Cryptography Stack Exchange
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Is it feasible to build a stream cipher from a cryptographic hash function?

A few years ago I devised a symmetric-key system that worked like so: H() = some hashing function h = the number of bits in the result of H() key = bits to be used as a key ^ = the XOR operation + = concatenation len() = the length…
John Gietzen
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How are the names of cryptographic algorithms (like RSA, AES, SHA-256, Curve25519, etc.) pronounced?

I'll have to give a spoken presentation on cryptography and I don't want to make any pronunciation mistakes. Therefore I'm asking how I should pronounce acronyms like RSA, AES, SHA-1, SHA-256, IGE and CBC, Curve25519, ECDH, MAC, HMAC, etc., both in…
M-elman
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Does the Balloon hashing paper deprecate Argon2?

Does the recent Balloon hashing paper and the included attack on Argon2 effectively negate the result of the Password Hashing Competition? On one hand it seems that only a constant-factor improvement has been achieved, which is rarely critical in…
rmalayter
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What tests can I do to ensure my random number generator is working correctly?

In the past I have used the Chi-squared test to check the statistical randomness of my generator. Is this a good test to use? Are there other tests?
this.josh
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In layman's terms, how does Shor's algorithm work?

I've just been reading up on Shor's algorithm, and I find it both fascinating and baffling. I don't understand much about it, other than that it can factor semiprimes in polynomial time. Could someone explain how it works in layman's terms and why…
Polynomial
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FIPS 140-2 Compliant Algorithms

Is there any reference to check the list of encryption & signing algorithms which are compliant to FIPS 140-2. After an exhaustive search I could find only "AES". Any suggestions would be much appreciated.
Siva Arunachalam
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Can Shannon's entropy be used to determine if a file is encrypted?

If we have to determine a file is encrypted or not, can we use Shannon's entropy algorithm on the file? As discussed here, the entropy (in bits per byte) being closer to 0 is considered as more orderly and being closer to 8 is considered more…
sashank
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How will Cryptography be changed by Quantum Computing?

I realise this isn't a 'yes or no' question, and I apologise for asking something that could be seen as a discussion thread, but I had to ask. I'm currently doing an EPQ in CS (specifically how QC will change Cryptography). I'm trying to gather up…
Cameron Allan
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PBKDF2 and salt

I want to ask some questions about the PBKDF2 function and generally about the password-based derivation functions. Actually we use the derivation function together with the salt to provide resistance against the dictionary attacks, right? One…
thrylos_7
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Purpose of DES parity bits

DES has a 64-bit key size, but only 56 of those are used during encryption. The other 8 are "parity bits". What was the intended purpose of the party bits, and why are they no longer used in modern ciphers?
user9070
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4 answers

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 identifier (be it an ID, user-name, or an Email…
GWLlosa
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RSA with probable primes

I am a bit of a newbie to RSA encryption, so please be patient. I understand that for a 4096 bit RSA, the numbers p and q should be prime. And to have the best security, the p and q should both be about 2048 bits long. However, we don't have a way…
Jug
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What is the purpose of using different hash functions for the leaves and internals of a hash tree?

I just learned that the THEX hash tree specification which is widely used in P2P requires that two different hash functions be used: one for the leaf nodes (hashes of input data) and one for the internal hashes (hashes of hashes). In order to…
Jeremy
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(Why) should I avoid using a randomized IV for CTR mode?

I'm currently reading the chapter of Cryptographic Engineering (Ferguson, Schneier, Kohno 2010) about block cipher modes of operation. They have recommended CBC with random IV instead of CTR due to the difficulty of generating nonces for CTR: In…
Jeremy
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Why does the padding in Merkle–Damgård hash functions like MD5 contain the message length?

I understand the need for padding in MD5 and other hash algorithms such as SHA-1, SHA-256, SHA-384 and SHA-512. But why do we append the message length to the padding? I heard it strengthens the hash but how? Please provide an example if possible…
Ibrahim Najjar
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