I guess not, but just in case it helps, in another topic, @matthijs suggested:
LMIC_setClockError(MAX_CLOCK_ERROR * 1 / 100);</pre>
This tells LMIC to make the receive windows bigger, in case your clock is 1% faster or slower.
(And as for encrypting: see the specifications: “The network server uses an AES decrypt operation in ECB mode to encrypt the join-accept message so that the end-device can use an AES encrypt operation to decrypt the message. This way an end-device only has to implement AES encrypt but not AES decrypt.”)