Centos7 通过SSH使用密钥实现免密登录

一、serverA 生成秘钥，遇到提示直接敲回车即可

CentOS7 默认使用RSA加密算法生成密钥对，保存在~/.ssh目录下的id_rsa（私钥）和id_rsa.pub（公钥）。也可以使用“-t DSA”参数指定为DSA算法，对应文件为id_dsa和id_dsa.pub，
密钥对生成过程会提示输入私钥加密密码，可以直接回车不使用密码保护。

 1 [root@localhost ~]# ssh-keygen
 2 Generating public/private rsa key pair.
 3 Enter file in which to save the key (/root/.ssh/id_rsa):    
 4 Enter passphrase (empty for no passphrase): 
 5 Enter same passphrase again: 
 6 Your identification has been saved in /root/.ssh/id_rsa.
 7 Your public key has been saved in /root/.ssh/id_rsa.pub.
 8 The key fingerprint is:
 9 SHA256:/gGrlDJN5euMS5aai5feBkEI/0WjEnzPzx1xGtdkKG4 root@localhost.localdomain
10 The key's randomart image is:
11 +---[RSA 2048]----+
12 |.o..  o      +o  |
13 | .o.oo .  + +..  |
14 |  oo.o. .. B     |
15 |   o..oo  E      |
16 |    ...oSo .     |
17 |    .o +o+.      |
18 |    ooB + .      |
19 |   .oX.= . .     |
20 |  .o=o=.o .      |
21 +----[SHA256]-----+
22 [root@localhost ~]# ls ~/.ssh/
23 id_rsa  id_rsa.pub  known_hosts
24 [root@localhost ~]#

二、解决找不到 .ssh 目录

如果在上面生成秘钥后，执行 cd ~/.ssh 找不到 .ssh 目录，是因为没有使用 ssh 登录过，使用 ssh 登录一下即可生成 .ssh 目录，之后再重新执行 ssh-keygen 生成秘钥即可

 1 [root@localhost ~]# ssh localhost
 2 The authenticity of host 'localhost (::1)' can't be established.
 3 ECDSA key fingerprint is SHA256:DYd7538oOsqpIIDTs01C3G4S6PRE7msA91yUgk9Dzxk.
 4 ECDSA key fingerprint is MD5:88:80:21:03:b2:52:6b:06:ff:c7:3b:d5:2d:47:c9:ad.
 5 Are you sure you want to continue connecting (yes/no)? yes
 6 Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
 7 root@localhost's password: 
 8 Last login: Fri Oct 26 16:15:57 2018 from localhost
 9 [root@localhost ~]# ls ~/.ssh/
10 known_hosts
11 [root@localhost ~]# exit
12 登出
13 Connection to localhost closed.
14 [root@localhost ~]#

三、在服务器上安装公钥

[root@ecs-326c-0001 .ssh]# cat id_rsa.pub >> authorized_keys

四、为了确保连接成功，需要设置文件权限

[root@ecs-326c-0001 .ssh]# chmod 600 authorized_keys

[root@ecs-326c-0001 .ssh]# chmod 700 ~/.ssh

五、设置ssh，打开秘钥登录功能

[root@ecs-326c-0001 .ssh]# vim /etc/ssh/sshd_config

去掉注释#

RSAAuthentication yes

PubkeyAuthentication yes

六、重启ssh服务

[root@ecs-326c-0001 ~]# systemctl restart sshd

七、拷贝私钥到PC端，使用软件导入秘钥，然后测试登录

这里需要 使用 使用PuTTYgen 把下载下来的key 转换ppk扩展的SSH 密钥

八、秘钥测试登录成功之后，可以禁用使用密码登录，提高服务器的安全性

[root@ecs-326c-0001 .ssh]# vim /etc/ssh/sshd_config

修改为no

PasswordAuthentication no