Why Encryption Alone Is Not Enough: The Case for Authenticated Encryption

Encryption ensures data confidentiality but does not by itself prevent tampering, meaning attackers can alter ciphertext without needing the decryption key. A developer building a cryptography project explains this gap in part four of an ongoing series. To address both confidentiality and integrity, the project uses AES-GCM, an Authenticated Encryption with Associated Data (AEAD) cipher mode that generates an authentication tag alongside the encrypted output. If even a single bit of the ciphertext is altered after encryption, AES-GCM refuses to decrypt and raises an exception rather than silently returning corrupted data. This is why modern cryptographic best practices favour AEAD modes like AES-GCM or ChaCha20-Poly1305 over legacy modes such as AES-CBC, which provide no built-in integrity verification.