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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Hashing or encrypting twice to increase security?
Over on the bitcoin forums I asked why the bitcoin client computes SHA-256(SHA-256(x)) as its cryptographic hash for a variety of purposes. The leading theory--since the bitcoin author has ...
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What is wrong with using SHA1 in digital signatures? Why is a robust hash function needed?
For the purposes of signing and verifying signatures, what is the value of the hash function?
Why would it matter if SHA1 is later determined to be easy to break? Since a Public/Private key process ...
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4answers
619 views
Webapp password storage: Salting a hash vs multiple hashes?
For security's sake, of course it's blasphemous to store passwords in plain-text; using a hash function and then doing a re-hash and comparison is considered much better.
But, if bad guys steal your ...
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Necessity of Randomness of Salts?
Given the desire to have unique salts for each user of your system, is it actually necessary to create a cryptographically-random salt for each user? If your system already has some other unique user ...
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Accelerating SHA-1
I have a program where computing SHA-1 is the bottleneck. This is using OpenSSL 1.0.0e on a 2.6Ghz 16-core Opteron where I get about 325MiB/s throughput. (SHA1 here is via Andy Polyakov's x86-64 ...
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Why use an Initialization Vector (IV)?
Why use an Initialization Vector (IV)?
How are IV's used?
What are the advantages/disadvantages of using an IV?
Why use an IV instead of a longer key in which some section of the key is pubic?
What ...
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1answer
202 views
How is the MJH double-block-length hash function constructed?
I'm looking for information on the MJH double-block-length hash function, but the best free source I could find is the diagram on page 18 of Efficient hashing using the AES Instruction Set (submitted ...
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How do I construct a 256-bit hash function from 128-bit AES?
I would like to generate a 256-bit hash on a microcontroller that has a 128-bit (only) AES engine. How can I construct a 256-bit hash function from a 128-bit cipher?
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Does MD5 generate 128 independent bits?
I heard that there are 128 stochastically independent bits in an MD5 output. Is that true?
If so, are there any citations or proofs for that?
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2answers
344 views
Is digest=HASH(HASH(a)+HASH(b)) equivalent to publishing two digests?
Is combining digests (created using a hash function) using arithmetic addition, and then hashing and publishing the result, less secure than publishing the set of digests?
Does the answer change if ...
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5answers
632 views
Why does PBKDF2 xor the iterations of the hash function together?
The definition of PBKDF2 states that I obtain a derived key* by calling a pseudorandom function a bunch of times recursively:
...
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3answers
415 views
Is the number of creatable torrents limited?
Currently, a magnet link containing a 40-digits long SHA-hash value, is assigned to every torrent which is created. Therefore, this hash should be unique to identify a torrent and send the right bytes ...
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7answers
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Is calculating a hash code for a large file in parallel less secure than doing it sequentially?
I would like to improve the performance of hashing large files, say for example in the tens of gigabytes in size.
Normally, you sequentially hash the bytes of the files using a hash function (say, ...
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4answers
611 views
Properties of PRNG / Hashes
There are a lot of quite elaborate PRNG's out there (e.g. Mersenne Twister et.al.), and they have some important properties, especially when it comes to crypto applications.
So, I was wondering how ...
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3answers
1k views
Reverse engineering a hash?
I understand this may not be the best place to ask a question like this, but I believe that this community may be the best/only place I can ask such a question.
I have inputs and outputs from an ...
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1answer
390 views
iSeries (AS/400) Database File: password encryption
I am helping with a project in which an old software system on an iSeries is having a brand new .NET UI applied to it. It's going well... except...
In order to allow users to login and maintain ...
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3answers
672 views
Is using slow password hashing on the client side easier attackable than on the server side?
As we know, one should use a slow password hashing algorithm instead of a fast one for storing passwords, to hinder brute force attacks when the database is compromised. The problem with this is that ...
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1answer
368 views
Change in probability of collision when removing digits from MD5 hexadecimal hash values
I am aware that MD5 has a known collision vulnerability and should not be relied upon when uniqueness is required, but in the environment I am working on I only have access to MD5 hash function. ...
7
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1answer
361 views
Should I use the first or last bits from a sha-256 hash?
I have the need for a hexadecimal token that is smaller than the normal length of the hexadecimal representation of a sha-256 hash.
Should I take the first bits or the last bits? Which of them ...
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2answers
439 views
Why do we append the length of the message in SHA-1 pre-processing?
As we know, SHA-1 is irreversible, so why do we append the length of the message to the preimage?
