# All Questions

141 views

### Partial encryption of a file?

I want to partially encrypt a large block of data using AES. Meaning: given plaintext[0:1100], I would like to encrypt ...
103 views

### What role plays Quantum Fourier Transformation in Shor's integer factorization algorithm?

I cannot seem to understand the role or goal of Quantum Fourier Transformation in Shor's integer factorization algorithm. Is it used to collapse all quantum states into one, in which it has a factor ...
461 views

### Since it gives negative power, how is rcon(0) calculated in AES?

I'm trying to calculate Rijndael key schedule "Rcon" values manually. I know how to calculate each value with the equation ...
1k views

### Two different approaches for Key Expansion using the AES-256 algorithm?

I am implementing AES 256-bit Algorithm from the Theory given in the book, "Cryptography and Network Security" by Behrouz A. Forouzan. The Algorithm described in the Book in relation to ...
2k views

### Brute forcing CRC-32

I'm working on a cryptosystem which uses IDEA. The designer made the mistake of including a CRC-32B hash of the password unencrypted in the header, so that the system can quickly reject bad ...
1k views

### Understanding CRC

There are zillions of articles describing CRC. What can I read to (more deeply) understand what's really going on? Both from an algebraic perspective and a bit-manipulation perspective, I'd like to ...
627 views

### 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 ...
58 views

On page 11, definition 2 of "Simultaneous Hardcore Bits and Cryptography Against Memory Attacks", the paper outlines the following steps (PK,SK) public key and secret key are generated by defender ...
116 views

### Cryptanalysis not based on method used to encrypt? [closed]

When doing cryptanalysis on RSA or something number theory based, there are various attacks that all seem to involve number theory (Wikipedia: RSA_(algorithm) ~ Attacks_against_plain_RSA). Similarly, ...
354 views

### Initialization Vector Properties

This is a multi-layer problem, and I want to take you through the whole thing rather than just asking about IVs. Bear with me. Also, all code below is in Common Lisp because that's what I'm using, but ...
797 views

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. $s = ... 1answer 325 views ### Key space: Dense and sparse I'm taking a cryptography class and I come across these terms dense and sparse key space allt he time. What do they mean? As far as I can I understand, dense key space means that there are more ... 1answer 72 views ### RSA Proof - di-mgt - modulo properties I´m trying to follow one of the very detailed RSA Proofs given by di-mgt: "RSA theory", but unfortunately I stuck at the beginning of solution (chapter 3). I don´t understand where the second part ... 1answer 2k views ### RSA square and multiply If an RSA encryption uses a modulus$n$of 15000 bits and$e = 3$or$e = 2^{16} + 1$, how many squarings and multiplications will we need for encryption, and for decryption? Could you please explain ... 1answer 351 views ### Testing if a password for an eCryptfs mount is valid [closed] I'm using "eCryptfs" on several directories on my dedicated Debian server. I mount them manually via mount -t ecryptfs [dir] [mountpoint] But after some weeks ... 1answer 166 views ### a possibly stronger type of attack on identity-based encryption What is known about the security of identity-based encryption schemes against attacks that involve seeing multiple ciphertexts and then receiving the private keys corresponding to some of those ... 1answer 169 views ### Intuition for random variables in cryptography I have a simple question about the use of random variables for encryption schemes, to make sure my intuition is correct. We say$P(K = k)$to represent the probability that a particular key$k$is ... 1answer 225 views ### DSA generate signature and verify I'm trying to generate a signature for DSA with the following parameters:$p = 23$,$q = 11$,$g = 3$,$H(m) = 8$,$x = 5$for the life of me, I cannot choose a random$k$($0 > k > q$) ... 1answer 328 views ### How is multiplication inverted in IDEA's decryption round? As we can see in the picture we have a multiplication in this algorithm, we know that two 16 bit inputs should have a 32 bit output, but here we just use 16 bits of the 32 bit output. For ... 2answers 1k views ### Examples of applications that use the Schnorr digital signature? I have made a study on digital signatures, especially on the Schnorr digital signature, and I was just wondering if there is some way I can find names of actual (known) applications that have applied ... 3answers 26k views ### Should we trust the NIST-recommended ECC parameters? Recent articles in the media, based upon Snowden documents, have suggested that the NSA has actively tried to enable surveillance by embedding weaknesses in commercially-deployed technology -- ... 1answer 51 views ### How can I evaluate the congruency of an AKS primality test? Despite the fact primality test is a mathematical issue, it plays a part on the security of many cryptosystems such as RSA. I was trying to understand how it works until I came to the following ... 1answer 4k views ### Decrypting encrypted files if i have the original files(Plain Text attack) [closed] I have the following A Encrypted file and the same file in its original(not encrypted) form Now will it be possible to find the encryption/decryption key by comparing the the above two files are ... 2answers 641 views ### RSA least significant bit oracle attack I have been reading up on RSA attacks and came across one that could be called a least-significant-bit (LSB) oracle attack. For the sake of clarity lets define RSA primes$(p, q)$, private key$d$... 3answers 359 views ### Encoding numbers that can be decoded mentally? I have a lot of objects, all of which need a particular number tagged on them so I can quickly tell the customer accordingly. But the problem is that the customer should not know what these numbers ... 2answers 303 views ### Solid summary of what encryption remains strong after recent events [closed] Following the recent government hacking (and subsequent news and fallout), I'm wondering what crypto-systems remain strong (and why) and what crypto-systems were exploited too heavily to be reliable. ... 1answer 228 views ### Hill Cipher - Unknown plaintext attack, known key [duplicate] I was wondering if I have the key and the encrypted Hill Cipher message(s). I can definitely figure out the charset involved. But the order is missing. Assuming that I use 37 modulo or higher. How ... 5answers 29k views ### Technical feasibility of decrypting https by replacing the computer's PRNG Intel has an on-chip RdRand function which supposedly bypasses the normally used entropy pool for /dev/urandom and directly injects output. Now rumors are going on that Intel works together with the ... 1answer 4k views ### PBKDF2WithHmacSHA512 Vs. PBKDF2WithHmacSHA1 I'm working on a Java authentication subsystem that specs the storage of passwords in the DB as PBKDF2-generated hashes, and I'm now trying to decide whether I ... 1answer 346 views ### What kind of machine can generate 100-400 digits prime number? RSA The 64 bit machine's biggest number can be 2^63 (9,223,372,036,854,775,807). So what kind of a monstrous machine can generate 100-400 digits prime number? I probably don't understand something, so ... 3answers 407 views ### Can one build a one-way function from AES? We change the AES block cipher encryption: we delete the key schedule algorithm the user now provides a string of 1408 bits we divide the string to 11 sub keys, and use them directly in the ... 0answers 158 views ### PGP encryption options I recently began using PGP desktop and found several options for my encryption capabilities. Which of these (AES, Cast, Triple DES, TwoFish, IDEA) is the most recent, firstly, secondly may the NSA not ... 2answers 4k views ### How does GCM (Galois/Counter Mode) work? [closed] Can somebody explain how this mode works? What view has cipher text and how does it help to authenticate input’s data? 1answer 494 views ### Where could I submit my algorithm? I have come up with an encryption algorithm and I am looking for a place to possibly publish it. Any ideas? 1answer 173 views ### Is AES a linear hash? So, having read a variety of documentations on AES encryption, I came to the unknowledgeable conclusion that the key schedule applied to the array of chunks, and not just the 14 cycles on a single ... 2answers 440 views ### Is scrypt a hashing function, encryption, or PBKDF? I have installed a python implementation of scrypt and noticed it has several functions, both an encrypt and hash function. Yet Wikipedia lists it as being used for PBKDF instead of PBKDF2. Is scrypt ... 2answers 218 views ### Random session key + predictable IV I'm using Blowfish in a toy Diffie-Hellman communications scheme. Random session keys are generated for each connection. In this case I can simply feed a null array to the IV right? The same ... 4answers 2k views ### 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: ... 1answer 7k views ### How are the AES S-Boxes calculated? I'm trying to understand how the AES S-Boxes are calculated. I understand how the multiplicative inverse is calculated over GF(2^8), but I'm confused by the description of the affine transformation. I ... 0answers 335 views ### Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? [closed] Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? I know you can, of course, use a 4096 bit key for your server certificate, but I usually see 2048 bit ... 1answer 2k views ### How much is slower GCM AES-128 than one of the stream chipher eSTREAM? Evaluate the speed of the algorithm GCM AES-128 and compare it whith speed of one of the stream chipher in eSTREAM. Can someone give such an assessment? 2answers 3k views ### Which stream cipher can we replace the RC4 in the SSL? In cryptography, the Fluhrer, Mantin and Shamir attack is a particular stream cipher attack, a dedicated form of cryptanalysis for attacking the widely-used stream cipher RC4. The attack allows an ... 2answers 1k views ### ChaCha cipher + Poly1305 The Poly1305-AES paper summarizes the MAC as $$\mathrm{Poly1305}(m, \mathrm{AES}_k(n)) = {H_r(m) + \mathrm{AES}_k(n)} \mod 2^{128}$$ Can I presume that$+$here is just meant as a form of 16-byte ... 1answer 518 views ### Why does NaCl's crypto_secretbox for xsalsa20-poly1305 require the first 32 bytes to be zero? The NaCl web site says this is a requirement of the API, but its seems more than just an API issue. It means the first 32 bytes of the first salsa20 block are effectively ignored. I didn't see ... 2answers 486 views ### Do we have to use an IV for AES encryption to be FIPS 140-2 compliant? I asked this question Will our app be FIPS 140-2 compliant if we use our own AES algorithm implementation here before and although there are some different thoughts about this, the general consensus ... 0answers 135 views ### How many messages needs to be send to server to get AES key in Cache-timing Attack I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on ... 1answer 235 views ### 2 comparable hashes generated from one string Assume a website where people log in with their password. The password is now stored in sql database as: md5(password + random_salt) We are adding the ... 1answer 104 views ### Quadratic Residues in identification setting Suppose Alice has two primes$p$and$q$such that$p\equiv q \equiv 3 \pmod 4$.$n=p\cdot q$is part of her certificate to identify her. A party say Bob, sends her a random quadratic residue${}\bmod ...
Suppose we consider the space of $\lbrace 0,1 \rbrace^{256}$ as the domain and SHA-256 as our hash function. Does SHA-256 become a one way permutation? Has anyone tried to prove this? Or can it be ...