I started to get this error after installing the new firmware of D3 so I did exactly the same Mike showed me how to.But Didn't work! then I realized in the www/pages/cgi-bin there is 3 file connecting each other and this three are calling each other.
"upgrade.cgi"
"upgrade_clear.cgi"
"upload_conf.cgi"
so I edited with this files in ssh editor I searched in existing "Cannot Find Signature" so I put # type before words as like Mike's codes. and worked for me. Thank you again Mike. Yes I think with the latest firmware having strong security with this 3 files I think.
There is a much much simpler way to do this.
mv /usr/bin/openssl /usr/bin/openssl.orig
echo > /usr/bin/openssl <#!/bin/sh
return 1
!
chmod +x /usr/bin/openssl
Done. Fixed. /usr/bin/openssl will return true, the "check" will pass... the only caveat is sometimes the firmware you want to upgrade to will need a 0 byte .signature file to pass the "-f" exists check.
-j