# All Questions

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### Silent Oblivious Transfer Question

Recently, Boyle et. al. proposed silent OT extension. In the paper, silent OT, it seems that a GGM based PPRF used as building blocks. However, after reading the paper, I have two questions that are ...
9 views

### regarding usage of hashing

So I have a question regarding pitfalls of using only encryption Suppose Bob and Alice want to flip a coin over a network. Alice proposes the following protocol. Alice randomly selects a value X ∈ {0,...
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### how to decode a cipher string

kind of a noob question, but I am doing this CTF and I got stuck here ...
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### Showing a CBC-MAC is not preimage resistant with a proof

So hypothetically I have a an arbitrary block cipher operating in CBC-MAC mode that makes use of a public and static $IV$ as well as a static key $K$. I want to be able to that this won't be preimage ...
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### Figure out chosen-plaintext-attack in Zerologon attack

Actually, I'm reading the description about Zerologon attack from the original whitepaper document. In there, Tom Tervoort mention these sentences: "So I tried to come up with some chosen-...
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### Difference between server salt and client salt?

Basically I am trying to understand the difference between server salt and client salt. I know that the client salt is used to make encryption harder for hackers, but I can't seem to grasp the concept ...
32 views

### Which operations are possible on ciphered data?

I heard something that it is possible to manipulate ciphered data without deciphering. Tell me more about it, which operations are possible on ciphered data?
50 views

### Security of block cipher PRP(k⊕m)⊕k

Let $\mathcal S=\{0,1\}^n$ be the set of bitstrinsg of $n$ bits (for security parameter $n$). Let $P$ be a public Pseudo-Random Permutation of $\mathcal S$, efficiently computable in both directions. ...
15 views

### zkSnark Circuit

In practice, the circuit need to be proved always has a large size, maybe nearly billion gates, when turns such circuit to QAP, it will generate a large polynomial, which is a high cost to use zkSNARK....
104 views

### Differential privacy noise that scales with $L_p$-sensitivity with $p>2$?

It is well-known that to make the result of a $\mathbb{R}^d$-valued query $(\varepsilon,\delta)$-differentially private, you can add noise to it. If you add Laplace noise, you need to scale the noise ...
39 views

### Why does PBKDF2 use HMAC?

When I learn PBKDF2, I found out most of the articles say that the PBKDF2 use HMAC as PRF. Why is HMAC? Can I use other pseudorandom functions? Is HMAC safer than any other functions for PBKDF2?
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### Formal proof that the following definitions of perfect secrecy are equivalent

I've seen the following two definitions of perfect secrecy for an encryption scheme (Gen, Enc, Dec). ...
46 views

### Brute force and DES encryption

If 10^6 computers work in parallel on a brute force attack and each computer can test 10^9 keys per second, how long will it take on average to find a DES encryption key? How long on average to find a ...
25 views

### Can you break a Vigenere cipher with key length of 2 and message/cipher text length of 4?

I am currently working on a problem where an attacker knows that a user's password is either "pqrs" or "jmlo" and also knows that the encryption scheme is using the Vigenere cipher ...
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### Safety of a private key when knowing the full content of an ecrypted message in case of fixed initialization vector

When knowing the full content of the original message, will I be able to derive the private key from the encrypted message when the underlying encryption uses a fixed initialization vector? Meaning if ...
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### How to split sbox input 4bit into 12 bit and how to find algebraic normal form(ANF) equation of SBox

I am new to Cryptography field and try to implement Threshold Implementation. In Decomposition of SBox into composition of two quadratic SBox. I am not getting how to split SBox input of 4bit into ...
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### Possibility of computing a and b values from the ciphertext?

Using paillier encryption, $N$ is the product of two large prime numbers, $s$ is sampled randomly from $Z_{N^2}$ we get $C \leftarrow g^ms^N \bmod N^2$ where $g=1+N$, By multiplying the cipher $c$ ...
13 views

### Difference between SHVZK and HVZK?

What is the difference between Special Honest Verifier Zero-Knowledge (SHVZK) and Honest Verifier Zero-Knowledge (HVZK)? Sometimes I see one term being used, other times the other. Do they mean the ...
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### Can I set certificate purpose in Android API 22?

In android api 22 I can use only this function to create keys and certificate: ...
41 views

### OpenSSL cipher suite support / key requirement for ecdhe_ecdsa_with_aes128_cbc_sha256

I hope this is the right place for that kind of question. So actually I am trying to test the TLS implementation of some industrial device. I have to write my own TLS implementation for this, for ...
1k views

### How to calculate the odds of finding “20” at least three times in a sha256 string?

For example, what are the odds of this happening: Can this even be calculated?
40 views

### How to choose parameters for Argon2 for password vault

I'm creating a password vault and I'm planning on using Argon2id to derive the master key from the master password. For encryption I'm planning on using XChaCha20 with Poly1305. To be clear: a set of ...
Let's consider linear congruential generator: $X_{k+1} = a \cdot X_{k} \mod 2^{128}$ Such that $a$ is some number which for every 128-bit input $X_{k}$ from $0$ to $2^{128}-1$ will give us different ...