All Questions

0
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0answers
7 views

SHA256 Message schedule function and examples

I'm trying to implement the SHA256 algorithm in python. It is not working. I think the first problem that occurs is with the function for creating words 17-64 in the message schedule. I looked at this ...
0
votes
1answer
23 views

RSA calculate public exponent

Suppose I have two messages $m_1$ and $m_2$ as well as $c_1$ and $n$. It's standard RSA so $c_1 = m_1^e \ mod \ n$, $c_2 = m_2^e \ mod \ n$. Further assume the only information we have about e is that ...
0
votes
0answers
14 views

Miners and the calculations to create bitcoins

i'd really like to know in detail the tipe of cryptographic elaborations miner do to generate bitcoin. Can someone help me? Thank you very much.
0
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0answers
5 views

Revoke user ID from revoked gpg key?

Being a total gpg noob, I fooled around generating keys on my ubuntu pc and copying those keys to the OpenKeychain phone app. I managed to successfully revoke a key from the app, so now that key sits ...
0
votes
1answer
26 views

How to generate a unique numerical value for an alpha-numeric string?

I need to create a unique numerical value for every alpha-numeric string input. Size of output numerical value can be of any size like 32, 64 128 bits. The input string will always be a mongoID type ...
-1
votes
0answers
32 views

Is there any way of decrypt ciphers without sharing the key? [use case IoT]

in symmetric cryptography, key sharing is a big issue. suppose in a IoT environment, the nodes will encrypt a message with the encryption key and receiver need that key to decrypt the message for ...
0
votes
0answers
24 views

Computing a sextic twist

Let $(x,y) \in E'_{\mathbb{F}_{p^2}}$ be a point of the sextic twist. I am currently trying to compute: $\psi : (x, y) \leftarrow (\mu^2x,\mu^3y)$ with $\mu \in \mathbb{F}_{p^{12}}$ the root of $(Y^...
2
votes
0answers
27 views

Doubt in computing $g^\frac{1}{\delta+x}$ where $x \in \mathbb{Z}$

I was going through Zero Knowledge Set Membership and came across the following: Given $x \in \mathbb{Z}$ and $g$ is the generator of a multiplicative group $\mathbb{G}$ how do we compute $g^\frac{1}{...
-5
votes
0answers
37 views

RSA -Diffie-Hellman [on hold]

problem1: The security of the RSA encryption approach relies mainly on the difficulty of the prime factorization of large integer and the difficulty of calculating the Euler Totient function of large ...
-5
votes
0answers
34 views

one time pad cryptography [duplicate]

For One-time pad, it is required to never reuse the same key to encrypt two different messages. Suppose that Alice ignored this recommendation and decided to reuse the same key to encrypt two messages ...
0
votes
0answers
35 views

Key Reduction in symmetric cryptography

The number of keys in a system with $n$ users where every possible pair of users desire to securely communicate between themselves using symmetric cryptography is $n(n−1)/2$. Is there a way to reduce ...
0
votes
0answers
11 views

Simulator in the ideal world computes the proof for parties for $F_{NIZK}$

In the definition of $F_{NIZK}$ in [GOS06b], on receiving prove from a party, the functionality forwards the statement to the ideal world adversary $S$. This ideal world adversary then creates a ...
0
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0answers
47 views

Is it possible to recover the key to a decrypted file? [duplicate]

Is it possible to recover the key to a decrypted file if you have the initialization vector and it uses RijndaelManaged in CBC mode? If so how? The file I want to recover the key from is a xml that ...
0
votes
1answer
47 views

Finding a base of an exponent in mod field

I have the following equation: $$base^{exp} = number \pmod n : base,exp \in \mathbb{N}$$ and another known fact is: $$gcd(base, number) = 1$$ $$n = 2^{2048}$$ base=...
2
votes
1answer
56 views

Discrete logarithm with exponentiation oracle

Suppose $(n, d)$ is an RSA private keypair. We know the public key only (wlog suppose it's $(n, 2^{16}+1)$ and we are given oracle $E$, decryption oracle for $(n, d)$. Is there any efficient algorithm ...
0
votes
0answers
44 views

Prove if AES, DES, Pseudo OTP are valid symmetric cipher [on hold]

Could somebody give me mathematical proof if AES, DES, Pseudo OTP are valid symmetric cipher? Basically, I want the mathematical explanation of the encryption and decryption steps so that decryption ...
3
votes
1answer
130 views

How will be cipher selected when Client is running on version TLS 1.3 and server is running on TLS 1.2?

How will be cipher selected when a Client is running on version TLS 1.3 and server is running on TLS 1.2 knowing that cipher list provided by TLS 1.3 client will be different than the version ...
0
votes
0answers
23 views

Regarding the isogeny path problem

Given two elliptic curves, it is hard to calculate an isogeny of large degree between them. Does this only apply to supersingular isogenies or to ordinary ones as well? Additionally, is the mapping ...
0
votes
2answers
52 views

How to understand Authenticated Key Exchange?

I am reading some articles about Key Exchange. I know classic key exchange,such as Diffie-Hellman key Exchange. This type algorithm is vulnerable to man-in-the-middle attack. However, When using ...
0
votes
0answers
22 views

Recovering password from zip file [migrated]

I have a few zip files from a long time ago but they are encrypted and I don't know the passwords. I have the unencrypted, uncompressed file that is in one of them. With this pair, I am trying to ...
-1
votes
1answer
21 views

Converting a message from one PGP key to another PGP key

I have a message $M$ that is encrypted using a public key $P_1$. I lost the associated private key $p_1$. I have another public/private key pair $(P_2, p_2)$. Is it possible to "translate" the ...
1
vote
0answers
48 views

RSA low exponent with padded plain-text

Considering a case, when modulus is large and hard to factor, exponent e=3 and there is a cipher-text which is created by padding plain-text with ...
5
votes
1answer
342 views

Is openssl rand command cryptographically secure?

I'm wondering if the openssl rand command produces cryptographically secure random bytes. For example when in need for a random password or token: ...
2
votes
2answers
236 views

RSA find public exponent

Suppose I have an encryption oracle which can encrypt $m^e \mod n$ for any $m$. I know $n$ and I know $\varphi(n)$. However the public exponent $e$ is secret. Is it possible to figure out it's value ...
3
votes
0answers
44 views

Why doesn't “Classic McEliece” need scrambling?

The original McEliece scheme uses two random matrices S and P to scramble the generator matrix and uses $\mathsf S·\mathsf G·\mathsf P$ as the public key. The Niederreiter variant also does about the ...
0
votes
0answers
46 views

Which functions can be used as Pseudo Random functions? Can block Ciphers be used for this purpose with our own encryption function?

Since the cloud security algorithm I am trying to implement says that for a PRF, any secure encryption algorithm or a keyed hash function can be used. The security parameter I have chosen is 15 bits ...
0
votes
0answers
41 views

Unique numbers with $P^aQ^bR^c \mod N$ for each combination of $a,b,c$ possible? Would it be safer than separate form (like $T^a \mod P$ for each)?

Main question: Is the computation of $a,b,c$ in $P^aQ^bR^c \mod N$ (much) harder than in $T_p^a \mod P$, $T_q^b \mod Q$, $T_r^c \mod R$ ? (assuming the first form exists) $P^aQ^bR^c \mod N$ With $P^...
0
votes
0answers
40 views

Brute-force threshold of Secret Sharing using XOR and checksum

I came about a realization of how feasible and fast is this kind of secret sharing, but we can split secrets by just using XOR and random numbers. Suppose that: ...
0
votes
1answer
43 views

Comparison on Gentry's Fully homomorphic Encryption?

This topic is very new to me. Is it possible to do comparison on the encrypted data(data is encrypted using Gentry's FHE)? If so, how can it be done?
1
vote
1answer
68 views

Simulation based proofs, what am I missing?

In the example given by in the top answer of Simulation based proofs: Simple examples claims that this is insecure the semi-honest, and I need assistance in where I am failing to reason why that this ...
0
votes
1answer
38 views

How much more secure is $c = mg_1^r + g_2(g_1(g_1^r-1)/(g_1-1)) \mod p$ compared to just $c = mg_1^r \mod p$ (dis. log), all known but $r$?

To encode a message $m$ to a cipher $c$ you can use the only hard solvable problem of computing the discrete logarithm with a generator $g$ in base over a prime $p$. $c = mg_1^r$ mod p If an ...
0
votes
1answer
45 views

Searching for a dining cryptographers problem variant

When I frist read about the famous dining cryptographers problem, in a book years ago I remember the author made a twist on it, demonstrating the generalization of the problem. Basically the dining ...
0
votes
0answers
43 views

Perfect Secrecy for Message Subset

In "Introduction to Modern Cryptography" by Jonathan Katz exercise 2.6 goes like this: "Say encryption scheme (Gen, Enc, Dec) satisfies DEFINITION 2.1 for all distributions over ℳ that assign non-zero ...
1
vote
1answer
31 views

Can I do a forward secure half-round ephemeral-static ECDH?

In the context of the project we are working on recently, we would like to enable users to "leave a message" to someone on the Internet securely. Our setting is as below: ECC key pairs for open ID ...
0
votes
0answers
43 views

Decrypting using ECC [on hold]

Alice and Bob are again exchanging messages using ECC. I have all my curve parameters $A,B,p$ and $g$ as well as Alice's private key $k_a$ and Bob's private key $k_b$. I also have what i think is the ...
2
votes
1answer
644 views

Proof of work - 51% attack

In the 51% attack on the Proof Of Work Consensus Mechanism, it's often said that you need more hashing power than the rest of the network combined. Though I can't understand why you need that much. ...
3
votes
1answer
34 views

What is the RFC order of peer certificate verification, trust chain or expiry first?

If a certificate received from a peer: Is expired, has a valid signature, but from an untrusted root CA What error should be thrown? Untrusted certificate or expired certificate? I can't seem to ...
1
vote
1answer
29 views

ECDSA over $\mathbb{F}_{p^n}$ for $n>1$. How to calculate $r$ and $s$

I'm having some trouble understanding how to calculate $r$ and $s$ as specified in the wikipedia page for ECDSA (https://en.wikipedia.org/wiki/Elliptic_Curve_Digital_Signature_Algorithm) We can see ...
0
votes
1answer
75 views

Cryptographic equivalent of family coat of arms

As a layman when it comes to cryptography, I have recently been asking myself if there was a cryptographic equivalent of a family code of arms. I'm thinking of something asymmetric, that is future ...
-1
votes
0answers
43 views

Is there a collision free Hash Function for dynamic data that preserves already created hashes? [migrated]

I am familiar with the concept of hash functions and fingerprints but I am new to the implementation of functions and the specific characteristics of all those hash functions out there. What I need ...
0
votes
0answers
46 views

I need help understanding and answering this question about RSA Enc/Dec [on hold]

Let's assume, Alice's public key is ($N = 15,\space e= 3$), private key is ($N=15, \space d=3$). Bob sends message $m = 5$ by encrypting it with Alice's public key. Attacker Eve intercepts that ...
0
votes
1answer
52 views

Euler's totient function and Carmichael's totient function in RSA [duplicate]

I'm a high school student taking IB and I'm doing my EE on Maths, more specifically on the effectiveness of Euler's totient function and Carmichael's totient function in RSA. Am I right in thinking ...
1
vote
0answers
15 views

Why does ε-differential privacy protect the subset of 1/ε edges in terms of graphs?

In the book The Algorithmic Foundations of Differential Privacy by Cynthia Dwork, Aaron Roth on page 24, databases that take the form of graphs are discussed. We could on the other hand consider ...
1
vote
1answer
50 views

Proof of correctness of an ElGamal encryption given a specific public key

Suppose Alice sends an ElGamal encryption of a value $v$ to Bob (using either the normal or exponential version of ElGamal). E.g. assuming publicly-known $pk_{BOB} = h$ and a generator $g$, Alice ...
0
votes
0answers
26 views

Need help deciphering this ciphertext which I don't know its algorithm [on hold]

I got a base 32 code which I decrypted to get another ciper but don't know how to decrypt. base32 code: ...
3
votes
0answers
33 views

What is the difference between discrete-then-gaussian and gaussian-then-discrete?

In lattice cryptography, we always face the probem of discrete gaussian sampling. To the beginners, it is a bit complex. However, gaussian sampling from a continous space is much easier to understand, ...
1
vote
0answers
32 views

Protocol Design for IoT devices having PSK using AES-GCM

Handshake: 1) Client To Server: "AES-GCM(Client_random_128bit,client_iv,psk),client_id,tag,client_iv" 2) Server To Client: "AES-GCM(Server_random_128bit,client_iv++,psk),tag ...
0
votes
1answer
22 views

Is OpenSSL HMAC vulnerable to length extesion attacks when using MD5 as hash algorithm?

Given that a valid hash for a specific payload is known, would some C code like this be vulnerable to a length extension attack? ...
0
votes
0answers
43 views

Hill cipher — obtain matrix key

I have to solve Hill's cipher. I have only cipher text: CGQIYN and key: CFDG. I don't know how to decrypt it, because in all ...
2
votes
2answers
272 views

Does classifying an integer as a discrete log require it be part of a multiplicative group?

This question is not a question about the discrete log problem, the generalized discrete log problem, or an additive group. The confusion is whether any integer can be considered a discrete log or ...

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