I was going to reply to the person that replied to you (I had agreed with you and thought it was just beefier hardware they'd need to handle the encryption demands) but it turns out they specifically require a certain type of coprocessor:

> Where many companies fail to secure their products at all or use simple 128-bit encryption, all HomeKit certified hardware includes a dedicated security co-processor paired with 3072-bit keys and the very secure Curve25519 key exchange system

http://www.howtogeek.com/232235/htg-explains-why-does-apples...