# All Questions

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### How to alter text that was encrypted with AES CBC using PKCSPadding7

Assuming, I had a ciphertext along with its decrypted plain text result but not the IV or the Secret Key. (keep in mind that the text was encrypted with AES/CBC/PKCSPadding7). How would I go about ...
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### How to find the co-efficients of a function within Zp[x]?

I am a newbie in Field arithmetic and while trying to implement an Elliptic Curve Cryptography based ABE scheme in a programming language, I am unable to understand how to implement function fields. I ...
8 views

### Can you change an AES encrypted message if you control the IV?

Let's say that an attacker has the plaintext, the ciphertext and the IV of a specific message. If the attacker can control the ciphertext and the IV, could he forge valid plaintext? Let's say that the ...
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### AES-CBC encryption and key size and questions

I am on my first AES-CBC (256 bit) encrytion project. I created a function $$\text{key_iv_generatorformechanics(passwd)}$$ which uses $\text{os.urandom()}$ to generate a random IV and Salt to use them ...
32 views

### How to prove document ownership at a specific time

Problem Given any piece of data, I could sign it with public key and made available online. This proves I am in possession of given data, but it doesn't tell I am the creator. The only possibility (I'...
2k views

### Simulation-based proofs and universal composability proofs

I recently read Ran Canetti's famous UC paper but I'm still trying to wrap my head around the concepts. I think this answer has me confused a bit, particularly where it says The stand-alone ...
60 views

### Finding RSA private exponent with a chosen ciphertext attack?

Let's say there's this blackbox app that has a known modulus $N$, private exponent $e$, and takes ciphertext $C$ encrypted against $N$ and $e$ input and outputs plaintext $M$. The encryption is done ...
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### Differential privacy what does “where the probability is taken over the randomness used by the algorithm” mean?

The definition of differential privacy is as follows: A randomized mechanism $\mathcal{M}$ is $(\epsilon, \delta)$-differentially private, where $\epsilon \leq 0$ and $\delta \leq 0$, if for any ...
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### Criteria for public modulus of RSA accumulator

What are criteria for generation of an RSA public modulus used in an RSA accumulator, and their rationale? Are there special requirements in some sub-cases, like for «one-way» accumulators? Josh ...
16 views

### RSA decrypton correct? [closed]

Given $C_i$ = [176, 12, 64, 98, 185, 64, 98, 176, 138, 127, 45, 176, 35, 156, 138, 45, 45, 45, 98, 138, 104, 138, 51, 65, 138, 35, 168, 12, 22, 138, 176, 45, 12, 22] and $187, 3$ as public key. The ...
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### Confusing Encryption Mode [duplicate]

I have an API that accepts plain-text and IV as input and I'm trying to identify the encryption mode for that API. I have already tested this API for ECB, CBC, OFB, CFB and CTR and it doesn't seem to ...
31 views

### Key renewal when the sequence counter is only 32-bit

If we look at the use-case that our sequence counter within our TLS communication is only 32-bit, would an automatic key re-newal be necessary a lot more frequently? We're going to use state-of-the-...
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### Hashing of variable-length chunked data leading to leakage of secret key from side channel?

Hypothetically, secret data could be hashed in some schemes in one way or another. Could chunking of the data lead to exposure of secret component through side channel? Say converting a randomized ...
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### What is universal composability guaranteeing, specifically? Where does it apply, and where does it not?

I don't have a proper computer science education, so bear with my misunderstandings. UC is supposed to "guarantee strong security properties". From what I stand, if you have some secure ...
5k views

### RSA Signature : Process of Sign the message and Verify

I have read that the RSA numeric signature works as the following: Generation of keys : $p,q,N,e,d$ Process of signing the message $m$ (which is BigInteger) : it uses the secret key $sk=(p,q,d)$ so ...
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### Spontaneous parametric down-conversion

we generate heralded single pho- tons via spontaneous parametric downconversion using a 5 mm long periodically-poled potassium titanyl phosphate (ppKTP) crystal pumped with a 405 nm diode laser (200 ...
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### Nonce of AES-GCM generated by Counters

i am trying to generate the nonce for AES-GCM. I know people usually generate it by Counters and LFSRs. I am confused about the meaning of Counters. Is that means Counter (CTR)? Why it can generate ...
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### Converting a plaintext to hex for AES encryption

Looking through AES process I see it uses a substitution table which need the input in the form of hex. Im wondering if i have a plaintext of 16 bytes such as 'j±…<Ãà!DÈ¶;5˜‰*', how can I convert ...
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### how to verify the digital signature in a zero knowledge proof

I know that the zero knowledge proof is able to prove to the verifier that the holder does in fact posess the digital signature issued from an issuing 3rd party but... How does the verifier validate ...
13 views

### How Bob detect the Eve in QKD BB84 protocol

1- how is eve have access to quantum channel? How bob will know there is eyedropper? 2-what is different between quantum channel and classical channel?
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### Issue with only applying key addition layer before first round of AES

What would be the issue if AES only applied the key addition layer once, before the first round? As in, how would this make the algorithm vulnerable to attack?
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### Converting normal alphabets to 64 bit plain text

How can I convert a normal alphabetical text (say hi) to a 64 bit or 128 bit binary digit input for DES?
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### The Meet In The Middle Or Collision Algorithm [closed]

I'm working on the Meet In The Middle Algorithm; also known as the "Collision Algorithm". Here's the code Python 3 Program To Calculate The Discrete Logarithm Problem Using The Collision ...
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### Why mounting/dismounting an encrypted file container takes only a few seconds?

When the encrypted file container contains 100000 files and 500 GB of data, all of them must be decrypted/encrypted when the container is mounted/dismounted. How can Truecrypt/Veracrypt perform this ...
371 views

### Rijndael S-boxes: Where do the $\mu$ and $\nu$ polynomial ring elements come from?

I've asked some other questions before about Rijndael's S-boxes, and step by step I'm coming to an understanding; but those steps often guide me to new questions. I did some lines of code to ...
138 views

### Using Hadamard Form of a Matrix in the Block Cipher

Definition: A matrix A of size $2^n$ is a Hadamard matrix, if has the following form $$A= \left( \begin{array}{cc} U & V \\ V & U \end{array} \right)_{2^n\times 2^n}\, ,$$ where $U$ and $V$...
1k views

### How to find the AES branch number?

By definition, branch number Definition: The branch number of a linear transformation $F$ is $$min_{a\neq0}(W(a) + W(F(a)))$$ Source here (7.3.1) For AES MixColumns $a \in GF(2^8)^4$ since ...
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### Choosing a suitable prime for accumulators

I am trying to work out accumulators and generate $S = \{ e_1,e_2 \ldots, e_n \}$ from this (Section 3.4 - Choosing a Suitable Prime). For each element of $e_i$ compute its representation $x_i$.(This ...
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### Are there any universal PRG’s or PRF’s?

Leonid Levin constructed a universal one-way function, i.e. a function $f$ such that if any one-way functions exist, then $f$ is a one-way function. My question is, what universal pseudorandom ...
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### Security of LWE when a small leakage is allowed on the noise

Short version: Is there some results that are known on the security of the Learning With Error problem when there are some leakages, notably on the noise? (In my case these leakage come from a bit ...
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### The space required to store brute forced results in python [closed]

If I wanted to store a 32 bit number I brute forced; How much space and time would the 4.2 billion iterations consume in python?(And I know that at most, it takes at least a second to brute force a 32 ...
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### Cold storage on paper: ASCII of an AES-256 crypted text (gpg)? [migrated]

I want to encrypt a passphrase offline using an air-gapped computer and print it for cold storaging. I'm using this command to encrypt: ...
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### How to forge a CBC-MAC

I'm looking for a very clear explanation of how to forge a CBC-MAC. Given M1 = m1 and M2 = m1||m2 and M3 = m1|| m2 || m3 and their respective MACs are MAC1 MAC2 and MAC3 how would I go about forging a ...
1k views

### Determine if a public key point y is negative or positive, odd or even?

Take an elliptic curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Examples: Private key 1 -> (x,...
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### Generating a random point on an elliptic curve over a finite field

I have coded an implementation of elliptic curves in order to apply some of the ECC algorithms. However, in most of them, Alice needs to choose a point P on a given curve. What is the general ...
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### Questions about Symmetric Encryption part of TLS

In TLS, we use DHKE for establishing the session key & then encrypt the actual communication with session key using symmetric encryption. While reading about DHKE, I learnt that you could use the ...
3k views

### How does Python's pycrypto library generate primes?

The pycrypto library in Python can generate random n-bit prime numbers. The syntax I use is as follows: from Crypto.Util import number number.getPrime(2048) The ...
7k views

In this question on StackOverflow https://stackoverflow.com/questions/31248777/can-pkcs5padding-be-in-aes-gcm-mode it's said that GCM doesn't require a padding: why?
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### Attacking a variation of the Vigenere with very long key length

I am to decrypt the ciphertext YVBCXGJRYHHRCJIUL into its plaintext message. The information that I am given is that the key used in the cipher is very long (equivalent to the length of an entire book)...
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### Is it possible to recover the key from HMAC-SHA512 given the original text and the hash? [closed]

I'm trying to do a CTF challenge where you have to find the key of HMAC-SHA512 given the hash and the original text of a couple of strings. You are also given a hint to use a number between 40 and 50 (...
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### Hypothetical AES CBC hash function collision resistant?

If we consider a hypothetical hash function H defined by AES-CBC where it encrypts n-blocks (C1,C2,C3..Cn) and the hash value is the last cipher text block - Cn. IV and Key are predefined values ...
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### Should I use 2x the number of CPU / core for Argon2id parallelism?

I've read that I should use 2x the number of CPU available from some documentation while others suggest using between 1 and the number of CPU. I realize there is no hard answer here but I'm curious ...
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### What are examples of mechanical dictionaries?

My question is not about en/decrypting words but rather using a mechanical device to compute some basic words and letters manipulations such as finding anagrams. I of course realise that storing and ...
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### Identify AES Mode

Let's say I have an API that accepts Plaintext and IV as input parameter and returns the ciphertext. I know that API is using AES 128 encryption but now I need to identify which encryption mode (ECB, ...
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### Proving G(x)=x||[x^2 mod 2^N] is not a PRG

This was a question from my exam yesterday. We have that $G:\{0, 1\}^n\rightarrow \{0, 1\}^{2n}$ and $$G(x)=x\mathbin\|[x^2 \bmod 2^n]$$ with $x$ is uniform and $|x|=n$, give an efficient ...
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### Can anyone detect which cryptography method is used from the cypher?

i want to know which cryptography method is used to encrypt below cypher. ...