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12 views

Image points over extensions fields

While trying to understand isogeny-based cryptography I stumbled over a passage in a paper by Galbraith. On p.4 he explains how to calculate the image points of an isogeny $\phi:E\to E^{\prime}$: ...
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0answers
20 views

ECDSA signature verification checks

From Wikipedia: Check that $Q_a$ is not equal to the identity element $O$, and its coordinates are otherwise valid. Check that $Q_a$ lies on the curve. Check that $n*Q_a = O$ Verify that $r$ and $s$ ...
1
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1answer
41 views

Understanding LFSR stream ciphers and the content scrambling system

I'm a little confused over how exactly Linear Feedback Shift Registers (LFSR) work, I kind of get it, but not really, can someone help me understand it? I know it XORs bits in a loop against some mask,...
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1answer
35 views

blake2b length extension attack approach

I understand that a completion flag parameter with Boolean value of 1 is used by Blake2 when it’s compressing the final block of the digested message. This ensures that one cannot load the state of a ...
8
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1answer
406 views

Which block cipher parameters should be kept secret?

Which of the parameters of a block cipher (e.g., algorithm name, mode of operation, IV (if any), key length) are essential to keep secret?
0
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1answer
50 views

(Whitebox Crypto) Using ChaCha20, is it safe to reduce the nonce length in a single block cipher?

I am willing to write a Whitebox Crypto unit using ChaCha20 algorithm (Bernstein, D. 2008) for an input consisting of a single block. The fact it is going to be a single block cipher is of special ...
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0answers
30 views

Difference in elliptic curve order and finite field size

Must the prime finite field, Fp, an elliptic curve is defined over always have a greater number of elements than the cardinality of an elliptic curve. For example, If I have ...
1
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2answers
42 views

Hybrid cryptosystem

I'm using RSA (4096) and AES GCM (256) to exchange messages between A and B. A random key for AES is generated, the plain message is encrypted with AES, and the random AES key is encrypted with Bs ...
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0answers
11 views

PHP encrypt string using blowfish [migrated]

I have an application running on php 7.2 and I need to encrypt a string using the following criteria: Cipher: NCFB Output encoding: Base64 Initialization Vector (IV) = 8 I already know the output I ...
1
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1answer
34 views

BGV for three multiplication level/depth

Can BGV homomorphic encryption scheme support three multiplication level/depth with the help of key switching and modulus switching? If Yes, how does one set up the parameter to achieve that?
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0answers
35 views

Is it possible to encrypt a message stream with the same IV each time and for it to be secure?

I know we should ideally never reuse the IV (Depending upon the mode of encryption used), but is it possible to have a protocol which uses the same IV for the message stream and is as safe as one ...
1
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1answer
59 views

Why is AES in XTS mode insecure for data stream encryption?

Can anybody explain to me why AES in XTS mode is supposedly insecure for data stream encryption? I have been unable to find a clear explanation for this.
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0answers
34 views

A5/1 Formula Question's

So before I start I'm learning how this algorithm still works so my first question is for the x,y, and z steps (of getting the keystream I believe). The formula is t = y 20 XOR y 21 for y. There is ...
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0answers
29 views

Keyspace of monoalphabetic substitution cipher

Assume that the length of the key is known. What is the smallest value this can take and still have the number of possible keys exceed the keyspace of a monoalphabetic substitution cipher?
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1answer
38 views

what are the benefits/limits of constructing AEAD using Duplex mode with ARX primitive (chacha20 for example)?

I understand that WAGE cipher uses duplex/sponge mode with stream based cipher for Authenticated encryption with associated data (AEAD) and NORX uses duplex/sponge mode with LRX structure , so , Is ...
0
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1answer
33 views

Is it possible to find what is the random generated key if I know the plaintext and ciphertext? [on hold]

Is it possible to find what is the key with only plaintext and ciphertext? For example, My plaintext is: hi My ciphertext is: 0x1db5
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1answer
47 views

Which is the best AES mode of operation? [on hold]

Is there any reason to choose, say ECB over CBC? Or GCM over AEX? Or CTR over CFB? Is there a best AES mode of operation? And, when required, which is the best padding to use?
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0answers
27 views

Finding repeated groups of letters in the Kasiski examination

While doing the Kasiski examination I came to a problem. If there is the following group of letters in the cipher: AA and later on a group AAA is found. Does it count as two repeats or just one? And ...
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0answers
18 views

Fully homomorphic encryption - modulus switching

How to apply modulus switching technique on gorti's enhanced homomorphic encryption schemes to reduce noise occurred during multiple addition and multiplication operations?
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1answer
79 views

Why is $S(y) = y^{2^8-2} = y^{254}$ a one-to-one function and a permutation on $GF(2^8)$

I'm taking a course on cryptography and I have some confusions concerning the materials in our notes. Say we have the field $GF(2^8)$, we create a substitution algorithm (the S Box in AES) so we need ...
1
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1answer
97 views

Is Mathematics or Computer Science more important for a career in cryptography [on hold]

I'm a Mathematics Major, and I currently enjoy the mathematical aspects of cryptography. I intend to pursue a career in cryptography research. https://www.csit.gov.sg/join-us/job-opportunities/job-...
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0answers
23 views

Perfect secrecy public key scheme [duplicate]

Are there public key schemes that have perfect secrecy? The perfect secrecy notion is defined for symmetric key encryption. If P is a message and C the corresponding ciphertext then the cipher has ...
0
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1answer
42 views

Calculating DES key knowing message before and after encryption

I've 8 bytes before encryption (for example: 01 02 03 04 05 06 07 08) and 8 bytes after DES encryption: ...
5
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0answers
46 views

Most influential/illuminating papers/books/courses on lattice based cryptography?

I'm interested in some sort of "compendium" on lattice based crypto. There are a bunch of maths behind FALCON and other stuff. A lot of articles are devoted to lattice crypto, but not of them are of ...
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0answers
44 views

homomorphic encryption function representation

As it known, Homomorphic encryption can be used for privacy-preserving outsourced storage and computation. In various constructions, the computations are represented as either Boolean or arithmetic ...
0
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0answers
18 views

Analyze output of openssl ciphers with haproxy default ciphers configuration [migrated]

I am trying to analyze the different cryptographic algorithms used by the default haproxy configuration in an audit purpose as it obviously contains some deprecated stuff in it. The configuration line ...
1
vote
1answer
39 views

Purpose of using a=2 in Pollard p-1 factorization method

The Pollard p-1 factorization method states if $\gcd(2^{B!}-1,n)=p$ where $p>1$ and $B$ bounds the prime factors of $p$, then $p$ is a prime factor of $n$. Shouldn't it be $\gcd(a^{B!}-1,n)$ for ...
1
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1answer
40 views

Attacks against RC4 when index $i$ is unknown

RC4 uses two 8-bit indices. One, $j$, is key-dependent and secret, and the other, $i$, increments by one for each byte output. The $i$ index is typically considered to be public, but what if the RC4 ...
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0answers
23 views

What is cipher type and ways of attack [on hold]

I want to know what is the cipher type with below specification and how attack it: 1- ask me to enter serial number (20 bits) 2- generate a random number(32 bits) 3- waiting for me entering a key to ...
1
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1answer
36 views

Attacking Double DES (OFB Mode) given the initialization vector and not much else?

I'm given a Plaintext/Ciphertext pair, a Ciphertext to break, and the IV. One thing of note is that the same IV is used for both DES Encryptions, so $$C = E_{K_2}(E_{K_1}(P, IV), IV)$$ I have limited ...
0
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1answer
36 views

Man Made ELS Codes

This is more steganography, not cyptography, but I don't know where else to post this. Are you familiar with ELS (Equidistant Letter Sequence) codes that some have said are found in the Bible? I know ...
0
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0answers
29 views

End to End Encryption Implementation [on hold]

I'm looking to implement an end to end protocol which will be used by a few people, it won't be public. I was thinking about using ECDSA + ECDH (using P-521 curve) + AES GCM 256 and SHA256. If that is ...
1
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0answers
28 views

RSA Modulus doesn't match the primes [on hold]

I generated a 2048-bit RSA key with ssh-keygen. When running: openssl rsa -in key -noout -text The result is: ...
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0answers
23 views

Trapdoors of Lattices: SampleD and SamplePre

In Trapdoors for Hard Lattices and New Cryptographic Constructions by Gentry et. al, they discuss SamplePre and in Trapdoors for Lattices: Simpler, Tighter, Faster, Smaller by Micciancio et.al, they ...
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0answers
36 views

statistical distance in symmetric-key encryption

Prove that for any symmetric-key encrytion scheme $\Pi=(Gen, Enc, Dec)$ with message space $M$ and key space $K$, there exist $m_0, m_1 \in M$ such that $\Delta(Enc(K, m_0), Enc(K, m_1))\ge 1-\frac{|K|...
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0answers
28 views

finding key for caesarciphertext [on hold]

I have been given this caesar cipher text https://imgur.com/a/10GOjYD and I have been told to (i) Count the number of occurrences of each letter. (ii) Based on the results of (i), use frequency ...
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0answers
41 views

Why does using infinite fields leak secrets in Shamirs Secret Sharing Scheme? [duplicate]

There is a similar question here, but the answers as I understand them basically say (1) you can leak the parity of the secret and (2) you can run into over/underflow issues as well as floating point ...
2
votes
1answer
59 views

Does RSA key transmit with OAEP insecure?

In the Key encapsulation article of Wikipedia, the RSA-KEM is described shortly, as follows; Generate a random element $1<m<n$ then drive your symmetric key by $M=\text{KDF}(m)$ Then compute ...
0
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1answer
42 views

How are blockchain keypair private keys hidden from miners, and how are they generated in the first place? [on hold]

I don't know how blockchain keypairs are programmatically generated, and equally important - how they are able to verify their keypair using a private key to a remote server - while keeping their ...
1
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3answers
81 views

Expanding Key Material

Is there a way to take key material (for example 256 random bits for an AES key) and "expand" it over to a larger amount of data? Or can I go the opposite way and take a large amount of random data ...
0
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0answers
40 views

Benefits of signing a random number [migrated]

Is there any benefit to signing a random number? e.g. a link for password reset, sent to email, often includes a base64 encoded random number to prevent someone guessing what the password reset link ...
0
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0answers
6 views

SonarQube: Make sure that encrypting data is safe here. AES/GCM/NoPadding, RSA/ECB/PKCS1Padding [migrated]

I'm using: 1. RSA/ECB/PKCS1Padding 2. AES/GCM/NoPadding To encrypt my data in my Android (Java) application. At the documentation of SonarQube it states that: The Advanced Encryption Standard (AES)...
1
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0answers
32 views

Commitment to a degree of a polynomial

Is there a way to commit to a degree of a polynomial without committing to every single one of its coefficients? The problem I am trying to solve is to prove that two polynomials are the same in a ...
0
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0answers
35 views

Differences between MAC and HMAC [duplicate]

After reading many posts, I am still confused about the differences between these two. Let me know if my understanding is correct: MAC is encrypted string that is generated using a secret key and a ...
1
vote
1answer
46 views

How android apk file signing works?

There are a number of pages on web to tell how to sign apk file for Android. But none I've found telling how it works under-the-...
2
votes
1answer
85 views

Proof of application of $f(x)$ without disclosing input $x$

I have three nodes in a network: $\mathcal{S}$,$\mathcal{T}$,$\mathcal{R}$. $\mathcal{S}$ supplies data $x$ to $\mathcal{T}$. $x$ is signed so $\mathcal{T}$ knows it actually comes from $\mathcal{S}$...
0
votes
1answer
57 views

Is this PGP key exchange secure?

I am currently trying to create a secure key exchange between two parties. I have a good implementation of PGP that works well for my app, but my DH is really slow and doesn't work well; so I was ...
82
votes
4answers
10k views

Has SHA256 been broken by Treadwell Stanton DuPont?

In a recent press release issued by Treadwell Stanton DuPont the claim is made that their research laboratories have successfully broken all 64 rounds of the SHA256 hashing algorithm. They further ...
0
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0answers
5 views

Elliptic Curve 256 public key in readable (DER?) format in .NET Core [migrated]

I have .NET core application and EC 256 public key as point of a curve (x and y) in the following format ...
1
vote
1answer
37 views

Explanation of the tables found in Kyber round1 code?

The precomp.c file in Kyber NIST round 1 submission has three tables, could you please let me know how to generate these three tables? If I want to understand how ...

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