We can use pem file to login into remote server from our local machines. Infact if you use AWS, the only way to SSH into the server is using pem file.

### 1. On your local Machine from where you require access, Home directory of the user is preferable
```
cd ~
ssh-keygen -t rsa -b 2048
```
```
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in example
Your public key has been saved in example.pub
The key fingerprint is:
SHA256:3IJlrYwRCxzGkaZwoXG0OSaJi8bHTLtzXLyC6GMZHLI mahmud@3xp1r3
The key's randomart image is:
+---[RSA 2048]----+
|..++=+.          |
|o=.+=. o .       |
|=o=+  o o .      |
|+==.. .O o       |
|=+.=  ooS .      |
|Eoo + . ..       |
| .o+ + .         |
|.+  o .          |
|...              |
+----[SHA256]-----+
```
```
In this case i have used example as a file name. so there will be two files example and example.pub
example : is your private key
example.pub : is your public key
```

### 2. Now it's time to create example.pem file from private key
```
rsa -in example -outform pem > example.pem
```
writing RSA key
#### If you don't have rsa utility you can create .pem file by using copy command
```
cp -p example example.pem
```
Now the pem file is created. Next step to copy public key(example.pub) to remote server

### 3. Copy the public key into your remote server, which needs to be accessed
```
ssh-copy-id -i example.pub root@1.2.3.4
```
```
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "example.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@1.2.3.4's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'root@1.2.3.4'"
and check to make sure that only the key(s) you wanted were added.
```
### 4. Change the permissions of your example.pem file
```
chmod 400 example.pem
```
### 5. Login to your remote server using example.pem file
```
ssh -i example.pem root@1.2.3.4
```

### 6. Disable SSH Access to remote server using password authentication
On the remote server with root access
```
nano /etc/ssh/sshd_config
```
Change parameter PasswordAuthentication yes to PasswordAuthentication no
Restart SSH Daemon
```
systemctl restart sshd
or
service sshd restart
```