Both Encryption and decryption are based on the content of messages used for communications.
ENCRYPTION is the process of encoding a message so that only authorized entities are allowed to have access to the contents of the message. It converts a plaintext( original message) to ciphertext( encrypted message) using an encryption key and encryption algorithm.
Thus it means that ENCRYPTION WORKS WITH CONTENTS OF MESSAGE.
ENCRYPTION IS A FUNCTION OF APPLICATION LAYER [ APPLICATION LAYER IS LAYER WHOSE PROTOCOL DATA UNIT IS MESSAGE].
DECRYPTION is reverse process of ENCRYPTION. It converts a ciphertext( encrypted message) to plaintext( original message) using an decryption key and decryption algorithm.
Thus it means that DECRYPTION ALSO WORKS WITH CONTENTS OF MESSAGE.
Thus, DECRYPTION IS A FUNCTION OF APPLICATION LAYER.
Hence, both encryption and decryption are functions of application layer.
Therefore, answer is OPTION 4.
PROTOCOL DATA UNIT of a layer is the term used to describe the unit of data transferred from one end to another end or vice-versa in that layer. The PDU of various layers in TCP/IP protocol suite is shown in the table below:
|DATA LINK LAYER