1
vote
1answer
24 views

Camellia Key Schedule

Camellia is a widely used International standard now. Its Key Schedule seems to be too simple as compared other famous Ciphers like Twofish and CAST-256. What are the per-requisites for the ...
0
votes
0answers
37 views

Can a neural network be trained to simulate a cipher?

I believe there are two problems with this in practice: Choosing the components of the network in such a way as to allow them to simulate the operation of the circuitry of the cipher. These ...
2
votes
1answer
165 views

How does this Caesar cipher work?

Suppose I have this cryptogram: ...
3
votes
0answers
34 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 ...
0
votes
1answer
36 views

If I encrypt data with two different ECC Private keys, how secure is the result?

I'm wondering whether encrypting data with two different 256-bit ECC keys will result in a more secure encryption (minimum 384 bit equivalent) or will result in data that's effectively encrypted with ...
19
votes
2answers
10k views

Are there any known collisions for the SHA (1 & 2) family of hash functions?

Are there any known collisions for the hash functions SHA-1, SHA-224, SHA-256, SHA-384, and SHA-512? By that, I mean are there known values of $a$ and $b$ where $F(a) = F(b)$ and $a ≠ b$?
0
votes
0answers
12 views

Measuring execution time for BCrypt's HashPassword function [on hold]

I am working on a project in ASP.NET where I use this package for hashing passwords. I want to measure how long it takes to hash a password. I wrote the following code but it says it takes 202.5913 ...
1
vote
1answer
208 views

CLEFIA vs AES 128-bit

I am running a comparison between CLEFIA(Lightweight cipher from Sony Corporation which is a standard now http://www.sony.net/Products/cryptography/clefia/standard/index.html) and AES 128-bit. The ...
0
votes
0answers
15 views

Is normal to take wrong values of the polynomial for given x while applying Horner's rule

I want to evaluate the polynomial $a_0+a_1x+a_2x^2+...a_nx^n$ using Horner's evaluation due to i want to speed up my performance of application written in Java. The problem is that sometimes it gives ...
1
vote
1answer
153 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 ...
2
votes
1answer
117 views

RSA: special parameters construction

I have to show that the following construction of $q$ allows to factorize $N$ : $p \in \mathbb{P}$, the set of primes $q \gets p \cdot \left((p - 1)^{-1} \bmod e\right) \bmod e$ $k=1$ while $q \not ...
0
votes
1answer
15 views

How many field operations are needed when you compute kG in elliptic curves with a multiple additions or the double-ans-add-algorithm?

For an assignment, we have to calculate how many field computations are needed to calculate kG in an elliptic curve. They want us to show this for two different ways of calculating kG. The first way: ...
6
votes
2answers
499 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 ...
4
votes
1answer
99 views

Comparison Vigènere vs. Monoalphabetic cipher

I have a question for a class of secure communication, but I have no idea about how to proceed in order to answer it. I'll be very grateful to whom replies to me. Assuming that brute force attack ...
3
votes
1answer
42 views

Insecure third party connection

My organization processes some PII data and shares it with an outbound connection (outflow only) that is a third party. The data transfer transactions occur without human intervention. That outbound ...
0
votes
0answers
17 views

How to generate an El Gamal signature without knowing the private key x?

Let $x$ be the private key. Let $k$ be a random generated number $< p-1$, with $p$ the large prime. Let $g$ be the generator of $p$ the large prime. Let $r$ be the equality $r=g^k$ Let $m_e$ be an ...
0
votes
1answer
17 views

Digital signature with collision

Let's assume a digital signature scheme such that there's a probability of 0.2 for two random messages to have the same signature. How can I exploit this sheme? I'm having difficulties in finding an ...
8
votes
2answers
72 views

Do I need to worry about timing attacks in Base64 encoding/decoding of private keys?

Do I need to worry about timing attacks in Base64 encoding/decoding of private keys? This is a common operation (ex. PEM keys) and is variable time in typical implementations.
0
votes
1answer
23 views

X509 Cert exploit CA check

Assumptions Let's theoretically assume that a browser skips the check that a certificate it receives belongs to the stated CA (that's an exercise). How could I exploit this in order to impersonate ...
0
votes
1answer
54 views

Why is it better to have the private key as the multiplicative inverse mod phi(n) in RSA?

I'm studying the RSA algorithm and the theory says to select $d$ to be the multiplicative inverse of. $$ e \mod \phi(n) $$ If we take this approach I know that it is important that $e$ and ...
33
votes
5answers
6k views

In RSA, how does the CPU deal with this huge modulus (8192 bits)?

Whilst I understand how the RSA algorithm works, I don't understand how the CPU operates when it needs to use the mod function with a huge number $n$, for example. ...
3
votes
1answer
46 views

El Gamal special construction

The algorithm: I have to determine if the following algorithm is secure: $p,q \in \mathbb{P}$ and $N = p \cdot q$ $e \in [2, N - 1]$ such that $\gcd(e, N) = 1$ $r_1, r_2$ are random numbers ...
4
votes
0answers
31 views

How to forge signatures in the Schnorr scheme if $r=g^k$ is eliminated?

I need some help to demonstrate how to forge signatures in the Schnorr scheme if I eliminate the random string $r=g^k$ used in the hash – using $H(M)$ instead of $H(M||r)$. How would one be able to ...
1
vote
1answer
114 views

Authentication protocol which detects client impersonation from another machine

Consider following authentication protocol. Client ClientA knows some initial secret KeyA shared with server. Client also knows IP of legitimate server. Now when client wants to establish connection ...
1
vote
0answers
33 views

cumulative secrets

Imagine a server with an authentication scheme that utilizes an element of randomness in new sessions (i.e. one that uses the secure remote password protocol). At the end of a successful ...
2
votes
2answers
154 views

Is it practical to use a stream cipher in a block cipher mode?

My idea is to use a stream cipher encrypting 16 bytes at a time as a primative block cipher in a mode of operation such as CBC mode. Is this practical or useful in any way?
1
vote
0answers
36 views

Issue Factorization Quadratic Sieve

Good evening, I'm about to write my own quadratic sieve implementation in C using GMP library for large numbers. I'm facing an issue while attempting to do the last factorization step for the number: ...
2
votes
0answers
7 views

How to decrypt SSL data on a considered-to-be-compromised host? [on hold]

I have a package which I want to encrypt on my machine and send it to another remote machine. If I use asymmetric encryption, I must have the private key on the remote side. However, I don't trust the ...
0
votes
1answer
15 views

Is it possible to extract the decryption key from a locked android device

Is it possible to extract the decryption key from a FDE android device while the screen is locked but the phone is powered on. Is the data only safe when the phone is off ?
3
votes
0answers
45 views

What is the restriction on $k$, for the $k$th composite residuosity problem to be hard?

The paper “Residuosity Problem and Its Applications to Cryptography” considers the exponent to be an odd integer. When $k = 2$, it is called the quadratic residuosity problem (mod $n$, where $n$ is ...
1
vote
1answer
31 views

How to brute force sqlcipher encrypted file with MD5 hash of a 7 bit key?

I have a database file that is encrypted using sqlcipher and MD5 hash. Sqlcipher to my understanding provides 256 bit AES encryption. The key is 7 bits long. How do I brute force it?
3
votes
1answer
30 views

Not-So-Simple Substitution Cipher?

The first go-to weakness when talking about substitution ciphers is frequency analysis. It assumes that there's a simple 1 to 1 character mapping between the plain text and the cipher text. Could a ...
2
votes
1answer
854 views

Using Chi-Square for Vigenère Cipher

I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher. I came across a website that describes the Chi-Square statistics in a ...
-1
votes
0answers
12 views

Packet Filter with Access Control List [on hold]

Can anyone explain how to read and understand row 1,2 and 3? My understanding for row 1 is : If any inside packets want to go to outside via any source port to destination port number 80 using HTTP ...
53
votes
3answers
24k views

How should I calculate the entropy of a password?

If part of the password is a whole regular English word, does the entropy of that part depend on the number of English words in existence, the number of English words known by the choosing algorithm, ...
13
votes
3answers
2k views

Can you create a strong blockcipher with small blocksize, given a strong blockcipher of conventional blocksize?

Suppose I want a strong 20-bit blockcipher. In other words, I want a function that takes a key (suppose the key is 128 bits), and implements a permutation from 20 bits to 20 bits. The set of ...
0
votes
3answers
106 views

Can $d$ and $e$ be the same number in RSA?

I'm reading about RSA and I have doubts: 1) To choose $e$, this value have to be between $1$ and $\phi=(p-1)(q-1)$, with $\gcd(\phi, e) = 1$, right? 2) In my example, $p = 139$ and $q = 491$. So $n ...
12
votes
4answers
1k views

Are any of the major asymmetric ciphers distinguishable (EG, RSA, ECC)?

Related to "Is it possible to derive the encryption method from encrypted text?". Given ciphertexts generated by any of the major asymmetric ciphers (RSA, ElGamal, ECC, etc..) can these ciphertexts ...
48
votes
7answers
37k views

Taking advantage of one-time pad key reuse?

Suppose Alice wants to send encryptions (under a one-time pad) of $m_1$ and $m_2$ to Bob over a public channel. Alice and Bob have a shared key $k$; however, both messages are the same length as the ...
59
votes
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 ...
4
votes
1answer
116 views

How does the ring settings of enigma change wiring tables?

EDIT: The model I'm trying to make is "Enigma 1". I learned initially about it from a book called "Code Book" and then looked at it in detail from its wikipedia page. The site wont allow me too add ...
-3
votes
1answer
32 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 ...
16
votes
3answers
1k views

How robust is discrete logarithm in $GF(2^n)$?

"Normal" discrete logarithm based cryptosystems (DSA, Diffie-Hellman, ElGamal) work in the finite field of integers modulo a big prime $p$. However, there exist other finite fields out there, in ...
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 ...
6
votes
2answers
221 views

How are constructs with data-dependent swaps and rotations cryptanalyzed?

Linear and differential cryptanalysis seem well suited for constructs with a (relatively) simple fixed structure of boolean expressions. But some ciphers incorporate swaps of array elements where the ...
4
votes
2answers
904 views

What is the smallest plaintext/ciphertext size for an algorithm like?

When I read about a choosen plaintext attack, for example on AES the block size is always 128 bits, does it mean the attacker will only supply 128 bits data words as "plain text" ?
11
votes
3answers
961 views

UMAC: to what extent is it in use today?

Inspired slightly by the Encrypt-then-MAC question. The most obvious message authentication code is probably HMAC or RFC 2104 which is basically a hash of the input, an xor with a key... you get the ...
13
votes
2answers
5k views

Unpredictability of X.509 serial numbers

About X.509 certificates serial numbers the RFC 5280 says: The serial number MUST be a positive integer assigned by the CA to each certificate. It MUST be unique for each certificate issued by a ...
7
votes
1answer
222 views

Are there security issues with discrete logarithm keys not being uniformly distributed?

Generally, algorithms based on discrete logarithm specify that private keys are chosen as scalars between 1 and the order of the group (denoted $q$ here). For instance IEEE P1363 and FIPS 186-3 both ...
17
votes
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, ...

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