SUBSTITUTION BOXES (S-BOX)

• In cryptography , a S-box is a basic component of symmetric key algorithm, which performs substitution . In block cipher, they are typically used to obscure the relationship between the key ciphertext.

• The S-boxes carry out the real mixing (confusion).

• It takes in m number of input bits and gives out m bits of output where m and n are not equal.

• DES uses 8 S-boxes each with a 6-bit input and 4-bit output.

• Each S-box is actually 4 little 4 bit boxes.

• outer bits 1 &6 are known as row bit.

• inner bit 2 & 5 are known as column bit.