What is one of the advantages of using both symmetric and asymmetric cryptography in SSL/TLS?

The Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols utilize a hybrid cryptosystem to provide both security and performance. Asymmetric cryptography, while highly secure for key exchange, is computationally intensive and too slow for encrypting large volumes of data. Therefore, SSL/TLS uses asymmetric algorithms (like RSA or Elliptic Curve Diffie-Hellman) only during the initial handshake phase. The primary purpose of this phase is to authenticate the server (and optionally the client) and to securely negotiate a shared secret key. This shared key is then used to derive session keys for a symmetric algorithm (like AES), which is far more efficient and is used to encrypt the actual application data for the remainder of the session.

A. Symmetric algorithms are used after the asymmetric key exchange succeeds; they do not function as a failsafe if the initial asymmetric negotiation fails.

C. Asymmetric, not symmetric, encryption is used to securely establish the session keys in-band during the TLS handshake, not out-of-band.

D. All modern devices capable of TLS, including mobile phones, use both asymmetric and symmetric encryption in every session. It is not an either/or choice.

1. Internet Engineering Task Force (IETF) RFC 8446

"The Transport Layer Security (TLS) Protocol Version 1.3": Section 2

"Protocol Overview

" describes the handshake process where key establishment (asymmetric) and record protection (symmetric) are distinct phases. It states

"The primary goal of the handshake is to establish a set of shared keys... The keys established in the handshake are used to protect the rest of the session." This highlights the use of the handshake (asymmetric) to establish keys for the session (symmetric).

2. NIST Special Publication 800-52 Revision 2

"Guidelines for the Selection

Configuration

and Use of Transport Layer Security (TLS) Implementations": Section 3.3

"TLS Handshake Protocol

" details the process. It explains that the handshake authenticates the server and establishes a shared "master secret

" which is then used to generate symmetric keys for encrypting and authenticating the session data. This confirms the separate

specialized roles of asymmetric and symmetric crypto.

3. Boneh

D.

& Shoup

V. (2020). A Graduate Course in Applied Cryptography. Stanford University. Chapter 12

"Public-Key Encryption

" Version 0.5

page 409

discusses hybrid encryption. It states

"In practice

public-key encryption is much slower than symmetric encryption... To encrypt a long message... one should use hybrid encryption... This is how public-key encryption is used in many systems

including in TLS." This academic source confirms that the combination is used to overcome the performance limitations of asymmetric cryptography.