Symmetric Encryption

is a method of encrypting and decrypting data using the same secret key.

AKA: secret-key, single-key, or private-key encryption.
The secret key is shared between both parties. (increases the risk)
The same key is used to encrypt and decrypt the message.
It can use block or stream ciphers.
Pros: good for volumes of data, files, databases, and networks. Fast.
Pros: confidentiality, integrity, and authentication
Cons: How do I share the key? How do I scale for multiple users? (multiple keys)
Cons: Doesn’t support non-repudiation.
Examples: Blowfish, RC4, DES, Triple DES (3DES), and AES (most popular).
Examples: ChaCha20 (used by TLS 1.3, for instance)