DES S-Box
The DES S-boxes are eight 4×16 substitution tables, the only nonlinear component of the DES round function, compressing a 48-bit input to a 32-bit output.
Purpose
They provide the nonlinear confusion of the DES Feistel round function and are the core of DES security (their design criteria were kept secret and were later shown to resist differential attacks).
Mechanism
The 48-bit input splits into eight 6-bit groups, each looked up in its own S-box: the first and last bits select the row, the middle four the column, yielding a 4-bit output; the eight outputs concatenate into 32 bits.
Use cases
- Core of DES encryption
- 3DES round function
- Differential cryptanalysis research