# All Questions

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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 $\phi:E\to E^{\prime}$: ...
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 $s$ ...
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,...
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 ...
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?
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### (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 ...
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 ...
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 ...
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 ...
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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### 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 ...
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.
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 ...
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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### 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 ...
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### 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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### 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?
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 ...
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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### 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 ...
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-...
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 ...
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: ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
36 views

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 ...
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 ...
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: ...
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 ...
36 views

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### 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 ...
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 ...