What Symmetric Means
Symmetric encryption uses one shared key for both encrypting and decrypting. The same secret that scrambles the message also unscrambles it, so both parties must already share that key safely.
Why AES Won
The Advanced Encryption Standard was chosen in 2001 as a public, openly analyzed cipher. It operates on fixed blocks of 128 bits and supports key sizes of 128, 192, or 256 bits. A larger key means more possible keys and a harder brute force search.
- AES runs a series of rounds that mix and substitute bytes.
- Each round uses substitution, shifting, mixing, and key addition.
- Hardware acceleration on modern CPUs makes it extremely fast.
What It Does Not Do
AES alone only provides confidentiality. It does not prove who sent a message or that it was unaltered. For that you combine AES with a mode that adds authentication, such as one that produces an integrity tag.
Key idea
AES is the trusted, fast symmetric block cipher that uses one shared key on 128 bit blocks to provide confidentiality, but it needs an authenticated mode to also guarantee integrity.