Simplify the following text for a Grade 14 native English-speaking person.
Original: In cryptography , an SP-network , or substitution-permutation network ( SPN ) , is a series of linked mathematical operations used in block cipher algorithms such as AES ( Rijndael ) .
Simplified: In cryptography , an SP-network , or substitution-permutation network ( SPN ) , is a series of linked mathematical operations used in block cipher algorithms such as AES .