Cryptography Stack Exchange
Cryptography Stack Exchange

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.

In practice, block ciphers are usually used with a mode of operation, effectively creating stream ciphers from them.

Known block ciphers are , , ,.

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Which block cipher parameters should be kept secret?

Which of the parameters of a block cipher (e.g., algorithm name, mode of operation, IV (if any), key length) are essential to keep secret?
Emily
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Where would a "half round" come from?

In the hierocrypt-L3 description, the cipher takes 6, 7, or 8 rounds. Example source code also seems to follow this same specification of 8 rounds for 256-bit keys. Wikipedia shows 8.5 rounds for 256-bits. I found it some other literature as…
b degnan
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Block cipher with key longer than block size

When a block cipher key length is greater than the block length, is it the case that for some keys $k_0, k_1$ (with $k_0 \not= k_1$) and plaintext message $m$ that $E_{k_0}(m) = E_{k_1}(m)$?
user7139
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Are block ciphers used in public key crypto?

I was reading about block ciphers and most articles state they are being used in symmetric key cryptography. Are they also being used in public key cryptography? if not, what alternative pkc use? Thanks,
soso
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Clear Lucifer example and explanation?

I am trying to understand the Lucifer cipher and I cant find any clear understandable example of the cipher. Can anyone please provide me with a step-by-step example of an encryption using the Lucifer cipher? Can you describe the relation between…
alfaraqed school
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Cipher that interleaves rounds from other ciphers?

Is there a cipher that interleaves rounds from other ciphers (with the same block size)? For example, interleaving the rounds of AES/Twofish/Serpent/RC6?
DepressedDaniel
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What are the issues of look-up table based implementations?

Cryptographic libraries mostly use pre-computed lookup tables to implement block ciphers. These lookup tables require large amout of memory and a series of cache miss/hit makes them vulnerable to cache timing attacks. Are there any other…
crypt
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Could a larger block size increase the security of the block cipher?

I want to know if a larger block size increase the security of the block cipher?
Ahmed Rayan
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Which block cipher mode(s) is most appropriate in these applications?

I have a few questions I'm stuck on for a cryptography course I'm doing, any help would be much appreciated. The first application is for decryption on a multicore processor. I assume any of ECB, CBC, CFB or CTR would be suitable since decryption…
DavidR
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KeeLoq showing that decryption is indeed the inverse of encryption?

In some text I am reading, there is an exercise asking to show that KeeLoq decryption function is the inverse of the encryption function. Details about KeeLoq are given in the Wikipedia article. As I am no hardware guy, I have no clue how to…
Azooo
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Most secure 32-bit block cipher

I have very short messages which I want to keep to 32-bits encrypted (ie one block). The keys can (and should) be as large as possible to maximize security. However, I don't know many ciphers with 32-bit modes. Are there any that offer 90+ bit…
Schuyler
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Are there any online, single pass, AE with associated data auth?

AE comparison summarizes features of nine AE ciphers and none of them combine features online, one pass, AD auth (see table below). Are out there such ciphers or such combination was proved to be unsecure?
hutorny
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Diffusion in a block cipher?

For a given block cipher, I would like to verify if any input word diffuses to all output words. For example in Twine block cipher, they define diffusion as "every output word is dependent of every input word". How can we check by the program? Is…
Vahid
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How to compare security between S-Box and Addition in the block ciphers?

I'm studying a block cipher based on ARX(Addition, Rotation, XOR). In a block cipher, nonlinearity comes from S-box or modular addition($Z=X\boxplus Y$ mod $2^n$). As far as I know, in the case of S-Box, its security can be explained in the…
Tylor Yoo
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What are the qualities of a good block cipher? Beginner, Intermediate, Advanced, Expert

Notice: I'm doing this to learn. I know not to use a homemade cipher for anything that requires security. I also have heard before I'm not supposed to be trying this, but I learn best through trying to make things from scratch, even if I…
Seph Reed
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