# All Questions

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### Cryptanalysis on two time pad ciphers? [duplicate]

One time pad ciphers are unbreakable if the message is encrypted correctly and if only used once. However if used more than once, it becomes decipherable. How come? Also, would it be smart to use one ...
23 views

### Let $F$ be a PRF, is the following $G(x)=F_{0…0}(x)∥F_{0…1}(x)|| … ||F_{1…1}(x)$ a PRG?

$F$ is a PRF with $n$ bit key, input, and output length. I know the answer is "NO it isn't!", but I can't understand why. Is that because on any input $x$, the keys for every $F$ in the concatenation ...
16 views

### How to verify perfect secrecy of a cryptosystem? [on hold]

I’m playing with a self-made encryption algorithm: “a new approach to data encryption” by Suhail Yazji (video available at youtube.com/watch?v=h1kABn5dfXc). How can I prove my algorithm to be ...
40 views

### Present an attack for the combination of OTP and textbook RSA

Let $N=p \times q$ where $p$ and $q$ are two primes. Compute $\Phi (N) = (p-1)(q-1)$. Choose $e$ s.t. $1 < e < \Phi(N)$ and $gcd(e,\Phi(N))=1$. Compute $d = e^{-1}(mod \ \Phi(N))$. ...
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### Prove that certain amount of data was stored

I'm looking for a way to prove that a certain amount of data was stored, through some easily verifiable piece of information. Similarly to how proof-of-work can prove through a hash that a certain ...
31 views

### Can we solve the Hidden Number Problem in $GF(2^n)$?

Is it possible to solve the Hidden Number Problem in extension fields? In particular in $GF(2^n)$? Let's suppose an attacker knows some least/most significant bits of $r_i = a_i \times k$ in a given ...
26 views

### getting different wrong decryption points on elliptic curve [on hold]

i am working on image encryption using elliptic curve cryptography, and i am using MATLAB and -- pair{KG, Pm+KPb} is for encryption and to decrypt it subtract Y*(KG)from Pm+KPb ie. Pm+KPb-Y*(KG), ...
41 views

### Knowing that $G(s)$ is a PRG, is the following construction $G'(s) = G(s||0)$ a PRG?

I know there already is a very similar question. However, I can't understand why $G'(s)$ is not a PRG. If $G(s)$ is a PRG, then why $G(s||0)$ can't also be a PRG? How can the distribution over ...
28 views