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70 views

Proper way of encrypting large files with AES-256-GCM

I would like to encrypt and decrypt files with AES-256-GCM. I need a solution that works with Java, PHP and JavaScript. In practice, users can upload, download files via web browser and/or desktop app ...
1
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0answers
36 views

Is using Fiat-shamir Heuristic safe?

What I'd like to do is to have the Prover store a value x where x remains hidden. From x, I'...
0
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1answer
76 views

How to convert from small field to large field

If I have number $2$, which is additively shared into $3+4 \bmod 5$. Now I need to change the filed to a large one, like $500$. How to convert the shares, so that I can have a new number or shares $a+...
1
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1answer
70 views

Is AES S-Box resistant to side-channel attacks?

I know that implemntations with T-tables such as Golang's are prone to side-channel attacks, but is AES's S-Box wihtout any additional table also insecure ?
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0answers
19 views

Generate version 3 x509 certificate from version 1 CA

Please do forgive me for my naivety. I have inherited a legacy system wherein the CA which signs the certificate is of version 1. Is it possible to generate a x509 version 3 certificate which is ...
2
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0answers
53 views

How to construct a set in which the elements in $\mathbb{Z}[x]/(x^n+1)$ and their differences are invertible and with coefficients in $\{-1,0,1\}$?

I know that in IACR - Better Zero-Knowledge Proofs for Lattice Encryption and Their Application to Group Signatures it constructs such a challenge set: {$ x^i $}. But the inverse of the difference of ...
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0answers
79 views

RNG to hide some bits

Suppose I have a sequence of bits of length M. I need to hide N out of M bits (hiding means forcing them to be 0) using RNG with a key. How I can relate the output of RNG to the number and positions ...
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1answer
52 views

How to provide secure password based encryption with password reset option

I am trying to build website that will encrypt some data for the user using his/her the output of scrypt on it, now the idea is that this schema is not flexible because if the user loose their ...
1
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0answers
25 views

Calculating the privacy that Renyi ($\epsilon, \delta$) Differential Privacy satisfies

I add differential privacy (DP) to my machine learning models by using PyTorch-DP. PyTorch-DP supplies me with the values: $\epsilon$ and $\delta $. I know that the $\epsilon$ tells us something about ...
0
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1answer
92 views

Symmetric key validity hypothesis?

Can I use something like Shannon entropy to determine the suitability of a symmetric key? I found a symmetric key which wasn't generated using a CSPRNG and it had a very low Shannon entropy. I ran an ...
1
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0answers
28 views

Fixed variable in Groth16

In the paper On the Size of Pairing-based Non-interactive Arguments by Jens Groth, it is always referred in the equations to satisfy that $a_0 = 1$ and the others $a_1, ..., a_m \in \mathbb{F}$. I am ...
2
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1answer
100 views

Is it necessary to use Fermat's Little Theorem to prove the 'correctness' of the RSA Encryption method?

Given a 'message' $M$, a proof of the 'correctness' of RSA encryption means to show that $(M^e)^d \equiv M \pmod{n}$, where $n=pq$ is a product of primes, and $ed \equiv 1 \pmod{\phi(n)}$, where $\phi$...
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0answers
56 views

Which public-key cryptosystems are used the most?

Does anybody know if there is some kind of measure on how often public-key cryptosystems like El Gamal, RSA,... are implemented. Which ones are most common?
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0answers
37 views

Quantum resistant voting scheme

I am looking for a fully (or partially) implemented quantum resistant e-voting scheme. I know the problems and issues that one deals (from an efficient and secure point of view) whenever he decides to ...
2
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3answers
305 views

Multi Factor Encryption?

I got an alert last night to the keywords above and was curious, so took a look at the tor site flagged which is the following one: http://nsrz5iogimqwgeax3clpp6hvfy6viom2woy7dghgxes4sqk63r7svoqd....
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1answer
51 views

Is AES ECB mode with salt and frame counter still comparatively weak?

Many advice against using AES in ECB mode as it always produces same cipher text for a given plain text. That shortcoming can be addressed by using salt appended to original message so that the ...
0
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1answer
78 views

What kind of a strategy can be used to crack this password?

The password is 11 chars. It has 5 letters and 6 numeric characters. There is at least 1 uppercase and 1 lowercase in it at the same time. Can an attacker benefit from these information even though he ...
6
votes
1answer
110 views

If OWF were to exist, do we know for sure that one of the candidate OWF would indeed be a OWF?

We have several candidates for OWF, like multiplication/factoring and discrete exponencial/logarithm. What I am asking is: Does the existence of one way functions imply that our candidate functions ...
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0answers
44 views

How do you determine the recorded value of a cipher when using the shift key?

I am taking a cryptography class and having a hard time understanding how to utilize Ceasar Cipher and how to determine the shift key values. Is it based on many characters are in the cipher or is it ...
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0answers
17 views

How do NTLMv2 hashed passwords work?

We have an application which embeds NTLMv2 password hashes into its configuration. In attempting to assess the security of this practice, I'm not finding much straightforward information about how an ...
1
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1answer
76 views

RSA: Is there a way to digitally sign a message without knowing the private key?

So, I am following an online course about cryptography these days, and I am stuck in an assignment. Here it is: ---------Known-------------- $m_1$: message 1 $m_1$ = 387 $s_1$: digital signature for $...
2
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2answers
259 views

Is it reasonable to consider that an encryption scheme must be invertible?

I am in a dispute regarding a test question in an exam. The question is something like that: What would happen if one were to use RSA with $n=100$ and $e=13$ to encrypt a message $m$? a) You would be ...
1
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1answer
58 views

Calculate share for a specific value of $x$ in Shamir's Secret Sharing scheme

I am currently reading the book Cryptography: Theory and Practice (4th edition) by Stinson and Paterson and going through the exercises. I have reached the Threshold schemes section and am currently ...
0
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1answer
46 views

Practical Threshold Signatures

In Practical Threshold Signature it says that there is a requirement in which the RSA public exponent $e$ must be more than $l$. $l$ in this case is the number of players in the threshold group. My ...
1
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1answer
59 views

Combining algorithms for password storage?

Is it more secure to combine algorithms for password hashing, for example, Scrypt, Bcrypt, SHA-3, etc.? If an attacker wants to use dedicated hardware, he would need one for each algorithm. However, I ...
1
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2answers
57 views

How to derive a private/public keypair from a random seed?

For RSA, my understanding is that large primes are found randomly to build a private/public keypair. If a static seed can be used in that random search process, it should be possible to derive the ...
8
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0answers
960 views

Does there exist a hash function which has a fixed point? [duplicate]

Does there exist a hash function $h$ and an input $x$ such that $h(x) = x$? I believe this is a special case of collision-resistance. I imagine such a case is guaranteed not to be possible (otherwise ...
1
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0answers
23 views

How to handle IKEv1 and IKEv2 diffie-hellman shared secret bits length not multiple of 8?

In Cryptographic Algorithm Validation Program for KDF document, here, page 9, it says "If a field size that is not a multiple of 8 bits, the shared secret is represented by a string of bytes that ...
2
votes
1answer
132 views

Negative numbers with additive ElGamal

I'm trying to implement Private Set Intersection using the additive ElGamal public key encryption system. The code I've written can encrypt and decrypt numbers using the ElGamal system, so far so good....
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0answers
35 views

What's the difference between compromise and corruption in MPC?

What is the difference between corruption and compromise? Are Compromising a user and ...
2
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1answer
70 views

How convert Point on Curve into AES key?

I'm playing around with ECC, trying to encrypt traffic between my webapp and backend (its not a product, im trying to learn and understand more about ECC) I managed to generate keys, successful run ...
4
votes
1answer
102 views

Why AEAD instead of encrypting with a simple hash?

I hear a lot about AEAD encryption (GCM, EAX, ...). Why is it unsecure (it seems to be as AEAD exists) to do do that: Imagine a block of data, hash it, append the hash to the data, then encrypt the ...
1
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1answer
33 views

What can be said about the order of short Weierstrass curves with $a=1$ and $b=0$?

I am looking at a elliptic curves of the form $E:y^2=x^3+x$, i.e. short Weierstrass curves wtih $a=1$ and $b=0$, defined over a field $\mathbb{F}_p$ with $p$ being a safe prime. Somewhat interestingly,...
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0answers
30 views

What kind of approach can I use to reverse the following encryption scheme?

I'm trying to reverse an encryption scheme without success. I have several pairs of ciphertext + plaintext and found the encryption method to be something like this: ...
0
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0answers
23 views

Stable coin values [migrated]

(not sure this is the right stack exchange to ask crypto-economics questions, if not please direct :) ) Why are stable coin values not exactly the value they're pegged against? For example as of this ...
0
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1answer
84 views

If $((p-1)*(q-1) -1)$ divisible by $e$ ($e$ is odd number) , then $\text{gcd}(e,(p-1)*(q-1)) = 1$

If $((p-1)(q-1) -1)$ divisible by $e$ ($e$ is odd number) , then $\text{gcd}(e,(p-1)(q-1)) = 1$. ($p,q$ are prime numbers ) Is this true, if yes why, if not why not ?
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2answers
172 views

How to convert random bytes into blocks of numbers without weakening entropy?

Let's say you have a, or several random byte(s) 0-255 and would like to derive numbers 0-9 for a One Time Pad (OTP) of them. What would be a non-naïve approach to represent 256 possible values onto 10 ...
0
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0answers
31 views

Attack on Many Time Pad

I have 7 ciphertexts that have been XORed with the same key. I'm writing a program to figure out what the plaintexts are and possibly maybe recover the key. I have managed to convert the HEX ...
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0answers
5 views

Use of encrypting data in transit over a HTTPS connection [migrated]

I find certain APIs (that provide sensitive information) using algorithms like ECDHE with X25519, on top of the already ...
0
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1answer
63 views

RSA Encryption that only my family could decrypt

I was doing some thinking about what would happen to my computer and passwords if I fell off the earth tomorrow. I wanted to have a message that only they would have the ability to decrypt and I ...
0
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1answer
52 views

Can two traitors safely reveal themselves to each other?

Suppose Alice is a traitor and suspects Bob might also be a traitor. If Bob is a traitor, she would like to conspire with him together, if not she doesn't want to reveal that she is a traitor. Is ...
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0answers
23 views

Authentication using a nonce

For an authentication problem imagine the following scenario with two devices: 1 server 1 client. The client starts a conversation with the server and sends him his public key. All public keys in ...
1
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0answers
47 views

Pohlig-Hellman on ECDLP over extension field $\mathbb{F_p}^6$

Suppose there is an elliptic curve $E$ in form $y^2=x^3+b$ defined over $\mathbb{F_p}$, where $p$ is large prime. #$E(\mathbb{F_p})$ is also a large prime but #$E(\mathbb{F_p})\ne p$. ECDLP on this ...
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0answers
47 views

How to design number of rounds in my cipher?

I have specific cipher which is built from permutations. It has or should has few rounds. If we do 2 rounds it is like 2 permutation composition. 3 rounds are like composition of 3 permutations and so ...
2
votes
1answer
100 views

Using SHA2 as random number generator?

I need to generate secure pseudorandom numbers in an embedded system. Instead of having to port some RNG library, could I just use an existing SHA2 function as a random number generator (n-th random ...
0
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1answer
43 views

What if the CSR is intercepted in transit while sending it to CA?

I was studying PKI the other day and I had a serious thinking about the following question. What is CSR? - It is a block of encoded text that is given to the CA when applying for an SSL certificate ...
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0answers
61 views

Why cant we use AES to hash a password, instead of a hash function?

AES needs a key in order to work, hashing-algorithms do not. Suppose we have a fixed key for AES, why don't we simply hash our keys with that? As with hash functions, AES has arbitrary input size, ...
1
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0answers
23 views

Range Proof without trusted set-up

If verifiers are public blockchain nodes, which might leak information. Does this imply that range proofs such as Boudot's and Lipmma's (squaring based) approach could not be applied, unless a trusted ...
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0answers
41 views

Secretbox- algorithm Poly1305 and cipher Xsalsa20

I use Rclone, which uses Secretbox to authenticate and encrypt data. Secretbox uses the Poly1305 authentication algorithm and the Xsalsa20 symmetric flow cipher. This whole process takes some time (...
2
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1answer
47 views

Is ShiftRows(SubtBytes(x)) = SubtBytes(ShiftRows(x)) the same for the same entry : in AES

Is ShiftRows(SubtBytes(x)) = SubtBytes(ShiftRows(x)) the same for the same entry : in AES It seems like these two are equal, can someone explain in theoretically?

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