空のパスフレーズを使用し、~/.ssh/id_rsa に 2048 ビットの RSA キーペアを生成するコマンドはどれですか？
~/.ssh/id_rsa
ssh-keygen -t rsa -b 2048 -N ~/.ssh/id_rsa
ssh-keygen -t rsa -b 2048 -N "" -f ~/.ssh/id_rsa
ssh -t rsa -b 2048 -N "" ~/.ssh/id_rsa
ssh-keygen -t rsa -b 2048 -N "" -f ~/.ssh/authorized_keys