Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [key-schedule]

A key schedule is an algorithm that expands a relatively short master key to a relatively large expanded key for later use in an encryption and decryption algorithm.

12
votes
1answer
2k views

What are the requirements of a key schedule?

In the first block cipher I designed I used a CSPRNG to generate the round keys. The purpose was to at least have a chance of creating a (hopefully!) secure cipher on the first try (but please don't ...
3
votes
1answer
305 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 ...
4
votes
1answer
488 views

More rounds after AES related key attack?

In his blog Schneier discusses that there is a new related key attack on 10 rounds of AES-256 "Another attack can break a 10 round version of AES-256 in 245 time, but it uses a stronger type of ...
3
votes
2answers
302 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 ...
10
votes
2answers
2k views

How secure is the AES master key if Round Keys are found

If an attacker finds some round key of AES256, is it possible to find the master key? How safe is the master key if an attackers finds multiple round keys?
10
votes
2answers
3k views

AES Inverse Key Schedule

I have a 128-bit input-block and the corresponding cipher-block given. Additionally I have the last round-key given. Is it now possible to get (calculate) the associated cipher-key? I already ...
14
votes
3answers
2k views

Why do Feistel ciphers need round keys?

Looking at the design for Feistel ciphers, they use a list of round keys which are generated from the main key using the key schedule of the associated block cipher. Some block ciphers need this as to ...
1
vote
2answers
234 views

Camellia Key Schedule

Camellia is a widely used International standard now. Its Key Schedule seems to be too simple as compared other famous Ciphers like Twofish and CAST-256. What are the per-requisites for the key-...
5
votes
1answer
152 views

Why do block ciphers use key schedules instead of round constants? (Even-Mansour)

Let's take AES as an example. What would be wrong with just having a 256 bit key that you XOR into your input and then XOR into your output? No key expansion at all. I believe it's even known as the ...
2
votes
1answer
1k views

Compression in key generation of DES algorithm

Does anyone have a pseudo-code or an algorithm or even a diagram of the compression (pc2) of the DES algorithm? I can't find a relation between the bits that are dropped, even when I do it manually ...
2
votes
2answers
139 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 \...