Usually stock firmware for Poray devices (as can be obtained from their webpage) is obfuscated with a simple XOR obfuscation.
Furthermore the upgrade mechanism incorporated into the stock firmware expects firmware files to be checksummed.
To deobfuscate stock firmware images you can use a special tool that has been developed for the OpenWrt project. The tool is called mkporayfw and can be found in the tools/firmware-utils directory of the OpenWrt tree.
The rootfs of the stock images can be unpacked with binwalk after having been deobfuscated.
To do this please use this command:
binwalk -e --matryoshka input.bin