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 do you construct a practical full-domain hash function?
I am looking for practical constructions for Full Domain Hash.
I have read Random Oracles are Practical by M. Bellare and P. Rogaway, the construction suggested on page 8, under "Uniformity: a ...
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Does Keccak have an eTCR mode?
On page 7 of NIST's views on SHA-3's security requirements and Evaluation of attacks, I see that, at least at this point, NIST planned on offering SHA-3 having eTCR security (defined on page 3):
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3answers
304 views
reverse of md5sum
This might be out of ignorance, I apologize, but how complex of a problem might it be to generate a file of size N whose md5sum is X?
For example,
...
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4answers
292 views
Looking for cryptographic secure hash algorithm(s) that produces identical root hash for differently sliced hash list
I have a scenario similar to the one described in Wikipedia: hash list, but with a twist. I'm looking for a cryptographically secure hash function that would create the same root hash for the same ...
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2answers
182 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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3answers
213 views
Getting started [closed]
I'm looking for a good place to start in cryptography and places to go to get free books etc on the topic.
I have been looking online but I always get stuck at some point or another. I need something ...
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2answers
444 views
Why do all hash functions use big-endian data?
I've looked at several hash function specifications, and they all emphasize the need for big-endian byte ordering. Is there a reason for this that has to do with security, or is it simply convention?
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1answer
99 views
Secure order preserving hash function
Is there a construction of an order preserving hash function that keeps the preimage property of a crypto hash function? By order preserving hash function (OPHF) i mean for $x<y$ then $OPHF(x) < ...
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1answer
152 views
Why are these specific values used to initialise the hash buffer in SHA-512?
I'm reading the book Network Security Essentials written by William Stallings.
To create a message digest with SHA-512, we have to go through some steps:
append padding bits.
append length
...
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2answers
87 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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2answers
242 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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2answers
90 views
Many consecutive hashes to slow down brute force attack?
I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to prute force, without a noticable ...
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1answer
106 views
Why do we need extra hashing if we could use simpler scheme?
Lets say that we use init vector IV, key K and HMAC key H. Message is M.
Mode of operation is CBC !!!
We usually encrypt as this
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215 views
How to generate successive stream-cipher keys?
I've identified a weakness in a distributed simulation system I'm looking at, and I'm looking for some advice on how to fix it.
Clients initially negotiate an authentication token with a login server ...
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1answer
689 views
How does PBKDF1 work?
I need some basic guideline on Password Based Key Derivation Function. PBKDF1 generates a key from password and salt using Hashing algorithm (like SHA1, SHA256, MD5).
What is the step behind this?
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1answer
230 views
Verifying the integrity of ciphertext using the cleartext hash?
I want to be able to verify the integrity of a ciphertext by providing the cleartext hash, for this to work it would need to:
$$hash(crypt(cleartext)) = f(hash(cleartext))$$
Where $f$ is an ...
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2answers
95 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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1answer
74 views
What's the difference between “HashX-512” and “HashX-1024”?
I need to make a Skein hash's, specifically, Skein-1024; however, I only have access currently to Skein-512. Is there any way to utilize a Skein-512 function to get the result of a Skein-1024 hash?
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1answer
48 views
Selecting a large NUMS Safe prime
Suppose I want to use the following simple hash function.
For a mesage $m$, take some public $a$ and prime $p$ and raise $a^m \bmod p$ (never mind the computational expense of this operation).
This ...
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2answers
203 views
Can one build a one-way function from AES?
We change the AES block cipher encryption:
we delete the key schedule algorithm
the user now provides a string of 1408 bits
we divide the string to 11 sub keys, and use them directly in the ...
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1answer
125 views
Crack cryptographic hash functions using Toffoli gates?
Might it be possible that reversible combinatorial circuits (or some emulating software) are going to be used to get the input of the white box?
I mean if I have constructed a proper reversible ...
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1answer
191 views
How to test distribution of a hash function?
From what I've found, it is generally accepted a cryptographic hash function like SHA-2 has an evenly, randomly distributed output. Is there a way to test this without running through the entire ...
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1answer
343 views
Can I combine two of SHA-3 candidates cryptography hash functions and obtain more secure Algorithm?
For example, Is possible to combine (Concatenate or Chain or XOR) Skein SHA-3 candidate with Grostl SHA-3 candidate to increase security?
Note: I just want more secure output and CPU cycles does not ...
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1answer
283 views
How to implement order preserving encryption or order preserving hashing
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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1answer
190 views
“Signing” with public key
For this question, the following caveats and assumptions hold:
There exists a 2048-bit RSA key pair used exclusively for signing/verification
The private key is kept completely private
There exists ...
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2answers
193 views
Seeking special-use fingerprinting/hashing algorithm
For a project I wonder if there exists some kind of fixed-size checksumming/fingerprinting function in which based on this fingerprint given data block 1, it is easy to generate more data blocks that ...
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1answer
170 views
Can one group the SHA-256 outputs depending on partial inputs?
Is it possible to predict a hash key based on half key?
Let's have some example:
I have 100000000 hash results, and they are generated by either
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1answer
84 views
How can a key pair be derived from an arbitrary hash?
If I correctly understand the concept of a "brain wallet" in BitCoin, you start with a passphrase, generate the hash of the passphrase, then somehow derive a public / private key from that to use as ...
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2answers
121 views
Store hashed email and compare hash values
I have a number of different systems sending me email addresses, but I don't actually need the underlying email, just a hash of the email address. I know I can compare hash values to find matches ...
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1answer
62 views
Ensuring integrity of a client side script
I want a script that is running on the client to compute a collision resistant hash and send it to a server. I need to ensure that the script which performs this hash is not altered in any malicious ...
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1answer
186 views
How do unkeyed hash functions (for MDCs) provide security?
Unkeyed hash functions are, by definition, hash functions computed without a key. SHA-1 is an example. MDCs (message digest codes) are a subclass of unkeyed hash functions. How are unkeyed hash ...
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1answer
327 views
Crack SHA1 hash code
Given a set of SHA1 hash code, if we knew a portion of the plaintext for each particular hash code, and also the remaining portion of the plaintext is a constant value for each hash code.
Is it ...
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1answer
192 views
How to represent a 32-byte SHA2 hash in the shortest possible string?
I'm calculating a SHA2 hash of a certain sensitive key value. I need to store files on disk using this hash a directory path prefix. So lets say I hash the key value 150023, I get a 32-byte value ...
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1answer
107 views
Tips on conceiving safe software messaging platform
I have a personal project in mind in which I plan to use cryptography in order to let the users be confident in the fact that, even if all data get's stolen, it would be virtually impossible to crack ...
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1answer
316 views
How to generate one-time password
Through my reading about the generation of one-time password (OTP) I found that there are many algorithms that generate OTP and they are either based on time such as TOTP or based on mathematical ...
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1answer
41 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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1answer
60 views
Why are the Davies-Meyer and Miyaguchi-Preneel constructions secure?
The Davies-Meyer compression function $h(H, m) = E_m(H) \oplus H$ is said to be secure. So too is the Miyaguchi-Preneel compression function $h(H, m) = E_m(H) \oplus m \oplus H$. Why are these ...
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1answer
103 views
Finding a collision for a hash function
I'm trying to find a collision for the following (modified) Merkle-Damgard hash function.
Suppose we already have a hash function $h : \mathbb{Z}_2^{2·n} \to \mathbb{Z}_2^n$ for fixed length bit ...
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1answer
103 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
263 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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67 views
Hash function with values in a multiplicative group of prime order
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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70 views
Is SHA-1 collision free on data up to 20 bytes long? [duplicate]
Is SHA-1 collision free on data up to 20 bytes long (lenght of hash / internal state)? That means that every input produce unique output, but you surely know that, i just write it in order my question ...
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41 views
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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40 views
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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48 views
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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0answers
60 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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195 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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2answers
203 views
SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?
Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
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4answers
228 views
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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3answers
103 views
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,
