# All Questions

18,928 questions
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### Cipher Block Chaining - How do you change the plaintext of all blocks?

I've just read about CBC encryption and decryption and was wondering how you can change every plaintext block? Let's say you have an initialization vector, 3 ciphertext blocks, know each block-cipher-...
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### what is the difference between a prime field $F_p$ and binary field $F_{2^m}$ in the elliptic curves

i am using elliptic curves to encrypt a voip application but i can not understand the difference between using an algorithm based on the binary field or the primary field I wish that any one can ...
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### Where does the certification come from

In the book : applied Cryptography 2nd(Bruce Schneier), chapter 2 I don't understand step(5), the 'certification' didn't mention in previous steps. does it mean 'a statement that he has received this ...
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### Usage of the nth-root function in cryptography

Having offered a fast integer nth-root algorithm to a bigint library that is also used for cryptography I was asked if it does its work in constant time, so I took a look at the literature to see how ...
73 views

### Is this paper's technique for factoring RSA 2048 with noisy qubits realistic?

A paper titled How to factor 2048 bit RSA integers in 8 hours using 20 million noisy qubits has just come out which proposes a technique to factor RSA keys with moduli up to 2048 bits with a design ...
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### What state does a qbit look like before it collapses [migrated]

Which is the correct depiction of a qbit state showing the possibilities before it collapses? Is it like: MODEL 1: 1000 0100 0010 0001 MODEL 2: 1000 0100 0010 0001 0111 1011 1101 1110 MODEL 3: ...
25 views

### design a secret sharing scheme [on hold]

Suppose you are an army cryptographer. In the army there are one General and five Lieutenant Generals. Your mission is to design a secret sharing scheme allowing one General and one Lieutenant General ...
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### IETF Recommendations for preparation for PQC- clarify in what way they are referring to bits

In the IETF mtg in 2017, in the recommended actions, are they saying leave enough flexibility in terms of bit usage for key sizes to throw in/switch out anything NIST picks out, or sufficient key ...
25 views

### Root Certificate Authority of National Identity Cards [on hold]

We're collecting a list of all the Root Certificate Authorities of National Identity Cards but due to language issues and the relative obscurity of the government pages on which they are listed, we're ...
47 views

### Do Weil, Tate, and Ate pairings exist on all elliptic curves?

I don't know much about the math behind elliptic curves. Do Weil, Tate and Ate pairings exist on all elliptic curves? If the answer is negative, then what pairings do MNT, BN and SS curves have? ...
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### What does the number 256 in pairing curve BN256 indicate?

There are many pairing based elliptic curves like MNT curves, BN curves, SS curves etc., When we say BN256 curve, what does the number 256 indicate? Is it some group order or number of bits required ...
42 views

### Is there a concept of embedding degree for non-pairing based elliptic curves?

From this post, I learned the concept of embedding degree. Intuitively, if embedding degree of an elliptic curve $E(F_p)$ is $k$, it means there is a way to transform points in $E(F_p)$ to $F_{p^k}$. ...
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### How would I get the issuer's public key from two RSA-signed certificates? [migrated]

I'm trying to get the issuer's public key from two SSL client certificates signed with a 2048-bit RSA key, SHA-256 hashing and PKCS#1 padding, as I only know the issuer's DN and I wish to verify all ...
41 views

### Signal Protocol Header key encryption initialization vector

In Signal Protocol when you use a Double Ratchet you have 2 options: Normal encryption = header + ciphertext Encrypted header encryption = ...
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### Using Chameleon-HF-enabled security in practice

If one were to implement a digital signature scheme that is only EUF-CMA-secure when using Chameleon Hash Functions, would one actually use a Chameleon Hash Function or a standard cryptographic hash ...
33 views

### Construction PRF from PRG

As discussed here, a classic and secure construction of PRF from PRG is: $F_k(x_1x_2\cdots x_n) = G_{x_n}(\cdots(G_{x_2}(G_{x_1}(k)))\cdots)$ where $G$ is a secure pseudorandom generator. I was ...
54 views

### How to actually compute the statistical distance?

I have an algorithm for discrete sampling that I've defined. This is to say that $A$, upon input some pdf $p(x)$, outputs samples from the pdf $p(x)$. There are some nuances (you have to make the ...
46 views

### “Work factor” and “iteration count” nomenclature in adaptive functions

In adaptive functions like PBKDF2 / bcrypt I often read people refer to "iteration count" and others refer to "work factor", and they seem to be used interchangeably (even though they're not - the ...
56 views

### Is NIST testing all the round 2 submissions to quantum-resistant crypto?

Is NIST confirming the self-published quantum-resistant crypto round 2 data and do they make that available to the public when they do?
47 views

### RSA How to find the exponent ($e$) of the Public key with the values $p$ $q$ and an example are given

I'm wondering if it's possible to find the public exponent ($e$) with an example and the (rather small) values of $p$ and $q$ given. Currently the only option I found is bruteforcing this value, but ...
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### Binary Cryptography Problem [on hold]

i have some problem about a binary crypthography. i have the code and the solution but i can't found the key to understand the meaning. our value is ...
14 views

### Is it possible to verify the requesting user for a REST transaction secured by JWT at a later date? [migrated]

I have a React (Javascript) single-page application that authenticates users via username/password/MFA to Keycloak, receives a signed JWT upon successful authentication, and then uses that JWT to call ...
104 views

### Does lagrange interpolation work with points in an elliptic curve?

Defining the lagrange interpolation for $x=0$ as $\mathcal{L} = \sum_{i=1}^{t+1} y_{i} \cdot l_{i}$ with $l_{i}$ as the lagrange basis polynomials. Does this hold if we apply the elliptic curve ...
45 views

### EC Key Compression

Using the secp256k1 curve, will the below yield the same result? Generate private key -> compress private key -> generate public key Generate private key -> generate public key -> compress public key ...
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### How to securely store encryption keys in android? [migrated]

I want to know how to securely store encryption key in Android(API Level < 23)? What is the best scenario to protect encryption and secrete keys?
65 views

### How to encrypt data when send over https [on hold]

I know its not practical to encrypt data when you send over https for widespread consumer use. But if i had to, how would i do that?. One way is for the server and client to agree upon an additional ...
50 views

### What makes the quadratic residuosity problem hard?

The quadratic residuosity problem is the problem of determining whether, for given $r$, $m$, $\exists a.a^2\equiv r\mod m$. This problem's believed to be hard to solve in general (e.g. an efficient ...
43 views

### Why did Rabin use $x(x + b)$ instead of just $x^2$ in the original paper?

Encryption in the original Rabin scheme took a message $x$ and computed $x(x + b) \bmod n$, where $0 \le b \lt n$ and $n$ is the product of two secret primes $p$ and $q$. The private key is defined as ...
59 views

### Is this man in middle atack possible in quantum cryptography? [duplicate]

Lets consider there is channel between Alice and Bob, sequered with quantum cryptography. To put it simple, Alice is left, Bob is right and the quantum states are 'up' ~ U and 'down' ~ D. Alice ...
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### DES parity bits

The key is nominally stored or transmitted as 8 bytes, each with odd parity. According to ANSI X3.92-1981 (Now, known as ANSI INCITS 92-1981), section 3.5: One bit in each 8-bit byte of ...
91 views

### Can Reed Solomon parity blocks be used as an all-or-nothing transform?

Consider the following scheme: Perform an (N,N) Reed-Solomon encoding (i.e. N data blocks, N parity blocks) Drop the N data blocks and keep only the N parity blocks. Are these N parity blocks an all-...
26 views

### how do we calculate set intersection using homomorphic encryption?

I am new to this field. I want to learn how homomorphic encryption can be used for PSI. I am aware of other SMC protocols but I never understood how to use schemes like Paillier for PSI calculation. ...
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### Group Encryption or Multi-Party Encryption

I came accross a privacy and cofidentiality problem in medical field where patients medical record is available to certain doctors in full, but researchers/pharmacutical companies can only view the ...
27 views

### LoRaWAN 1.0.2 Session Key Security

I am reading about LoRaWAN 1.0.2 specification. For the confidentiality and integrity of the comunication the protocol generate two session keys, the NwkSKey and the AppSKey (part 6.2.5 of the ...
51 views

### Can $AES_{k1}(m)$ be equal to $AES_{k2}(m)$? [duplicate]

Context: We have a generic bloc cipher composed of an encryption function $E_k$ and a decryption function $D_k$ operating on blocs of $n$ bits. For a key $k$ fixed, we can see $E_k$ as a pseudo-...
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### Preferred SHA-2 hash algorithm for MGF1 in RSA

Does it make any difference to the security and efficiency if we use SHA-256 or SHA-512 for the Mask Generation Function MGF1 that generates the masking / padding within the OAEP encryption scheme and ...
26 views

### Accessing Firefox key store for signing [on hold]

Is there any way we can digitally sign the transaction in a web app by using the certificate stored at Firefox's key store.
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### Computing kasumi algorithm in java [on hold]

I want to comput kasumi algorithm using programming language java ..I need someone do it computing for me and with my thanks
104 views

### Key Derivation Functions vs. Password Hashing Schemes

Key derivation functions, such as HKDF (standardized in RFC 5869), are meant to stretch some initial keying material having enough entropy, like a Diffie-Hellman shared value, into one or more strong ...
22 views

### Decryption pgp secret key possible? [on hold]

i need help. i have a public and secret key at pgp. for now, i have a massage encrypted BY publ.key, i decrypt it by secret key and send massege to "bad guys", so can they decrypt my communications ...
48 views

### Birthday attack on hash functions derived from a collision-resistant hash function

$H_1$ is a collision-resistant hash function with an $L$-bit output. 2 hash functions are created based on it as follows: $$H_2((k_1,k_2);m) = (H_1(k_1;m), \space H_1(k_2;m))$$ H_3((k_1,k_2);(m_1,...
19 views

### Affine cipher text [on hold]

I just wanna know the methods that I can force cipher text without knowing the key and the length for this cipher text is random, any ideas?