This is a sensational ROM! It is beautiful and fluid, please continue your development
can this probably help?
GitHub - bkerler/oppo_ozip_decrypt: Oppo Firmware .ozip decrypter
oppo_decrypt_ozip
Oppo/Oneplus .ozip Firmware decrypter
Tested with CPH1707EX, CPH1611EX OTA Zip and Python 3.6...