For SLE-15-SP6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/isv:SUSE:Edge:EdgeImageBuilder/SLE-15-SP6/isv:SUSE:Edge:EdgeImageBuilder.repo
zypper refresh
zypper install cosign
For SLE-15-SP5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/isv:SUSE:Edge:EdgeImageBuilder/SLE-15-SP5/isv:SUSE:Edge:EdgeImageBuilder.repo
zypper refresh
zypper install cosign
For Leap-15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/isv:SUSE:Edge:EdgeImageBuilder/Leap-15.6/isv:SUSE:Edge:EdgeImageBuilder.repo
zypper refresh
zypper install cosign