hello ragony2001,
as mentioned by developer guide,
The flash.sh command line switch ‑i specifies the key to be used for disk encryption. The reference implementation described above uses the EKB key.
you may refer to Tool for EKB Generation for the steps to run the EKB generation tool,
please also check Flashing a Specific Partition to update EKS partition.
furthermore, you may looking for similar discussion threads,
such as… Topic 196140, Topic 307116, Topic 283443 as see-also.