CODEWITHSUNDEEP
encryptionaesencryption-symmetric
Prasanth Kumar Arisetti
Prasanth Kumar Arisetti

Reputation: 737

S-box in AES CCM 128 bit

I am working on encryption & decryption of data using AES-CCM.

While studying AES, I came across a word called S-Box.

What is S-Box, and the relationship with AES? How can it be calculated? Is it depends on symmetric key or not?

How will cypher text be generated in AES-CCM 128 bit?

Upvotes: 1

Views: 393

Answers (2)

Andy
Andy

Reputation: 14194

As @CGG said, S-boxes are a component of a Substitution-Permutation Network. The Wikipedia entry has good diagrams which will help explain how they work.

Think of an S-box as a simple substitution cipher -- A=1, B=2, etc. In an SPN, you run input through an S-box to substitute new values, then you run that result through a P-box (permutation) to distribute the modified bits out to as many S-boxes as possible. This loop repeats to spread the changes throughout the entire cipher text.

In general, an S-box replaces the input bits with an identical number of output bits. This exchange should be 1:1 to provide invertibility (i.e. you must be able to reverse the operation in order to decrypt), should employ the avalanche effect (so changing 1 bit of input changes about half the output bits), and should depend on every bit of input.

Upvotes: 1

CGG
CGG

Reputation: 273

The S-Boxes are a system that is used in symmetric cryptographic algorithms to substitute and obscure the relationship between the key and the text that you want to cypher.

You can see more in this article. Here, you have a part:

There are different types of cyphers according to their design [68]. One of these is the ​Substitution–PermutationNetwork (SPN) that generates the ciphered text by applying substitution and permutation rounds to the original text and the symmetric key to create confusion. To do this, it must be used the Substitution boxes (S-boxes) and Permutation boxes (P-boxes). The S-boxes substitute one-to-one the bits of a block of the input text in the round with bits of the output text. This output is taken as an input in the P-boxes and then it permutes all the bits that will be used as S-box input in the next round.

Upvotes: 2

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