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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How does BLAKE2 ensure that hash(A) != hash(B) when B = A||0 and both A & B have the same number of blocks?

Suppose I have two arrays : A = a single byte, being zero. B = two bytes, both being zero. B = A||0 (i.e. B starts with A, and differs only by appending a zero byte) BLAKE2(A) != BLAKE2(B) Yet, ...
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117 views

Memory-expensive hash from an array of hashes?

Why can't people make a hash function that requires dozens of mega bytes of memory instead of cpu to avoid all the cracking and hacking? What I have in mind myself is this: We have an input $X$, we ...
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195 views

Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?

Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity? My reasoning is that the attacker doesn't know all the plaintext, so by having a hash, the ...
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503 views

Using GMAC for Authentication without encrypting the message

I am pretty new to cryptography and have a sample of GCM mode of operation for AES. PFB the code ...
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109 views

Is there a practical upper limit for password rehashing?

When using PBKDF2, is there a practical upper limit to the iteration count above which we lose security? Note: If you answer “No”, that's fine. But if you answer: “There can't be an upper limit“, ...
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207 views

Does adding a salt to the message before HMAC processing add any security?

An HMAC function is designed to verify message integrity, i.e., that the message has not been tampered with. It is generally (always?) implemented by using a hashing function ...
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325 views

Is SHA-256 safe when used in this way?

I am wondering whether an attacker can gain any useful information from having several hashes of an unknown plaintext that differs in relatively few bits. For example, if provided with: ...
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218 views

Increased security weaknesses when truncating SHA1

Given the following preconditions: A plaintext A (~512bit length), that is hashed by using SHA-1 and truncated to (the first) 64 bits. I know both, the plaintext and the truncated hash, and want ...
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409 views

File Hash of Encrypted File

Simple question. I have a source file and I have encrypted it with a certain public key. If I take this exact same source file, encrypt it with the exact same key a few hours later would the file hash ...
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150 views

Feedback requested on a method of posting a message without revealing the author

So I was thinking about variations on the Dining Cryptographers problem - In some cases, it's useful to be able to post a message without revealing the source, but with the additional constraint of ...
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3answers
270 views

Stream cipher with Diffie-Hellman and Cryptographic Hash Function? [duplicate]

I know: Never do your own crypto. But this question is just theoretical. Assume you do a Diffie-Hellman Key Exchange with a server to produce a shared secret $x$. Then use a cryptographic hash ...
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158 views

How to compare two datasets „anonymously”?

Ok, I hope this question makes some sense because I am not so sure how to word it any differently… Imagine the following situation: There are 10 defined colors (blue, orange, yellow etc.) There are ...
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950 views

Why are the Davies-Meyer and Miyaguchi-Preneel constructions secure?

The Davies-Meyer compression function $h(H, m) = E_m(H) \oplus H$ is said to be secure. So too is the Miyaguchi-Preneel compression function $h(H, m) = E_m(H) \oplus m \oplus H$. Why are these ...
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851 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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113 views

Is there any such thing as “proof of location”?

I'm looking for a way for someone to prove to me their geographical location without a trusted third-party. Imagine wanting to prove to someone you're actually physically in a specific place. I'd ...
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1answer
104 views

How can I generate a good password from a SHA512 hash?

I have to change local administrator passwords on machines. I don't want to store password in a database. I have to generate a password that I can find later to connect to the machine again. So I ...
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113 views

Proof that two parties can communicate

Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if ...
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98 views

Do hand-based hash functions / MACs exist?

Is there research on a hash function or a MAC that can be executed without computers? I know there's a lot of history on hand-based ciphers and the OTP can easily be excecuted by hand. (By using ...
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97 views

Security concern about reducing hash value using modulo operation

As stated in the title, what I am looking for is information about a "technique" that I would like to use in some of my algorithms. Sometimes I need to map a hash function's result into a range of ...
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115 views

Is this an acceptable All-or-Nothing Transform?

I was thinking about AONTs, and designed the one below, I call it CHANT for Chained-Hash All-or-Nothing Transform; it's my very first shot at something of the sort, and was hoping I could get your ...
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564 views

Cryptographic hash function for 32-bit length input keys

Since I'm unfamiliar with cryptography area I haven't been able to find cryptographic hash functions for 32 bit integer keys. It seems all such functions (as I saw here) are designed to digest a ...
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116 views

Key-dependent encryption in TAHOE-LAFS

TAHOE-LAFS uses a form of "key-dependent encryption", in that a private key SK is encrypted with the truncated hash of the private key: ...
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117 views

Combining two hashing functions

I have been working on a Bloom Filter implementation recently and after a discussion with a co-worker about how many hashing functions to use I told him I was limited with using hashing functions that ...
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272 views

Is there a cryptographic hash function that can be performed with pencil and paper?

Imagine I'm signing up for the 99th new web site this month. I somehow take my secret key (which I have written down on a card in my wallet) and the domain name of the site and feed them both into ...
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235 views

Parallel-resistant proof-of-work scheme?

I am looking for a proof-of-work scheme which cannot be effectively parallelized. For example, in hashcash (and by extension bitcoin) you have some collision-resistant hash function $f()$, a target ...
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329 views

Is it possible to anonymize web traffic so that the IP Address cannot be determined while still being able to determine distinct IPs?

I'd like to find a way to anonymize IP addresses in web logs to ensure user privacy given the following requirements: If given an IP address, there is no way to look up which requests came from the ...
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535 views

What does “message schedule” mean in SHA-256?

I am trying to understand the sha-256 algorithm from FIPS 180-2. I understood the padding and parsing of the message string. However after that it states (page 15): For $i = 1$ to $N$: { ...
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378 views

Order of hashing concatenation

A = hash("blue" + X); B = hash("pink" + X); If A and the literals are known and X is unknown, are there attacks on B aside from the attacks on directly on hash()? ...
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83 views

Why would you use a weaker hash function than cipher strength?

Some cryptographic libraries (like “Bouncy Castle”) support many modes where the maximum number of bits which can be produced by the hash are significantly fewer than the cipher strength. For ...
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92 views

Why is C_digest defined in PKCS#11?

Digesting doesn't require any key and can be performed on the client side. Why does the PKCS#11 token interface standard have a C_digest method? For example, why should I send my data to a PKCS11 HSM ...
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160 views

Can a secret message be securely transmitted within a MAC tag?

A sender wants to transmit an ultra secret code $M$ which could be either 'go', 'stop' or 'wait'. This could be any selection of code words really and adopted for any use such as transmitting short ...
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126 views

Partial hash code protocol for security tokens providing signatures

I've read the following two sentences within a beta protocol specification, which references ISO/IEC 7816-8 for PSO:HASH which already contains notions of a "partial hash". The off-card entity is ...
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144 views

Skein state size advantages

Skein is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as the “primary proposal”. Is there any advantage – other than potential memory or speed ...
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270 views

A fast non-cryptographic hash function that is “strong enough”?

I'm designing a simple one-time-password mechanism for authentication against a possibly-insecure server - i.e. I don't want to use symmetric shared secrets. The first idea that came into mind was ...
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128 views

What security differences are there between E(p',“well-known-plaintext”) vs. hash(p') where p'=KDF(p)

I am using a KDF to derive a key, p' from a password p. I would like to know if the password is correct before using the derived ...
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46 views

Distributing blocks with validation and non-dependant list generation

Problem Suppose I have a system of nodes that can communicate with a parent node, but not among each other. Suppose then a file on the parent node is split up into blocks and divided among the ...
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190 views

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 ...
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101 views

HMAC definition by using only one key

Suppose $H$ is a hash function; why is $H(k||H(k||m))$ not secure? See this HMAC definition. In there, indeed two keys are used and the mac algorithm is $H(k_1 ||H(k_2 ||m))$ . Why don't we use ...
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204 views

Prove preimage resistance property

Let $ f : \{0,1\}^* \rightarrow \{0,1\}^n$ and $ g : \{0,1\}^* \rightarrow \{0,1\}^m$. $h$ is created by concatenate f and g: $ h : \{0,1\}^* \to \{0,1\}^{n+m}$ with $h(x) = f(x) || g(x)$. How do I ...
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Is SHA-1 collision free on data up to 20 bytes long? [duplicate]

Is SHA-1 collision free on data up to 20 bytes long (lenght of hash / internal state)? That means that every input produce unique output, but you surely know that, i just write it in order my question ...
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66 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 ...
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171 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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469 views

SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?

Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
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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 ...
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4answers
354 views

Looking for cryptographic secure hash algorithm(s) that produces identical root hash for differently sliced hash list

I have a scenario similar to the one described in Wikipedia: hash list, but with a twist. I'm looking for a cryptographically secure hash function that would create the same root hash for the same ...
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540 views

Can hashing become encrypting?

hashing some data and encrypting data share some similar attributes. Surely this is why "Difference between encrypting something and hashing something" has been asked. The point of this question is ...
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reverse of md5sum

This might be out of ignorance, I apologize, but how complex of a problem might it be to generate a file of size N whose md5sum is X? For example, ...
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Are there ANY text strings that will generate the same SHA-512 Hash output? [duplicate]

Are there ANY text strings that will generate the same SHA-512 Hash output? Please provide an example, and how you came to that conclusion. I've tried thousands of variations, including ".." vs. "." ...
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600 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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721 views

I hashed my bag and in it I put… “Is there a hash for unordered items?”

(By items I mean hashable objects.) As an example (with obviously way too short hashes for readability), say I packed my bag and in it I put a shovel (hashed to ...