thinQmaster Virtual testing partner Adaptive practice exams that find your weak spots and drill them. Every answer explained. From $69
Enroll

thinQmaster

Find your exam

Five questions free, before you decide.

Step 1 · choose a vendor

In one of our camps? Your practice exams come with the tuition — they are on your study page already.

Security Fundamentals & Crypto · Foundational

Symmetric Encryption

Encryption in which the same secret key is used to both encrypt and decrypt data.

Definition

Symmetric algorithms such as AES and ChaCha20 are fast and efficient for bulk data. Their main challenge is key distribution, since every pair of parties needs a shared secret: n users need n(n-1)/2 keys. They provide confidentiality but not non-repudiation.

Example

A VPN tunnel encrypts all traffic with an AES-256-GCM session key shared by both endpoints.

Exam tip

Use the n(n-1)/2 formula for key counts; 10 users need 45 symmetric keys but only 20 asymmetric keys.

Don't confuse it with

Related terms