With no active Authenticate() data waiting, write 160-bit message M to Authenticate() in the format: 0xAABBCCDDEEFFGGHHIIJJKKLLMMNNOOPPQQRRSSTT, where AA is LSB.
Wait 250 ms, then read Authenticate() for HMAC3.
Compare host HMAC2 with device HMAC3. If it matches, both host and device have the same key KD and the device is authenticated.