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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How bad are human-generated random numbers really (One Time Pad)?

This is a pretty open question, so I'm mostly looking for gut reactions from experts more educated than I. Given these assumptions which are easy to verify with a quick Google search: One Time Pads ...
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1 answer
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Is combining hybrid encryption with OTP worthy?

I'm considering a case when after hybrid encryption (AES Key encrypted via RSA) RSA key will be "splited" like in OTP. On the end one side gets encrypted AES key and "half" key RSA,...
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5 votes
2 answers
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Is it possible to create a pseudo-One Time Pad by using a key smaller than the plaintext?

Let's suppose I want to encrypt a 10GiB file but I don't want to use a One Time Pad, just a 1MiB key taken from /dev/random (in Linux). I know that the key should not be repeated, but is it possible ...
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Question regarding a subset of p=?np

We consider a language that is $\{0,1\}^n$. We consider three variables $A$, $B$ and $K$ part of that language. A and K are generated through true random generator. We consider not two as is ...
4 votes
3 answers
342 views

Why is AES better than one-time pad?

From my limited research into this topic, it seems that AES can be brute-forced. One-time pad, on the other hand, cannot. Why then is it better to use AES than it is to use one-time pad? The only ...
3 votes
3 answers
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Is there a security risk to use AES-CBC as stream cipher?

I am building a chat application where I want to encrypt each character while they are typing. I would require a stream cipher for that. I am planning to use AES-CBC mode with HMAC. Are there any ...
1 vote
1 answer
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(In)security of multiplicative blinding / one-time-pad in a commutative ring

As I understand, the one-time pad can be generalized to any finite group. So, for example, if you consider $\mathcal{P} := \mathcal{C} := \mathcal{K} := \{0, 1, ..., 2^{n}-1\}$ for an integer n, and ...
1 vote
1 answer
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Security of Reusing a One-Time Pad with Complement Messages with Errors

Let's say I have two binary messages ($m_0$ and $m_1$) of length $n$ which are bitwise complements of each other such that $$m_0 \xleftarrow{r} \{0,1\}^n \text{ and } m_1 = \overline{m_0}$$ If I ...
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1 answer
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Can cryptographically secure randomness be used to implement one time pad?

if I use an one time pad key generated using a cryptographically secure random source like python's secret module , to encrypt a message, will the one time pad scheme be secure? I think the entire ...
0 votes
1 answer
82 views

Is this possible?

So I've been working on a project that aims to allow online distribution of one-time-pads securely. I understand that a pad cannot be reused and must be truly random, and that if it is compromised, ...
2 votes
2 answers
321 views

Security of using AND instead of XOR operation for an OTP

With One-Time-Pads I have heard that it is preferential to use XOR because the ciphertext reveals no information about what the plaintext may have been (for each 0 ...
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1 vote
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Is it necessary to (length) pad a fixed length one time pad in the presence of a HMAC?

Imagine a protocol where all one time pad messages are of a fixed length. And they're textual only, à la Truths/Tweets. So a short message would be padded with spaces (ASCII 32) up to the protocol's ...
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3 votes
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Proof that the Family of Toeplitz Matrices is XOR-Universal

Definition of XOR-Universal hash functions by Abidin[1]: A class $H$ of hash functions from $M$ to $T$ is XOR-Universal$_2$ ($XU_2$) if there exist at most $|H|/|T|$ hash functions $h$ $\in$ $H$ such ...
2 votes
3 answers
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Doing OTP two or more times with a biased TRNG: Will this have the same security as if was done with a non-biased TRNG?

Let's suppose I want to do One-Time-Pad but I only have a biased true random number generator (TRNG). I XOR to the ciphertext block with another with random data got from the TRNG, e repeat the ...
1 vote
1 answer
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What is the Work Factor of the one time pad?

Work Factor is defined as the minimum amount of work (can be the length of the key) to determine the secret key of an cryptosystem (HAC, Menezes, Alfred J. et al). And One time pad have unconditional ...
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Compute OTP key if set of plain texts and its set of cipher texts are known

Given a set of plain texts $P \subseteq \{0, 1\}^n$. Assume we know the corresponding set of cipher texts $C \subseteq \{0, 1\}^n$ produced by applying one-time pad with an unknown key $k \in \{0, 1\}^...
5 votes
1 answer
187 views

Perfectly secret variable one-time pad

Consider a variable one-time pad, that is, $\mathcal{M}:=\{0,1\}^{\leq \ell}$ is the set of plain text. Now, this scheme is not perfectly secret, since you can take two plain text of different size, ...
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1 vote
1 answer
158 views

How could unbreakable encryption be used?

I'm part of a team of students from the Vienna University of Economics, which have the task to find application fields for a new technology. The technology itself is provided by an external partner, ...
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140 views

Is this a scenario where reuse of a One Time Pad is acceptable?

I require an encryption algorithm that requires two parties with two different keys to be able to decrypt it. I could double AES encrypt, but I am instead considering AES encryption followed by a OTP ...
1 vote
1 answer
127 views

Is it possible to decrypt my message if encrypt it twice using different keys each time?

Suppose I want to encrypt $mssg$ using One-Time-Pad, and I want the $mssg$ to be encrypted twice. Once with $k_1$ and second with $k_2$ Is it still possible to detect my $mssg$? lets say: $c_1 = mssg ...
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1 vote
1 answer
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Where should MAC keys come from in a one time pad situation?

I refer to questions For a one-time pad, which MAC method is information-theoretically secure?, Seeking clarification of OTP & MAC discussion and this page illustrating various MACi. And the ...
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Why do we need to use PRGs to generate random numbers for a one-time-pad? [duplicate]

I'm looking at the following idea for using a symmetric key to encrypt multiple messages (back & forth communication between Alice & Bob). It can be summarized as follows: Both sides agree ...
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2 answers
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What's bad about idea of public-key/one-time-pad hybrid cryptosystem?

As i know, generally nowadays hybrid protocols are more widely used than either symmetric or public key cryptosystems separately. I read that public key system is used to exchange and share secret via ...
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Purpose of modulus in one-time pad?

I have the following question and don't really understand it. I thought OTP offers perfect secrecy, why do we need modulus? Can somebody please help me answer the question? $Z_n$ denotes the ring of ...
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One time pad, Proof for a problem

We know 2 plaintexts of length L and 2 ciphertexts of length L(we don't know which one belongs which), assuming each given ciphertext is generated by encrypting one of the given plaintexts by XOR'ing (...
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1 vote
1 answer
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cracking a one time pad using key reuse

There is a one time pad which works as follows: given message "hello" and key "asdfg", it produces "hwoqu". It only works with the 26 english letters. The output is (h(7) ...
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1 answer
132 views

One-time pad without zero: proof check

I started learning cryptography and tried to work through this problem: consider one-time pad where $\mathcal{M}=\mathcal{C}=\{0,1\}^n$ and $\mathcal{K}=\{0,1\}^n\setminus 0^n$ (call this scheme $\Pi$)...
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Derivating random numbers from random numbers

If I have a "truly random number" $K$ of $L$ bits (whatever "truly random" means... is it a value from a normal distribution a truly random number, or only uniform distributions ...
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1 answer
1k views

Is OTP still perfectly secure if we limit message and key space

If we have a message space M {0,1,2,3,4,5,6} and likewise keyspace is K = {0,1,2,3,4,5,6} (generator choosen uniform keys k) We define our encryption to be the XOR of their bitwise rep on K and M ...
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6 votes
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Why is mod calculation necessary in a one time pad encryption?

Considering the English alphabets to be encrypted why is the computation of mod 26 necessary after adding the pad to plain text. Is it just that it adds to another level of encryption or is it used so ...
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1 answer
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What is the correct order of operations for one-time pad cipher when using subtraction and mod 10 arithmetic?

What would be the proper order of operations for OTP encryption/decryption when using subtraction and mod 10? E.g. P - K = C or K - P = C Most of the sources I have seen do not cover this topic or I ...
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What is a ciphertext only attack and how OTP is unbreakable using this attack

I was wondering that what actually is cipherText-only attack and how the One Time Pad Encryption cant be broken by this attack?
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One-time-pad Encryption in C

I have been messing around with cryptography (for recreational use), and I created my own one-time-pad encryption script in C. Now, with that being said, I freely admit that I am by no means a ...
1 vote
1 answer
49 views

Securing counter value for OTP [closed]

I'm working on a project that needs an OTP based on counter value and needs some advice. Suppose we encrypt the counter value C in this way and let's say our sending packet is P = AES(key,C). If ...
2 votes
2 answers
122 views

Combining ECC and AES for a Web Chat system

I am working on a portable secure chat via desktop or mobile, which adopts OTP plus asymmetric encryption. The idea goes like this: Suppose that Alice and Bob are clients, and the server is run by ...
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3 votes
2 answers
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Using $key^{th}$ multiple of $\pi$ as a one-time pad

With a key $k$ of sufficient length, say 128 bits, is it possible to use $k^{th}$ multiple of $\pi$ as a one-time pad? Please enlighten on the security as well as practical aspects (only if secure of ...
2 votes
1 answer
843 views

AES or One-time-pad for encrypting a single 128bit block?

I just started my network security course and came across the below question. Could some one help me here. User A wish to send a 128-bit secret message, S, to user B. As the preliminary step, both A ...
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1 vote
3 answers
397 views

Is collision resistant hash enough for one-block counter mode?

Let $H:\{0,1\}^*\rightarrow \{0,1\}^\ell$ be a collision resistant hash function (CRH), and let $\Pi = (\mathsf{enc,dec})$ be an encryption scheme with the following properties: $\Pi.\mathsf{enc}: \...
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1 answer
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Is it possible to attack a one-time pad encrypting only slightly more than its length?

This question might be uncannily similiar to this one posted over 6 years ago, but the structure is completely different. It's written nearly everywhere that OTPs are incapable of sustaining more than ...
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2 votes
1 answer
159 views

basic question regarding two-time pad attack

Dan Boneh's Crypto 1 Course includes a lesson on stream ciphers with the following slide: He asks the question: And the answer he gives is $m \oplus p$, which is why this is insecure. But I don't ...
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If $\mathrm{P}=\mathrm{NP}$ were efficiently solvable, how would Internet security work? [duplicate]

Suppose $\mathrm{P}=\mathrm{NP}$ were proven and a practical low-degree (2 or 3) polynomial algorithm was found before widespread quantum key distribution was available. How would internet security ...
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One Time Pad Low Bandwidth Doubt from the book

Following is a sentence from the book "Cryptography and Network Security - Principle and Practices" by William Stallings [Fourth Edition] Sentence - " ... the 'one-time pad' is of ...
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How to decrypt two images encrypted using XOR with the same key?

I am trying to solve the following puzzle from CryptoHack involving two images encrypted with the same key: I've hidden two cool images by XOR with the same secret key so you can't see them! lemur....
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One-time pad: Using Cribdrag for Decipherment and Key Recovery

I have been given three different strings: ...
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Can anyone explain to me the difference between the OTP (one-time pad) and Vernam Cipher?

I heard they are very similar, although there are subtle differences between the two.
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Pencil & paper encryption, some thoughts on polyalphabetic techniques [closed]

I have an idea for a simple cipher that builds on old techniques that I thought I would share with this group. It has probably been done but I have not been able to find a reference to it. Given two ...
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4 votes
1 answer
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Does a one-time pad of digits 0-9 have any weaknesses?

I'm working on one of those unsolved puzzles, and one theory I have is that one or more sections of it are using digits of pi, e, or some other irrational number as a one-time pad. (The obvious ...
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1 vote
2 answers
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Stream cipher vs OTP, with /dev/urandom and secure key exchange

My application will work in an office setting where a user can directly and securely collect a long One Time Pad. For example, it may be 16Gb on a USB drive. This would fill me with joy except that ...
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Practical One Time Pad Based on Diminished Rate of Random Number Exhaustion [duplicate]

One reason why One Time Pads are impractical is that sender and receiver need copies of the same random numbers. This can quickly exhaust the set of numbers if communication is frequent. Proposal: The ...
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Is this a provably secure scheme to encrypt a private key?

I got this idea to use the features of the one-time pad, an encryption technique that provably cannot be cracked, but this time applied to encrypt a private key. A possible application could be to ...
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