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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 ...
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0answers
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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0answers
11 views

how to decode a cipher string

kind of a noob question, but I am doing this CTF and I got stuck here ...
0
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1answer
16 views

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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0answers
10 views

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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0answers
14 views

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 ...
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0answers
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?
1
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1answer
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. ...
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0answers
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....
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2answers
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 ...
3
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1answer
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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0answers
17 views

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). ...
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0answers
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 ...
0
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1answer
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 ...
0
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1answer
20 views

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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0answers
25 views

Matrix cipher - symmetric or asymmetric cryptosystem?

Matrix cipher is defined by: a) Encryption: $C = K \times Z$, where $C$ is a cryptogram vector, $Z$ is a message vector and $K$ is encryption matrix (encryption key) b) Decryption: $Z = K^{-1} \times ...
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0answers
13 views

Given the anonymity in the blockchain under Mimblewimble - how would you identify whether a transaction had already been spent?

I have searched high and low, but can't see any explanation of an algorithm that could take a Mimblewimble based blockchain and identify the unspent transactions (so if someone tried to spend a ...
0
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1answer
33 views

Shamir secret sharing with no dealer

Suppose we have a set of $N$ parties. I am looking for a scheme to generate shares of a random secret $s$ where any subset of the participants with size $k$ can recover the secret similar to Shamir's ...
0
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1answer
47 views

Security of a custom AES-based attack model

Provided that: $AES(plaintext, key)$ is the standard AES block cipher for a 128 bits block. $\oplus$ is the standard XOR operation. $K$ is a constant 128 bits pseudorandom value, which is used as the ...
3
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0answers
33 views

References about a boolean function involving hamming weight

Some weeks ago, I read an article about an interesting boolean function with some applications to cryptography. Then, I forgot about the article and now I cannot find it. Hence here I am asking if ...
-2
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0answers
10 views

Verificatum:Issue in running demo [closed]

I am getting errors while running demo. When I run 'info_files'of demo,I get error as follows Generate info files... Making directories of servers.... done. Generating protocol stub file...Exception ...
-3
votes
1answer
63 views

Compute the number of permutation functions $f : \{1, … , n\} \mapsto \{1, … , n\}!$

So this question is what professor gave me, which is related to DES & AES block cipher. I'm not sure how to answer this (mostly because I don't get the question). If someone could help me, that ...
1
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0answers
45 views

Cryptography that lets you conceal a secret, but also alerts others of the exposure of the concealed secret?

Is there such a cryptography where I can prove that someone decrypted an encrypted string? Say I wanted to attach a Bitcoin private key in some type of digital container, but in order to open this ...
-1
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1answer
62 views

Hash function construction

I recently studied a Hash function and its security requirement. I have studied that simple hash construction from XOR is weak. My question is if a construction from RSA encryption satisfies all ...
0
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1answer
55 views

What MAC did SSLv3.0 use? How did it compare to HMAC in TLS 1.0 and above?

According to Wikipedia: TLS has a variety of security measures: Using a message digest enhanced with a key (so only a key-holder can check the MAC). The HMAC construction used by most TLS cipher ...
4
votes
2answers
99 views

MLWE (and RLWE) to LWE reductions proof

In crypto papers, cryptanalysis of MLWE/RLWE/etc. is often reduced to LWE. Why can we do this? Is there strict proof of such reductions?
1
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2answers
78 views

Proving security of $\Pi' = E_k(E_k(m))$ knowing $\Pi = E_k(m)$ is secure

I recently started studying cryptography but I am not sure I quite understand the concept of proof by reduction. Question I am trying to solve is as follow: Suppose $\Pi$ is a symmetric encryption ...
0
votes
1answer
34 views

Is it possible to safely implement the Signal Protocol (X3DH) without using XEdDSA

In the X3DH specification of the Signal Protocol it mentions having a signed pre-key in the key bundle. This pre-key is signed using the identity private-key. Because the identity private-key is in ...
1
vote
2answers
50 views

Is it safe to use RSA multiple times

Assuming I have multiple symmetric keys on specific machine(more than 10000 probably), can I use the same rsa key to encrypt all of those keys? I'm a bit concerned from a situation where multiple ...
0
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0answers
28 views

Breaking vulnerable ElGamal encryption

In a ctf, I encountered this problem: ...
0
votes
1answer
20 views

Attacking a variation of the Vigenere with very long key length

I am to decrypt the ciphertext YVBCXGJRYHHRCJIUL into its plaintext message. The information that I am given is that the key used in the cipher is very long (equivalent to the length of an entire book)...
-1
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0answers
42 views

Modifying the One-Time Pad so that one key can be used two times

I'm currently working on a modified one time pad and I'm trying to use the encryption scheme such that the key will be used twice. I have written a small pseudo code but I'm stuck. Here is my attempt: ...
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0answers
18 views

E.T.P …LCM can you decipher this / how to? [closed]

How to go about deciphering the text below? E.T.P. CAM 381A2LC M Any ideas would be gladly welcomed
0
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1answer
36 views

best padding scheme for RSA

So i came across three padding scheme for RSA: PKCS1, PSS and OAEP. My intention here is to encrypt a file using AES key. then, encrypt the AES key with the RSA key and save the encrypted AES key ...
2
votes
1answer
21 views

Best suitable column type for openssl $tag,$iv,$key,$encrypted?

Which column type is best for storing $tag, $iv, $key, $encryptedData generated by openssl_encryption, and in which format I should save these values? I am using &...
3
votes
0answers
40 views

trust-less blind execution environment (thought experiment)

I apologize for the theoretical nature of this question, but It has cost me a lot of sleep over the past months. Querying my immediate peers has so far failed to produce results. I assume this ...
1
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0answers
12 views

how do i optimize the parameters of extended merkle signature scheme?

Given the parameters which include: tree height, winternitz parameter, security parameter, sha512 or sha256, tree level.
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0answers
27 views

(key) Target Collision Resistance (kTCR)?

The enhanced Target Collision Resistance (eTCR) game implies that an adversary is allowed to choose a target message $M$. Upon choosing this target message, the attacker learns the function $\mathcal{...
0
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0answers
6 views

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 ...
2
votes
0answers
29 views

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 $c$ ...
2
votes
1answer
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 ...
1
vote
1answer
20 views

Guessing the Secret in RLWE Search-to-Decision

In On Ideal Lattices and Learning with Errors over Rings, the authors prove a search-to-decision reduction by guessing the RLWE secret $s$, and using the guess to transform a sample from $\mathfrak{q}...
2
votes
2answers
208 views

Symmetric-keys algorithms with different keys for encryption and decryption

The Symmetric-key algorithm article from Wikipedia states: The keys may be identical or there may be a simple transformation to go between the two keys. I am not aware of any symmetric-key ...
0
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0answers
13 views

Integrated Signatures and Encryption Scheme

Suppose we have a scheme ISE that combines $n$ signature schemes and one encryption scheme, where the same keys are used. It is composed of the following algorithms: Setup, KeyGen, $Sign_1,...,Sign_n, ...
0
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0answers
12 views

Can I set certificate purpose in Android API 22?

In android api 22 I can use only this function to create keys and certificate: ...
0
votes
1answer
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 ...
3
votes
4answers
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?
1
vote
1answer
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 ...
0
votes
0answers
12 views

Lehmer random number generator cipher scheme with moving bits

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 ...
2
votes
1answer
52 views

Why is the point at infinity on Edwards Curve different to Weierstrass curves?

If I understand correctly, the identity point on all elliptic curves is the point at infinity. But on the Edwards curve, this can be written in Affine form? Does this have something to do with the ...

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