# 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).

248 questions
Filter by
Sorted by
Tagged with
1k views

### AES VS PRNG+HASH+XOR

I was thinking of doing symmetric encryption using just hashing and simple XOR encryption. It would work as: Alice and Bob share a symmetric key Alice manages to send an (authenticated) IV to Bob Bob ...
1k views

### SHA256-based stream cipher

Can anyone comment if the stream cipher described here is safe? The author claims it to be unbreakable, but does not provide any evidence or proof to support this. For completeness, I have reproduced ...
2k views

### Can we replace the XOR operation in DES with some other operation?

Can we replace the XOR operation in the DES algorithm with some other operation? If so, does it work for both encryption and decryption?
675 views

### Does XOR have diffusion properties?

Does the XOR operator provide diffusion if the right side of plain text is XORed against a round key which is then XORed against the left side to produce that side of cipher text, for example in a ...
423 views

### AES in Counter mode for 64 bit input

I was reading how AES can be used for 64 bit data. Than i came to this answer :Is it possible to implement AES with a 64-bit I/O block size? The answer here is given that by running AES in counter ...
321 views

### Decrypting two XORed compressed messages?

If through a previous attack, cipher misuse or two time pad etc. I receive $c=m_1 \oplus m_2$. Where $m_1$ and $m_2$ are compressed messages, for instance GZIPped English text documents. Can we ...
143 views

### (Non-) Perfect Secrecy of Vernam Cipher Using $E(m) = m \oplus k \oplus \operatorname{rev}(k)$

Given the cipher $$E(k, m) = m \oplus k \oplus \operatorname{rev}(k)$$ where $\operatorname{rev}(k)$ is the reversed binary of $k$, how would one prove that the cipher is not perfectly secret. I ...
973 views

For a one-time pad to be truly secure, do I need to use XOR? In other words, is a numerical OTP as secure as a XORed one? I'm new to cryptography, so this might not even make sense.
450 views

### In what sense addition modulo $n$ ($n>2$) isn't linear in the field $\mathbb{F}_2$?

I've been reading the Reason why “XOR” is a linear operation, but ordinary “addition” isn’t? question, in which one of the answers states that addition modulo $n$ ($n>2$) is linear in $\mathbb{Z}_n$...
665 views

### Plaintext XOR'd with keylength-shifted plaintext

While solving a (easy...) Project Euler cipher problem this week I repeatedly saw instructions for breaking ciphers after identifying the keylength as: 'shift the ciphertext by that key length and ...
1k views

### XOR cipher for encrypting compiled C code

I'm exploring ways of encrypting Intel hex files we send to customers for flashing onto an embedded device. The embedded processor itself has a built-in mechanism that prevents anyone from reading the ...
102 views

### 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....
218 views

### Can OTP still be broken if there are several messages being sent with only a slight variation in a password?

If an attacker were able to get a hold of 2 encrypted messages that were both encrypted in a one time pad with a password that were each similar but had one change in the first character, could it ...
237 views

### A set of key pairs and one hash to secure them

I have a simple problem: I have a set of users' ECDSA key pairs, and say I want to encrypt them with a simple algorithm. I have access to one variable that uniquely identifies the user, so I hash it ...
167 views

### 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 ...
187 views

### 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 ...
6k views

### Cryptanalysis of XOR cipher with repeated key phrase

My assignment is to cryptanalyze cipher text that we know was encrypted with a stream cipher (bitwise XOR of plain text and key stream), and decrypt to plain text. We know the key stream is a repeated ...
333 views

### Is this OTP scheme safe?

I have a message $m_1$ and I want to encrypt it by XORing it with two keys $k_1$ and $k_2$: $$c_1 = m_1 \oplus k_1 \oplus k_2$$ So far so good. Now I was wondering if I could create a "fake" result ...
459 views

### 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 ...
81 views

### Can a CSPRNG, seeded with a key, be used to generate a byte sequence as long as the plaintext to XOR it with that?

Given a “safe” (meaning: brute-force is your only shot) cryptographically strong PRNG, wouldn't it be safe to encrypt data using the CSPRNG to create a key as long as the data and then encrypt the ...
166 views

### Block Cipher Mode Amicable to Fast Key Change/Rotation Like XOR?

I'm working with documents encrypted in long term storage. When a client requests the document, the document should be delivered encrypted under a distinct key (distinct from the long term storage key)...
172 views

### Feedback requested on a method of posting a message without revealing the author

So I was thinking about variations on the Dining Cryptographers problem - In some cases, it's useful to be able to post a message without revealing the source, but with the additional constraint of ...
178 views

502 views

### Is it safe to use XOR to encrypt data key using master key

I am implementing a hierarchical key system with a randomly generated master key and many randomly generated data keys that should be encrypted using the master key. I am wondering what the best way ...
734 views

### 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 ...
279 views

### Applying differential cryptanalysis to ciphers with addition mod $2^{32}$

I am studying differential analysis and have a question. Consider the following simple cipher: $$c_1 = S(m_1 \oplus k_1) \oplus k_2$$ (Plaintext $m_1$ xor with key $K_1$, then result goes into an S-...
361 views

### Encryption based solely on XORing with concatenated hash values

I have recently read a bit about Lamport signatures (especially the approach using hash ladders to save disk space) and I found it very interesting that it entirely depends on a hash function. So I ...
391 views

### The existence of partial homomorphic additive encryption with bit-wise XOR operation

According to Protocol A that was presented in Section 3.1 paper entitled "Some Efficient Solutions to Yao’s Millionaire Problem" (2013).  In that protocol they used an assumption that there is ...
102 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 ...
83 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 ...
981 views

### 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 ...
531 views

### 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 ...
1k views

### Any reason to use Shamir given faster XOR threshold secret sharing algos?

TL;DR: Is the Kurihara algorithm really what it purports to be (dramatically faster but equally secure replacement for Shamir Secret Sharing)? https://scholar.google.com/scholar?q=kurihara+secret+...
2k views

### Reversing Rotation + XOR

I have this cypher which is as follows : Take 2 numbers : A=1011 and B=1010 if the ith bit of A is 1 then shift B i times to the left. So in the end you will get ...
137 views

### RFID Protocol Cryptanalysis

Assume we have the following scheme for RFID: TAG & READER both have initially k keys. Every session the TAG computes $k_i$=F($k_{i-1})$ where F is a function which computes XOR of previous key ...
662 views

### Proof of the standard pseudorandom generator + XOR encryption scheme in Goldreich

Reading Goldreich's Foundations of Cryptography II, I found this proof for the security of the common pseudorandom generator + XOR encryption scheme (Proposition 5.2.12 in the book): Assume you ...
1k views

### Prove that the following private-key encryption scheme is not CPA-secure

Consider the following private-key encryption scheme : The shared key is k $\in$ {0,1}n. To encrypt the message m $\in$ {0,1}n, choose random r $\in$ {0,1}n and output $(r, F_r(k)\oplus \overline{m})$,...
77 views

### Combined message separation?

I have two ciphertexts, I suppose that its RC4 with reused key. I have XORed both ciphertexts and obtained message containing combined cleartexts. I suppose that the underlaying messages are written ...
2k views

### Using Whirlpool hashing function to encrypt data

I've read that the Whirlpool hash function can produce footprints that could be used as a pseudorandom generator. Is it "OK" to use it to encrypt some data using something like the following? ...
66 views

### 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?
158 views

### 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 ...
94 views

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 ...