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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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Thinking of using One Time Pad? Think again! Never use modular math in your One Time Pad Sheme [closed]

If you want to use One Time Pad encryption, never use "modular mathematics" along with your One Time Pad implementation. If you use "Modular mathematics", then your secret code will be forever linked ...
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1answer
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One Time Pad OTP: with modular math, ciphertext reveals modulus always, yes or no?

Assuming that in the OTP scheme, the key has more values than the alphabet, then: using modular math predetermines that the highest possible value in the ciphertext will reveal the modulus used in ...
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0answers
31 views

One-time pad encryption of ASCII characters

I can't understand a question I came across in a course. You observe three ciphertexts all resulting from encryption of ASCII plaintexts containing English letters and spaces only, using the ...
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4answers
961 views

Can the same One-Time-Pad be re-used with some tricks

Let’s say I have a message $m$ of $n$ bits. And a predetermined pad of $k*n$ bits. And for every bit $b$ of this message $m$, I’m creating random sequence $s$ of $k$ bits. I also have a predetermined ...
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2answers
116 views

OTP One Time Pad : How does modulus size greater than alphabet size eliminate perfect secrecy?

If my plaintext alphabet is {0,1,2}, it has three characters, and I understand why I cannot use a modulus less than 3 (decryption won't work). My key has 100 different values, {0,1,2 .....99} . ...
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2answers
51 views

One Time Pad OTP : Optimal modular base per given plaintext space?

Background: my question at : My pencil and paper One Time Pad works fine without modular math ...... or does it? I am trying to understand, from a layman's point of view, how to make the best one ...
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2answers
120 views

My pencil and paper One Time Pad works fine without modular math … or does it?

With no background in higher math or computer science, I could not quite grasp the value of modular math for simple OTP systems as described in other posts here. I have an alphabet size of 40 ...
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2answers
87 views

is it possible to get key in One time pad

In one time pad cipherText1 xor cipherText2 == plainText1 xor plainText2 so is it possible to find out key by 2 cipherText and plainText's xor?
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3answers
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Can multiplication of two primes be seen as a strong cipher?

If we were define such a cipher: A reversible function that would accept a message $M$ and an initialization vector $\text{IV}_1$ $\operatorname{map}(\text{IV}_1, M)$ which can map an input $M$ to a ...
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0answers
67 views

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

I want to generate 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?
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1answer
57 views

breaking one-time pad with key reuse

Suppose I have the message $m_1 = \sf{i\ like\ dogs}$. Suppose its one-time pad encryption with key $k$ is a given hexadecimal string of 22 characters. How would I encrypt a message $m_2 = \sf{i\ ...
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5answers
75 views

Multiple Encryption - One-Time Pad

It is known that One-Time Pad(OTP)s are theoretically unbreakable but impractical for use because of the size of the key length. But what if multiple encryption is used? Not to encrypt the first ...
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3answers
134 views

Why wouldn't everyone encrypt with a One Time Pad? [duplicate]

A One Time Pad (OTP) sounds perfectly secure if we are to believe Wikipedia. But on the surface it also sounds ridiculously impractical - how does one securely distribute the OTP? Idea: why not have ...
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1answer
43 views

How to be sure to retrieve the good key when brute-forcing a cipher?

Imagine the case of the one-time pad. It is proved to be secure because the key could be everything. We have no guarantee that this key or that key was the one used while encrypting our data. ...
3
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1answer
109 views

Proving one time pad is perfectly secret

I'm reading about one-time pad in "Introduction to Modern Cryptography" by Katz and Lindell. I can understand the definition of perfect secrecy. However, how is OTP proven to be perfectly secure ? I'm ...
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2answers
67 views

Is There any Risk to Using Meaningful Text as One Time Pad Key?

Let's say two people have the same edition of the same magazine. The knowledge that the magazine will be used as a one time pad is secret. Is there any risk to using this as opposed to randomly ...
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0answers
13 views

Perfect secrecy of OTP [duplicate]

When using the one-time pad with the key k = 0l, we have Enck(m) = k ⊕ m = m and the message is sent in the clear! It has therefore been suggested to modify the one-time pad by only encrypting with k ...
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1answer
143 views

Is the one-time pad still perfectly secret if all-zero keys are excluded?

I'm trying to solve this question related to one-time pads and perfect secrecy: My solution is: I assumed that the current message space is $M = \left\{ 0,1 \right\}^l$ and the new keyspace after ...
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1answer
41 views

Question on probability distribution

I computed $\Pr[\mathsf{CT} = 1] = \Pr[\mathsf{CT} = 2] = \Pr[\mathsf{CT} = 4] = 2/9$ and $\Pr[\mathsf{CT} = 3] = 1/3$. When I calculate the first entry in the table, I get 1/2 not 1/9. Is my ...
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0answers
67 views

One-time-pad with message and key stream: encrypting two messages

Consider the one time pad with messages and keystreams in binary strings. Suppose that the system is used erroneously, so that two messages have been encrypted using the same key. What information can ...
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3answers
143 views

Strictly, is length(key) >= length(message) wrong for one time pads?

It's a common adage that for a perfectly secret one time pad, length(key) >= length(message) must hold. But that's wrong isn't it? At least very sloppy maths. Isn't the strict mathematical ...
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0answers
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How is a Vernam cipher's security compromised when key is used multiple times? [duplicate]

I'm learning about basic cryptography at university, and I'm reading that reusing a key in a stream cipher such as the Vernam cipher compromises its security. Because XOR is a reversible operation, ...
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2answers
252 views

How were one-time pads and keys historically generated?

In the 20th century, it was common for various intelligence agencies and military organizations to use ciphering machines and one-time pads. However, no source I've seen ever mentions the process of ...
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3answers
423 views

Is the Vernam (One Time Pad) cipher useful?

By profession I’m a programmer. I don’t know a lot about how cryptographic algorithms are implemented, or even where I’d start, and I don’t know about cryptanalysis, but as I work in Blockchain ...
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3answers
744 views

Non-malleability of One Time Pad Encryption

Can anyone explain to me what the following means in relation to one time pad security? It's from the book 'Serious Cryptography: A Practical Introduction' and my logic knowledge seems to have lost ...
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1answer
148 views

Can I use a key twice if the message is longer than the key in one-time pad?

I have a key for a one-time pad. Its length is 512, and I have a message to encrypt whose length is 600. Can I reuse the first 88 chars of the key to encrypt the end of the message? The key is still ...
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2answers
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Can one claim that AES has perfect secrecy for a key size and message size of 128 bits?

While looking at this question I discovered the following here (question 5), and wanted to ask it as a separate question. Alice knows that she will want to send a single 128-bit message to Bob ...
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1answer
181 views

Analyzing/Breaking a strange One-Time-Pad

In my assignment there is a bonus question: It asks me to decrypt a file which has been encrypted using an One-Time-Pad. But the ciphertext seems to contain english word fragments and other parts ...
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0answers
74 views

OTP PRNG re-use

I'm setting up some external hardware for OTP encryption to take care of all the issues that can arise with key storage, re-use etc. I'm using the ISAAC secure PRNG to get my stream of numbers which ...
3
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1answer
73 views

One Time Pad change by third party?

I was reading about how a one time pad output can be changed by a third party without the receiving person realising. Surely the output at the other end would be garbage? Also, could you not ...
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2answers
160 views

Can OTP be used with RSA

Considering that a PKI has already been established, why can't we use RSA to send the One Time Pad instead of using AES? It makes sense to me since: A trusts the CA which is providing the identity ...
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1answer
242 views

Given a list of ciphertexts, how to identify the ones that used the same key for encryption

I'll start off by saying I am not looking for solutions here, just suggestions on how to proceed. I am given a short list of ciphertexts (20something) and I know that one of the ciphertexts has been ...
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2answers
239 views

Can I generate OTP secrets by using a hash?

Since I learned about one time pads in last security lecture, I'm quite fascinated how easy the concept is, but how it still is absolutely safe. Learning from implementing a multi time pad attack, ...
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3answers
275 views

Why in one time pad must the key distribution to be truly random

One time pad required a truly random key. Why canwt it be a psudo-random key? For example, if the key distribution is that for each bit the probability to get 1 is 0.6 and the probability to get 0 is ...
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1answer
101 views

is the perfect secrecy of one time pad dependent on the xor randomness preserving property?

Is the perfect secrecy of the one time pad dependent upon the xor "randomness preserving" property (xoring a uniformly random string with any string yields a uniformly random string)? I have seen ...
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4answers
178 views

Including the next random One Time Pad as part of the encoded message?

I've tried to do something very simple here, which is to encrypt a message with a one-time-pad (OTP) and include the next OTP as part of that same encrypted message. i.e. The first message consists of ...
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3answers
156 views

Transferring Encrypted One-time pad over the internet

I was working with one-time pad, and as I understand , for one time pad to be 100% secure a key shouldn't be repeated. So assuming Alice and Bob have to exchange messages over the network secured over ...
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2answers
238 views

Decrypting two XORed compressed messages?

If through a previous attack, cipher misuse or two time pad etc. I receive $c=m_1 \oplus m_2$. Where $m_1$ and $m_2$ are compressed messages, for instance GZIPped English text documents. Can we ...
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1answer
69 views

Stuck on finding M2 knowing M1 in One Time Pad

Lets say I have a plaintext M1 and a plaintext M2, I know both the ciphers C1 and C2 from these M1 and M2. But from M1 I also know a piece of M1 or maybe even the whole text. And I also know C1 XOR C2 ...
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1answer
224 views

Is a one-time pad secure if the encryption method is not?

(The following situation is hypothetical.) I need to communicate something securely and I have decided to use one-time pads. I am going to be using human genes as the source of the OTP data (this is ...
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3answers
145 views

Generating OTP using Digital Dead Drop

I've had a thought and I'm wondering if this would be a useful way to devise and distribute a one-time pad. It relies on a digital dead drop and a hash function. The digital dead drop could take a ...
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1answer
195 views

One way communication with forward secrecy?

Is it possible to achieve forward secrecy using a one way communication channel with pre-shared secret? I have a setup where I need to send some information across a unsafe channel between server A ...
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3answers
144 views

What are the vulnerabilities of this OTP-like system?

I've read that a OTP is only perfectly secure if the key is perfectly random, and the pad is never reused. If you encrypt documents using two keys, where one is random but stays constant for some ...
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1answer
179 views

Is creating an OTP of a key to some data a secure secret sharing scheme?

Suppose I have some data that has been encrypted with a known, secure algorithm and a key k. I want to distribute "pieces" of the key to n of my colleagues, and only be able to access the data when ...
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1answer
97 views

Multi-Embedded Xor for Perfect OTP

I am looking for a perfect OTP design, so let's see if this design is good. There are 2 issues when it comes to a good OTP system, the key and the plaintext, we will use XOR as cypher: If the ...
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2answers
180 views

Viability of using One-Time-Pad + HMAC in low-volume IoT communications

In the Internet-of-Things world there are certain applications that produce very low volume communications. For example reading a water meter once every hour comes to mind. If the reading could be ...
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1answer
136 views

How to attack a two time pad if the plain text is randomized?

As an extension to this quesiton, or this one how would you go about attacking a re used pad if the plaintext was randomized before being encrypted? ...
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3answers
475 views

Is Poly1305 an information-theoretically secure MAC?

I have heard some people say that the Poly1305 authenticator is a "nuclear" MAC i.e. it is information-theoretically secure. After reading the paper I see it is based on the Wegman-Carter MAC which is ...
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1answer
56 views

Perfect Deniability of a MAC Protocol

I proposed an idea of Perfect Deniability of a MAC I tried to come up with a protocol that satisfies those security requirements as well as the normal security requirements of a MAC One-Time MAC ...
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2answers
155 views

Perfect Deniability of a MAC

Overview One feature that is often underlooked of the One-Time Pad is its perfect deniability. i.e. If Alice sends a message to Bob that is seen by Eve then if Eve later goes to Alice with the ...