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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Publicly exposed hash of private key

Would exposing a cryptographic hash function's digest (e.g. SHA-3) of RSA private key data compromise the key? If so, what are the possible (cryptanalysis-) vectors for attacking the key if an ...
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233 views

Can you help me understand hash-preserving encryption?

I have rather simplistic understanding of cryptography, so I have to beg a pardon in advance if the question has internal contradictions. Imagine data $A$ with a hash $hashA$. This data is encrypted ...
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54 views

are ideal hashes possible to create?

In a hash function, you map an input of arbitrary length to an output of finite length such that the relationship is one-to-one (or at least that's what you are trying to achieve). Hence, isn't it ...
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Can the XOR of two non-collision-resistant hashes be collision resistant?

Suppose I have two hash functions, of which neither (or only one) is collision resistant, and I want to create a new hash function by taking the bitwise exclusive or (XOR) of the results of those two ...
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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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218 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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117 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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1answer
75 views

Adversary to Any Collision Resistance Hash Function

I'm reading a notion Any Collision Resistance for Hash Functions. In the lecture define a collision finder CF. CF is said to $(t,\epsilon)$-break the family of hash functions $F_K$ if the ...
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216 views

scrypt and bcrypt for benefits of both?

I've been reading about bcrypt and scrypt, and it seems that the general consensus is that bcrypt is more "tried and true", but scrypt is better in theory. Couldn't you just hash something with ...
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137 views

Tamper-evident audit logs

I want to be able to detect tampering in a log file that is under the control of an untrusted party. I am not interested in secrecy, only the integrity of the contents in the file - so I want to ...
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1k views

How is the MD2 hash function S-table constructed from Pi?

For fun, I'm learning more about cryptography and hashing. I'm implementing the MD2 hash function following RFC 1319 (http://tools.ietf.org/html/rfc1319). I'll preface by saying I know there are ...
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40 views

Merkle-Damgard transform: necessity of the Length block [duplicate]

The Merkel-Damgard transform append the message length (in blocks) to the message itself and then computing the 'chained hash' algorithm. Does the last block (which contains the length of the ...
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226 views

How to put the hash of a PDF file in the PDF file? [duplicate]

I know it sounds strange.. but, are there any ways in practice to put the hash of a PDF file in the PDF file? And after geting the hash in the PDF file - if someone would do a hash check of the PDF ...
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170 views

Is there a cryptographic hash function that can be performed with pencil and paper?

Imagine I'm signing up for the 99th new web site this month. I somehow take my secret key (which I have written down on a card in my wallet) and the domain name of the site and feed them both into ...
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2answers
86 views

MD5 theoretical question

Ok, so this is a very possible stupid question, but one of those things that has sat at the back of my mind for a while. We all know that MD5 has issues, and these have been known for about a decade. ...
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1answer
89 views

SHA-1 Keyed Hash Function

I know that SHA-1 is an unkeyed cryptographic hash function when used in practice. But, in the theory, all hash function are defined with keys. My question is: How I will be able to formalize the ...
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1answer
94 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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1answer
101 views

Why is appending the key to a mesage and then hashing that insecure if the hash isn't weakly collision resistant? [duplicate]

Suppose I have H(M|K) and that H is not weakly collision resistant. If I have a message mac pair (M,MAC), how is it possible to find another message mac pair (M2,MAC2)? My thinking for this problem is ...
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105 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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55 views

Weaker Notion of Target Collision Resistance

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” which states: While it might be easy to find a collision $M,M'$ in $F_K$ by making both $M,M'$ depend on $K$ ...
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1answer
69 views

Dependence on Keyed Hash Function

I'm reading the paper “Collision-Resistant Hashing? Towards Making UOWHFs Practical” which states: With an ACR hash function $F$ the key $K$ is announced and the adversary wins if she manages to ...
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131 views

Splitting a password for dual roles [duplicate]

I would like to prompt users for a single passphrase to establish trust with separate, normally (but not always) complementary systems from one password input. I'm essentially looking for a box where ...
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244 views

Difference between collision resistance and target collision resistance

For a hash function, what's the difference between Collision Resistance and Target Collision Resistance?. I understand the definition of hash function collision resistance, but I don't know about ...
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189 views

What are the pros and cons of deterministic site-specific password generation from a master pass?

I've been reading up a bit on deterministic password generators. All the ones I can find basically do something like this: Pick a master username and a master passphrase. The username could be your ...
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620 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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60 views

Hash of multiset of values, which lets me compute the hash of the union

Cryptographic hash functions normally take as input a bitstring. I am looking for a hash function that takes as input a finite multiset of values. In other words, given $S \subset \{0,1\}^*$, I want ...
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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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Why are the initial states of hashes functions (like SHA-1) often non-zero?

There is already a question asking "Why initialize SHA1 with specific buffer?" and my question follows on from this: Why are the initial states of hash functions often non-zero? For most, I have ...
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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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64 views

How do you use the Tiger hash function with GPG?

I've searched Google and the GnuPG documentation and I haven't been able to find an answer. Some pointers in the right direction would be greatly appreciated.
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340 views

Would it be possible to generate the original data from a SHA-512 checksum?

So, I have a file that is XY Exabytes big. I create a SHA-512 hash from it. Are there any theoretical chances that I can retrieve the original data just from the sha512 hash? Also, are there any ...
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465 views

Estimating random number entropy for input into 256 bit hash

Assuming a random number generation process outputs lots of numbers between 0-9. First I gathered up a bunch of the numbers, converted them to binary and created a bitmap. Not so random as you can ...
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Complexity class of an idealised version of Bitcoin's proof-of-work (hashcash)? [closed]

To formulate this question precisely, I will define an idealized hypothetical "perfect" hash function $H(n)$ which has nice scalability properties, and will formulate a problem PERFECT HASHCASH in ...
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Proof that MACing a hash of the message is also a secure MAC

I found a theorem that says: Let $MAC = (S,V)$ be a MAC for short messages over $(K,M,T)$. Let $H: M^{big} → M$. Define $MAC^{big} = (S^{big},V^{big})$ over $(K,M^{big},T)$ as: $S^{big}(k,m) = ...
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223 views

Does encrypting a hash of the message yield a secure MAC?

Is $mac = enc(hash(x))$ a secure MAC for hash = SHA256 and enc AES in CBC mode or ECB mode. Normally AES-CBC is malleable. But in this case I use a hash function for the one-way property. For ...
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1answer
177 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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1answer
371 views

Hash functions throughput performance [closed]

Without taking into account security, which hash function is the fastest one among the following: MD5, SHA-1, SHA-2 (for various internal size), Keccak, and other… ?
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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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324 views

WIN LM Password Hashes (using John the ripper) [closed]

In a problem set, we've been asked to use John The Ripper to crack a list of Win LANMAN passwords. They are of the following form: 953A55E36AB85C0B9DA92C18555E42E1:0169295E0A6A6B35B2DD9932D10C1978 ...
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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 ...
6
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1answer
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Formal definition of “explicit” algorithm?

A long time ago, I read that the definition of "cryptographic hash function" is "collision-resistant one-way function". (A similar definition shows up in the FIPS standards for SHA-1 etc.) But this ...
2
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1answer
280 views

Is this a good entropy collector and whitening technique?

I'm just reviewing a program someone wrote to provide high quality random data using an entropy collector and a hash based whitening technique. I'll try summarize the process: Collect entropy from ...
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1answer
381 views

How hard/easy will be to break a SHA-1 or SHA-256 hash if the attacker knows part of the original text?

I'm creating an algorithm to hash some text variables (20/30 characters long) to send them across an insecure channel. I'm not dealing with high security data, so no credits card numbers or any other ...
3
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1answer
88 views

Hashing a message with a length that isn't a multiple of 8 bits

NIST FIPS 180-4. “5.1. Padding the Message.” Suppose that the length of the message, $M$, is $l$ bits. Is there any library that can receive a message of length (in bits) which is not a multiple ...
3
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453 views

Difference between salted hash and keyed hashing?

A cryptographic salt is additional input other than message itself for a hash function so that it prevents attacker from launching dictionary attacks . Usually the salt is stored along with the hash ...
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375 views

Why must curve25519 shared secret be hashed?

When using the curve25519 DH function, D.J. Bernstein recommends hashing the shared secret before using it as a session key for a symmetric block cipher. Why is that? Hashing won't increase the ...
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Are NIST's changes to Keccak/SHA-3 problematic?

NIST is working on standardizing SHA-3. They have selected Keccak as the basis for SHA-3, and they plan to make some small changes to it; the result (with NIST's changes) will be standardized as ...
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413 views

Why does second pre-image resistance imply pre-image resistance

I am studying hash functions. I can understand why collision resistance implies second preimage resistance, but I don't get why second preimage resistance should imply first preimage resistance. ...
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111 views

What security differences are there between E(p',“well-known-plaintext”) vs. hash(p') where p'=KDF(p)

I am using a KDF to derive a key, p' from a password p. I would like to know if the password is correct before using the derived ...
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Could completely public passphrase hashes ever be reliably secure?

This is a hypothetical question and I only have a basic understanding of Cryptography. If one were to follow the very best cryptographic practices for storing passphrases, could it ever be possible ...