ubuntu 18.04 Generating a new ubuntu-keyring .deb to sign your CD failed

hi,
i am trying to create customize ISO base on ubuntu 18.04.
i followed https://help.ubuntu.com/community/InstallCDCustomization guide.
first the section of the kerying need to be change cause the keys now are not 8 Bytes its 16 Bytes.
the fail is when i tried to build the packages again:

root@isoMaker18:/opt/build/ubuntu-keyring-2018.02.28# dpkg-buildpackage -d -m"Shalom David <email address hidden>" -k982935729B2F5DD
dpkg-buildpackage: info: source package ubuntu-keyring
dpkg-buildpackage: info: source version 2018.02.28
dpkg-buildpackage: info: source distribution bionic
dpkg-buildpackage: info: host architecture amd64
 dpkg-source --before-build ubuntu-keyring-2018.02.28
 debian/rules clean
dh clean
   dh_clean
 dpkg-source -b ubuntu-keyring-2018.02.28
dpkg-source: warning: no source format specified in debian/source/format, see dpkg-source(1)
dpkg-source: info: using source format '1.0'
dpkg-source: info: building ubuntu-keyring in ubuntu-keyring_2018.02.28.tar.gz
dpkg-source: info: building ubuntu-keyring in ubuntu-keyring_2018.02.28.dsc
 debian/rules build
dh build
   dh_update_autotools_config
   dh_autoreconf
   create-stamp debian/debhelper-build-stamp
 debian/rules binary
HOME=/opt/build/ubuntu-keyring-2018.02.28 gpg --no-default-keyring --keyring /usr/share/keyrings/debian-keyring.gpg --decrypt SHA512SUMS.txt.asc | sha512sum -c -
keyrings/ubuntu-archive-keyring.gpg: FAILED
keyrings/ubuntu-archive-removed-keys.gpg: OK
keyrings/ubuntu-cloud-keyring.gpg: OK
keyrings/ubuntu-cloud-removed-keys.gpg: OK
keyrings/ubuntu-cloudimage-keyring.gpg: OK
keyrings/ubuntu-cloudimage-removed-keys.gpg: OK
keyrings/ubuntu-dbgsym-keyring.gpg: OK
keyrings/ubuntu-dbgsym-removed-keys.gpg: OK
keyrings/ubuntu-keyring-2012-archive.gpg: OK
keyrings/ubuntu-keyring-2012-cdimage.gpg: OK
keyrings/ubuntu-keyring-2012-cloud-archive.gpg: OK
keyrings/ubuntu-keyring-2016-dbgsym.gpg: OK
keyrings/ubuntu-master-keyring.gpg: OK
gpg: Signature made Tue 06 Feb 2018 07:15:42 PM IST
gpg: using RSA key 773C99EBD0A11172217A7C3FCAC2D8B9CD2CA5F9
gpg: Can't check signature: No public key
gpg: can't create `/opt/build/ubuntu-keyring-2018.02.28/.gnupg/random_seed': No such file or directory
sha512sum: WARNING: 1 computed checksum did NOT match
debian/rules:18: recipe for target 'checkkeyrings' failed
make: *** [checkkeyrings] Error 1
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2

its failed on the keyrings/ubuntu-archive-keyring.gpg: FAILED
i did exactly as written in the guide, can you verify and update the guide?
thanks
shalom david