Linked Questions

35 votes
3 answers
5k views

What are recommended, general strategies to start block-cipher design and/or analysis?

I (and many others for that matter) have always been fascinated by the inner workings of the modern building block of cryptography: block ciphers. Now, the resources on the "black art" of ...
SEJPM's user avatar
  • 45.9k
11 votes
1 answer
2k views

Why expand keys? Why not rather generate a longer key?

AES-128 takes a 128-bit key (four 32-bit words), and expands it to a 352-bit key schedule (11 words). Speck48/72 takes a 72-bit key (three 24-bit words), and expands it to a 528-bit key schedule (22 ...
Chris Morgan's user avatar
3 votes
1 answer
2k views

What are the qualities of a good block cipher? Beginner, Intermediate, Advanced, Expert [closed]

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 ...
Seph Reed's user avatar
  • 205
7 votes
2 answers
768 views

Security importance of Key Schedule in Block Cipher

For example block cipher AES-128, Key size is 128bit and it is used to make a 10 round key which is total 320bit. Question 1. If i use another Key schedule algorithm in AES, then security decreased ...
Seonghwan Cho's user avatar
9 votes
1 answer
2k views

Is the AES Key Schedule weak?

After reading this paper entitled Key Recovery Attacks of Practical Complexity on AES Variants With Up To 10 Rounds, I was left wondering why AES's key schedule is invertible. In the paper, the ...
user avatar
0 votes
2 answers
2k views

Perfect secrecy with XOR & SHIFT?

I have read that XOR provides perfect secrecy, when the key is perfectly random. However it's technically hard to generate truly random numbers, especially on computers, so that is why people use AES, ...
cryptonoob400's user avatar
6 votes
2 answers
359 views

A block cipher whose key changes after each block

I have been reading about various block cipher modes of operation, and all of them seem to treat the block cipher (including it's key and key schedule) as a sort of immutable black box. I would like ...
BenGoldberg's user avatar
3 votes
2 answers
199 views

Security of key schedule that only XORs a key with constants

Suppose that: $MK \in \{0, 1\}^{n}$ and the main key of a block cipher. $RK_{r} \in \{0, 1\}^{n}$ and is the $r$th round key. $RC_{r} \in \{0, 1\}^{n}$ and is the $r$th round constant. $RK_{r} = MK \...
Melab's user avatar
  • 3,645
3 votes
1 answer
373 views

Does the key schedule function need to be a one-way function?

For some key schedule $e_n(e_{n-1}(k))$ (where $e_{n-1}(k)$ is the result of the previous round) , does $e$ need to be a one-way function? In the case of DES or Rijndael the key schedule doesn't ...
rath's user avatar
  • 2,548
2 votes
2 answers
451 views

Camellia Key Schedule

Camellia is widely used, an international standard now. Its key schedule seems to be too simple compared to other famous ciphers like Twofish and CAST-256. What are the prerequisites for the key ...
crypt's user avatar
  • 2,397
6 votes
1 answer
202 views

Replacing a block cipher's key schedule with a stream cipher

Take Rijndael (AES) of block size 128 and reformulate it with a tweakable number of rounds and no key schedule. Suppose we obtain: Rijndael128(r, k) where r is ...
user avatar
1 vote
1 answer
314 views

How should the key schedule be designed for this general block cipher?

After looking at the Wikipedia page for the Fiestel cipher, I thought about making a variation of it that is very general. I basically followed the diagram on Wikipedia in order to structure the ...
Lasagnenator's user avatar
2 votes
1 answer
233 views

AES key schedule. Does it use a KDF to generate the round keys?

So for each round in AES a different key is used, and as I saw the keys are created form a master key. My question is how these round keys are generated. Are they created via a Key Derivation ...
user67441's user avatar
1 vote
1 answer
149 views

DES security if used a SHA3 function instead of Normal DES function?

I was practicing some python programming and I decided to implement a simple DES encryption function, so i decided to take some shortcuts so instead of DES expansion boxes and s-Boxes i just used a ...
KMG's user avatar
  • 403
3 votes
1 answer
76 views

Desirable Property of Block Sub-Keys

What is the more desirable for a block cipher's sub-keys ? Given two blocks ciphers, letting all other properties be equal (they have the same strength), the only difference between them is that: ...
Mandalf The Beige's user avatar

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