The Secure Sockets Layer (SSL) and its successor, Transport Layer Security (TLS), employ a hybrid cryptosystem to leverage the strengths of both asymmetric and symmetric cryptography. Asymmetric (public-key) cryptography, while secure for key exchange without a pre-shared secret, is computationally intensive and slow, making it impractical for encrypting large volumes of data. Conversely, symmetric cryptography is significantly faster and more efficient for bulk data encryption. The TLS handshake uses asymmetric algorithms to authenticate the server and securely negotiate a shared secret. This secret is then used to generate a temporary, symmetric "session key" for encrypting the actual application data, thus combining the secure key exchange of asymmetric methods with the high performance of symmetric ones.

A. This is misleading. All devices using TLS, regardless of power, must use the hybrid model (both asymmetric for the handshake and symmetric for data). They cannot opt to use symmetric encryption "instead."
B. The two cryptographic methods are complementary, not failsafes. If the asymmetric key exchange fails during the handshake, the secure session is never established, and symmetric encryption cannot begin.
C. This statement reverses the process. Asymmetric encryption is used to securely establish and transmit the session key in-band during the handshake, which is then used for symmetric encryption.

1. Internet Engineering Task Force (IETF) RFC 8446: The Transport Layer Security (TLS) Protocol Version 1.3.

Section 1

Introduction: "The primary goal of TLS is to provide a secure channel between two communicating peers... This is achieved by using a handshake procedure to establish shared secret keys

authenticating the server (and optionally the client)

and then using the established keys to protect the traffic between the peers." This outlines the two-phase process.

Appendix B.1

Performance: "Public-key operations are relatively expensive... For this reason

TLS is designed to establish a secret key using public-key cryptography and then to use that key with a symmetric-key cipher to protect the application data."

2. Dierks

T.

& Rescorla

E. (2008). The Transport Layer Security (TLS) Protocol Version 1.2 (RFC 5246).

Section 1

Introduction: "The TLS Protocol is designed to provide privacy and data integrity between two communicating applications... The protocol is composed of two layers: the TLS Record Protocol and the TLS Handshake Protocol. At the lowest level... the Record Protocol uses the keys created during the handshake to secure application data." This clearly separates the handshake (which uses asymmetric crypto) from the record layer (which uses symmetric crypto).

3. Boneh

D. (2013). Cryptography I

Week 5

Lecture 5.1

"Session Keys": Professor Boneh explains that public-key encryption is used to establish a short-term

shared symmetric key (session key). He states

"The reason we do this is that public key encryption is much much slower than symmetric encryption... So what we do is we only use public key encryption to establish a shared secret key... and then we use that symmetric key to encrypt all the data that we need to send." This directly supports the rationale in option D.