Decrypt dir 867 firmware from d'link

Hello. Who can help me decrypt the original factory firmware for d'link DIR-867 router

https://support.dlink.ca/ProductInfo.aspx?m=dir-867 ..

I want to revert back to the original firmware and this model needs a decrypted firmware for a successful install via recovery console...

thank you very much...

you can try this i uploaded it into my 878 & then saved it back out

http://luckys.onmypc.net/openwrt/DIR-867/DIR-867_REVA_FIRMWARE_1.20B10_BETA_unencrypted.bin