您需要安装存储库的密钥。
对于稳定的存储库,使用:
$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 8AA7AF1F1091A5FD
$ sudo add-apt-repository 'deb [arch=amd64] http://repo.sawtooth.me/ubuntu/bumper/stable xenial universe'
$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 44FC67F19B2466EA
$ sudo apt-add-repository 'deb [arch=amd64] http://repo.sawtooth.me/ubuntu/nightly xenial universe'