0
votes
1answer
10 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 ...
0
votes
0answers
12 views

DES Encryption Implementation

My program allows for the key and plaintext input to only be in numbers. However, I also need it to work when the input is in letters. For example the first input should be 0000000000000000 for both ...
0
votes
0answers
6 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 ...
1
vote
1answer
66 views

Ciphers providing Deniable encryption?

I stumbled on the concept of Deniable encryption on Wikipedia, with the following scenario: Deniable encryption allows the sender of an encrypted message to deny sending that message. This ...
0
votes
0answers
8 views

Factorization of RSA modulus using a qubic residue

Suppose that someone uses RSA with $n = pq$, exponent $3$, also $3$ divides $\varphi(n) = (p-1)(q-1)$ and $2$ different roots $y$ and $z$ of the equation: $$x \equiv c \ (mod \ n)$$ are known (for ...
1
vote
1answer
4 views

How to find the keyword of the Playfair text knowing/not knowing the plaintext and having decrypted text?

I know how the Playfair cipher works. I would like to know how can I find the keyword of the play fair cipher in two cases: 1) knowing the plaintext 2) not knowing the plaintext? Some examples: ...
3
votes
1answer
44 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 ...
0
votes
0answers
4 views

Meeting people interested in Crypto and Programing [migrated]

I have done some basic Micro controller programming in the past. I am now just starting to learn C++ and plan to move into Java and SQL eventually. I just got done reading one of Simmons books. It was ...
1
vote
2answers
417 views

About the Rijndael/AES sbox polynomial (subBytes)

I've recently read a question about the irreducible polynomial behind the subBytes() operation in the Rijndael that has awakened and old curiosity I have: Why $\,m(x)$ was chosen as ...
8
votes
1answer
317 views

Qubit / Qutrit - Is there a theoretical limit on how many orthogonal states a quantum bit has?

Seems like a quantum bit with $3$ orthogonal quantum states is called a qutrit - and they have been demonstrated practically. In comparison with $n$ qubits that have ~$2^{n}$ states, these have ...
8
votes
9answers
3k views

Are there any advantages in using proprietary encryption?

Proprietary software generally relies on the fact that in keeping the encryption algorithm private, it gets an extra layer of security implying "Security through Obscurity." Obviously this phrase has ...
0
votes
1answer
18 views

Why does OpenPGP encryption produce different ciphertexts from the same plain text?

With the same plain text to be encrypted and the same public key, OpenPGP tends to produce a different ciphertext every time I run the encryption operation. Why is this?
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 ...
2
votes
1answer
50 views

Is predictable ciphertext/plaintext bad?

I have a cryptosystem that I'm using for secure chat. It is using AES 256 (with RSA 2048 for key exchange). Would a predictable, and repetitively sent ciphertext plaintext compromise the ...
0
votes
1answer
24 views

Is there a difference between $\mathbb{Z}_2^b$, $\text{GF}(2^b)$ and $\text{GF}(2)^b$?

I have read a lot about Galois Fields (GF). They are also presented in The Design of Rinjdael on page 13. In computer memory, the polynomials in $F[x]|_l$ with $F$ a finite field can be stored ...
8
votes
2answers
107 views

In the Quadratic Sieve, why restrict the factor base?

In the Quadratic Sieve, when factoring a number $N$, many descriptions and most implementations select as the factor base the set of small primes $p_j$ less than some bound $B$ restricted to having ...
2
votes
2answers
415 views

What is the difference between chosen-plaintext attack and adaptive-chosen-plaintext attack?

I've just dived in cryptography and would like to learn basics of this science. Currently I can't understand the difference between these two types of attacks. As I understood from Bruce Schneier's ...
1
vote
1answer
21 views

Security Strength of Double Substitution Ciphers

I am wondering why people are using RSA keys when some types of double substitution ciphers seem to be just as secure if not better off. By some types of double substitution ciphers I mean one Which ...
2
votes
1answer
27 views

Different kind of PGP keys or IDs, how to interpret them?

When people say "Here's my PGP key", they tend to come up with all sorts of different stuff. Sometimes they provide an 8-digit hexadecimal number, which seems to be a key ID (although I'm not sure). ...
2
votes
2answers
325 views

Perfectly secure shift cipher

Prove that if only one character is encrypted using a shift cipher, then the shift cipher is perfectly secure. I want to show that $P(P=p | C=c)=P(P=p)$. But I don't know how to relate. Can anyone ...
1
vote
0answers
20 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. $h(.) : \{(x,y) \in E_p(a,b)\} \rightarrow \mathbb{Z}$
6
votes
1answer
848 views

how to prove our algorithm is secure against chosen plaintext attack?

I am working on a topic in cryptography where I have tried to develop an encryption scheme. How could I prove mathematically that my algorithm is secure against chosen plaintext attacks?. Will it ...
4
votes
1answer
30 views

Can you decrypt with 1 round key?

If one has the last round key in an SP or Feistel network (the 16th round key in DES for example), would that someone be able to decrypt the rest of the encryption?
0
votes
1answer
22 views

El Gamal existential forgery using Pointcheval–Stern signature algorithm

I found that there exists an algorithm that claims to make the El Gamal signature generation more secure. The algorithm can be found here as a pdf. I'm mainly interested in the two-parameter forgery ...
1
vote
1answer
50 views

SIV - Synthetic IV - S2V Construction? Benefits over a MAC or Hash?

Looking at the SIV construction in rfc-5297 - https://tools.ietf.org/html/rfc5297 With regards to the generation of the SIV, using S2V construction, I am struggling to find the benefits of the chosen ...
3
votes
1answer
28 views

Number of Sbox in a Cipher

Camellia has 4 SBOX and so does the TwoFish(key dependent 4 Sboxes). Where as AES uses only one. Would it have made AES more secure if AES had 4 or more SBOX too? Does using more Sbox with similar ...
3
votes
1answer
325 views

Where is the authentication tag stored in file encrypted using AES-GCM?

So I am using cryptopp to encrypt a file in a project and I am using AES-GCM. I have a 256bit key and a 128bit ivec and a 128bit tag that I use to encrypt files. However, I want to know where the ...
1
vote
1answer
185 views

Rijndael S-boxes: Where do the $\mu$ and $\nu$ polynomial ring elements come from?

I've asked some other questions before about Rijndael's S-boxes, and step by step I'm coming to an understanding; but those steps often guide me to new questions. I did some lines of code to ...
1
vote
0answers
21 views

is Authentication tag always appended at last to ciphertext in AES-GCM 256? [duplicate]

I am using AES GCM 256 to encrypt/decrypt a UUID string,We are using java 7 + bouncy castle library for this,We are getting authentication tag of 128 bit ,i am confused ,whether it's position is ...
1
vote
1answer
72 views

Sieving the sequence $x^2-n$ to recognize b-smooth numbers

I am currently programming the quadratic sieve and have several literature books / papers and will take an example out of [1] for my question: [1] An Introduction to Mathemtaical Cryptography by J. ...
2
votes
1answer
27 views

Why is it that most messages seem to be expanded?

Whenever I have seen a more secure version of a message, the message seems to be expanded by some factor. One example is RSA encryption, but whenever a message does not appear to be expanded it is ...
2
votes
0answers
20 views

On a proposition in NTRU original paper: $\gamma_1 |f|_2 |g|_2 \leq |f \circledast g|_\infty \leq \gamma_2 |f|_2 |g|_2$

In the original paper of NTRU cryptosystem, we have the following proposition (that is said to be suggested by Don Coppersmith): For any $\epsilon > 0$, there are constants $\gamma_1,\gamma_2 ...
3
votes
2answers
56 views

Chosen-Message-Attack RSA-Signature

I know that because of the multplicative property of RSA $s =(s_1s_2) \bmod n = (m_1m_2)^d \bmod n$ If Oscar wants to sign now an own message $m$ he chooses another message $m_1$ with ...
0
votes
0answers
24 views

Example of Software Security (White Box Cryptography) is not strong as Hardware Security?

I have been reading about White Box Cryptography in the last 2-3 days but I was wondering what are the example of White Box Cryptograhy that are quickly broken by Cracker / Hacker? Would the fact ...
1
vote
1answer
23 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
36 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
164 views

How does this Caesar cipher work?

Suppose I have this cryptogram: ...
3
votes
0answers
31 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 $a ≠ b$?
2
votes
0answers
17 views

Numeric base conversion in cryptosystems?

I have been wondering if numeric base conversion has ever found an application in cryptography. By base conversion, an example that is probably familiar is Base64 encoding. This is an example of ...
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
206 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
152 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
116 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
14 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
98 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 ...
2
votes
1answer
37 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 ...

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