Starting from openssh 7.8 the default format for private keys has changed from PEM to OpenSSH:
That means that private keys generated with the referenced command (
ssh-keygen -t rsa -b 4096
) are not accepted by Circle CI anymore. PEM format can still be generated using
ssh-keygen -t rsa -b 4096 -m PEM
however this is not documented when following the instructions found in the Circle CI / github documentation
CCI-I-583