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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1answer
156 views

Is there a name for encrypting a decimal number using a one time pad?

I asked a question somewhere else on stack exchange and had to put something like "using the numerical one time pad the user can create their encrypted message by hand". Is there a better way of ...
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101 views

How to detect if n long messages have encrypted with the same one-time pad?

I have a slight idea on what the attack would be. But my question is: how would one detect if n long messages (n>5) have been encrypted with the same one time pad, K?
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What to do with this specific scenario of a key reuse [duplicate]

I am brand new to the world of cryptogrophy. I am trying to decrypt a many-time-pad. I understand the methodology of using the XOR to get the messages. C1 XOR C2 = M1 XOR M2 Now my question lies in ...
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4answers
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Would using a one-time pad multiple times with some conditions be safe?

I understand why |one-time pad|=|message| using a normal one-time pad, but I don't understand why for perfect secrecy it must alway be that |key|>|all messages exchanged|. What if, for example, I had ...
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6answers
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Does one time pad randomness help brute force attacks?

I understand that attempting to brute force the decryption of a message coded with a one time pad results in generating every possible message. The Wikipedia example is that decoding "EQNVZ" with key ...
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1answer
785 views

Why is pseudorandom OTP (P-OTP) IND-CPA insecure

My lecture notes state that P-OTP is IND-COA but not IND-CPA insecure. I understand IND-COA secure, assuming PRG is secure, as that is the whole point of a OTP, but why is it IND-CPA insecure? Surely, ...
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One time pad encryption

I hope, as we know intercepted ciphertext created by One-time pad encryption tells only length of the message, and that is only information attacker can get since this ciphertext its unbreakable to ...
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108 views

Split encryption into two steps

Are there two step encryption systems that - given the same plain text - support choosing two keys ($k_{A_1}, k_{A_2}$) for a first encryption so, that you can calculate another pair of keys ($k_{B_1},...
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861 views

One-time pad XOR question

For a one-time pad to be truly secure, do I need to use XOR? In other words, is a numerical OTP as secure as a XORed one? I'm new to cryptography, so this might not even make sense.
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Non malleable Encryption scheme

I know that one time pad is malleable. Can you give me an example of an encryption scheme which is non-malleable?
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Seeking clarification of OTP & MAC discussion

I refer to the question for-a-one-time-pad-which-mac-method-is-information-theoretically-secure, and specifically the exchange between lightspeeder & kasperd. I've found the discussion a little ...
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881 views

Vigenère cipher with sha512 and a little foresight turns to one-time pad. How safe can be?

I'm doing some exercises and of course I have read about the weaknesses of Vigenère cipher because it repeats the key. But what if I use a different hash every time? The hash of the "key + an ...
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1answer
153 views

What if an attacker knows 1 bit of a OTP ciphertext

I want to know the answer for the question above, given that we encrypt a message that ends with a "0" and the encryption key is concatenated with a "0" to, in that case that case the cyphertext ...
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1answer
52 views

Data switching on one time pad and Data leakage

Assume all the values and operations defined over $\mathbb{F}_p$. For the sake of simplicity assume all the values are non-zero. Let $(-r)$ denote additive inverse of value $r$. We have one fixed ...
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1answer
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Clarification of Proof: Proving perfect secrecy for One Time Pads

I came across a version of a proof that One Time Pads have perfect secrecy and have a few questions with this version of the proof. The proof is attributed to Dan Boneh (the proof starts on slide 10), ...
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Cryptanalysis of this one-time pad

My question is related to this: Security of one-time-pad without $\bmod $ operation? but the way we mask values is different here. We consider a finite field, $\mathbb{F}_p$, and a ring $\mathbb{Z}_N$...
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Security of one-time-pad without $\bmod $ operation?

Assume $r_1,r_2$ are used only once, and picked uniformly at random (each time we want to mask a value) from finite field $\mathbb{F}_p$, where $p$ is a large prime number. Assume $r_i\neq0$ and $b$ ...
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1answer
355 views

Is a stream cipher similar to One-Time Pad using hash secure?

I've read some Q&A about combining OTP with hash on this site, but I still wonder why some answers said that using hash for OTP key is not strong enough to resist brute force attack? Assuming ...
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Why would Carter-Wegman-style message authentication not be broken by P = NP?

Researching about the implications of P = NP to cryptography I found someone say that the only cryptography left standing would be the one time pad and Carter-Wegman-Style message authentication. ...
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253 views

How can I determine key length for message encrypted by many-time-pad?

For message $ m $ and key $ k $ I get encrypted message $ c $ ($ m \oplus k = c $) where $ length(k) < length(m) $. Additionally I know that message $ m $ is English text. Instead of using pure ...
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2answers
270 views

How can I create pre-determined encrypted results?

I want my encryption results to be the lyrics to Star Spangled Banner. The original text I'm encrypting would be, for instance, the menu to a local pizza place. I know what I want my passphrase to be. ...
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Truly Random Values [duplicate]

I am trying to build a one-time pad encryption software and I am thinking about simply using /dev/random to generate keys. My question is: Is it ...
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What are the correct order of operations for One Time Pad Cipher?

According to Wikipedia the One Time Pad Cipher is unbreakable. On the Wikipedia page it explains how to perform this simple encryption process by hand. For the encryption it adds (+) the message and ...
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Is the one-time pad secure?

I have read about one-time pads (OTP) on Wikipedia. Is this secure? Can I actually use modular addition as ecryption like it said in Wikipedia? And the plaintext is as long as the OTP, so when I send ...
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Randomness of a Key in a One Time Pad

The keys used in an One Time Pad are required to be randomly generated from a keyspace $\mathcal{K}$, we require 256 bit random keys, i.e. $\mathcal{K}=\{0,1\}^{256}.$ Suppose we randomly select an ...
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Does sending the same message with 2 different keys in OTP leak information?

Suppose a common message ($M$) is XOR'ed with two different keys $K_1,K_2$ producing two ciphertexts $C_1,C_2$. Thus, $$M \oplus K_1 = C_1\\ M \oplus K_2 = C_2$$ On observing $C_1$ and $C_2$, an ...
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If I am about to generate one-time pad, where should I generate my pads from?

If I want to generate a few one-time pads, is it OK to just read required number of bytes from /dev/urandom without weakening information-theoretical security?
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CPA on theoretical OTP with CBC mode

Body of question Note: this is THEORETICAL exercise. I understand OTP and CBC does not get along. I have to find a CPA on CBC enc-mode using OTP as the encryption algorithm, s.t a new key is ...
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One-time pad using RSA and Diffie-Hellman functions

Suppose that Alice and Bob use an encryption algorithm based on a one-way function $F$ (Eve knows it), and $r$, a secret key shared between Alice and Bob (Eve doesn't know it). Key is computed as: $K =...
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Breaking One Time Pad with CCA

I was taught that: although OTP is CPA secure, it is not the case with CCA. I'm trying to figure how to break OTP with CCA by showing how it fails the IND test. ...
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Is “reused one time pad” safe to encrypt a message like “random number + mod”?

I want to encrypt a message that contains a fixed length random number and a long mod. i.e. 1234564284 (created like this 123456 + (123456 mod 9931)) I assume that reusing the same key is not a ...
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1answer
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Exploiting XOR one-time-pads with alphabet size that isn't a power of 2

I realized that if the key is chosen randomly from a range that isn't a power of $2$, the one-time-pad leaks information about the plaintext. For example, if the alphabet was the first 20 naturals, ...
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1answer
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Many time pad attack (XOR) [duplicate]

The question is quite similar to Many time pad attack and I was trying to rely on the top answer, but still am a bit confused, so any explanation and help will be much appreciated. Assume I have a ...
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Using a one-time pad with a block cipher

The one-time pad is often described with a simple XOR cipher. This is nice for showing the theoretical strengths of the one-time pad, but not so great in real-world scenarios where key reuse is a ...
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How to XOR two hex values and am I doing crib dragging correctly? (OTP)

Let's say I have the two cipher texts 7ECC555AB95BF6EC605E5F22B772D2B34FF4636340D32FABC29B 73CB4855BE44F6EC60594C2BB47997B60EEE303049CD3CABC29B According to this website http://xor.pw/? the result ...
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Is there any difference between a one-time pad and a Vigenère cipher with a long key? [duplicate]

I've been browsing Wikipedia and stumbled on the article for the Vigenère cipher. I realized after seeing the example that it's quite similar to the one time pad, except with a short key repeated as ...
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What to do when crib dragging does not work in OTP (One-time pad) ciphers?

With a Cipher text of ...
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1answer
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Solving for a One-time pad cipher help ; crib dragging doesnt work (no surprise) [duplicate]

Basically we're given the text 7ECC555AB95BF6EC605E5F22B772D2B34FF4636340D32FABC29B 73CB4855BE44F6EC60594C2BB47997B60EEE303049CD3CABC29B 64C6401BAF45F6A930435F3DF875C4E102F8742A45C824AFCA9B ...
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Why is OTP not vulnerable to brute-force attacks?

I saw this question on the book Understanding Cryptography. At first glance it seems as though an exhaustive key search is possible against an OTP system. Given is a short message, let’s say 5 ...
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Can shuffling plaintext produce a useable key?

If I 'shuffle' the characters in a long text, is there some number of shuffles that will produce apparent randomness approaching a cryptographically secure random number generator? A chapter in a ...
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813 views

Decrypting messages crypted with one time pad (used more than once)

I have a stream cipher with a key (that is unknown to me) that is used more than once. Messages are ciphered in this way: ciphered_message = message XOR key Let'...
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1answer
487 views

One time pad (OTP) perfect secrecy with different key space

Let say $K_{0} = \left \{ 0,1\right \}^n$ $K_{1} = K=\left \{ 0,1\right \}^n$ \ $0^n$ $[b\leftarrow \left \{0,1 \right\}, k \leftarrow K_{b}:b=1|k \neq 0^n]$ --- (1) Key is chosen using ...
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Are there any historic examples of breaking the one-time pad because of a careless key re-use? i.e simple attack on a multiple-time pad?

It doesn't have be using a truly random key, (it could be the Enigma) but the attack must be based on XORing two parts of ciphertext.
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Does a stream cipher provide perfect secrecy?

From WAR10CK here: If I actually do create a machine using RC4 or AES-CTR and have a TRNG continually feed it a constant steady stream of random bits. Provided that the stream of bits is purged ...
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How vulnerable is one-time pad (OTP) encryption, if the OTP is used twice, with a random substitution scheme

After reading up on the one-time pad (OTP) encryption method, I could see how it would offer unbreakable encryption if used properly. Moreover, I looked at how the OTP could be broken if the OTP-key ...
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3answers
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Is multiplicative blinding less secure than additive?

It's easy to see that additive blinding (e.g., $x+r$ for secret x and random r) is perfectly secure in a finite field (this is a one-time-pad) and statistically secure for $r$ uniformly distributed in ...
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1answer
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Can OTP be made practical by using stretched hash algorithms? [duplicate]

One of the main reasons for not using OTP in everydays life is that it is highly impractical - for encrypting 4GB of files we need a 4GB key that needs to be exchanged secure. I've had an idea on how ...
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1answer
426 views

Is XOR adequate for encrypting truly random data? [duplicate]

It is well-known that the two-time pad is very insecure. However, it seems unexploitable in the case where the plaintext is indistinguishable from random (ex. symmetric keys). Is this property ...
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1answer
250 views

XOR or add in one time pads? [duplicate]

Is there any difference in adding the plain text and key vs using xor instead(apart from the performance improvements)?