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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### 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 ...
74 views

### 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 (...
52 views

### 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) ...
73 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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### Decrypting two time pad using the Vigenère scheme

If I define that $$m\oplus k :=(m+k) \mod 26$$ where A is 0 and Z is 25. How do I efficiently/properly decrypt if I was given two-time pad ciphered texts? I know that $m_1\oplus m_2 = c_1\oplus c_2$. ...
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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### 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 ...
129 views

### 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 ...
65 views

### 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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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 ...
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### 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 ...
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### 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 ...
71 views

### Multiplication encryption with a small number

Given a big number $x$(1024 bits) and a large prime $N$($N>x$), I want to encrypt it with a smaller number $y$(128 bits). $$Enc(x) = xy \mod{N}.$$ Is it safe? If not, how do I evaluate its leakage?
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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 ...
208 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 ...
336 views

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### Are there any known problems performing a One-time pad with 2 keys stored separately - AKA 2 part Symmetric key exchange over TLS

If this is something that already has a name, please tell me to look at that, but I have not been able to find one yet. I am considering this process for storing some data securely. I want to ...
151 views

### How many perfect secrecy systems are there?

How many non-trivial*, interesting perfect secrecy systems are there other than the one-time-pad? Does it seem that the one-time-pad and perfect secrecy are synonymous, but are there any other ...