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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Can I find two specific words with the same md5 hash?
I want to find two strings containing special words like "yes" or "no", mixed with random characters, for which the MD5 hash is equal.
An example of what I'm looking for:
...
3
votes
3answers
133 views
What is the difference between a HMAC and a hash of data?
On a recent question it became apparent that there's a significant difference between an HMAC of input data and a hash of input data.
What exactly is the difference between an HMAC and a hash of a ...
3
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4answers
136 views
Turning a cipher into a hashing function
This is theoretical question. I'd like to know if it's possible (and what are eventually the consequences), not that I'm going to do it in one of my projects. ;)
The first hashing functions created ...
4
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1answer
306 views
From hash to Cryptographic hash
After reading some excellent papers on SipHash, I understood that good non-cryptographic hashes such as MurmurHash and CityHash are not secure for MAC usage, due to a certain type of DDos attack ...
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0answers
32 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
bit-length(Z) = 256 (such as in SHA-256)
bit-length(X) = 128
...
1
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0answers
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 ...
2
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2answers
204 views
what kind of hash function can provide a short hash and be collision resistant?
When you try to connect via SSH, you see a signature which is short but I heard it is even stronger than sha256. It is perhaps stronger because it uses more rounds. Is there a hash function or a ...
0
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0answers
67 views
MD5 > Would multiple hashings increase security? [closed]
A Simple question,
if i run a string trough the standard md5 encryption function multiple times, does it increase security the more i do it? does it protect against rainbow tables? etc.
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2answers
131 views
Can the hash of one message be used to make it easier to find the hash of a very similar message?
Background:
I am trying to get an understanding of using a hash of a passphrase as a secret.
Example:
...
-1
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2answers
152 views
What are alternatives to the random oracle model for modelling hash functions? [closed]
I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as ...
27
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5answers
2k views
Guarding against cryptanalytic breakthroughs: combining multiple hash functions
Assume I want to design a protocol (or data format or similar) including some cryptographic hash, and want it to be as future-proof as possible, i.e. I want to avoid that breakthroughs in cryptography ...
2
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2answers
118 views
Commutativity of keyed hashes
Definition
${H_1}^{K_1}(X)$ means data $X$ hashed by keyed hashing algorithm $H_1$ with key $K_1$.
Short question
Is $H_1^{K_1}(H_2^{K_2}(X))$ equal to $H_2^{K_2}(H_1^{K_1}(X))$?
Is ...
0
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1answer
58 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 ...
0
votes
1answer
80 views
Trapdoor implementation
Please refer to this secure index paper. On page#6, a trapdoor is defined as
...
1
vote
2answers
100 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 ...
2
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0answers
54 views
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 ...
4
votes
1answer
90 views
Why is feed-forward mechanism used in hash functions?
The compression function of SHA-1 when used in Davies-Meyer mode adds its input to the chaining values at the final step. For the first message block, the IV is used as the input and in the next step, ...
1
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0answers
38 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 ...
2
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2answers
174 views
Hashing passwords with a salt - why use different salt for everyone?
Given a database where we have usernames and passwords, we want to secure users' passwords by hashing them. We should not use only username and passwords in this hash, as someone having data from ...
-2
votes
1answer
60 views
Cryptographic Primitive Method
Is there any cryptographic primitive bijective (one-to-one and onto) function for creating cryptographic tools like symmetric encryption/decryption, Hash code generator, MAC, HMAC and Random number ...
2
votes
1answer
90 views
Hashing a password with the password?
I was wondering if hashing a password with the password would be a good way of encrypting the password. So, the user must know his/her password to get the same result as the one in the database. Also, ...
2
votes
5answers
601 views
Are there hash algorithms with variable length output?
I understand that for example MD5 produces a 128 bit hash value from a given text of variable size. My question is if there is a hash-like algorithm that will produce a hash value where one can ...
1
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1answer
100 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 ...
3
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2answers
116 views
How does using salt reduce rainbow table attack?
I could create a rainbow table for a particular salt value and still create a successful attack similar to one without salt value.
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3answers
305 views
Is it safe to use file's hash as IV?
I'm encrypting some files using AES in CBC mode.
I'm also using file's digest (SHA-1) to check that data is decrypted correctly (so I need to store it with file).
Is it safe to use this digest as ...
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4answers
218 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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2answers
159 views
Is it possible to break a hash-based block cipher?
Let's define the following block cipher:
$C_n = M_n \oplus H(k + n)$ where $C_n$ is the nth block of ciphertext, $M_n$ is the nth block of plaintext, $H$ is a cryptographic hash function, and $k$ is ...
5
votes
1answer
139 views
How secure is the knapsack?
Can the knapsack be used in cryptography in a secure sense (described below)?
Knapsack problem: Given some number $X$ and a set $W$ of weights $w_1, w_2, ... w_n$, find a subset $S$ of $W$ (if it ...
5
votes
4answers
356 views
Creating an encryption key from several other keys and using hash functions
I want to combine two or more keys to create a single encryption key that relies on all of them. What is the proper method for doing that? Simple XOR? Using hash functions? Something else?
I ...
2
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1answer
286 views
Example Rainbow Table Generation
I have read up on rainbow tables and think I understand the idea behind them. However, I find that it would be better for me to actually attempt to implement a (very basic) rainbow table generator in ...
11
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1answer
818 views
No SHA-1 Collision? Yet SHA1 is broken?
Is there a known pair of distinct bit strings (A,B) such that SHA1(A) == SHA1(B)?
If the answer is no than how can SHA1 be considered broken?
3
votes
2answers
334 views
Difference between symmetric and asymmetric hash function?
The Linux kernel supports symmetric and asymmetric hash functions. E.g. sha1, sha256, ...
See tcrypt.c and search for test_hash_speed and ...
1
vote
2answers
197 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 ...
4
votes
3answers
191 views
How many bits of hash are realistically needed for key verification?
Say I'm connecting to a web server secured with TLS but with a self-signed certificate. Accordingly, I call the owner of the server and ask him what SHA1 fingerprint he has.
He starts reading out the ...
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0answers
47 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 ...
5
votes
1answer
151 views
Did Merkle invent cryptographic hashing?
Chapter II of Merkle's 1979 PhD thesis is titled "One Way Hash Functions." The chapter appears to be the first reference to cryptographic hashing. The chapter has no references. Is there an earlier ...
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2answers
115 views
Good enough deterministic PRNG based on hashes
Lets say I have a seed named iv which has a decent amount of entropy.
Are there any glaring issues with the following?
First 64 bytes are generated by SHA512(iv)
Next 64 bytes are generated by ...
2
votes
1answer
105 views
A question regarding relevance of vulnerability of MD5 when linking multiple records together
I have been studying a Supreme Court case "IMS Health vs Sorrel".
In this case a Friend of Court brief filled by "Electronic Privacy Information Center" states that use of MD5 hash function to link ...
1
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1answer
174 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 ...
3
votes
1answer
184 views
A single password manager vs password generator/hash
I have been wondering about the options available for managing passwords. However, they all seem to fail if the master password is compromised (which isn't a big surprise).
On one hand you have ...
3
votes
1answer
404 views
What are the differences between a digital signature, a MAC and a hash?
A message may be accompanied with a digital signature, a MAC or a message hash, as a proof of some kind.
Which assurances does each primitive provide to the recipient?
What kind of keys are needed?
2
votes
1answer
143 views
Why are protocols often proven secure under the random oracle model instead of a hash assumption?
Is this true that whenever you design a protocol using a hash function, you must prove its security under the random oracle?
I mean, is it possible to devise a protocol $P$ using a function $H$, and ...
4
votes
4answers
263 views
How to prove membership of a list without disclosing the list members?
I'm designing a messaging system where the sender A sends a message m with a signature s to n Receivers.
A Receiver Ri should then be able to prove to a Verifier V that he is one of the receivers of ...
4
votes
4answers
213 views
How is it possible to parallelize a hashing function to crack an iteratively hashed password?
Suppose I have an algorithm that relies on multiple iterations of a hash function like SHA1 to slow down an attacker trying to bruteforce a hash.
...
5
votes
2answers
158 views
Is there any research on the problem of making a number more memorable to humans?
Authentication protocols often rely on humans dealing with large numbers correctly. For example, when a user logs into a remote machine using SSH for the first time, she is prompted to confirm that ...
1
vote
1answer
61 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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4answers
486 views
How can I validate a hashed password if all I have is another hash?
The Scenario
I have a client-side web application that bounces requests against a server-side API. For the sake of simplicity, every request must pass a username and password. This is similar to ...
3
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1answer
167 views
Exhausting the entropy of a hash function
In the case of password storage, consider the following:
I have an idea that one can exhaust the entropy of input to the MD5 function by using a 128 bit random value as the password (indeed, any hash ...
3
votes
2answers
108 views
Is there an advantage to storing keys split between several hashes?
I have a question about the way to store a key or password that was used for encryption, so that the application can check if the user put in the right key for decryption. If I make a mistake, please ...
2
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0answers
147 views
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):
...
