Shannon contributed to the field of cryptanalysis for national defense of the United States during World War II, including his fundamental work on codebreaking and secure telecommunications, writing a paper which is considered one of the foundational pieces of modern cryptography,[15] with his work described as "a turning point, and marked the closure of classical cryptography and the beginning of modern cryptography".[16] His work was foundational for symmetric-key cryptography, including the work of Horst Feistel, the Data Encryption Standard (DES), and the Advanced Encryption Standard (AES).[16] As a result, Shannon has been called the "founding father of modern cryptography".
