Questions tagged [xor]

XOR, often written ⊕, is one of the basic operations on bits and bit-sequences. It is a building block of many cryptographic primitives (and some higher-level algorithms, like modes of operations).

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Is Fibonacci-XOR-rotate one-way-ish?

Fix $n\in\mathbb{N}$ with $n > 2$ and consider the following method. Pick relatively prime seeds $x_1, x_2 \in \{0,1\}^n$ (where $x_1, x_2$ are interpreted as binary numbers. Then proceed with the ...
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basic question regarding two-time pad attack

Dan Boneh's Crypto 1 Course includes a lesson on stream ciphers with the following slide: He asks the question: And the answer he gives is $m \oplus p$, which is why this is insecure. But I don't ...
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How to decrypt two images encrypted using XOR with the same key?

I am trying to solve the following puzzle from CryptoHack involving two images encrypted with the same key: I've hidden two cool images by XOR with the same secret key so you can't see them! lemur....
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Recreate RC4 Stream cipher

I'm trying to learn how to go about cracking RC4 ciphers (nothing illegal, its an old, i.e., not active challenge for a job application, so no cheating). I have nine md5 hashes with their own ciphers. ...
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Help me understand how to do a crypto assignment about AES/CBC

I'm doing the Coursera cryptography I course from Dan Boneh. I am attempting to do week 2's programming assignment, but I think I am having some sort of misunderstanding of either the theory, the ...
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44 views

Is this a good implementation of digital signature with timestamp?

Is this a good practice ?. How good or bad is this compared to appending a timestamp to the actual data and hashing it as represented below. ...
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424 views

What is most secure way for one party to encrypt 4 bytes in less than 40 bytes, which will be publicly available?

I have a project where a user needs to store a U32 encrypted on a blockchain such that they can recover it themselves: the user will always have their key available but may "forget" the U32 ...
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48 views

AES MDS D-XOR and S-XOR count

I am trying to implement the D-XOR and S-XOR count in python but despite reading multiple articles on how to perform the calculation I have failed to understand the process used. I would appreciate it ...
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Splitting Secret Key

If I split a key $k$ into three pieces as $k1, k2$ and $k3$ how should I distribute the keys among three people such that any two of them are able to evaluate PRF, but be secure from any one of them ...
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Need help finding keysize for Vigenere cipher

I am doing a crypto challenge for breaking a Vigenere style repeating XOR encryption (https://cryptopals.com/sets/1/challenges/6). I have looked at similar questions asked here, mainly this one: ...
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Formula for bits of entropy per bit, when combining bits with XOR

Assume that bits $A$ and $B$ each have .5 bits of entropy per bit. The two-bit result of the concatenation $A‖B$ has 1 bit of entropy total, and it retains the entropy density of .5 bits of entropy ...
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Using sha3 as a deterministic source of psuedo-random bytes for xor encryption

The following code generates a deterministic stream of pseudo-random bytes, using SHA3. ...
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172 views

Is it safe to XOR-combine hashes by rotating them first?

I have a small number of hashes. I would like to combine them into a single hash. XORing the hashes ignores their order, which is important. Also, it could lead to a result of zero if there were an ...
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1answer
77 views

Using xor encryption in the following use case

I use an encryption scheme based on a symmetric cipher, with the corresponding symmetric key encrypted with RSA/OAEP using the public RSA key of the recipient. I now want to use ECC crypto in ...
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Generating a XOR Hash function for a given group of numbers to maximise collisions

Given $x$, a vector of $m$ distinct bit vectors of bit length $N$, I want to use an XOR-hash $h$ such that all $x_i$ collide to the same value. I define an XOR hash $h$ which takes bit vector $q$ as ...
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1answer
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Can i XOR an array of bytes with an equal length key securely

If i have say 64 bytes, can i XOR those bytes with another 64 random bytes, and have two new arrays, where both are needed to reconstruct the first? Intuetively i need some symmetric encryption like ...
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Assignment: XOR-cipher [duplicate]

I am currently attending a IT-Security course at the Tel Aviv University and I stuck with the an assignment task. Please DO NOT post the solution if you know it. But I would be very grateful for any ...
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Can I encrypt a message by swapping bits in the text?

I have tried out an encryption method, in which I swap bits in the text. The text length is N bit, then I generate several random number pairs in the range 0..N-1, as [n,k] pairs. After that, I swap ...
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Approach used with XOR cipher in black box scenery

What's the approach used in cryptanalysis to make an decrypter for a simple xor stream cipher in a Black Box scenery with only the output?
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XOR cipher with fixed key and known relation among plaintexts

I have three messages, each known to be XOR-encoded, with the same key used for each message of this XOR cipher. Encoded message 1: $e_1\,=\,00100111010$ Encoded message 2: $e_2\,=\,01001110110$ ...
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2answers
184 views

Secret sharing scheme WITHOUT Shamir Secrete Sharing

I am planning to use the following XOR scheme to divide a secret into only 2 shares (I do not want to use Shamir Secret Sharing for different reasons that are beyond the scope of this post). Here's ...
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1answer
93 views

Potential weaknesses when combining hash functions?

For consistency's sake, M is the message, H1 and H2 are separate hash functions. I've heard that concatenation or XORing hash outputs together do not provide improved security against preimage and ...
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Weakness in a CBC-like XOR cipher

A simple symmetric encryption algorithm can be written as follows: Input message M and 64 bit key $K$ Divide M into 64 bit size blocks $B_1...B_n$ Get first block $B_1$ and perform bit-wise $\oplus$ ...
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Boolean XOR function a valid way to verify the integrity of a message

Does the Boolean XOR function represent a valid way to verify the integrity of a message ?
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GMW Multiplication AND for 2 parties

I am looking into the GMW protocol's evaluation for multiplication in 2 parties. I have referred to different materials on it but I didn't exactly understand how $a_i b_j + a_j b_i$ is calculated in a ...
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Example of a Two-party GMW Protocol

I have been looking for a concrete example of GMW protocol for two parties. I was trying with the following example for computing $XOR$ of two parties: A's secret bit is $a = 0$, B's secret bit is $b ...
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Using Diffie–Hellman without a key derivation function

In an answer to another question, it was suggested that the shared secret derived from Diffie–Hellman key exchange could then be used directly as a one-time pad to encrypt a message (by XORing the ...
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1answer
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Meaning of difference Δ delta

I tried to understand some crypto text but I am new to this. Does this: Let $X,X'$ be $\ell$-bit values, and $\Delta X=X\oplus X'$ means that $X$ and $X'$ have $\ell$ bits and $\Delta X=X-X'$ or ...
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What does a repeated byte between two XORed hexadecimal ciphers mean?

I have two different hexadecimal strings (of same length) that I think are encoded plain text strings. Out of curiosity I XORed them and I found a single hex byte repeated for the length of the two ...
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How to reverse this simple xor encryption function? [closed]

this code decrypts encrypted rom code from an arcade game pcb (it is from source code of Mame emulator) for each byte in rom... ...
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Dining-Cryptographer Net (DC-Net) Scheme that Handles Collisions?

[Question edited at the request of Mods] I recently became fascinated with the elegant and simple solution that Chaum proposed for the Dining Cryptographers problem. If you are unfamiliar, please ...
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1answer
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Solving a system of equations using both arithmetic and bitwise operations

At first I asked this question on Stackoverflow, where I was advised to ask here. So there is the question: I have a system of pretty simple equations: $x + y = A$ $f(x,y) + y = B$ $A, B$ are known....
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1answer
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XOR PSK with random buffer

I need some guidance here: assuming I have the following: (PreSharedKey of 32 bytes) XOR (one time Random Buffer of 32 bytes) The only way to crack this should be brute forcing, correct? One of the ...
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Break an encryption made with XOR of a key and a known Nonce

My questions is general, but in my case regards the Kerberos protocol and the communication between the client first message and the KDC. Is there some problem in encrypting using a: (secret key XOR ...
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1answer
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Is there any security issue if an attacker recovers the key stream generated by a stream cipher?

I've learned that a stream cipher like ChaCha20 generates a key stream that gets XORed with the plaintext to get the ciphertext... If an attacker knows the plaintext, he could just simply XOR that ...
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1answer
183 views

XOR of 16-bytes variables gives a result of size not equal to 16

I'm trying to write a XOR code for implementing CBC mode of operation from scratch but i seem to have some problem.The function takes two byte variables of 16bytes and the expected output should be ...
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Is there any vulnerability in this scheme?

We want to design a symmetric encryption scheme. Note that the following things are true for our system: The plaintext P will change every time for a given user. A user will choose a password which ...
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1answer
109 views

Why is the second XOR operation in OCB mode necessary?

In Rogaway's OCB mode, the offset (derived from the key) ist XOR-added twice: Once to the plaintext block, and a second time after the Encryption. I am wondering, why the second XOR operation is ...
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327 views

How secure is XOR-CBC?

How secure would this be? To be clear, I mean replacing the block cipher encryption step in the Wikipedia diagram explaining CBC with plain old XOR? EDIT: Replace ...
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1answer
65 views

Stream cipher - Many time pad

I understand the concept that when you xor the cipher texts you get the XOR messages cause the keys get XOR-ed and cancel out... This is at least the case when both the messages are of equal lengths. ...
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OTP Random Pad Renewal Without Extending Message [duplicate]

So I recently learned about the concept of a One Time Pad; and I from what I understand it means that if a XOR key is completely random and equal to or longer than the plaintext, it makes it so that ...
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1answer
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PRNG XOR Pipeline

For an OTP I need the 'best' random data I can acquire. Please check if my thinking for stacking PRNGs together in a pipeline can only make the output statistically better, never worse?! So take a ...
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Key size of a repeating key XOR-encrypted message using Hamming distance

To find possible key sizes for an encrypted message, I break the message into blocks with length s, ...
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651 views

How strong is XOR encryption of 256 bit plain text with 256 bit key?

I was wondering if we take just 256 bits of plain text and simply XOR every bit with a 256 bit key, how strong can it be ?
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Would XOR'ing two Argon2 keys add extra security?

When a user registers on the app, they need to provide a password they create and we provide them with a randomly generated passphrase (e.g. Apple Cat Ladder Fire). We then use Libsodium's ...
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1answer
374 views

Simple block cipher

I came up with this concept, which I thought would be pretty secure. So the idea is this, you have a message $M$, which you split up in blocks of each 256 bits. You generate a random (pseudo-random ...
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1answer
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Secret Sharing between $x$ parties

So for an unknown number of parties $x$, I make $x-1$ random $n$-bit strings represented by {$r_1, r_2,...,r_{x-1}$}. Where $s$ is the complete string split up between $x$ parties (yes?). I then ...
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1answer
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Definition of diffusion matrix

I've been studying this article and since I'm not studying cryptography in English and it is not my native language, I don't understand some of the terminology. More precisely: what are diffusion ...
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ChaCha20: is this a potentially safe way of using nonce derived from private key if the key/nonce pair is never reused, for a given plaintext?

Note: I realize in ChaCha20 the nonce should be random and unique each time follow certain constraints but am trying to determine whether there could be a safe way to use it just once if other ...
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Why is this OTP decryption wrong? [closed]

i have a problem that goes: ...

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