In symmetric encryption we use ONE SHARED KEY to encrypt and decrypt.
It only provides confidentiality.
Input of fixed length → Output in the same length
Most block ciphers are SP-Networks. AES (Advanced Encryption Standard) is an SP-Network. AES is used by almost everything in security.
We have a translation table which changes depending on how the S-Box is designed. Here we have a random example of one, which is a 4-bit S-Box. AES uses 8-bit S-Boxes.
Here we exchange/switch certain bits. In our example we do this every 8-bits. We would call this an 8-bit P-Box. AES uses 128, 256 or even more bits.
Here is an example in which we combine the two to encrypt and decrypt. This would be a very simple block cipher.
