Message Encryption Source a Destination B M M K E(K, M K (a) Symmetric encryption: confidentiality and authentication It may be difficult to determine automatically if incoming ciphertext decrypts to intelligible plaintext message should have suitable structure redundancy or a checksum to detect any changes 復大软件学院11 Message Encryption • It may be difficult to determine automatically if incoming ciphertext decrypts to intelligible plaintext • message should have suitable structure, redundancy or a checksum to detect any changes