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.

learn more… | top users | synonyms

33
votes
3answers
31k 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 ...
41
votes
7answers
33k 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 ...
15
votes
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 ...
13
votes
1answer
14k views

Many time pad attack [duplicate]

I've already sent my correct solution to a homework exercise from Dan Boneh's Introduction to Cryptography class on Coursera: "Let us see what goes wrong when a stream cipher key is used more than ...
1
vote
1answer
115 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 ...
11
votes
4answers
4k views

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 ...
2
votes
2answers
309 views

Using hash for one time pad key

Recently I've been delving into security algorithms, I already knew some of the (easy) math behind AES and RSA and how to and not to implement it. But well, i got a bit bored so i thought I'd just do ...
2
votes
2answers
484 views

Proving the semantic security of the One Time pad

Currently hearing a lecture on cryptography, and the professor gave us the definition of semantic security, which is roughly the following (formally not quite complete, but you get the idea): ...
3
votes
1answer
135 views

Hash functions to generate one time pad

Newbie question... may be... Stream cypher, will XOR message bits with one time pad bits Suppose I have a pseudo random number generator, like a Mersenne twister or sort of. I could use the ...
3
votes
3answers
725 views

Implementing a one-time pad without binary?

This is a program that I found which takes a purely alphabetical message, converts the letters to their ASCII values and combines them with the ASCII values of an alphabetical key (wrapping around ...
2
votes
2answers
101 views

Present an attack for the combination of OTP and textbook RSA

Let $N=p \times q$ where $p$ and $q$ are two primes. Compute $\Phi (N) = (p-1)(q-1)$. Choose $e$ s.t. $1 < e < \Phi(N)$ and $gcd(e,\Phi(N))=1$. Compute $d = e^{-1}(mod \ \Phi(N))$. ...
-2
votes
1answer
104 views

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

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question ...
-7
votes
2answers
233 views

OTP - Reusing key IS SECURE! PROVED! [duplicate]

EDIT: This is not a duplicate, in this I have explained WHY this should be secure and not if it is secure, so please stop down-vote if you haven't read everything. I have questioned before about my ...
11
votes
6answers
6k 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 ...
5
votes
1answer
309 views

Can two people with different one time pads securely exchange a message like this?

Alice has a message, generates a one time pad, encrypts her message and sends it to Bob. Bob generates his own one time pad, encrypts the message again, and sends it back to Alice. Alice then decrypts ...
4
votes
1answer
465 views

How secure is my OTP program?

I'm writing an One-Time Pad encryption program, because I got really interested in the idea of " encryption which has been proven to be impossible to crack if used correctly". I'm writing the program ...
3
votes
1answer
1k views

One-time pad and zero key

I'm doing some exercises before my exam, and I am stuck with task number 4 in this file: http://www.cs.umd.edu/~jkatz/crypto/f10/hw1.pdf Could you help me with this task? When using the one-time ...
3
votes
1answer
312 views

What is the name of this kind of protocol

There is a communication protocol that I believe creates the equivalent of a one time pad, with the downside that the secret message must be transferred multiple times. The protocol is so simple that ...
2
votes
1answer
361 views

One time pad: why is it useless in practice?

The symmetric cryptosystem One time pad (OTP) seems to be very beautiful since it is perfectly secret according to Shannon. Many books, however, point out that the main drawback is that one must ...
2
votes
1answer
225 views

Having 4096 bit keys and short (< 256 byte) messages, can I simply use the key as OTP?

Assumptions: Alice and Bob use (cryptographically secure, hardware-rng generated) 4096 bit keys. Each message is encrypted using a new key; meaning: once a key is used, it's destroyed. Alice and Bob ...
2
votes
2answers
465 views

Is OTP useful in modern electronic communication?

I have seen from time to time questions about various OTP schemes and "OTP" (i.e. stream cipher) schemes. The most common OTP troubles appear to be: How to extend size of previously generated key or ...
2
votes
3answers
289 views

One-Time Pad Distribution of Keys Between Two Parties

Consider the One-Time Pad (OTP). Suppose two parties, A and B, generate a completely random secret key in a real-life meeting, and they keep this secret. Now A wants to send some message to B using ...
1
vote
1answer
109 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 ...
1
vote
4answers
617 views

Is the One Time Pad (OTP) considered a cryptographic hash function?

As the title states, would the One Time Pad (OTP) be considered a cryptographic hash function?
5
votes
1answer
542 views

For a one-time pad, which MAC method is information-theoretically secure?

In the the main post about MAC methods it mentions a few methods: Authenticate And Encrypt: The sender computes a MAC of the plaintext, encrypts the plaintext, and then appends the MAC to the ...
3
votes
2answers
492 views

Two-timing a one-time pad [duplicate]

Is a one-time pad still breakable on a depth of 2+ if the plaintext is completely random? I'm assuming this idea is wrong, mostly because it occurred to me, but let me walk you through my logic so ...
3
votes
4answers
661 views

Randomized algorithms and the one time pad

The way I understand it, an algorithm is said to be randomized if it uses randomness as part of its logic (quoting Wikipedia). Now, in the case of encryption algorithms, I assume this means that for ...
2
votes
1answer
148 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 ...
2
votes
2answers
733 views

Avalanche noise RNG for one-time pad use

I came across this little HRNG widget and was really intrigued as I have been looking for a decent but afordable source for truly random bits to use in a one-time pad. The question is, would a HRNG ...
1
vote
1answer
3k views

decryption many time pad [duplicate]

I have eleven ciphertexts that were encrypted with the same key (which I don't know). I want to decrypt the last ciphertext. I read similar question like Many time pad attack but I can't solve my ...
0
votes
2answers
156 views

Reusing a one-time pad?

I have an embedded device. It produces larges files (200 MB). I want the device to encrypt the file before writing to disk, so I gave them all a 16-byte random key. How can I transform the large ...