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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Why is this OTP decryption wrong? [on hold]

i have a problem that goes: ...
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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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Circular hash collision where digest is pre-image: Could hash(a) = b, hash(b)=c, then hash(c)=a?

For any SHA-family of algorithms (including Keccak) except for SHA1, would it be theoretically possible for there to exist a pre-image a whose hash digest ...
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Does XOR'ing a random number with its inverse reduce its security if the result is a palindrome?

[And four related questions/examples below:] 2) If a random 256-bit number is XOR'ed with its reverse (i.e. the big-endian version XOR'ed with the little-endian version), does this reduce the ...
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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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Collision resistance of partial SHA-256 hashes XOR'ed

My hashing algorithm computes the SHA-256 for each of 12 input strings and XORs them to get the final hash. Is there a risk of an attacker being able to forge 2 sets of inputs that yield the same ...
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Can I use XOR to establish a longer shared secret?

SIKEp434 can only be used to encapsulate a 16 byte (128 bit) shared secret key. Most encryption algorithms these days (specifically (X)ChaCha20) require a 256 bit key to be secure, especially in a ...
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What's the number of unique possible Cayley tables in a 16*16 grid for XOR'ing single hex characters?

A few days ago, I designed and s-box then derived the following Cayley table of all possible XOR outputs of hex digits in the range of ${2^4}$ and was curious how many such "valid" possible ...
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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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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 ...
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What are linear and non-linear elements in cryptography?

I was reading this answer, How secure is XOR for encryption, and it stated that XOR's aren't good for securing messages as they are linear in Nature. And therefore should be paired with some non-...
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Hamming distance in xor decryption

I've been working on cryptopals 1.6, breaking xor and have got it working. I found this answer that explains why hamming distance works and I think after some thinking I believe I'm starting to ...
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Help understanding how to decrypt cipher

I am trying to create a padding oracle attack to decrypt a cipher that is encrypted with cbc and PKCS#7 padding. My first step is just to try and decrypt the second block. I have read a lot about it,...
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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 can I calculate the feasibility of brute-forcing missing secret shares against the secret checksum?

Secret sharing has the problem of player cheating, where a forged share $s'_i$ can be sent to generate a fake secret $m'$ during reconstruction (and the cheaters can even collude to generate the real ...
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How to determine if a generalized $\sigma$ function (similar to what is defined in SHA-2) is invertible?

Let $ROTR^n(x)$ and $SHR^n(x)$ denote the rotate right (circular right shift) and the right shift operations, as defined in SHA-2 standard. Consider any function of the form $$f(x) = ROTR^{n_1}(x) \...
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XOR operation to uncover plain-text out of given cipher-texts [duplicate]

I have a set of 11 hex coded strings that have been encrypted using XOR operation each with the same stream cipher key. How do I decrypt the 11th hex-coded string to arrive at the plain-text without ...
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Is there an efficient 2 out of 3 secret sharing scheme based on XOR?

I want to know if there is an efficient secret sharing scheme based on XOR such that a share of the message is given to three people and at least two must combine their share in order to construct the ...
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Storing secrets on a peer-to-peer network by splitting up AONT data

I've come up with a way to transform a stream of bytes such that if any single bit is modified, it cannot be transformed back into its original state. Here's how it works: Encoding Get hash ...
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Salsa20 Implementation: Sum of 2 Words with Carries Suppressed

I'm working on the 2nd part of the Salsa20 spec, and I want to implement a closure for the exclusive-or of two words(u32). The author defines the operation as the sum of two words with carries ...
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Why is this MAC flawed?

Consider a function to create a tamperproof cookie as follows: $$\text{cookie}(m, k) = m \| \text{hash}(m \oplus k)$$ where $m$ is a message provided by Alice, and k is a secret key known only to ...
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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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Multiplication instead of Key Derivation Function?

context In a one message communication. We are right after 2 DHKE (instead of one). Both users then have 2 secret numbers, J and K. question Is it a risk to replace the use of a Key Derivation ...
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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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How to break RSA signature on XOR of hashed blocks

I'm trying to figure out if there's a way of breaking or weakening the following method of signing long messages Given $M=m_{1}m_{2}...m_{n},\,\,|m_i|=64b, \,\,h=h(m_{1})\oplus h(m_{2})\oplus\cdots\...
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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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Is this MAC correct and secure?

Let $m \in \{0, 1\}^{2n} = m_1 || m_2$. Let's also assume that $F_k$ is a PRF and $G$ is a PRG defined as $G: \{0, 1\}^n \rightarrow \{0, 1\}^n$. Now, Let's define the $MAC$ scheme as follows: $$MAC(...
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Decrypting a vigenere cipher with a reused one-time pad

I understand that when a plaintext is encrypted with a key of the same length, it is referred to as a one-time pad. Now when this key is reused to encrypt another plaintext, there is potential for ...
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What are the disadvantages of XOR key derivation?

Assume a 256-bit Key and a 256-bit Salt, with uniformly distributed entropy, both fully independent. Assume ...
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Upgrading key derivation by adding a XOR with a known value

In general keys for password based key derivation are derived from a password hash such as the old PBKDF2 function or Argon2, possibly followed by another derivation function to derive data and ...
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How is n-bit security calculated with nested encryption?

What will the total $n$-bit security be if I encrypt a message with a 128-bit XOR cipher and then take that ciphertext and encrypt it with a 128-bit key. Is the total security level now 256? One ...
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Is this a PRP? How can I create a distinguisher to show it isn't?

Consider the keyed permutation $F_k : \{0,1\}^2 \to \{0,1\}^2$ with two-bit keys defined as $F_k(x) = k\oplus x$. Is this F a PRP? How can I create a distinguisher D and calculate the difference ...
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Is it possible to use crib drag on base64 cipher text?

I am pretty new to the cryptography scene but I wanted to know if it is possible to use crib dragging on cipher text which doesn't contain words? This data would be encrypted using the same key with a ...
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Replacement for XOR in CBC?

In CBC mode, the XOR operation is used to combine the previous encrypted block with the current plaintext, to be used as the block to encrypt. Apart from other known disadvantages inherent to the mode ...
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Does repeated xoring of the (same) key K lower the entropy of K?

If a symmetric encryption key $K$ has been generated by some recommended (NIST for example) RBG then we should have a key with high entropy. But if we xor other bit-strings (e.g. IVs, other keys, etc....
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Common cyphers where the plaintext is the same length as the cyphertext

What are the common cyphers where the cyphertext is always the same length as the plaintext? I can think of XOR cyphers, and letter-substitution cyphers, what others are there?
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How to decode function that returns number of 1s of the XOR of (target, a number you choose, and a biased random value)?

I received this problem and unsure how to figure it out. Apparently it is possible to decode the value correctly 99% of the time. An example: Suppose the target is 20, and there is a function (let's ...
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How can a XOR encryption be cracked systematically?

It's given that a string, encoded in hex format, is obtained by XOR encryption of a plain text and a key. The key is unknown (not even the length). What are the ...
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Can one trade off the number of iterations for key length with the PBKDF2?

When using the PBKDF2, is one taking on significant risk if one chooses to lower the number of iterations and choose to have very long keys? Can I XOR my message with a a very long key (plain-text ...
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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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Is “hash-then-XOR” a good way of incrementally hashing an unordered set? [duplicate]

Is hashing the individual items, and then XOR-ing the results together, a good way of uniquely hashing an arbitrary unordered set of items? I am thinking of using hash-then-XOR since I want some sort ...
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GCM mode of operation with long-term keys

Cross-post: https://cstheory.stackexchange.com/q/41435/873 Regarding GCM, NIST specifies the following: The total number of invocations of the authenticated encryption function shall not exceed $2^...
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Practical perfect security in bitwise XOR vs integer addition/subtraction cipher

XOR already provides perfect security in theory but it's hard to apply it in practice due to strict requirements. I was thinking about whether simple addition/subtraction in integer format would not ...
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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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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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Password protection in ARJ: 3 characters of password are retrievable

On this site there is information that one can know first 3 characters (bytes) of the password without brute force. I know that ARJ in older versions has very simple encryption, i.e. XOR with ...
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How many primitive cryptography operations are there? [closed]

Every cipher I've encountered seems to be built from slight variations of only three basic operations: the S-box, the P-box, and the XOR. I’m just wondering, are there any others? And if there aren'...
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is XOR-hash difference-unpredictable

Let $F$ be a PRF. The $XOR\text{-hash}$ is defined as: ...
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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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A problem in secret sharing and mixed operators over $\mathbb{Z}$

Recently, I studied an article in which it was written that having $(A-B)\oplus C$ and $B\oplus C$, we cannot find $A$. The authors used this result to build a secret sharing scheme, but they did not ...