Secure Sockets Layer (SSL) and its successor, Transport Layer Security (TLS), employ a hybrid cryptographic model. The protocol uses asymmetric (public-key) cryptography for the initial handshake. This phase authenticates the server to the client and allows them to securely negotiate and exchange a shared secret key over an insecure network. Once this shared key is established, the protocol switches to the more computationally efficient symmetric (secret-key) cryptography for encrypting all subsequent data exchanged during the session. This dual approach leverages the security of asymmetric key exchange and the performance of symmetric bulk encryption.

A. Synchronous: This term describes a property of some stream ciphers or communication timing, not a fundamental category of encryption like symmetric or asymmetric.
B. Secret: While "secret key cryptography" is a synonym for symmetric encryption, "Symmetric" is the more formal and standard technical term in this context.

1. National Institute of Standards and Technology (NIST)

Special Publication 800-52 Revision 2

Guidelines for the Selection

Configuration

and Use of Transport Layer Security (TLS) Implementations

May 2019. Section 3.3.1

"TLS Handshake Protocol

" describes the use of asymmetric cryptography for authentication and key establishment

followed by the use of symmetric cryptography for protecting the application data.

2. Internet Engineering Task Force (IETF)

RFC 5246

The Transport Layer Security (TLS) Protocol Version 1.2

August 2008. Section 1.1

"Requirements Terminology

" and the overview in Section 7.4

"Handshake Protocol

" detail the process where a public-key algorithm is used to establish a shared symmetric key

which is then used for bulk encryption.

3. Dierks

T.

& Rescorla

E. (2006). The Secure Sockets Layer (SSL) Protocol Version 3.0. IETF RFC 6101. Section 5.6

"The SSL Handshake Protocol

" explicitly states

"The handshake protocol uses public-key cryptography to establish a shared secret key between the client and the server." It then describes the use of this secret key for symmetric encryption.