Fucc is a project mainly written in C, it's free.
Firmware Upload Certificate Corrupter 0.1
./fucc WTF.x1223.RELEASE.dfu x1223.exec 0xBC 0x22000800 x1223.exec.cert ./fucc WTF.x1231.RELEASE.dfu x1231.exec 0xBC 0x22000600 x1231.exec.cert