The DIR-3040 models of DLINK routers feature encrypted firmware images in the most recent versions of the firmware. https://support.dlink.com/ProductInfo.aspx?m=DIR-3040-US details the firmware images available for this product.
1.11B02- ftp://ftp2.dlink.com/PRODUCTS/DIR-3040/REVA/DIR-3040_REVA_FIRMWARE_v1.11B02.zip1.02B03- ftp://ftp2.dlink.com/PRODUCTS/DIR-3040/REVA/DIR-3040_REVA_FIRMWARE_v1.02B03.zip
Unzipping the first reveals two files:
DIR-3040_REVA_RELEASE_NOTES_v1.11B02.pdf