IMX6ULLSRM.pdf, page 162, section 188.8.131.52 "AES OTP Key"
Depending on the key path control fuse, the DCP receives the CRYTPO KEY either directly or indirectly through the SNVS trust controller module. The CRYPTO KEY in fuses is actually 256-bit and a mux is used to select the high or low 128 bits of the key.
I couldn't find the "key path control fuse". Where is it located and which paths are set for the values 0 (intact) and 1 (blown)? How do I select the low or high 128 bits of the key?