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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4
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PGP String-to-Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
6
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1answer
1k views

Description of signatures with message recovery (as in ISO/IEC 9796-2 and EMV Signatures)

I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the ...
2
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3answers
62 views

Is there a method/protocol to validate a self-signed certificate by comparing a shortened hash?

I'm working on a solution where an iPad should connect to a server software running on a laptop using TLS with a self-signed certificate that was automatically generated on the laptop during the ...
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0answers
26 views

Identify a hash which was already seen? [on hold]

I have a question. In our group we are processing a large number of datasets. Each one is identified by its hash (pseudo-random ASCII string). We are currently looking for a way to tell if we already ...
3
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1answer
80 views

Salting Hash stored on RFID tag?

In my application, I am trying to prevent counterfeit widgets from being used on our gadgets; think HP ink-cartridges. I will be doing such with UHF RFID tags embedded in the widgets. Unfortunately, ...
4
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1answer
72 views

Enhance security by combining bits of 4 different hashes

Assuming that performances do not matter, is there any real benefit in terms of security (in general) in combine hashes in this way: hash functions: ...
3
votes
1answer
98 views

Change initial hash value of SHA512/t

Fips 180-4 defines under 5.3.6 how to calculate initial hash values for SHA512/t for a given value t. Can someone explain me how the t actually affects the outcome of the procedure (which, as far as I ...
45
votes
5answers
31k views

Can you help me understand what a cryptographic “salt” is?

I'm a beginner to cryptography and looking to understand in very simple terms what a cryptographic "salt" is, when I might need to use it, and why I should or should not use it. Can anyone offer me a ...
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0answers
15 views

How does the input of (0..11) (512 bit) impact on the SHA-1 algorithm [duplicate]

If my H0(A0=B0=...=000hex) I think i wouldnt´t change anything and and my output for Round 1 would be K1 = 5A827999(hex)
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0answers
18 views

C# to PHP partially decoded string [closed]

Hello I am trying to send data from c# application to my webserver. And I got like 99% of data decrypted right now the use of URI.encode helped me a lot to increase sucessfull decryption by many %. ...
1
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2answers
85 views

Appropriate scrypt parameters when generating an scrypt hash

What values for CPU, memory and parallel difficulty should be used when generating an scrypt hash? i.e. ...
0
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3answers
149 views

Is it possible to brute-force a hash algorithm of 32 bits

I have a 30000 user passwords and usernames stored in a table on a database in which the passwords are stored as hash where ,I need to guess the passwords for all users and I have the hash function ...
8
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2answers
3k views

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 ...
11
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1answer
1k views

Password hashing security of argon2 versus bcrypt/PBKDF2?

I wonder if it can be approximated how much of a security margin the new argon2 hash, winner of the password hashing competition, can give over bcrypt or PBKDF2, for an attacker using large GPU ...
8
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3answers
625 views

Advantages/disadvantages of using symmetric encryption function as hash function?

Next to the traditional MD5 and SHA-1, other hashing algorithms exist based on symmetric encryption algorithms. An example is the Matyas–Meyer–Oseas construction. What are the advantages/...
2
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2answers
83 views

comparison of security for identity based signature and Hashing (SHA-1) the identities

I would like to know which method can provide better security: using identity based signature or hashing the identities and message (using SHA-1) for authentication?
0
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1answer
57 views

How hard is it to generate a simultaneous MD5 and SHA1 collision?

I was recently reading that MD5 is "broken" because it's pretty easy to generate collisions (like 2^(L/2)). And the SHA1 (theoretically) fares no better. The ...
0
votes
1answer
21 views

Hash system to generate same (specified) hash from multiple datasets?

I have a hashed value $X$ and need to ensure that any of the data sets $D_1...D_n$ can be concatenated with a correctional value $C_1...C_n$ and passed into a hashing algorithm to result in the value ...
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1answer
83 views

Is it safer to use timestamp in REST authentication?

I am working on a personal project to build a REST authentication system which authenticate clients via three parameters: ...
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1answer
39 views

Is the “Hash Tree” described in this paper the same as a Merkle Hash Tree?

I'm implementing an algorithm from a paper, and part of it calls for using a "hash tree". Since I'd never heard of that data structure I looked it up on Wikipedia. It turns out that the name hash tree ...
7
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2answers
535 views

Is HMAC needed for a SHA-3 based MAC?

HMAC does nested hashing in order to prevent Length Extension Attacks. Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that ...
-2
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1answer
81 views

How many hashes one needs in order to reverse engineer hash function?

If I know the pattern of a hash string, particularly dllldlll or llldllld (d=digit, l=low case letter), is it possible to reverse engineer the hash function? If so, how many hashes ones needs to do so,...
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4answers
207 views

Can you use a hash as a password?

There are several methods of making a strong password, making it longer is one of them. now we also have hashing algorithms which have outputs of 512, so i wonder, would it be safe to basiclly use a ...
4
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1answer
111 views

Calculation of the avalanche effect coefficient

Given a strict avalanche criterion matrix/dependence matrix for a hash function,how do I calculate the avalanche coefficient for it. I want to calculate a single parameter(value) which represents the ...
3
votes
1answer
87 views

How to hash a set of elements

Imagine the following senario. We have $n$ participants. Participant $i$ has a set of elements $S_i$ with the elements being in a random order, possibly different for each participant. The ...
1
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1answer
39 views

Why Rabin fingerprints assumes data is prefixed with a “1” bit?

(I know that a Rabin fingerprint is not a cryptographic hash, sorry in advance if my question is considered out of topic) In the paper Some applications of Rabin's fingerprinting method, it is ...
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2answers
62 views

How secure is HMAC SHA256

I have a message (UUID) in this form 406a5830-2a6a-11e6-bdf4-0800200c9a66. I also use a secret key for example ...
6
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0answers
36 views

Does a partial preimage attack imply a preimage attack?

Let's assume we have an $n$-bit hash function and a $b$-bit partial preimage attack that is faster than brute force. Does this imply a faster than brute force preimage attack on the whole hash? It ...
2
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2answers
60 views

Probability of hash collision in exhaustive mapping from input to output

Suppose I had a hash function which produced a 256-bits output for any given input (such as SHA-3-256). Now suppose i did an exhaustive mapping from every possible 512-bits input to a given 256-bits ...
2
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1answer
53 views

Why are the bit lengths of keys and digests equal in Lamport signatures?

In Lamport's one time signature scheme: One way function to convert a pseudo random number private key to a public key takes $\{0,1\}^n$ and returns $\{0,1\}^n$. Cryptographic hash function to ...
3
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2answers
69 views

Is it possible to securely combine multiple hashes without hashing them?

Let's say we have 1000 files and 1000 already computed cryptographic hashes for those files. Now we want to derive a single hash that authenticates all of them. Is there a more efficient way to do ...
4
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0answers
109 views

Efficient proof of knowledge using Wegman-Carter hash

A verifier wants to ensure, with only little exchange of data with other systems, that a large block of data $M$ that the verifier holds is also available to some other system(s). It is not an ...
3
votes
1answer
56 views

If I don't use XOR in Davies–Meyer, does it remain collision resistant?

If I don't use XOR in Davies–Meyer construction like in picture 2, does the function remain collision resistant?
2
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1answer
29 views

First preimage resistance check

So I have $H: \{0,1\}^* \rightarrow\{0,1\}^n$ a hash function resistant to the second preimage and to collisions. Let there be a function $H' : \{0,1\}^* \rightarrow \{0,1\}^{n+1}$ with the following ...
3
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0answers
28 views

How feasible is a preimage attack or speedups to brute force a substring of MD5?

Beyond the birthday problem analysis how feasible is a preimage attack or speed up brute force on a substring of MD5. For instance let's say from the 128 bits I decide to strip 24 bits, the first four ...
3
votes
1answer
74 views

Combining secure hashes with insecure hashes?

Assuming I'm a bank which seeks for secure hash functions to use in the process of signing on digital contents. I'd like to explain / prove why using each one of the following hash functions might ...
20
votes
4answers
3k views

Why is plain-hash-then-encrypt not a secure MAC?

It seems that even in MAC-then-encrypt systems like SSL, something like HMAC is used rather than a plain hash. Why? Suppose we use some stream cipher; then why can't we use $Encrypt(m | H(m))$ as ...
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0answers
33 views

hash function for elliptic curve co-ordinates

Is there any hash function which takes the co-ordinates of an elliptic curve $E_p(a,b)$ as input and gives an integer value i.e. $h(.) : \{(x,y) \in E_p(a,b)\} \rightarrow \mathbb{Z}$
3
votes
0answers
45 views

Calculating probability of finding collisions in an invertible hash function

Assuming we have an invertible hash function H that takes inputs of size 2n and outputs hashes of size n, I use the following algorithm to find collisions: Choose a random M as input. Compute its ...
2
votes
1answer
159 views

Security of basic SHA256 MAC in an authenticate-then-encrypt scheme

I know the following construct is insecure if the MAC as defined below is appended to the encrypted message in an Encrypt then Authenticate (EtA) scheme. $k_1$: encryption key $k_2$: authentication ...
6
votes
2answers
513 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 ...
59
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8answers
8k 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 ...
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1answer
44 views

Is SHA-256 safe and difficult to crack? [duplicate]

I am trying to crack a SHA-256 hash but I am not sure how to approach this in an efficient way. The following is known of the original non-hashed content: 64 characters long only consists 0-9 and a-...
5
votes
3answers
1k 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 ...
17
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7answers
4k views

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, ...
9
votes
1answer
1k 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. ...
12
votes
1answer
451 views

Can one efficiently iterate valid bcrypt hash output values?

bcrypt is an intentionally slow hash algorithm. In my last protocol idea, I wanted to use it to expand a password and then only transfer the bcrypt-hashed password. An efficient attack on this would ...
12
votes
6answers
1k views

Why does PBKDF2 xor the iterations of the hash function together?

The definition of PBKDF2 states that I obtain a derived key (1) by calling a pseudorandom function a bunch of times recursively: $U_1 = PRF(password, salt)$ $U_2 = PRF(password, U_1)$ … $U_n ...
1
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1answer
34 views

What is the starting point of Hellman's TMTO method?

I understand what is happening and how the endpoint is computed but I'm still a bit unsure of where "SP" (Staring Point) came from. Are the starting points, randomly selected keys from the key-space n?...
2
votes
3answers
859 views

Salts, how does the script know what the salt is?

I am new to PHP programming and trying to grasp the idea of hashing and encryption for protecting passwords, credit card details and such. I've done a lot of reading about MD5 which I think I ...