Questions tagged [one-time-pad]
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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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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Why does the one-time pad not imply $P \not= NP$?
I apologize that this is a rather trivial question, but I haven't been able to find an answer anywhere. If the one-time pad is unconditionally secure and impossible to crack (with just ciphertext), ...
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Can a message and one time pad each encrypted with separate ciphers be weaker than the stronger of either cipher?
Assume you have:
A truly random one time pad, $P$
A plain text message, $M$
Two symmetric ciphers, $C_S$ and $C_W$, where $C_S$ is always more secure than $C_W$
Assume the keys have already been ...
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1answer
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Key length and message length in AES and perfect secrecy if plaintext length <= key length
As I understand it, a plaintext encrypted using a One Time Pad is uncrackable because all possible plaintexts of the same length are possible. As a concrete example, if you decrypt the first 3 bytes ...
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One-Time Pad: True or False
Suppose a message $M$ was encrypted with a one-time pad. If we learned the first half of the original text is some substring $s$, would we have a better chance of cracking the rest of the message?
Is ...
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How to make this cipher strong?
Suppose I have an arbitrary 256 bit number $m$ another secret number $k$ of the same bit length, and then I multiply them both modulo a 256 bit prime number $p$ to get $c$ as follows:
$$
c = (m\cdot k)...
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Attackability of one-time MAC when using block mode
Consider an encrypted message m which is encrypted with AES-CBC, so in addition to the message there is an IV supplied initially....
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How can I find the original message of two encrypted (Vernam Cipher) text without the key [duplicate]
Can I get the steps or the solution if possible?
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How much long the key should be to create a secure encryption with One Time Pad? [closed]
For example would a key with 15 random letters be enough to protect a 52 letters plain text?
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OTP Random Pad Renewal Without Extending Message
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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3answers
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Why use an OTP if you already have a secure channel
Let's say I have some sensitive information, and I want to encrypt it with a OTP and send it to the FBI or something. Now, in order for the recipient to successfully decrypt the message, he needs to ...
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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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618 views
In laymans terms, what exactly is a “One time pad”?
Background
I am an undergraduate novice learning about cryptography. Recently my professor introduced us to the concept of a "One time pad".
According to my professor:
A one time pad is a cipher ...
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Infinite one time pads using a pseudorandom hash function [duplicate]
Paul Christiano writes (source):
I’ll assume that we have some 256 bit cryptographic hash function F [...] The first important observation is that a 256-bit shared secret allows Alice and Bob to ...
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One Time Pad Key Distribution
For multiple OTP keys, why not do this:
Key = Hash[(EC)DH Shared Secret + Counter]
The counter will increase per message, and the output of the hash will be random for each new unique input into it. ...
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One Time Pad proof for Perfect Secrecy
In the book "Introduction to Cryptography with Coding Theory" by Trappe, in the paragraph about the security of the One Time Pad, is it told that given the set of possible plaintexts $P$, the set of ...
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decrypting a one-time-pad that outputs 0,1 in preknown probabilities
assuming a two users want to use a one time pad ciphersystem, and they are using a program that was developed by a third party that was supposed to create random undependable bits, but for some reason ...
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Two possible plaintext's using OTP decryption
I am using this cipher-text
c = 04 10 12 00 01 08 67 0A 19 65 0F 03 0A 00
with two possible keys
...
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2answers
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What operations provide perfect secrecy other than modulo addition
As far as I know OTP is the only algorithm proven to provide perfect secrecy. It can work with XOR which is addition modulo 2 and obviously it can work with additions modulo N. What other operations ...
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Running Key Gibbs Sampling
I am trying to implement the algorithm described in this paper. It uses blocked Gibbs sampling to perform a ciphertext-only attack on text encrypted with a running key cipher. However, I am confused ...
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Using same key twice with Vigenere cipher
Could someone please give a walkthrough of how this works: Decrypting a vigenere cipher with a reused one-time pad.
It was never fully answered with the example given in the comment.
e.g
Plaintext ...
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2answers
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Is it possible to use an algorithm to generate an OTP?
I am a software developer, not a cryptologist.
I like the idea of perfect secrecy and would like to use a one-time pad (OTP) to encrypt/decrypt files up to, say, 50Mb. Is there a way that I can use ...
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Why use complex encryption algorithms? [duplicate]
I have recently gotten interested in cryptography, so I looked some things up.
I thought, why even use AES or DES or any other complex way for encrypting data when there are far simpler ways, like ...
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Why do one-time pads not provide message authentication?
It is often said that one-time pads do not provide message authentication. But, if you and I have a one-time symmetric key, and I send you a message, and it is not complete gibberish, is that itself ...
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How can I quickly generate thousands of letters randomly, and strongly mitigate the risk of any compromise?
I want to generate English letters in a truly random manner without resorting to hand-thrown dice, despite their advantages. Rolling dice would be too slow and tiring as I need four thousand letters.
...
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Read-once memory
So I've been reading about cryptography and one-time pads, which seem to provide theoretically perfect secrecy. My question is does any form of technology today allow data to be stored in a practical ...
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1answer
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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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Modification of vigenere cipher cryptographically secure?
After looking for ages online for a python implementation of the Vigenere cipher, and finding few, I decided to implement it myself. After ironing out all of the flaws, it's now a working (and secure) ...
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Partial key reuse in hash for one time pad cipher
There are 2 computers who are going to exchange lots of small packets of data between each other. To generate a shared secret, an elliptic key exchange takes place. If this key is hashed with the ...
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1answer
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Can Shannon's proof be applied to all ciphers
I have been studying Shannon's proof of Vernams (1917) unbreakable cipher. Can His proof be applied to positional ciphers?
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1answer
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How does bit-wise operation work for encrypting grayscale images? [closed]
How does bit-wise operation work for encrypting grayscale images?
In my Khan Academy course they encrypt an image with bitwise_and, ...
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2answers
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Robust authentication and integrity for short OTP message
Using any of the wonders of modern cryptographic technology, how is it possible to package a tweet-sized plaintext, which is to be encrypted with a proper one-time pad, to ensure its integrity and ...
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What encryption shoud I use for single char encryption?
I'm very new to encryption and I wanted to know if it is secure or just possible to use encryption on single chars. I did some research, but nothing to clear and i'm a bit confused.
The modes I think ...
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Are one time pads still secure when using randomly generated words as the pad?
I was researching the US military's DIANA one-time-pad system and came across the following quote purportedly from a former US Special Forces soldier:
Special Forces were one of (if not the only) ...
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Decrypting two ciphertexts using the same key
I'm currently trying to solve an online challenge, where I'm given two ciphertexts, encrypted using a one-time pad and the same key for both messages. The task is to decrypt those messages.
What I'm ...
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Perfect secrecy and known ciphertext length
From what I understand perfect secrecy means that the probability distribution of the messages are independent of the cipertext, right? How can the one time-pad be perfectly secret when the ciphertext ...
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2answers
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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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Many time pad if cleartext contains arbitrary bytes
I understand the problem of reusing the same key in the one-time pad if the cleartext message only contains characters such as A-Z, a-z and spaces.
But what if our cleartext is composed of arbitrary ...
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1answer
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Is it easier to crack the Vernam Cipher with more than two ciphertexts
I have just started looking into the cracking of the Vernam cipher with two ciphertexts encrypted with the same key by XORing them and then crib dragging and I was wondering if it is made easier if ...
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When Shamir secret sharing used in one time pad scheme
In the following, all operations are defined over a finite field of prime order. Please note that what I'm explaining below is a part of a bigger protocol, however, to keep things simple I just ...
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double encryption - One Time Pad
Can the security of the encryption system be improved by using double encryption with two randomly chosen keys?
By double encryption I mean using two keys K1 and K2, each 20-bit long, to obtain ...
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Is the One Time Pad secure in additive Rings?
Let's assume all operations are done on $\mathbb{Z}_p$ where $p$ is a large non-prime number.
To mask a value $a$, we do the following:
Pick a uniformly random value: $r$, from the ring.
Do as ...
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2answers
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When does multiple OTP encryption become insecure if new keys are permuted?
I understand that OTP encryption fulfils perfect secrecy, meaning you can't decrypt the encrypted text to it's original plaintext (and know that this plaintext is indeed the original plaintext) unless ...
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1answer
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One-Time Pad Vulnerabilities [duplicate]
Why is it that a one time pad is vulnerable is the key is shorter than the message?
I know that if a key is reused across multiple plaintexts, you can XOR two existing ciphertexts to get the pad, but ...
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1answer
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Simple One time Pad Probability
We have a one time pad where:
We have 8 bits. probability that a bit=0 is p.
The key is common for all 8 bits. It can have a value of 0 or 1 with equal probability.
After applying the XOR operation ...
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2answers
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Is one time pad cipher reuse and random key secure?
The sender and receiver share two different secret keys: s1 and s2 both y bit values. 'x' is a randomly generated y bit value. The reader sends to the tag a challenge y = x ⊕ s1, and the receiver ...
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Is OTP with homomorphic encryption trivial?
If my key size is as large as the data I'm encoding, is it trivial to devise a theoretically secure homomorphic encryption scheme for integers (or else any finite/infinite group with order) that ...
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What are some real world examples where one time pad encryption is used or can be used?
I understood that One-Time Pad (OTP) encryption ensures perfect secrecy. However, I couldn't find any real-world examples where the OTP is used.
Also, which are some real-world examples where it won'...
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What is the difference between a Vigenère cipher and a one time pad cipher?
I'm doing a decryption competition at a nearby college. We are allowed one cheat sheet so I'm trying to make one. I realized that the Vigenère cipher was very similar to the one time pad and wanted ...
