Symmetric key crypto:DES DES:Data Encryption Standard US encryption standard [NIST 1993] 56-bit symmetric key,64-bit plaintext input ▣How secure is DES? o DES Challenge:56-bit-key-encrypted phrase ("Strong cryptography makes the world a safer place")decrypted (brute force)in 4 months o no known "backdoor"decryption approach Omaking DES more secure: o use three keys sequentially(3-DES)on each datum o use cipher-block chaining 8:Network Security 8-128: Network Security 8-12 Symmetric key crypto: DES DES: Data Encryption Standard  US encryption standard [NIST 1993]  56-bit symmetric key, 64-bit plaintext input  How secure is DES?  DES Challenge: 56-bit-key-encrypted phrase (“Strong cryptography makes the world a safer place”) decrypted (brute force) in 4 months  no known “backdoor” decryption approach  making DES more secure:  use three keys sequentially (3-DES) on each datum  use cipher-block chaining