Cryptography

Questions tagged [one-time-pad]

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A cipher which uses a different encryption key every time, as long as the message. The key is XOR'ed with the message to render the cipher text which can then be XOR'ed with the same key to get the plain text.

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One time pad, Proof for a problem

We know 2 plaintexts of length L and 2 ciphertexts of length L(we don't know which one belongs which), assuming each given ciphertext is generated by encrypting one of the given plaintexts by XOR'ing (...
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crib drag additive one time pad with two ciphers encrypted with the same key

I have the following OTP: alphabet: a to z, where a = 0, b = 0, ... z = 25 the encryption/decryption is done as follows: ci = (mi + ki)%26 ...
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cracking a one time pad using key reuse

There is a one time pad which works as follows: given message "hello" and key "asdfg", it produces "hwoqu". It only works with the 26 english letters. The output is (h(7) ...
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One-time pad without zero: proof check

I started learning cryptography and tried to work through this problem: consider one-time pad where $\mathcal{M}=\mathcal{C}=\{0,1\}^n$ and $\mathcal{K}=\{0,1\}^n\setminus 0^n$ (call this scheme $\Pi$)...
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Derivating random numbers from random numbers

If I have a "truly random number" $K$ of $L$ bits (whatever "truly random" means... is it a value from a normal distribution a truly random number, or only uniform distributions ...
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Decrypting two time pad using the Vigenère scheme

If I define that $$m\oplus k :=(m+k) \mod 26$$ where A is 0 and Z is 25. How do I efficiently/properly decrypt if I was given two-time pad ciphered texts? I know that $m_1\oplus m_2 = c_1\oplus c_2$. ...
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Is OTP still perfectly secure if we limit message and key space

If we have a message space M {0,1,2,3,4,5,6} and likewise keyspace is K = {0,1,2,3,4,5,6} (generator choosen uniform keys k) We define our encryption to be the XOR of their bitwise rep on K and M ...
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Why is mod calculation necessary in a one time pad encryption?

Considering the English alphabets to be encrypted why is the computation of mod 26 necessary after adding the pad to plain text. Is it just that it adds to another level of encryption or is it used so ...
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What is the correct order of operations for one-time pad cipher when using subtraction and mod 10 arithmetic?

What would be the proper order of operations for OTP encryption/decryption when using subtraction and mod 10? E.g. P - K = C or K - P = C Most of the sources I have seen do not cover this topic or I ...
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What is a ciphertext only attack and how OTP is unbreakable using this attack

I was wondering that what actually is cipherText-only attack and how the One Time Pad Encryption cant be broken by this attack?
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One-time-pad Encryption in C

I have been messing around with cryptography (for recreational use), and I created my own one-time-pad encryption script in C. Now, with that being said, I freely admit that I am by no means a ...
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Securing counter value for OTP [closed]

I'm working on a project that needs an OTP based on counter value and needs some advice. Suppose we encrypt the counter value C in this way and let's say our sending packet is P = AES(key,C). If ...
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Combining ECC and AES for a Web Chat system

I am working on a portable secure chat via desktop or mobile, which adopts OTP plus asymmetric encryption. The idea goes like this: Suppose that Alice and Bob are clients, and the server is run by ...
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Multiplication encryption with a small number

Given a big number $x$(1024 bits) and a large prime $N$($N>x$), I want to encrypt it with a smaller number $y$(128 bits). $$Enc(x) = xy \mod{N}.$$ Is it safe? If not, how do I evaluate its leakage?
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Using $key^{th}$ multiple of $\pi$ as a one-time pad

With a key $k$ of sufficient length, say 128 bits, is it possible to use $k^{th}$ multiple of $\pi$ as a one-time pad? Please enlighten on the security as well as practical aspects (only if secure of ...
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AES or One-time-pad for encrypting a single 128bit block?

I just started my network security course and came across the below question. Could some one help me here. User A wish to send a 128-bit secret message, S, to user B. As the preliminary step, both A ...
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Is collision resistant hash enough for one-block counter mode?

Let $H:\{0,1\}^*\rightarrow \{0,1\}^\ell$ be a collision resistant hash function (CRH), and let $\Pi = (\mathsf{enc,dec})$ be an encryption scheme with the following properties: $\Pi.\mathsf{enc}: \...
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Is it possible to attack a one-time pad encrypting only slightly more than its length?

This question might be uncannily similiar to this one posted over 6 years ago, but the structure is completely different. It's written nearly everywhere that OTPs are incapable of sustaining more than ...
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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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If $\mathrm{P}=\mathrm{NP}$ were efficiently solvable, how would Internet security work? [duplicate]

Suppose $\mathrm{P}=\mathrm{NP}$ were proven and a practical low-degree (2 or 3) polynomial algorithm was found before widespread quantum key distribution was available. How would internet security ...
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One Time Pad Low Bandwidth Doubt from the book

Following is a sentence from the book "Cryptography and Network Security - Principle and Practices" by William Stallings [Fourth Edition] Sentence - " ... the 'one-time pad' is of ...
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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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One-time pad: Using Cribdrag for Decipherment and Key Recovery

I have been given three different strings: ...
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Can anyone explain to me the difference between the OTP (one-time pad) and Vernam Cipher?

I heard they are very similar, although there are subtle differences between the two.
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Pencil & paper encryption, some thoughts on polyalphabetic techniques [closed]

I have an idea for a simple cipher that builds on old techniques that I thought I would share with this group. It has probably been done but I have not been able to find a reference to it. Given two ...
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Does a one-time pad of digits 0-9 have any weaknesses?

I'm working on one of those unsolved puzzles, and one theory I have is that one or more sections of it are using digits of pi, e, or some other irrational number as a one-time pad. (The obvious ...
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Stream cipher vs OTP, with /dev/urandom and secure key exchange

My application will work in an office setting where a user can directly and securely collect a long One Time Pad. For example, it may be 16Gb on a USB drive. This would fill me with joy except that ...
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Practical One Time Pad Based on Diminished Rate of Random Number Exhaustion [duplicate]

One reason why One Time Pads are impractical is that sender and receiver need copies of the same random numbers. This can quickly exhaust the set of numbers if communication is frequent. Proposal: The ...
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Is this a provably secure scheme to encrypt a private key?

I got this idea to use the features of the one-time pad, an encryption technique that provably cannot be cracked, but this time applied to encrypt a private key. A possible application could be to ...
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Having two messages and a result ciphertext, is it possible to know which one was encrypted using One Time Pad?

I have two messages $m_1$ and $m_2$ and a result ciphertext $c$, one-time pad was used to create the ciphertext $c$, is it possible to know which message was used to generate the ciphertext $c$?
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Crypto scheme to map data to users in a way that is anonymous to database server

I am trying to finish a paper on censorship resistant data-sharing systems in semi-centralized ways. I know the below threat model can be mitigated by using decentralized system, but I am looking for ...
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How secure is the encryption with OTP and an OneRNG?

I bought an HWRND last week. What do you think, how secure is the encryption with that and the OTP? See the OneRNG theory of operation here.
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How to combine a PRG and a non-PRG to design a PRG?

I'm trying to solve the following exercise: Let $G_1, G_2: \{0,1\}^\lambda \to \{0,1\}^{\lambda + l}$ be two deterministic functions mapping $\lambda$ bits into $\lambda + l$ bits (for $l \ge 1$). You ...
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One time pad - how is the difference in length between the plain text & the OTP handled?

Since OTP have to be agreed upon in advance, they may be longer than the plaintext. So in this case, how is the encryption done? Is the OTP truncated to the same length of the plaintext before ...
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How does the entropy of $r$ influence the security of the one-time pad $F_k(r) \oplus m$?

In an one-time pad scheme, $s \oplus m$ is uniformly random for any $m \in \{ 0,1 \}^\ell$ if $s$ is uniform in $\{ 0,1 \}^\ell$. By the security of PRF, it seems to be secure to replace the truly ...
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GPG + OTP--Would that be authenticated encryption?

Here is a GPG message, signed and encrypted (strictly for demonstration, with test keys): ...
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Does the following protocol of secure a matrix satisfy one-time-pad?

Problem Definition: Alice wants to send a matrix $MR_A$ which encrypts its original private matrix $M_A$ ($M\times N$ size, all elements in $M_A$ is in {0,1,2,3,4,5}) to Bob without letting Bob knows ...
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Authenticated, Quantum-resistant GPG2?

GPG2 does not provide authentication. It still uses SHA-1 by default. It does not seem to get any stronger as time goes by. If one were to pass a randomly-generated symmetric key (from a TRNG) over ...
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Can you use repeating numbers like $\pi$, and $e$, as the Key to OTP ciphers?

Since $\pi$ and other numbers repeat could you use them as a OPT key. Ex: a 5 character message is sent and the first 5 digits of $\pi$ are used. after that the next $X$ number of digits are used and ...
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Security of the OTP

In ciphertext only attack, if I assume that the ciphertext is obtained by an OTP, then for a short length of ciphertext I can search over a random keystream of the same length and discover a plaintext ...
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Will OTP provide quantum resistance under 5 conditions?

We already have quantum computing, but when quantum computing becomes commercially available there is a problem for many but not all encryption algorithm. The One-Time-Pad or OTP is the one and only ...
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Can an observer deduce a pre-shared key used multiple times on (nearly) random messages?

Imagine you took a standard one-way hashing algorithm (like SHA-256), and you implement it in hardware using simple logic gates. Now, replace each logic gate with an equivalent reversible logic gate (...
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Is the one-time pad secure if the key is computed so the ciphertext will consist only of "A"?

I recently learned about the one-time pad method, which has perfect security if the following conditions are met : The key must be truly random. The key must be at least as long as the plaintext. The ...
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How to convert random bytes into blocks of numbers without weakening entropy?

Let's say you have a, or several random byte(s) 0-255 and would like to derive numbers 0-9 for a One Time Pad (OTP) of them. What would be a non-naïve approach to represent 256 possible values onto 10 ...
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Attack on Many Time Pad

I have 7 ciphertexts that have been XORed with the same key. I'm writing a program to figure out what the plaintexts are and possibly maybe recover the key. I have managed to convert the HEX ...
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One-time pad with public key changes

Let $k$ by a randomly generated $n$ bit string, and $m$ a $n$ bit message. Then putting $c = m \oplus k$ is the one-time pad and is perfectly secure. Now assume the transmitter and receiver wanted ...
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Are there any known problems performing a One-time pad with 2 keys stored separately - AKA 2 part Symmetric key exchange over TLS

If this is something that already has a name, please tell me to look at that, but I have not been able to find one yet. I am considering this process for storing some data securely. I want to ...
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144 views

How many perfect secrecy systems are there?

How many non-trivial*, interesting perfect secrecy systems are there other than the one-time-pad? Does it seem that the one-time-pad and perfect secrecy are synonymous, but are there any other ...
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141 views

How to Share One Time Pad? [duplicate]

Supposing I wanted to send a one-time pad to a friend. What would be a good way to do that, supposing that it could be intercepted? At first blush, encrypting it would seem safe, because the ...
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193 views

Which is more secure, AES CTR or OTP with generate key?

My idea of the OTP is to generate from 50 letters (5 words, each 10 letters) a new pad of 2000 random letters, then attach user email to the pad end (to make it unique). The keywords and the pad will ...

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