# Questions tagged [decryption]

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### Encrypt data. Create 5 keys. Just 3 keys are needed for decryption

I would like to encrypt some data and create 5 keys. These keys are stored in different places. If I want to decrypt the data I just need 3 of these 5 keys. Is there a way to do this?
50 views

### public key crypto example [closed]

I am trying to validate encryption and decryption process. After the encryption process, I have $C$ where $$C = (z_1^x, z_2^y, m\cdot z_3^{x+y})$$ I'm also given $(z_1,z_2,z_3)$ and $(a,b)$ tuples ...
53 views

### How to decrypt a combination of transposition and substitution cipher text

I'm having problems decrypting a cipher text that has an transposition cipher applied to it but also a substitution cipher. I don't know in which order they were applied. Does anyone know what steps I ...
30 views

### How to show that Affine crypto have a valid decryption

I just need to know how to attack a question I have in my textbook this is like: Let $E_1 (x) \equiv 17x + 7 \pmod{28}$ and $E_2(x) \equiv 23x + 11 \pmod{28}$ be encryption functions for two ...
23 views

### How would you decrypt an affine cipher with only the ciphertext? [duplicate]

If I have only the ciphertext but the alphabet and the value of a and b are all unknown ... how would I go about this? I understand decryption with the key and alphabet, that is fairly easy but if we ...
51 views

### Need help cracking a vigenere cypher with period 2

how do you crack a long vigenere cipher when the key is unknown , I have tried a frequency analysis but I'm not making any progress
46 views

### Decryption of RSA with e that has no inverse

I'm studying the RSA protocol and I was wondering if there was any way of decrypting a message if the $e$ doesn't have an inverse $\mod (p-1)(q-1)$. Usually, you have to choose a value of $e$ that is ...
72 views

### RSA - Calculating $d$ given $\varphi (N)$ and $N$

From this discussion, I know that if I know $\varphi (N)$ and $N$ (where $N=pq$, $p$ and $q$ prime), then I can very easily get $p$ and $q$. Suppose I have the encrypted message $c$. I want to get ...
67 views

### Using Viterbi algorithm to decrypt Vernam cipher

I'm reading a book on cryptography and it mentions the Viterbi algorithm being used to decrypt Vernam cipher if the same key is used multiple times. According to the book the Viterbi algorithm takes ...
5k views

### How are side-channel attacks executed? What does an attacker need to execute a side channel attack?

I've been reading about side-channel attacks on Wikipedia, and it seems that some of these can only be executed on the victim's computer. (I am specifically asking about the side-channel attacks ...
62 views

### Secure encryption to store credit card data

I need an encryption algorithm that would be secure enough to store credit card data. So it should be reasonably secure. Here's what I've come up with. I'd appreciate any constructive criticism. Is ...
93 views

### Known Plain-text Attack [closed]

How can I find the known plain text P2 based on the given information? Assuming that the encryption is made using a common initialization vector and the mode used for encryption is OFB. ...
113 views

### OpenSSL: How to maintain padding from encryption after decryption?

One of my professors mentioned in class that there is a way of using PKCS#7 padding to have the padding persistent after decryption. For example, if I encrypt a 20-byte file using ...
107 views

### “hex” vs. “base64” encoding when enciphering

Examining different implementations of encryption / decryption with cipher on Node.js, I paid attention that some implementations use hex encoding: ...
63 views

### Possible deciphering methods for the steganography on an old check? [closed]

This check was deposited in the 1930s, and it was issued by OCBL (an old bank in Singapore). The checks issued by this bank had an interesting feature - an obfuscated pattern printed on the back of ...
37 views

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

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

### Is an invulnerable code possible (including brute force attack)?

If I double encrypted a text with for example AES wouldn't it be invulnerable to bruteforce attacks due to the computer not knowing when it has reached the plain text? Plain text->1st layer of ...
72 views

### NaCl allows decryption with the same public key as for encryption

I followed the description here: Public-key authenticated encryption: crypto_box and created an example that encrypts a message with Bob's public key and signs it with Alice's secret key : ...
208 views

### Is this toy RSA demonstration flawed?

I want to present the basics of how RSA works to an audience of beginners in cryptography. The problem is that I am lightyears from being an expert. After reading about how RSA works in wikipedia, ...
62 views

### How secure is a 40 bytes hexadecimal string AES256 encrypted with 50 bytes random password

Problem Assume I have a 40 bytes hexadecimal ASCII string and a 50 bytes random password. ...
51 views

### Subexponential algorithms that apply only one of factoring and discrete logarithm?

Shor (quantum polynomial), Number Field Sieve (subexponential), Pollard rho (square root) all have both factoring and discrete logarithm over $\mathbb F_p^*$ variants. What are the subexponential ...
63 views

### Are there any asymmetric key encryption/decryption algorithms?

When it comes to encrypting some data (where data being something of a large size), symmetric key cryptosystem is predominant. Symmetric key algorithms like AES, DES, Blowfish, IDEA etc. are ...
81 views

### Cryptography on programming

In pursuit of understanding a randomly found topic I was interested in learning the connection between integer programming and cryptography and found Lenstra Jr.'s Integer Programming and Cryptography....
302 views

### Apple CryptoKit - Understanding its portability

I've been playing with Apple's CryptoKit (their effort to make their old CommonCrypto lib more modern and easy to use via Swift, their programming language). I'm interested to see how portable it is.....
491 views

### How to find the key of XOR encryption in Java?

I am trying to find the key of an XOR-encrypted string in Java. It is very probable that the key is eight characters long. I have the encrypted string. I do not understand how to go backwards and ...