AEAD
acronymcryptography
Stands for: Authenticated Encryption with Associated Data
A cipher that encrypts and authenticates in one step, so tampering fails as a single operation.
Authenticated Encryption with Associated Data (RFC 5116) combines confidentiality and integrity in one primitive - AES-GCM, AES-CCM, ChaCha20-Poly1305. TLS 1.3 permits AEAD ciphers only, because the older encrypt-then-separately-authenticate constructions kept producing padding-oracle attacks.
AEAD packages encryption and authentication into a single operation, which sounds like convenience and is actually a safety mechanism. The historical alternative was composing a cipher with a separate MAC, and the composition was where implementations went wrong: authenticate the wrong thing, do it in the wrong order, and the result is a padding oracle rather than a protocol.
The associated data part is the piece people overlook. Some fields must be visible to work at all, such as headers a router needs to read, yet still must not be tampered with. AEAD covers them with the authentication tag while leaving them unencrypted, so integrity extends beyond the ciphertext to the context around it.
The rule that matters operationally is that AEAD trades one class of failure for another. It removes composition mistakes and it is unforgiving about nonce reuse: repeating a nonce under the same key in GCM does not degrade security gracefully, it can expose the authentication key itself. TLS 1.3 kept only AEAD ciphers precisely because the alternatives had accumulated a decade of attacks, and the remaining sharp edge is nonce management rather than cipher choice.
Also known as: aead, authenticated encryption