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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### 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 ...
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 ...
32 views

### GPG + OTP--Would that be authenticated encryption?

Here is a GPG message, signed and encrypted (strictly for demonstration, with test keys): ...
36 views

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 ...
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 ...
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 ...
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 ...
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 (...
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 ...
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 ...
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 ...
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 ...
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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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
56 views

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 ...
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 ...
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), ...
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 ...
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 ...
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 ...
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)...
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....
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?
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?
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 ...
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 ...
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, ...
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 ...
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 ...
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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. ...
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 ...
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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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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. ...
860 views

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 ...
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 ...