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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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? (http://www.moonbaseotago.com/onerng/theory.html).
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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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Cracking Viginere Ciphers using same-length key used twice
Assuming I had two ciphertexts which were encrypted using the same key that has the same length with the ciphertexts. (However the keys didn't have any repetitions or features that would assist in ...
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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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Short one-time pad security
I am somewhat new to Cryptography and I'm struggling with this proof I came across in my Intro to Cryptography course. I understand the proof of security for a one-time pad:
Pr[M = m | C = c]
= Pr[M = ...
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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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Forge valid token with misuse of OTP key reuse
I'm new to OTP and received a challenge.
Challenge
Context: A server uses OTP to encrypt and decrypt authentication tokens.
Misuse: The server always uses the same key.
Objective: Forge a valid token ...
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1answer
69 views
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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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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2answers
233 views
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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1answer
103 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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117 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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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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1answer
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Is this the right way to implement one time pad?
I would like to know if this the right way to use the one time pad based on this table
Now, my idea is to use the same Ascii #2 to again if the message is longer, I know this is bad practice, what I ...
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1answer
101 views
Why isn't data encrypted with mutiple ciphers?
Why isn't data encrypted with multiple uncompromised (so far) ciphers? Feel free to answer for a single private key for both and separate private keys.
For example, encrypting data with TwoFish and ...
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1answer
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The security of adding random noise many time pad
In may application, I have a series of real number $\{v_1, v_2, \ldots, v_N\}, v_i\in\mathbb{R}$. To protect them, I add a random noise $r\in\mathbb{R}$ to each themselves like one-time-pad encryption ...
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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
842 views
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 [duplicate]
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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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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716 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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1answer
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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 ...
