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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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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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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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
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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2answers
250 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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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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2answers
304 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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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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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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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
193 views
Why does HOTP use such a complex truncate function?
In the HOTP protocol after calculating a 20 byte hash it is truncated to 4 bytes.
For this first an offset is calculated (low-order 4 bits of the last byte) which determines the four bytes to be ...
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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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0answers
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
104 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
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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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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4answers
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
621 views
understanding a length extension attack
I have been trying to understand exactly how a length extension attack works on SHA-1. I'll detail below what I've understood so far, so that I can convey my understanding of the same and hopefully ...
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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 ...
6
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1answer
212 views
Using SHA-256 with different initial hash value
FIPS 180-3 defines the initial hash value for SHA-256 as the first 32 bits of the fractional parts of the square roots of the first 8 primes 2..19. What would be the risks of using a different value ...
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1answer
192 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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3answers
317 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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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
952 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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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) ...
2
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1answer
108 views
Is there another resource for Carter-Wegman-style message authentication?
I'm wondering if there are other resources that cover Carter-Wegman style message authentication, besides the sources themselves.
Is there an online text or a book that covers their ideas? I'd ...
2
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5answers
702 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 ...
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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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2answers
192 views
Do MD5's weaknesses affect Oplop?
Oplop is an algorithm that generates account-specific passwords from a master password and user-chosen nickname (typically username@domain). From the website:
Concatenate the master password with ...
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2answers
132 views
Is stretching hash several times basically the same as bcrypt?
As I understand it, the main advantage of bcrypt is stretching so it becomes slower to crack overtime. But, is using a "good enough" algorithm (e.g., SHA-2 family) then stretching until it's slow ...
4
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1answer
407 views
Is a second preimage attack on MD5 feasible?
What's the practical status of MD5 w.r.t. second-preimage?
Integrity of a piece of data is protected by an MD5 hash, itself assumed genuine. The data (and thus the hash) is known to the adversary. ...
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Can I use a key-derivation-function as the hash function H in SRP?
In the Secure Remote Password Protocol, the verifier must be stored on the server. In the case of a server compromise, an attacker could obtain these verifiers. If nobody reused passwords, this ...
4
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1answer
218 views
Why x00 is usually avoided in salt?
In .NET Framework, there is a cryptographic Random Number Generator (RNG) provider which enables to generate a cryptographically strong sequence of random bytes. This provider contain, among others, ...
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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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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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2answers
180 views
Adaptive Hash Functions: How to tell how many iterations were used?
If an adaptive hash function like bcrypt or PBKDF2 is used in hashing passwords, the number of iterations used in the hashing process can be configured.
For a penetration tester or a malicious ...
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90 views
Pseudo preimage for a hash made from a cipher
Consider the Miyaguchi–Preneel construction:
$H_0 = E(0,m_0) \oplus m_0$ (0 here means a vector filled with zeros)
$H_1 = E(H_0,m_1) \oplus H_0 \oplus m_1$
where $E(K,M)$ is a block cipher (for ...
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3answers
149 views
Can I jettison MAC if I already have SHA1(M)?
I'm currently using SSL with AES-CBC and HMAC for a file transfer containing string M. Now suppose Alice already knows SHA1(M) (and the adversary does not), and she downloads M from Bob using only ...
6
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1answer
1k views
How does a birthday attack on a hashing algorithm work?
A "normal", brute-force attack on a cryptographic hashing algorithm $H$ should have a complexity of about $2^{n}$ for a hash algorithm with an output length of $n$ bits.
That means it takes about ...
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2answers
145 views
Can a “pattern” in a series of passwords be detected from their hashes (and maybe a single raw password)?
Let's say I'm a lazy user of a system with annoyingly frequent password change policies. I may have a "good" password I used initially that is only used for this system but since I have to change it ...
6
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2answers
350 views
Is bcrypt better than GnupPG's iterated+salted hashing method?
GnuPG has slow hash built-in in form of iterated+salted S2K.
Does it have disadvantages in comparance with bcrypt or scrypt? Is GnuPG's slow hash method easily automated in GPUs?
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2answers
244 views
Is the encryption of a hash a good MAC?
At university we were told that it is a bad idea to implement a MAC by simply concatenating a key with the data to sign and to run it through a hash function (e.g. $s = ...
2
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1answer
144 views
Signing 14 bytes of data
for an embedded device I need to sign a 14-byte string and want to verify that string on the device.
Since there is already an AES-Library on the device, I thought about using the following scheme:
...
6
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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 $|M|=m\cdot b$ ...
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3answers
235 views
What differentiates a password hash from a cryptographic hash besides speed?
I understand that password hashes like bcrypt have the principal property of taking a long time to run, but I'm wondering what if anything about password hashes make them superior to merely running a ...
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2answers
1k views
“SHA-256” vs “any 256 bits of SHA-512”, which is more secure?
In terms of security strength, Is there any difference in using the SHA-256 algorithm vs using any random 256 bits of the output of the SHA-512 algorithm?
Similarly, what is the security difference ...
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2answers
157 views
Idea for user/pass hashing to prevent rainbow tables, would it work?
I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
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3answers
252 views
Multiple Hash Functions that work in either nesting
Are there any hashing functions that, if two are used in conjunction (with the same salts) will return the same response regardless of ordering?
I.e. are there hash-functions $H_1$, $H_2$ such that ...
