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# Questions tagged [block-cipher]

A block cipher is an encryption algorithm which encrypts fixed-size blocks of plaintext to same-sized blocks of ciphertext. For good ciphers every bit of the ciphertext block depends on every bit of the plaintext block and every bit of the key.

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### Rivest Cipher 6 (RC6) Key Scheduler

I am trying to understand the Key Scheduler used in RC6 and I have a total of 3 questions. The RC6 Wikipedia page says that the only difference between the RC5 and RC6 key scheduler is that more words ...
• 21
1 vote
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### Are there on-line ways to use a block cipher to generate unique $n$ bits that guarantee collision-freeness for $2^n$ times?

$n$ is a run-time variable chosen each time the user runs the implementation. One way I can think is to use any block cipher, say AES, as a seeded CSPRNG to randomly shuffle list of numbers \$0, 1, \...
• 573
1 vote
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### Does keeping the IV secret in OFB mode makes brute-force more complex?

If we keep the IV secret, does that increase the complexity of finding the correct key? My first thought is that it increases complexity, but in real world, I can see that IV's aren't kept secret. We ...
• 117
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### does OFB mode has diffusion on the plaintext?

In some block modes, if we change one bit (or more) in the plaintext, the whole block\ciphertext will be changed (i.e ecb: block will be different. cbc: whole ciphertext will be different) Does ...
• 117
1 vote
148 views

### RC6 Integer operations in modulo 32 between two 32-bit blocks

I am new to cryptography and I am trying to code the RC6 (Rivest cipher 6) algorithm. The algorithm requires addition, subtraction and multiplication in modulo 232. If I am performing these operations ...
• 21
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### Any number-to-number cipher?

I am curious (not technically informed) if the number-to-number cipher is common/useful in cryptography. Imagine, we want to cipher integer y to integer ...
• 101