# All Questions

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### Measuring entropy for a ciphertext only attack

When bruteforcing a password (e.g. the common attacks on DES), where you have ciphertext only, you need a way to assess whether a decrypted plaintext is the right one. I believe the EFF DES machine ...
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### AES CBC mode or AES CTR mode recommended?

what's benefits and disadvantages of CBC vs CTR ? which one is more secure ?
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### Two mutually untrusted parties want to exchange data: how to ensure each one gets the data it needs?

I am trying to come up with what could maybe be a novel algorithm for an application I am writing. Client A has a file fA. Client B has file fB. Each party is untrustworthy and will try to rip off the ...
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### What are the requirements of a nonce?

Sometimes I read that a nonce has to be a random number but I disagree. A nonce just can't repeat itself. You could increase in by 1 every time if you are sure it would never repeat.
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I was looking at the algorithm for Twofish, and I noticed that in some places a XOR is used, but in others, they use "addition modulo-32." What makes modulo-32 special? Why not always use XOR? Why not ...
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### How does the key schedule of Rijndael looks for keysizes other than 128 bit?

It said in Wikipedia that: [....] Rijndael can be specified with block and key sizes in any multiple of 32 bits, with a minimum of 128 bits. The blocksize has a maximum of 256 bits, but the ...
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### What is the difference between CSPRNG and PRNG?

What is the difference between CSPRNG and PRNG? Is there performance differential between them? For example: We use PRNG for key generation which is very expensive and CSPRNG for IV/nonce in block ...
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### Low Public Exponent Attack for RSA

I'm having trouble understanding the algorithm for finding the original message $m$, when there is a small public exponent. Here is the example I'm trying to follow (you can also read it in the 'Low ...
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### Is a known plaintext, ciphertext, and public-key a viable attack on RSA?

Assume Alice and Bob are using RSA to create a common session key and Cindy is listening, attempting to obtain the session key. Alice and Bob each have their public- and private-key pairs ...
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### Besides key and ciphertext sizes what are other advantages of elliptic curve versions of various protocols?

There are elliptic curve variants of Diffie-Hellman, ElGamal, DSA and possibly other protocols/algorithms. I know that these elliptic curve variants have smaller key and ciphertext sizes which will ...
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### Does AES-CTR require an IV for any purpose other than distinguishing identical inputs?

I'd like to encrypt files deterministically, such that any users encrypting the same plaintext will use the same key and end up with the same ciphertext. The ciphertext should be private as long as ...
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### Is there a format preserving cryptographically secure hash?

I want a way to 'scramble' strings (like words, names) in a predictable way but I don't ever want to (myself or anyone else) be able to 'unscramble' the strings. I found that perhaps what I am ...