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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Vernam/OTP repeated pad vulnerability [duplicate]
One thing I know about the Vernam cipher is that the key must not be repeated over the plain-text, for example:
...
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1answer
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How to compare one time pad security and efficiency with AES?
It seems that the minimal size of Pseudorandom permutation (PRP) output is $128$ bits. In general, I'd like to see if there's any minimal size of the output of pseudorandom function (PRF) as well? for ...
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One Time Pad - does it work for long plain texts?
Reading Dirk Rijmenants's work on One Time Pad and he frequently mentions that it is suited to short plaintexts.
I presume this is just because of the practicality of encrypting and decrypting one ...
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One-Time-Pad with multiple keys?
Would it be more secure if we used multiple keys in a One-Time-Pad encryption?
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Attacks on one-time pad, given a property of keys
An adversary $A$, eavesdrops $n$ cipher-texts, $c_{1}, c_{2} ..., c{_n}$. It also knows a value $v$ and a function $f$ such that $$f(k_{1}, k_{2}, ..., k_{n}) = v$$ where, $k_{i}$ is used to encrypt $...
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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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1answer
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One-time pad question (Old ciphers) [closed]
The plaintext SECRETIVE is encrypted using One Time Pad with key DDDDDDDDD. Which of the following is TRUE?
The ciphertext will be the same as using Caesar cipher with key of 4
The ciphertext is the ...
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Little problem with Vernam Cipher
We have got a task with the following content:
Given is a language with 3 letters: A, B, C.
The binary expression is:
A = 000, B = 1111 and C = 0011
Two ...
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Proof one-time pad is perfectly secret with eavesdropping game definition
I have the following definition of perfect secrecy (please assume that the probabilistic version is not available):
If we consider the eavesdropping game given by:
$$\begin{array}{|r | r|} \...
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2answers
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Is it possible to use crib drag on base64 cipher text?
I am pretty new to the cryptography scene but I wanted to know if it is possible to use crib dragging on cipher text which doesn't contain words? This data would be encrypted using the same key with a ...
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5answers
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Is a PRG more costly than AES or any other encryption standard?
I know that there are many encryption standards that take a key and sometimes an IV, and produces a cipher-text (the most prominent one is AES). These standards usually involve many rounds of addition ...
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2answers
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Why does the key for a one-time pad have to be uniformly distributed? [duplicate]
I would like an intuitive argument for what goes wrong in the proof that that a one-time pad provides perfect secrecy, if the key $K$ is not chosen uniformly at random from the entire key space.
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One Time Pad small key multiple times
i'm ask what is the wrong if i used small key multiple times in OTP .?
for example :
key .. . 10 10 10 10 10 10
plain .. 11 01 01 11 01 00
cipher 01 11 11 01 11 10
what can hacker know about ...
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1answer
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What algorithms to use for a secure transport protocol on devices with limited computing power
I am new to cryptography. My questions is this: I process packets on runtime. I do not have time for advanced encryption or decryption techniques that take a long time.
As far as I know, going with ...
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2answers
52 views
Can one trade off the number of iterations for key length with the PBKDF2?
When using the PBKDF2, is one taking on significant risk if one chooses to lower the number of iterations and choose to have very long keys?
Can I XOR my message with a a very long key (plain-text ...
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1answer
52 views
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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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
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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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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
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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
130 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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3answers
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is it possible to get key in One time pad if key is reused?
In one time pad, if $$\text{cipherText1} \oplus \text{cipherText2} = \text{plainText1} \oplus \text{plainText2}$$ then is it possible to find out key by 2 cipherText and plainText's X-or?
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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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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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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
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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
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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
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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. ...
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1answer
218 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
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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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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
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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
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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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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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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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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
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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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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
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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
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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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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
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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
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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 ...
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1answer
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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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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
290 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
357 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
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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
112 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
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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 ...
