 128 bit hash value. However, these inputs are artificially created for this specific purpose. For normal, real life inputs I believe no ...
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On the privacy of perfect hash functions

I'm digging into the several algorithms for building (Minimal) Perfect Hash Functions. It seems that the recent works provide quite a few very efficient algorithms. However, I'm wondering how a ...