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 this an effective obfuscation technique?

Long ago I created a simple program which obfuscated a file by taking the first byte, then XORing it with the second, taking the (original) 2nd byte and X-ORing with the 3rd, etc, down the line. The ...
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algebraic attacks for mixed operations (mod 2 and mod 256) [closed]

If a cipher has mixed operations, e.g $\oplus$ (addition mod $2$), and addition modulo $2^8$. How we we going to express them mathematically? Thanks in advance!
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XOR cipher with three different ciphertexts and repeated key, key length known. How do I find the plaintexts?

Let us say we have three different plaintexts (all alphabets, A-Z): $x$, $y$ and $z$, each of length $21$. Let the key, $a$, be also of length $21$. Now, what we have is $x \oplus a$, $y \oplus a$ ...
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Significance of repetition in XOR cipher text

I'm attempting to recover plain-text ($P_1, P_2$) from two uneven cipher-text strings ($C_1, C_2$) that I suspect used the same key ($K$). When I XOR $C_1$ and $C_2$ together to obtain ($P_1 + P_2$),...
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Attack XOR encryption of binary data compressed by zlib with known key length (very short key)

I am trying to break a packet format. The packet format simply packs several files into one big file. The file contents are plain. But the index data which contain offsets, file sizes and filenames ...
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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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OTP with fixed plaintext

I have just learned about the OTP, how it uses XOR, and how it's secure if the keys are random. But what will happen when the same plaintext is used again with a new key? $c_1 = k_1 ⊕ p$ $c_2 = k_2 ...
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Attacks on one-time pad, given a property of keys

An adversary $A$, eavesdrops $n$ cipher-texts, $c_{1}, c_{2} ..., c{_n}$. It also knows a value $v$ and a function $f$ such that $$f(k_{1}, k_{2}, ..., k_{n}) = v$$ where, $k_{i}$ is used to encrypt $...
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Decomposing a vector of random bits into constituent XORed vectores

Suppose I have N potential predefined, publicly known (pseudo?) random bit vectors: sequence 1: 1001000101010111001... sequence 2: 0100101011101010100... ... sequence n: 0101101010111010001... ...
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Reversing a known encryption algorithm (4-byte repeating key XOR)

I've been practicing for an upcoming CTF competition, and I've finally reached the cryptography stage. I'm a complete newbie in this field (my knowledge is essentially that bcrypt is awesome and md5 ...
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Exploiting XOR one-time-pads with alphabet size that isn't a power of 2

I realized that if the key is chosen randomly from a range that isn't a power of $2$, the one-time-pad leaks information about the plaintext. For example, if the alphabet was the first 20 naturals, ...
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How secure is using a pad (using xor) on a encrypted data, for the purpose of obfuscating/hiding the underlying encryption?

Edit: I know this isn't really a one time pad (as pointed out), though I don't really know what to call it aside from just a pad, I guess. I have been reading around (mostly various stackexchange ...
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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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Is using derived keys for HKDF + AES-GCM safe

I have an existing system which takes a cryptographically secure BLOB from user and pass it to lower API which calls HKDF-Expand to get 2 keys: one is effectively discarded in this scenario and second ...
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Solve System of Equations including XOR and Modular Addition

A Dummy cipher is shown in figure below. Plaintext is 16 bits ($X_1$ and $X_2$ are 8 bit each). Ciphertext is computed after two rounds using two round keys $K_1$ and $K_2$. Can the round keys $K_1$ ...
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Reverse Encryption Algorithm from Decryption code

I have the code for a decryption algorithm but I'm struggling to figure out how to reverse it into the original encryption code. ...
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Calculating XOR Key Sizes [duplicate]

I've been playing around with the Matasano crypto challenges (cryptopals.com). I had a couple false-starts on the challenge that has you creating a program to calculate the key size of a XOR encrypted ...
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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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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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Help me understand how to actually break an XOR/Vigenère cipher [closed]

My friend's server was recently hacked and I'm trying to decipher the malicious files I found in hopes of understanding the hack better. I can tell that they're using an XOR/Vigenère cipher and I've ...
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How many Affine function can be made from $4 \times 4$ and $8 \times 8$ S-boxes?

The nonlinearity of an S-Box is defined as the non-linearity of its vectorial Boolean Function. Let $F$ be the hamming distance between the set of all non-constant linear combinations of component ...
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Android app cryptography does it fall under US Export laws? [closed]

Basically, I want to encrypt some strings in my app, strings like access tokens or passwords. I planned on using AES, and mainly saw a good library at https://github.com/tozny/java-aes-crypto. Note ...
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Infer encoding mechanism from $n$-grams distance?

I have a series of obfuscated strings which across the set of strings have regions of high variance and regions of low variance – implying some encoding mechanism as opposed to an encryption procedure ...
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How to XOR two hexa numbers by hand fast

I have an upcoming exam where I can use a simple Calculator. On some sample questions they ask us to XOR two values (for AES round key) and I know how to write it out by hand but is there any other ...
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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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Secure Hash Function based on AES

How secure would a hash function be which appends an extra block of 16 zeroed out bytes to the end of the message and then AES-encrypts it with a well-known password (say the first 128 bits of pi) ...
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If you XOR a random input with a biased input, the output is random - why?

Ive seen in an answer to this question here : https://stackoverflow.com/questions/5889238/why-is-xor-the-default-way-to-combine-hashes/5889288#5889288 that If you XOR a random input with a biased ...
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Is a one-time pad secure if the encryption method is not?

(The following situation is hypothetical.) I need to communicate something securely and I have decided to use one-time pads. I am going to be using human genes as the source of the OTP data (this is ...
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What makes an open source encryption algorithm safe?

Take for example the popular AES algorithm where we have a combination of substitution, shift row, mix column, and add key steps involved in encrypting plain test. All of the mathematical operations ...
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Cryptography XOR Question

Recently I encountered an interview question related to XOR and I have no idea how to figure it out. The question is as below: The algorithm is: $A\oplus B$ (operation) $C = D$ We have the value of $...
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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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XOR and key reuse [duplicate]

I've been doing a bit of reading on the use of XOR and the dangers of key reuse. I'm aware that reusing a key can open a door for a frequency analysis attack on my plain text. So far, everything ...
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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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What are the implications of XORing ciphertext with plaintext?

I was intrigued by this question: Does adding complexity mean a more secure cipher? And it led me to wonder: What are the implications (if any) of XORing a ciphertext with the original plaintext ...
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How safe is XOR with multiple independent but non random keys?

I will approach the question from practical side. All the examples are not real, but for illustration purpose only. I have a message, the secret Bitcoin key, which I want to store safely. MESSAGE = ...
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The relationship between the key length and encrypt time in Xor algorithm?

I did work on the encryption algorithm and the decryption using the XOR method noticed that when more the key length, the less time spent on encryption and decryption. I have two questions in ...
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Security of a sha-256 based stream xor cipher?

Provided that I have some data I want to cipher and a password to do it: I generate a random IV I define c = sha256(password) I generate an infinite stream where <...
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Equivalance Operator - Perfect Secrecy

The equivalance operator is the inverse of the XOR operator, it's symmetric. Would this mean that it would also provide theoretical perfect secrecy just like XOR? XOR ...
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Does sending the same message with 2 different keys in OTP leak information?

Suppose a common message ($M$) is XOR'ed with two different keys $K_1,K_2$ producing two ciphertexts $C_1,C_2$. Thus, $$M \oplus K_1 = C_1\\ M \oplus K_2 = C_2$$ On observing $C_1$ and $C_2$, an ...
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What does it mean when two encrypted files, encrypted with the same method but with different keys, when xor'd together, produce a repeating pattern?

Let's say I have fileA and fileB, both encrypted somehow, but in the same method with different keys. If I xor them together, they will make a repeating pattern of 32 bytes length. What does that say ...
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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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Do I need to keep a 64-bit version number secret?

Assume the following structure: version | iv | ciphertext | HMAC(version | iv | ciphertext | ..., key) The version starts out ...
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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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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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How to handle multiple key-agreements

If I would use two different key-agreements e.g. SIDH and ECDH how would I handle these both derived keys? Is there a different between XOR or SHA-256 the two keys? (Would one reduce the level of ...
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Reducing the XOR's in Implementation Cost

Suppose that we want to implement the following equations in binary finite field. $$ \begin{array}{l}\tag{1} y_{{1}}=x_{{1}}\oplus x_{{2}}\oplus x_{{7}}\oplus x_{{8}},\\ y_{{2}}=x_{{1}}\oplus x_{{2}}\...
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Decrypt simple CBC with XOR

I have searched and my problem is exactly the same as shown here: Decrypt simple CBC message with known IV using XOR encryption However, when I implement the solution it doesn't work, neither does ...
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mapping a 256 bit random number to a 3 bit number

I am making a 2 player dice game that runs for n rounds. To create random dice roles im using a concept a understood from randao. each user generates n sha3 hashes recursively of a random seed : e.g. ...
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Counting the $\operatorname{XOR}$ of an Element over the Finite Field $\operatorname{GF}(2^q)$

Definition: The $\operatorname{XOR}$ count of an element $\alpha$ in the finite field $\operatorname{GF}(2^q)$ is the number of $\operatorname{XOR}s$ required to implement the multiplication of $\...
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Practical BCrypt plus XOR encryption for small messages

This is a practical solution available and potentially useful to everyone, so please give some leeway not banning this question. Details are at the end, but here is the question: How secure is the ...