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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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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7answers
36k views

Taking advantage of one-time pad key reuse?

Suppose Alice wants to send encryptions (under a one-time pad) of $m_1$ and $m_2$ to Bob over a public channel. Alice and Bob have a shared key $k$; however, both messages are the same length as the ...
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2answers
92 views

Extend OTP on random data?

If Alice and Bob both start with a shared OTP $P_0$, which is 256-bytes long, and Alice wants to send a 512-byte message, would it be secure to send the first 256 bytes with standard OTP (...
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2answers
69 views

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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2answers
65 views

Exploiting XOR one-time-pads with dictionary length 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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79 views

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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2answers
55 views

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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2answers
87 views

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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60 views

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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3answers
141 views

OTP - Reuse key BUT add IV, is it secure enough?

I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question was about reusing key in OTP (One-Time-Pad). Now this question is ...
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7answers
6k views

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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1answer
47 views

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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5answers
888 views

Would this simple encrypted chat program be feasible using One Time Pads?

Lets say I want to build a simple chat program that has encryption that is impossible to crack for anyone, even a theoretical government with a massive super computer. Ok here's my idea. You'll need ...
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2answers
115 views

Using One Time Pad with a block cypher

The One Time Pad is often described with a xor cipher. This is nice to show the theoretical strengths of the one time pad but not so great in real world scenarios where key reuse is a danger. So Is ...
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1answer
51 views

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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0answers
20 views

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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1answer
73 views

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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3answers
1k views

How is the One Time Pad (OTP) perfectly secure?

The Wikipedia entry on One Time Pads (OTPs) states that if this cipher is used properly; ie, the keys are truly random and each "part" of the key is independent of every other "part", it's ...
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1answer
37 views

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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6answers
7k views

Simply put, what does “perfect secrecy” mean?

I would like to ask for a clear (but maybe not so deep) explanation of what the term "perfect secrecy" means. As far as I have researched and understood, it has to do with probabilities of assuming ...
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1answer
37 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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1answer
37 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 ...
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0answers
36 views

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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What is the difference between a stream cipher and a one-time-pad?

A (synchronous) stream cipher is an algorithm which maps some fixed-length key to an arbitrary-length key-stream (i.e. a sequence of bits): $C : \{0,1\}^k \to \{0,1\}^{\infty}$. This key-stream is ...
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1answer
168 views

Mathematical formula for switching the key for OTP?

Instead of generating the random key for the one time pad cipher over and over again, is there a mathematical formula that allows you to switch the key to a new key? The new key must be as random and ...
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1answer
123 views

How vulnerable is the one-time-pad (OTP) encryption, if the OTP is used twice, with a random substitution scheme

So I was wondering, I read up about OTP encrption and can see how using an OTP encryption is in itself unbreakable. However, I looked at how OTP is broken if the OTP-key is used on more than one ...
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3answers
2k views

HRNG for One Time Pad

I have just advanced to the last grade of high school (in Denmark). In this year, we all get to do one big project, where we can build/invent/create whatever we want to "solve a problem". As I study ...
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1answer
48 views

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 ...
36
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3answers
33k views

How does one attack a two-time pad (i.e. one time pad with key reuse)?

My question might appear the same as the question Taking advantage of one-time pad key reuse?, but actually I did read all the answers and none of them helped me with the details I need. I am new to ...
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3answers
1k views

Can I use a one time pad key twice with random plaintext?

I understand the basics of OTP: $|\text{key space}| = |\text{plaintext space}|$ implies perfect security, key reuse destroys this. Cryptanalysis on the $N$-Time Pad for $N > 1$ involves finding ...
3
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1answer
382 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
43 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)?
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60 views

Defining Symmetric vs Asymmetric cryptosystems

I'm writing a project on the advantages and disadvantages of symmetric vs asymmetric cryptosystems. At the moment I am trying to define both systems using mathematical notation. Under the heading ...
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2answers
381 views

Re-using parts of a one time pad to encrypt a new one?

The main problem with OTP's is the fact that they can only be used once. Would it be possible to use a random number that's, say, 512 digits, then use 256 of those for the (non-random) message, the ...
2
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1answer
152 views

Do any (non-hardware) RNGs exist which could be used to create an OTP for crypto purposes?

I've stumbled (jobwise) over a system where small messages (512 Bytes or less) are encrypted and decrypted using a simple XOR using a OTP. That OTP is created using a seed based on the individual user ...
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1answer
121 views

Combining a block cipher with a (pseudo) OTP

One of the drawbacks of OTP is that it can require an inconveniently long key. Besides that, it doesn’t provide data authentication. Therefore, I have been working on an algorithm idea, which I hope ...
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1answer
83 views

Unconditionally Secure Authentication

I'm trying to add the authentication for my One-Time Pad implementation. I know that to provide Unconditionally Secure Authentication I need to use the One-Time MAC authentication. But I don't ...
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How do we measure number of possible encryptions in One Time Pad [duplicate]

trying to brute force a specific length of ciphered pad, how do we measure the total number of possible encryptions in One Time Pad
3
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1answer
100 views

A “one time pad” can be thought of a Vigenere cipher with

A "One Time Pad" can be thought of a Vigenere cipher with... An infinitely long key A secure symmetric key Multiple ciphertext alphabets A columnar transposition I had this question come up ...
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1answer
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Why is the XOR of plaintexts equal to the XOR of ciphertexts with a two time pad?

I have been working in the vulnerabilities of the Two Time Pad. So i found in a lot of places, StackExchange included saying, that if two plain texts are encrypted (using XOR) with the same key the ...
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3answers
190 views

One Time Pads and reuse of the decrypted message?

How is it insecure when Alice encrypts a message with a One-Time-Pad to Bob, and Bob then uses the decrypted message from Alice as the next One-Time-Pad? For example: Alice sends Bob a message ...
2
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2answers
273 views

Reusing message in One Time Pad

One of the main rules of the OTP is, that a key should never ever be reused. But if we use some commutative operation (XOR for example) for generating the cipher text, then I don't see any difference ...
2
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3answers
89 views

Find plaintext from two ciphers encrypted with a one-time pad and the same key

I'm studying for a cryptography test and I came across this question: Assume a language has three letters: A=1111, B=0011 and C=1010. Two words in this language are encrypted with a one-time pad ...
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1answer
44 views

Is this distributed OTP scheme secure?

This is for a distributed system: we don't want to have to maintain synchronization of random streams neither enforce uniqueness of pads because this would require some synchronization. Alice and Bob ...
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1answer
60 views

Is it possible to add error propagation to OTP?

What would be the recipe to add error propagation to a one time pad? I.e. if I change a single letter in the clear text message, I want the encrypted message to change starting from that letter and up ...
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2answers
65 views

One time pad- XORing or substitution

I have come across 2 versions of otp while reading it and want to confirm it. they have taken a plain text consisting of alphabets where they are shifted and replaced by alphabets itself. XORing of ...
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4answers
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“Padless” One-time-Pad encryption

I have just read about the perfect security of an OTP encryption and what came to my mind was that what if the Pad used for encryption/decryption did not have to be transported separately from the ...
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4answers
933 views

With a true random number generator at hand, how to implement one-time pad?

I have a Raspberry Pi single-board computer that happened to have an hardware true random number generator, based on some quantum effects on the processor silicon, baked into its BCM2835 chip and I ...