All Questions

0
votes
0answers
11 views

Small solutions to modular arithmetic linear congruence

Let $p$ be a prime number with $N$ bits, let $a,b,c$ be constants. The problem is to find solutions to the equivalent $a x + b y \equiv c \pmod p$ with both having at most $N/2$ bits. What ...
2
votes
1answer
21 views

Does a regularly reseeded PRNG provide backtracking resistance?

I'm currently discussing a security topic with some of my classmates. A cryptographic PRNG typically provides backtracking resistance if an adversary that compromises the internal PRNG state cannot ...
1
vote
1answer
11 views

Generate a per data shared secret vs per session

I have read about SSL that they persist the shared-secret for the entire session. However, someone in stackoverflow suggested a way of generating a shared secret for each data to send and then send ...
1
vote
1answer
16 views

What are limitations of Universally Composable (UC) framework?

I am beginning to read some UC framework papers, and I guess it is similar to the simulation-based security analysis. I can understand the main advantage of UC is to assist us to analyze the ...
0
votes
2answers
17 views

Does this equation hold in a bilinear map?

I would like to verify whether or not the following equation holds: $e(a,c)^{c1\cdot c2\cdot c3}e(b,c)^{c1\cdot c2\cdot c4}==e(a,c)^{c2\cdot c3}e(b,c)^{c1^2\cdot c2\cdot c4}$ for appropriately ...
0
votes
0answers
8 views

How to prevent accidental nonce reuse with AEAD cipher

I'm trying to correctly implement ChaCha20-Poly1305 in my node.js app (...crypto is hard). I understand that the cipher requires a unique key/nonce pair for each message or the security breaks down. ...
3
votes
2answers
602 views

Symmetric Encryption in the P=NP world

I expected to find answers along the lines of quantum-computing insight into attacking AES; however, answers on this question aren't applicable because "Quantum computers give a quadratic speedup on a ...
0
votes
1answer
25 views

Does it make any difference when salting database passwords with Random vs SecureRandom?

I want to salt database passwords and then compute the hash but I wonder if I should use Random or SecureRandom? From an attacker perspective would it be easy to break if Random is used or ...
-1
votes
1answer
32 views

Finding a prime field with n-th roots of unity

How can I find the smallest prime $p$, such that field $GF(p)$ has $n$-th roots of unity? For example, I know that for $p=2^{256} - 351 \times 2^{32} + 1$ there exit roots of unity for $n=2^{32}$. ...
2
votes
1answer
34 views

1 round Feistel with birthday attack

This is a reprise of an earlier question of mine, and I'm sorry if it's repetitious; I'm going at it with a different strategy. In an exercise I was given a 1-round Feistel network which uses $H(k \...
1
vote
0answers
12 views

Monero Ring CT sj calculation

For a university project, I am currently implementing the RingCT Ring signatures as used in Monero (before the introduction of Bulletproofs) as laid out in this paper. To close the ring we calculate ...
0
votes
1answer
21 views

About the security of GnuPG private key on-disk storage

GnuPG on disk storage of secret key material is encrypted with AES-128, with an encryption key generated via a salted iterated SHA-1 hash of the given passphrase. Is this usage of SHA-1 hash function ...
1
vote
0answers
27 views

ZKP: Proving knowledge of a variable length hash preimage

I am currently trying to implement a proof of knowledge of the preimage to a public hash image using different zkp system implementations. There are a lot of examples that do exactly this (see this ...
2
votes
1answer
22 views

Variants of universal composability in security proofs

Universal composability (UC) framework seems to be a powerful framework for proving security of protocols, which guarantees security even in the presence of concurrent composition. Though, I see there ...
-1
votes
1answer
54 views

Is modular exponentiation always cyclical?

In RSA clock arithmetics is used, and as Fermat's little theorem says, $a^p \bmod p = a$. The exponentiation is cyclical, $a^x = a^{x \bmod p-1} \bmod p$, the same sequence of numbers is repeated in ...
0
votes
1answer
49 views

Why is lcm(n) used now instead of $\varphi(n)$ in RSA? [duplicate]

I know that lcm(n) or Carmichael's totient function $\lambda(n)$ is now used instead of $\varphi(n)$ or Euler's totient function to generate the public key in RSA encryption? Why is this so? Are there ...
0
votes
0answers
39 views

A problem with implementation of AES in Python [on hold]

I am learning Python implementation of AES on github And when I came across the encrypt() function, I got a problem. Compare with the Standard (Figure 5. Pseudo Code for the Cipher), it seems that ...
1
vote
2answers
47 views

What does it mean by 'cost' in CS?

I've seen the word 'cost' being used several times in describing algorithms e.g. algorithm A costs more to compute than algorithm B. What does 'cost' mean in this sense?
0
votes
0answers
47 views

Function F is not resistant to collisions

If we have the following block cipher, E(k,m), why is f(x,y) not collision resistant? $$f(x,y) = E(y,x) \oplus y$$
1
vote
0answers
31 views

Implementation of differential cryptanalysis

This question is a little bit more implementation based of differential cryptanalysis. I hope it is okay. I am working with the book "The Block Cipher Companion" on the topic differential ...
1
vote
1answer
43 views

Value of $\varphi(n)$ and $\lambda(n)$

Is it true that $\varphi(n)$ is generally larger than $\lambda(n)$ for the same $n$? If so, can anyone give me a proof?
1
vote
1answer
57 views

Prime numbers in RSA encryption

I'm studying how the selection of prime numbers in RSA encryption may affect the security of the encryption in regards to the public key. Essentially, are there any specific types of prime numbers ...
0
votes
0answers
19 views

Time complexity of Carmichael's totient function

I'm studying the efficiency of Euler's totient function and Carmichael's totient function used in RSA encryption. I do understand that Euler's totient function has several different time complexities ...
-6
votes
0answers
34 views

Welcome To Pyca Cryptography [on hold]

Cryptography includes both high level recipes and low level interfaces to common cryptographic algorithms such as symmetric ciphers, message digets,and key derivation functions.For example,to encript ...
0
votes
1answer
37 views

Secret sharing - Size of the share

I'm having some hard time understanding why the size of the share must be at least as large as the secret itself, why is this restriction imposed? What would happen if the share is smaller?
1
vote
1answer
23 views

Is it easier to crack the Vernam Cipher with more than two ciphertexts

I have just started looking into the cracking of the Vernam cipher with two ciphertexts encrypted with the same key by XORing them and then crib dragging and I was wondering if it is made easier if ...
2
votes
1answer
35 views

ECIES/ ECDHE/ EC-ElGamal encryption comparison

I need to choose an encryption system, so I am trying to understand the differences between the existing options. I always find that people compare ECIES (Elliptic Curve Integrated Encryption Scheme) ...
0
votes
1answer
57 views

Hashing functions - How to define them?

Let $\mathcal{G}$ be a cyclic additive group for an elliptic curve $E\, / \ \,\mathbb{F}_p$, and let $p, n$ be two large prime numbers (e.g., we can consider $\texttt{secp160r1}$ with $p = 160$ bit ...
0
votes
1answer
58 views

Will publishing two or more public keys of the same RSA private key cause a security risk?

I want to make an end-to-end messaging platform where everyone is identified with a unique random private key. Everyone uses other peers' public keys to identify and send encrypted messages and verify ...
4
votes
2answers
63 views

Is there a maximum amount of data which can be encrypted using a symmetric (AES256) key?

I am working on an application where we will be encrypting billions of small (< 2,000 bytes) records. Combined, we are facing many TB of data. Each record will be encrypted independently, using a ...
1
vote
0answers
51 views

Time complexity of Euler's totient function

I believe there are different time complexities for Euler's totient function depending on how you execute the algorithm. The two I know of are: Iterate through 1 to k and calculate each gcd. O(nlogn) ...
0
votes
1answer
58 views

Do Carmichael's and Euler's totient functions in RSA generate the same keys?

Starting with the same primes $p$ and $q$ to generate $n=pq$, will Carmichael's totient function and Euler's totient function give the same public key ($e,n$) and private key ($d,n$) in RSA encryption?...
2
votes
1answer
61 views

Cryptographic hash function based on logistic map?

Is there any secure cryptographic hash function based on the logistic map?
0
votes
1answer
30 views

Is there a lower limit on message length for signature?

I was working on a tool that signs small messages (~20 bytes) when a question occurred about message size: What would be the risk of using extremely small/restricted input (say, 5 bytes of hexadecimal ...
1
vote
1answer
58 views

Picking 'e' for RSA encryption

What is the reason behind picking either $3$ or $2^{16}+1$ for generating the public key in RSA?
0
votes
0answers
20 views

OpenSSL support for ed25519, encrypting content? [migrated]

Using OpenSSL 1.1.1.b-1, I can generate an RSA keypair and use them to encrypt content: ...
1
vote
1answer
26 views

Can the encrypt-and-authenticate method result in secure authenticated encryption if the MAC scheme has unique tags(non-deterministic)?

If we use non-deterministic MACs in encrypt-and-authenticate approach, is it secure?
0
votes
1answer
24 views

Security level in HORS signature scheme

I was reading the HORS One-Time-Signature scheme by Reyzin & Rezyin, but I could not understand how they derived their security equation $(rk⁄t)^k$. I understand that the total number of balls is $...
0
votes
0answers
29 views

Encrypt multiple RSA keys with same passphrase

I have to create and store a bunch of RSA key pairs with openssl. The private keys will be encrypted with the aes256 option and a very long, random password. Would it be safe to use the same password ...
7
votes
2answers
527 views

Are there any symmetric cryptosystems based on computational complexity assumptions?

Are there any symmetric cryptosystems which are provably secure in the sense that there exists a reduction from their security to the hardness of some underlying hard problem such as integer ...
0
votes
0answers
16 views

Question about using Montgomery form for elliptic curve operations on bls12-381

Since the prime for bls12-381 is not of a form to allow easy modular reduction , is the best approach to use the Montgomery multiplication + reduction algorithm? ...
0
votes
2answers
44 views

Understanding token security

I am having some problems, cryptographically speaking, digesting this information. There is a table that seems to say that tokens provide "end to end security" (I suppose we understand different ...
0
votes
1answer
48 views

DH prime size required to force an attack of $2^N$ steps

Why the size of a DH prime $p$ should be about 6800 bits long to force an attacker to perform $2^{128}$ steps to attack the system? How is this relationship 6800-128 established?
0
votes
0answers
12 views

Counter block problem using aes-ctr decrypt from pycryptodome [migrated]

So I am trying to decrypt a connection over SSH using pycryptodome. I have the key and the IV extracted from memory (I am working inside a virtual environment), which are 100% correct, which were used ...
0
votes
1answer
57 views

Password hashing alogirthm simple enough to implement myself?

I'm doing a password manager for a school project and I need to hash the master password for verification but I also need to write the hashing algorithm myself. However, most the algorithms I've come ...
0
votes
0answers
29 views

Performance evaluation in terms of Boolean operations

How can I conduct a performance evaluation in terms of Boolean operations for an access policy which supports them? Could someone explain this to me in simple terms or suggest some specific reading?
1
vote
0answers
41 views

Hamming distance in xor decryption

I've been working on cryptopals 1.6, breaking xor and have got it working. I found this answer that explains why hamming distance works and I think after some thinking I believe I'm starting to ...
0
votes
0answers
23 views

Convert a plain public key to PEM format [on hold]

I plan to generate an EC key pair using P-256v1 from a trusted application and export the public key to Normal OS. The public key will either be in plain format or have none (only key hex). The ...
0
votes
0answers
26 views

libsodium: crypto_stream_xor vs crypto_secretbox [migrated]

If I'm reading the documentation for crypto_stream_xor and crypto_secretbox correctly, both functions use XSalsa20. The former does not have any authentication whereas the latter does. Pursuant to ...
1
vote
0answers
29 views

generating HChaCha20 internal state with existant ChaCha20 implementation [migrated]

In RFC7539 § 2.3.2. Test Vector for the ChaCha20 Block Function it shows the "ChaCha state at the end of the ChaCha20 operation". I'm able to get that with PHP 7.2.8 and OpenSSL thusly: ...

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