# All Questions

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### Can BPS be used to encrypt a single integer, and restrict the output to a certain range?

As per specifications document, "We have the natural restriction that at least two characters must be ciphered, i.e. $b \geq 2$" where each character is represented by an integer of certain ...
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### Lagrange Coefficients & Polynomial in KP-ABE

My question is how these concepts relate in ABE. I am assuming that the attributes are used to share the master secret key and only a user with the right attributes for a particular access tree is ...
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### Stateless proof-of-work system with 0-roundtrip time

I'm designing an API. To avoid abuse, I need to rate limit the requests somehow, but I don't want to do it per user as it's very easy to create new accounts automatically. I think a proof of work ...
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### How can I study the math behind cryptography? [closed]

I am a junior in high school and I am currently studying algebra 2. Where can I go to learn about the mathematics behind cryptography? I have a very basic knowledge of cryptography, but I am really ...
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### Are there AES128 keys such that first round key equals last round key?

I am looking for AES128 keys such that the last round key is exactly the first round key (which is simply the key). Any pointer to a proof that they exist or that they don't would be welcome. In the ...
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### Why is it that in DSA, the order of the subgroup, $q$, is chosen such that it divides $p - 1$?

Consider the DSA key generation: A large prime $p$ is chosen; A smaller modulus $q$ is chosen such that $p - 1$ is a multiple of $q$; A generator $g$ s.t. $\operatorname{ord}_p(g) = q$ is chosen. ...
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### can session key be be used as digital signature?

if two communicating parties share a (symmetric) session key, k. When one of the party wants to send a message 'm' to other, is it okay use {m}k as a digital signature?
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### Doubts about Authenticated Data Structures logic

I am studying the theory of authenticated data structure, like Merkle Tree and I have a doubt: why use them? I explain better: why to be sure, for example, that a cloud provider didn't modify my files ...
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### Random Coin Flip

Quoting an old question: Consider the following protocol for two parties A and B to flip a fair coin (more complicated versions of this might be used for Internet gambling): A trusted ...
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### Unconditionally Secure Authentication

I'm trying to add the authentication for my One-Time Pad implementation. I know that to provide Unconditionally Secure Authentication I need to use the One-Time MAC authentication. But I don't ...
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### Comparing messages given only the ciphertext

Under RSA protocol I was wondering how a message sent could be verified under the following scenario Alice has a private (encryption key) and public key (decryption key) If Bob sends Alice cipher-...
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### Checking for factor base

In algorithms like Dixon's factorization a factor base is used, which contains all primes below a bound. Then calculates $x^2 \mod n$, and then checks it is in factor base or not. Suppose $P$ is ...
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### Stern identification scheme to signature scheme

I'm trying to understand the comment in the page 103 of the book Postquantum Cryptography. about convert the identification Stern procedure for signing. Can you write an example of signature of this ...
### Working on subgroup of $\mathbb{Z}^*_p$ in practice
It is said that, given a group $\mathbb{Z}^*_p$, we can always have a subgroup whose order is prime. To this end, for a safe prime $p=2q+1$, compute $x_i^2 \bmod p$ for all $x_i \in \mathbb{Z}^*_p$. ...
### RSA function over $Z_t^{*}$ where $t$ is prime
RSA function is defined over $Z_N^{*}$ where $N=pq$ with $p,q$ primes. A public key is a pair $(N,e)$ and a private key is $(N,d)$ where $d=e^{-1} \mod \phi(N)$. Assume that RSA function is defined ...