[seL4] Getting Started

I am in the process of reading the Getting Started documentation and building a development environment on Debian Linux. I thought RefOS would be the best example project to start with. When I execute the command: repo init -u ssh://git@github.com/seL4/refos-manifest -b master I get the response: Please make sure you have the correct access rights and the repository exists. Permission denied (publickey). fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists. fatal: cannot obtain manifest ssh://git@github.com/seL4/refos-manifest Apparently something has changed since the instructions were written. Dave