Encryption in IoT appears at several layers. Radio standards such as Zigbee and LoRaWAN encrypt at the link level; TLS and DTLS encrypt transport sessions between device and cloud; storage encryption protects data at rest in the database and in device flash memory. Symmetric ciphers such as AES do the bulk work, and many microcontrollers accelerate them in hardware so the energy cost is small.
Encryption alone does not prove who sent a message, which is why it is paired with authentication through authenticated cipher modes and certificates. The common weakness is key handling rather than the cipher: a key shared across every unit, stored in plain flash, or never rotated. IoT security fundamentals sets out where each layer belongs.
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