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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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### 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 ...
29k 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 ...
17k views

### Why must IV/key-pairs not be reused in CTR mode?

Many sources mention that IVs must not be reused with the same key in CTR mode, for encrypting 2 different pieces of data, because that totally destroys security - but I haven't found an explanation ...
3k views

### Which encryption method supports random reads?

I have a file containing 16-bit samples and I want to encrypt it, but the problem is that I need to be able to read any random 16-bit value from the file, and be to able to decrypt it, without reading ...
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### random access stream cipher

Some time ago I was working in a pet project for a type of database engine. And I thought about securing the data in disk with encryption.. and since the main code was already developed.. I had a few ...
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### Can the same One-Time-Pad be re-used with some tricks

Let’s say I have a message $m$ of $n$ bits. And a predetermined pad of $k*n$ bits. And for every bit $b$ of this message $m$, I’m creating random sequence $s$ of $k$ bits. I also have a predetermined ...
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### Security of very simple XOR with random? [duplicate]

I am currently trying to implement a very fast and simple encryption algorithm in Lua for the purpose of using it with ComputerCraft. The main problem is that bitwise operations in Lua (5.2 at least) ...
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### What is the role of IV in Stream Cipher? Why is it needed and what is it's importance?

I ran into this problem when I read the stream ciphers and did not find a satisfactory answer. Why is an IV needed in stream ciphers, and what is the importance of using it?
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### Vigenère cipher: Security when key length and plaintext length are the same

I have read the Vigenère cipher is secure as long as the key length is the same as the length of the data to be ciphered. Is this true when the same key is used multiple times? In such cases, after ...
281 views

### Is the following symmetric design secure?

Assume: $O$ be a reversible random permutation oracle on a finite set and $O^{-1}$ the inverse permutation (pretty much equivalent to a random permutation: What is the difference between a bijective ...
2k views

### is it possible to get key in One time pad if key is reused?

In one time pad, if $$\text{cipherText1} \oplus \text{cipherText2} = \text{plainText1} \oplus \text{plainText2}$$ then is it possible to find out key by 2 cipherText and plainText's X-or?
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### What is the significance of IV in stream ciphers like Trivium?

In Trivium cipher, an 80-bit key and 80-bit IV (initialization vector) are used initially to set up the initial state. I would like to know, Role of IV in stream cipher? Can we make IV a secret ...
970 views

### What if message is longer than keystream ?

I have read that stream ciphers can be used to encrypt messages/streams of arbitrary length (cf. the description of the stream cipher tag). However, there are stream ciphers that create a keystream of ...
878 views

### AES 128 bits with 12 bytes IV vector composed of a 4 bytes counter : safe?

I have a 128 bits AES cypher (GCM, Galois/Counter Mode) using a 12-byte initialization vector (IV) composed of: 8 constant bytes: 6 bytes (device ID) 2 bytes (zero) 4 bytes (incrementing frame ...

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