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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Cryptographic hash function for 32-bit length input keys

Since I'm unfamiliar with cryptography area I haven't been able to find cryptographic hash functions for 32 bit integer keys. It seems all such functions (as I saw here) are designed to digest a ...
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83 views

Associative standard cryptographic hash function

I am looking for a standard hash function which satisfies the following property: A hash function $H(a,b) = F(h(a),h(b))$ with $h$ (within $F$) any standard cryptographic hash function and $F$ an ...
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113 views

Is there a number of tries after which Hashcash is guaranted to be solved?

Hashcash is a proof-of-work system in which the Sender needs to find $Y$ such as the first (let's say 20) bits of $H(X+Y)$ are zeros where $H$ is a one-way hash function, $X$ is a fixed value and $+$ ...
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105 views

are deterministic pseudorandom based hash functions chaotic?

Im 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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80 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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150 views

Hash collision resistance of $\mathcal H^\prime(m) = \mathcal H(\mathcal H(m)|m)$

So far as I can find, every method better at producing hash collisions in cryptographic hashes than generic collision search involves finding some metric for the distance between two messages' hashes ...
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269 views

Cryptographically secure keyed rolling hash function

I could not find any mention on the Internet of a proven/known cryptographically secure keyed rolling hash function (ie rolling MAC). Has the question been studied, is it possible to build one ? By ...
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52 views

On modeling a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$

How can one model a random oracle hash function which maps $\mathbb{G}_1 \rightarrow \mathbb{G}_2$? (Assume $\mathbb{G}_1$ and $\mathbb{G}_2 $ to be additive and multiplicative groups of prime order ...
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31 views

Bit strength of combining hash functions? [duplicate]

Suppose there are hash functions H1 and H2 with bit strength of H1 and H2 is n1 and n2. A new good hash function is generated by combining H1 and H2. What will be the bit strength of these combined ...
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118 views

Skein state size advantages

Skein is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as the “primary proposal”. Is there any advantage – other than potential memory or speed ...
4
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1answer
155 views

Understanding hash entropy

I have been told that one advantage of using a hash function is that it spreads entropy over all input bits. But it also seems to be true that a bad hash algorithm can make things less random. But how ...
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77 views

PRF and hash functions

Is there a difference between PRF and a hash function? example: Creation of a secret key is using PRF and creating a secret key is using hash function.
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69 views

Accelerated hashing on consumer-grade CPU?

Question is a follow-up to this one. The question was about accelerating SHA1. I am writing an application, where I do have a choice of hash algorithm, as long as it's a strong one. I want to be able ...
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74 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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64 views

reverse an identicon to its source string

Identicons are used to create unique images based on IP address or strings. Lots of programs are available to generate identicons based on an input string. My ...
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0answers
51 views

Tiger Tree Hash vs generic Merkle Tree

Is there any advantage of using Tiger Tree Hash over any other hash function organized as the Merkle tree? Are there maybe any properties of TIGER that, say, SHA2 or BLAKE in Merkle tree do not have? ...
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130 views

Can Skein be used as a secure MAC in format H(k || m)?

Can Skein be used as a secure MAC in format H(k || m)? I understand it can work with HMAC, but it is fine as a one-pass MAC in the format above and resists length extension attacks. Is this ...
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77 views

Timestamping using a hashed linked list and public known events

Let's say we have a timestamping scheme of the following characteristics, The hashes of the documents we are trying to timestamp are XOR'ed with "events" whose time of occurrence are very publicly ...
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1answer
91 views

What's the entropy of the output for Tiger Encryption?

I'm tasked to apply tiger encryption to my string(key). Does anyone have any idea how to find the entropy of the hex output by tiger encryption?
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95 views

Generalize the Merkle-Damgard construction for any compression function

I am trying to figure out this question: Generalize the Merkle-Damgard construction for any compression func­tion that compresses by at least one bit . You should refer to a general input length ...
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85 views

Will hashing over and over eventually give the same hash?

There are many cases in maths where doing the same thing over and over again will bring you closer to a value. Derivation of polynomials is the striking example: no matter what you start with, you end ...
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1answer
124 views

Should HMAC or NMAC or plain Keccak be used for a secure MAC?

After some digging around in the HMAC spec I found this (paraphrased): Step 1: If the length of Key equals the block size of the hash function (512 bits/64 Bytes for SHA-256), set the key equal ...
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28 views

What can I change in Lane to

What can I change in Lane to increase memory (and compute) consumption. My first idea would be to change n, but with Lane hash function is there a way I can up the n to a level higher than 512. If I ...
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67 views

HMAC definition by using only one key

Suppose $H$ is a hash function; why is $H(k||H(k||m))$ not secure? See this HMAC definition. In there, indeed two keys are used and the mac algorithm is $H(k_1 ||H(k_2 ||m))$ . Why don't we use ...
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1answer
167 views

Are the MD5 constants an S-Box?

I noticed that several hash algorithms, in this case MD5, defines some constants. MD5 defines 64 constant values (the shift count per round) which also gets expand (via sine) to a summand for a ...
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81 views

Cryptography Implementation in software

I am trying to implement a password manager in C and I had a question about the proper steps in implementing the crypto. I looked at some implementations, google talks on crypto and what the standards ...
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108 views

XORing a header with SHA512-hash - secure?

I am writing a application that encrypts text several times and stores the result. The result looks like complete random bytes, therefore I add some random bytes at the end. To let the program know ...
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120 views

Is there a reason that the N value in scrypt is limited to powers of two?

I have been looking at the scrypt hashing algorithm and am confused as to why the N value, which determines the overall cost, is limited to powers of two. There are ...
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249 views

Security of KDF1 and KDF2 (hash based KDF's)

It's still common to come across implementations of KDF1 and KDF2. Basically these are KDF's that simply derive multiple keys from the key seed and a counter: $K_i = KDF(K_{master}, i) = H(K_{master} ...
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122 views

Constants Differ in SHA1 implementation

I am trying to understand why the constants differ in this SHA1 implementation: https://code.google.com/p/crypto-js/source/browse/tags/3.1.2/src/sha1.js ...
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65 views

Composing hashes and/or MACs

Suppose I have n hash/MAC functions, of which n-1 are extremely insecure, leaving only one that is in fact cryptographically secure. If I use all of them on a message and the XOR them together the ...
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233 views

How can I convert numbers into prime numbers?

I'm working with one-way accumulators, but I'm not knowledgable in cryptography. Is there an easy peasy way to hash numbers (or whatever) into prime numbers? Obviously I'd like it to be collision ...
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758 views

Are AES-256's related-key weaknesses exploitable if it is used to build a hash?

Assume it is made a hash based on AES-256 encryption (perhaps because this is hardware-accelerated, but no standard hash is); and it is used the Merkle–Damgård structure, that is padding of the ...
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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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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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Will repeated rounds of SHA-512 provide random numbers?

If I hash a keyword with SHA-512 and then feed the output as the key for the next round ....and keep repeating this process, will I gather a stream of random numbers?
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What's wrong with this “order-preserving MAC” function?

Please note: this is purely a thought experiment and not intended for any real-world usage! I came up with a simple function $\mathrm{OPF}$ to map the integers $[0,C)$ (where $C$ is the "ChunkSize") ...
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109 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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208 views

What is the difference between authenticating and signing a document?

Authenticating a document means to verify it is from the sender. But it seems like signing a document also verifies it’s from the sender. What exactly is the relationship or difference between ...
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1answer
115 views

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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1answer
957 views

HMAC-SHA1 vs HMAC-SHA256

I have three questions: Would you use HMAC-SHA1 or HMAC-SHA256 for message authentication? How much HMAC-SHA256 is slower than HMAC-SHA1? Are the security improvements of SHA256 (over SHA1) enough ...
3
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1answer
86 views

Key-dependent encryption in TAHOE-LAFS

TAHOE-LAFS uses a form of "key-dependent encryption", in that a private key SK is encrypted with the truncated hash of the private key: ...
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255 views

How do I create a short signature? (e.g. less than 100 bytes)

I want to put information into a QR code and have it signed so that the authenticity of the information can be verified. But QR codes have limited storage capacity and when I used e.g. gpg I get ...
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211 views

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 ...
2
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1answer
171 views

Why the need to hash before signing small data?

I’ve got two questions: I’m doing the following: Data : uuid + int + nonce Signature: ECDSA(sha256(Data) ) To verify the signature: ...
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63 views

How to make a crypto-currency robust to 51% attacks?

For Example: In Bitcoin it is theoretically possible to double spend if you control > 50% of the computational power in the network. Also it is possible to apply "selfish mining" with far less than ...
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1answer
104 views

Why does Fortuna RNG use double SHA-256?

In the paper for Fortuna the authors say that you can use any good digest algorithm (obviously as long as its output is 256 bit) and then they recommend double SHA-256. Why? What's the benefit? What ...
2
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4answers
166 views

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-way-function where we get the original ...
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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 ...
2
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1answer
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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 ...