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.

Filter by
Sorted by
Tagged with
85
votes
7answers
77k 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 ...
83
votes
11answers
9k views

Is modern encryption needlessly complicated?

RSA, DES, AES, etc., all use (relatively) complicated mathematics to encrypt some message with some key. For each of these methods, there have been several documented vulnerabilities found over the ...
68
votes
3answers
62k 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 ...
29
votes
8answers
27k 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 ...
26
votes
7answers
12k 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 ...
23
votes
3answers
6k 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 uncrackable, ...
20
votes
7answers
11k 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 ...
18
votes
12answers
13k views

Are one-time pads crackable in theory?

I've been taught that one-time pads are the only perfect encryption, since the only way to recover the message is by knowing the key. For example, for a target bitstring of 100 bits, I cannot scan ...
18
votes
3answers
3k 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 ...
18
votes
1answer
27k views

How to attack a “many-time pad” based on what happens when an ASCII space is XORed with a letter?

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 ...
17
votes
9answers
5k views

Is one-time pad encryption vulnerable when near identical data is sent many times with different OTP?

Let's assume a text file that grows at its very end but is otherwise not edited. We now have 100 transmissions of this, but OTP-encrypted (different OTP each time, of course). The first 50% of the ...
16
votes
5answers
3k views

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 ...
13
votes
2answers
452 views

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 ...
12
votes
4answers
3k views

Is the one-time-pad a secure system according to modern definitions?

Occasionally I hear people say that one-time pads are "useless" or even "broken". "modern cryptography knows more security definitions, under some of which the one-time pad is completely broken." ...
12
votes
2answers
2k views

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 ...
11
votes
2answers
2k views

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. ...
11
votes
3answers
4k 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 the main drawback: one must create a secret ...
10
votes
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 ...
10
votes
3answers
918 views

Is Poly1305 an information-theoretically secure MAC?

I have heard some people say that the Poly1305 authenticator is a "nuclear" MAC i.e. it is information-theoretically secure. After reading the paper I see it is based on the Wegman-Carter MAC which is ...
10
votes
1answer
1k 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 ...
8
votes
11answers
3k views

Algorithm: How to use x and y mouse movement co-ordinates to generate random data?

Background: I'm making a program for fun as a learning exercise. I want to generate some actual random key material (not pseudorandom) from a JavaScript program. For my program is just for encrypting/...
8
votes
6answers
1k views

Are picture files “random enough” to be usable as a one-time pad?

Say you have a picture with 1 megapixels taken at random and with $2^{24}$ possible colours per pixel (RGB-24). That image would be unique and the possible combinations $(2^{24})^{10^6}$ immense. ...
8
votes
4answers
1k views

Is there a way to generate sound one-time pads out of public information?

Is there a way to 'mangle' a public data-source (for example, the current date in YYYYMMDD or the top New York Times headline) to form a one-time pad that will sufficiently hide the pad's source? ...
8
votes
5answers
3k views

Is One Time Pad considered Chosen-Plaintext Attack Secure?

If we're considering Chosen-Plaintext Attack setting, then the adversary has access to the Encryption Oracle right, and we know that OTP is only considered secure if we use the key only once. How ...
8
votes
2answers
6k 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): Given ...
7
votes
4answers
2k views

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?
7
votes
6answers
689 views

Does humanly verifiable one time pad authentication exist?

Firstly some predicates:- Sufficient hardware generated one time pad key material. No pad reuse. Messages of 160 characters length (think Twitter). 28 characters only in use (A-Z, space and full stop ...
6
votes
4answers
3k views

One Time Pads and “Bit Flip” Attacks

One Time Pads and Vulnerability to "Bit-Flip" Attacks: I've seen it in this group, and apparently there are a (small) number of voices on the 'net opining that those relying on OTP are essentially "...
6
votes
1answer
5k 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 ...
6
votes
1answer
725 views

What do you call one time pad where pseudo-random numbers are used?

What is the encryption method called when pseudo-random numbers are used instead of true random numbers?
6
votes
2answers
691 views

Can we use numbers as a pad in the Vernam cipher - why or why not?

I was playing with the Vernam cipher on some online converter. But when I tried to encrypt my message string with numbers, it remained unchanged. Moreover, it was ignoring numbers and was encrypting ...
6
votes
2answers
611 views

Is there a companion algorithm for OTP to ensure integrity and/or authentication?

One-Time Padding is (theoretically) perfect encryption algorithm. Let's assume that these problems are solved: Fast generation of independent and identically distributed random variables Perfect key ...
6
votes
1answer
1k views

Hash functions to generate a one-time pad

Maybe this is a newbie question: Stream cypher, will XOR message bits with one-time pad bits. Suppose I have a pseudorandom number generator, like a Mersenne Twister or something similar. I could use ...
5
votes
4answers
1k 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 ...
5
votes
1answer
500 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 ...
5
votes
1answer
147 views

Can I securely refill a one time pad over the same connection?

If you have a channel where you are communicating using a one time key, is it possible to receive additional key over that same connection without compromising security? Naively sending it through ...
5
votes
3answers
2k views

If a cipher has key length shorter than plaintext, then it is not perfectly secure

I am trying to verify the statement above. So far I only know that a One-Time-Pad is the only “perfectly secure” cipher. It has a key length which is exactly the same as the plaintext. I think the ...
5
votes
3answers
551 views

One Time Pad Alphabet Size

I am building a simple one time pad system using a low-power microcontroller to XOR a stored key with an input string, and vice versa. Due to several internal factors, it's very preferable for the ...
5
votes
2answers
375 views

Is there a practical security difference between OTP with letters and OTP with numbers?

Is there a practical security difference between “OTP with letters” and “OTP with numbers”? If, for example, I encrypt a letter message using Tabula Recta with a random letter key, I would get: <...
5
votes
2answers
556 views

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 ...
5
votes
1answer
1k 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 ...
5
votes
2answers
229 views

Perfect Deniability of a MAC

Overview One feature that is often underlooked of the One-Time Pad is its perfect deniability. i.e. If Alice sends a message to Bob that is seen by Eve then if Eve later goes to Alice with the ...
5
votes
1answer
434 views

Hash function as secure as one-time pad?

We know that the one-time pad is provably secure as a cipher to encrypt some data. Is there an algorithm which does the same just as a hash function? Can we get a provably secure hash function? Maybe ...
4
votes
6answers
611 views

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 ...
4
votes
5answers
1k 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 ...
4
votes
2answers
443 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 ...
4
votes
2answers
1k views

Quantum key distribution and the one-time pad

Why is QKD usually associated with OTP ? QKD is about key distribution, where as OTP is about using key as long as message to get perfect secrecy, can any one explain how they are related ?
4
votes
4answers
1k 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 ...
4
votes
2answers
179 views

When does multiple OTP encryption become insecure if new keys are permuted? ​

I understand that OTP encryption fulfils perfect secrecy, meaning you can't decrypt the encrypted text to it's original plaintext (and know that this plaintext is indeed the original plaintext) unless ...
4
votes
4answers
307 views

Transferring Encrypted One-time pad over the internet

I was working with one-time pad, and as I understand , for one time pad to be 100% secure a key shouldn't be repeated. So assuming Alice and Bob have to exchange messages over the network secured over ...