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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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 ...
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342 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 ...
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950 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?
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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 ...
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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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3answers
193 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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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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155 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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128 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 ...
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1answer
112 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 ...
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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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209 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 ...
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1answer
543 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?
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147 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 ...
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4answers
267 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 ...
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216 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.
...
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2answers
162 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 ...
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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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513 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 ...
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1answer
181 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
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2answers
112 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 ...
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0answers
148 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):
...
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2answers
150 views
Looking for examples for “proof by reduction”
Im looking for examples for a proof by reduction. For example:
Let $A=(Gen, H)$ be a hash function. We define a new Hash function $A'=(Gen',H')$ with
Gen=Gen'
$H'_s(x)=H_s(H_s(x))$
It should be ...
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2answers
162 views
Is storing the hash of a key together with ciphertext encrypted with that key secure?
Is it secure to store the hash of a symmetric cipher key along with data encrypted with that key? Are there any circumstances or algorithms in which this combination could lead to potential weaknesses ...
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76 views
Does a break in a collision resistance property of a hash function by definition implies an attack at the first pre-image attack?
Is there a formal security proof in the shape of reduction that states that if an attacker manages to break the collision resistance property of a cryptographic hash function (a random oracle) he will ...
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249 views
Why do we need Hash by key?
(i'm just trying to find what am I missing...)
Assuming John have a clear text message , he can create a regular hash ( like md5 , or sha256) and then encrypt the ...
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50 views
why these specific values used to initialize ipad & opad in HMAC [duplicate]
Possible Duplicate:
What do the magic numbers 0x5c and 0x36 in the opad/ipad calc in HMAC do?
I'm reading the book Network Security Essentials written by William Stallings.
in this book,in ...
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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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70 views
Why do we always append padding bits in SHA-512? [duplicate]
Possible Duplicate:
In the SHA hash algorithm, why is the message always padded?
I'm reading the book Network Security Essentials written by William Stallings.
To create a message digest ...
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4answers
152 views
Can there be two hash functions without common collisions?
Is there a way to prove/create (or are there known hash functions) two hash functions that never have the same collision? I mean, like provable in way that someone who took one cryptography class in ...
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2answers
303 views
Constructing a block-cipher from a hash function
It is possible to use a hash function to construct a block cipher with a structure similar to DES? Because a hash function is one way and a block cipher must be reversible (to decrypt), how is it ...
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2answers
168 views
Finding partial pre-image of MD5 hash
I have the following requirement for hashing using MD5.
H(A,B,C,X);
Where values A,B & C are given. However X is not given.
I would like to find out what value of X would give a hash beginning ...
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1answer
89 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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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
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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135 views
Can a proof be constructed to show there is no distinguisher?
Let's assume a simple algorithm like the Skein hash function.
Is it possible, given the algorithm, to construct a proof that it does not have a particular distinguisher, something like:
$P(xyz)$ is ...
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280 views
SHA3 conference highlights? [closed]
Is there anyplace online that someone can find out a summary of some of the things that went on at the SHA3 conference on Mar 22-23?
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1answer
166 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 efficient?
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1answer
175 views
Recovering SHA1 knowing 2/3 of the hash generated
I am doing some research on cryptography, so I generated a random string of numbers resembling a creditcard number(according to MOD10 validation) and encrypted it with SHA1 algorithm for encryption. ...
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1answer
280 views
Hash function from narrower block cipher operated in CBC-encryption mode?
I am trying to build a public hash function (thus collision-resistant and preimage-resistant, and more generally behaving like a random oracle), with input a message $M$ of fixed size $|M|=m\cdot b$ ...
3
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1answer
239 views
Do Cryptographic Hashing Algorithms operate only on Integers?
Do all the Cryptographic hashing algorithms operate only on integers (32 bit or 64 bit)? Is there any operation performed on Floating Point Numbers as well?
The reason I ask this is because I read ...
6
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1answer
197 views
Why does Skein use an output transform, but other similar hashes don't?
Skein uses an additional compression function call to finalize the output, even when the output isn't larger than the native output size.
The Skein paper says:
Due to Skein’s output ...
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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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2answers
327 views
Proving knowledge of a preimage of a hash without disclosing it?
We consider a public hash function $H$, assumed collision-resistant and preimage-resistant (for both first and second preimage), similar in construction to SHA-1 or SHA-256.
Alice discloses a value ...
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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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3answers
212 views
Should I use md5 for my new application?
MD5 is a very fast hash and its output is short and easy to store. Should I use it for my non-security-sensitive application?
I don't think so, but I can't seem to convince anyone else that this is ...
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61 views
Hash Digest Legal Status [closed]
What is legal status of document digest? Are there special regulations which hash functions are considered in legalise?
Most important: Which digest functions would be reasonable nowadays for ...
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1answer
239 views
What's the difference between a Key Derivation Function and a Password-Hash?
It seems to me that anything that was sufficiently good as a KDF would work just fine as a password hash, though the reverse might not be true. Are there considerations specific to password-hashing ...
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1answer
202 views
What happens to the entropy of a password when you hash it?
For example, if the entropy of a password is 30 bits, what is the entropy of the password when you hash it with MD5?
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Strength of multiple hash iterations?
Is it correct that increasing the iteration possibly decreases the cipher strength but increases the amount of time it would take to find the original hash values if using brute-force on a given hash? ...
