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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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### 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 ...
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### 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 ...
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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 ...
285 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 ...
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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 ...
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### How can I find two strings $m_1$ and $m_2$, knowing that I know $m_1 \oplus m_2$? [duplicate]

Possible Duplicate: How does one attack a two-time pad (i.e. one time pad with key reuse)? I recently started to follow the cryptography class of Dan Boneh on coursera.org and the first part is ...
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### 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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### What are some real-world examples where one-time-pad encryption is used or can be used?

I understood that one-time-pad (OTP) encryption ensures perfect secrecy. However, I couldn't find any real-world examples where an OTP was used. Also, what are some real-world examples where it won't ...
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### One time pad - how is the difference in length between the plain text & the OTP handled?

Since OTP have to be agreed upon in advance, they may be longer than the plaintext. So in this case, how is the encryption done? Is the OTP truncated to the same length of the plaintext before ...
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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 ...
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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?
If through a previous attack, cipher misuse or two time pad etc. I receive $c=m_1 \oplus m_2$. Where $m_1$ and $m_2$ are compressed messages, for instance GZIPped English text documents. Can we ...