Trying to load source code for mint. Problem

I am following the users guide and have been stuck here

make[1]: Leaving directory '/home/keith/Sandbox/mintinstall'
dh_gencontrol
dpkg-gencontrol: warning: package mintinstall: unused substitution variable ${misc:Depends}
dh_md5sums
debian/rules override_dh_builddeb
make[1]: Entering directory '/home/keith/Sandbox/mintinstall'
dh_builddeb -- -Zxz -z9
dpkg-deb: building package 'mintinstall' in '../mintinstall_8.0.3_all.deb'.
make[1]: Leaving directory '/home/keith/Sandbox/mintinstall'
dpkg-genbuildinfo
dpkg-genchanges >../mintinstall_8.0.3_amd64.changes
dpkg-genchanges: info: including full source code in upload
dpkg-source --after-build mintinstall
dpkg-buildpackage: info: full upload; Debian-native package (full source is included)
signfile mintinstall_8.0.3.dsc
gpg: skipped "Clement Lefebvre <root@linuxmint.com>": No secret key
gpg: dpkg-sign.kuReNBfX/mintinstall_8.0.3.dsc: clear-sign failed: No secret key

dpkg-buildpackage: error: failed to sign .dsc file
keith@keith-To-be-filled-by-O-E-M:~/Sandbox/mintinstall$

Where do I get the secret key I can not see anything in the developers guide?