What’s the threat model exactly? Here AES is just a bijection between 128bit numbers. It’s not like the AES cipher is going to blow up when you try to decrypt

What’s the threat model exactly? Here AES is just a bijection between 128bit numbers. It’s not like the AES cipher is going to blow up when you try to decrypt a special harmful bit pattern! It’s just a bunch of ones and zeros… If someone gives you a bogus ID, then it’s gonna decrypt to a non-existent ID. Which can also happen with plaintext IDs…