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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### 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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### Modifying the One-Time Pad so that one key can be used two times

I'm currently working on a modified one time pad and I'm trying to use the encryption scheme such that the key will be used twice. I have written a small pseudo code but I'm stuck. Here is my attempt: ...
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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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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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### 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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### 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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### 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 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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### Which is more secure using a CSPRNG for a One-time pad, or AES?

In reading about the One-time pad it appears to need truly random key for the pad. Since true random values are not practical to generate this presents a problem (thus making One-time pad less ...
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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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### Does humanly verifiable one time pad authentication exist?

Firstly some predicates:- Sufficient hardware generated one time pad key material. No pad reuse. Messages of 160 characters length (think Twitter). 28 characters only in use (A-Z, space and full stop ...
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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-naĆÆve 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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### Are one-time pads crackable in theory?

I've been taught that one-time pads are the only perfect encryption since the only way to recover the message is by knowing the key. For example, for a target bitstring of 100 bits, I cannot scan all ...
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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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### 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 ...
108 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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### 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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### 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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### One time pad: why is it useless in practice?

The symmetric cryptosystem one-time pad (OTP) seems to be very beautiful since it is perfectly secret according to Shannon. Many books, however, point out the main drawback: one must create a secret ...
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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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### One-time pad encryption - how does the receiving side decrypt the message?

If a message is sent using one-time pad scheme, which generates random bits in order to, for example, XOR them with the message's bits - how does the receiving side generate the exact series of bits ? ...
238 views

### What is the fastest way to generate a truly random one-time pad without electrical or any other complicated device?

I want to generate a truly random one-time pad as fast as possible, but without the use of any electrical or any other complicated device. What is the fastest way to do that?
152 views

### Using DiffieāHellman without a key derivation function

In an answer to another question, it was suggested that the shared secret derived from DiffieāHellman key exchange could then be used directly as a one-time pad to encrypt a message (by XORing the ...
165 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), ...
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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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### 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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### How can recovered 5-letters plain text help me to recover reused OTP key

I have 10 cipher texts ciphered with One Time Pad (OTP) using the same key. I need to recover the key (or in other words, to recover the 11th cipher text which I assumed would require me to recover ...
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### Decrypting a vigenere cipher with a reused one-time pad

I understand that when a plaintext is encrypted with a key of the same length, it is referred to as a one-time pad. Now when this key is reused to encrypt another plaintext, there is potential for ...
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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 ...