clientA, key pair (privkeyA, pubkeyA), ip address ipA
clientB, ipB, key pair to be added
serverC (where sshd is running) ,
assume clientA can already connect to bob@serverC via ssh
/home/bob/.ssh/authorized_keys already contains pubkeyA
/etc/ssh/sshd_config contains "AllowUsers bob@ipA"
1. on clientB, create key pair (privkeyB, pubkeyB) via Git Bash
2. cp pubkeyB from clientB to clientA via clipboard/email/ftp/...
pubkeyB is like
"ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDc ... ... "
* take care not to wrap!
3. on clientA, ssh to connect to serverC via putty
[session: Data/Auto-login username, SSH/Auth]
* add pubkeyB to authorized_keys
bob@serverC$ nano .ssh/authorized_keys
* add ipB to sshd_config
bob@serverC$ sudo nano /etc/ssh/sshd_config
* reload sshd config
bob@serverC$ sudo service ssh reload
4. on clientB, ssh to connect to serverC with privkeyB
[for putty, has to convert privkeyB to .ppk format by puttyGen]