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.
332
questions
0
votes
0answers
50 views
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 ...
0
votes
0answers
46 views
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 ...
0
votes
0answers
32 views
GPG + OTP--Would that be authenticated encryption?
Here is a GPG message, signed and encrypted (strictly for demonstration, with test keys):
...
0
votes
0answers
36 views
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 = ...
-2
votes
1answer
108 views
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 ...
0
votes
0answers
23 views
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 ...
0
votes
1answer
52 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 ...
3
votes
2answers
2k views
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 ...
-1
votes
2answers
134 views
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 ...
1
vote
0answers
73 views
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 (...
3
votes
2answers
111 views
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 ...
0
votes
2answers
194 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 ...
0
votes
0answers
36 views
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 ...
1
vote
1answer
49 views
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 ...
0
votes
0answers
24 views
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 ...
2
votes
1answer
94 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 ...
0
votes
1answer
109 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 ...
-1
votes
1answer
72 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 ...
0
votes
1answer
59 views
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 ...
1
vote
1answer
100 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 ...
0
votes
1answer
56 views
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 ...
4
votes
1answer
158 views
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 ...
2
votes
1answer
168 views
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), ...
0
votes
1answer
87 views
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 ...
4
votes
1answer
657 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 ...
4
votes
2answers
242 views
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 ...
1
vote
1answer
76 views
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)...
2
votes
0answers
37 views
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....
0
votes
2answers
157 views
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?
-3
votes
1answer
59 views
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?
1
vote
0answers
42 views
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 ...
1
vote
3answers
100 views
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 ...
0
votes
0answers
55 views
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,
...
5
votes
3answers
672 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 ...
1
vote
1answer
64 views
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 ...
0
votes
3answers
171 views
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. ...
1
vote
0answers
50 views
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 ...
2
votes
0answers
37 views
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 ...
0
votes
2answers
108 views
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
...
0
votes
2answers
126 views
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 ...
2
votes
1answer
62 views
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 ...
0
votes
0answers
133 views
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 ...
1
vote
2answers
93 views
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 ...
5
votes
5answers
619 views
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 ...
0
votes
4answers
997 views
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 ...
1
vote
3answers
204 views
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.
...
3
votes
5answers
860 views
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 ...
2
votes
1answer
976 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 ...
1
vote
2answers
231 views
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) ...
0
votes
1answer
97 views
