User A is writing a sensitive email message to user B outside the local network. User A has chosen to use PKI to secure his message and ensure only user B can read the sensitive email. At what layer o

The Application layer (Layer 7) provides network services to end-user applications like email clients, but it does not perform the actual encryption or decryption of data.

The Transport layer (Layer 4) handles end-to-end communication, segmentation, and protocols like TCP and UDP, not encryption of message content.

The Session layer (Layer 5) manages establishment, maintenance, and termination of communication sessions between applications, not cryptographic operations.

The Presentation layer (Layer 6) is responsible for data encryption, decryption, compression, and translation between different data formats. When PKI is used to encrypt an email so only a specific recipient can decrypt it, the cryptographic operations are handled at this layer before the data is passed up or down the stack.