Long description

The hierarchy of the diagram is P (Plaintext.in) forward arrow block E (Encryption Algorithm) forward arrow labeled C equals E (P, K subscript E) (ciphertext) pointing to block D (Decryption Algorithm) forward arrow labeled P equals D (C, K subscript D) pointing to P (Plaintext out). There is a downward arrow labeled K subscript E (Encryption key) pointing to block E. There is another downward arrow labeled K subscript D (Decryption key) pointing to block D. From process P to block E to Ciphertext process, which is categorized as Encryption. From D to P process is categorized as Decryption.