我的linux学习之入坟到入门（二十）-服务管理之openssh

用户可通过使用公钥身份验证进行ssh登录身份验证。ssh允许用户使用私钥-公钥方案进行身份验证。这意味着将生成私钥和公钥这两个密钥。私钥文件用作身份验证凭据，像密码一样，必须妥善保管。公钥复制到用户希望登录的系统，用于验证私钥。公钥并不需要保密。拥有公钥的ssh服务器可以发布仅持有您私钥的系统才可解答的问题。因此，可以根据所持有的密钥进行验证。如此一来，就不必在每次访问系统时键入密码，但安全性仍能得到保证。

使用ssh-keygen命令生成密码。将会生成私钥~/.ssh/id_rsa和公钥~/.ssh/id_rsa.pub。

注意：

生成密钥时，系统将提供指定密码的选项，在访问私钥时必须提供该密码。如果私钥被偷，除颁发者之外的其他任何人很难使用该私钥，因为已使用密码对其进行保护。这样，在攻击者破解并使用私钥前，会有足够的时间生成新的密钥对并删除所有涉及旧密钥的内容。

生成ssh密钥后，密钥将默认存储在家目录下的.ssh/目录中。私钥和公钥的权限就分别为600和644。.ssh目录权限必须是700。

在可以使用基于密钥的身份验证前，需要将公钥复制到目标系统上。可以使用ssh-copy-id完成这一操作

[root@localhost ~]# ssh-copy-id remoteuser@remotehost

通过ssh-copy-id将密钥复制到另一系统时，它默认复制~/.ssh/id_rsa.pub文件

//SSH密钥演示
//使用 ssh-keygen 创建公钥-私钥对
[root@localhost ~]# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:8VyY3c3UEQvk1Pn95tYIF7sx9enlwG78hDjlX0entN0 root@localhost.localdomain
The key's randomart image is:
+---[RSA 2048]----+
|            .+.o*|
|           +o..*o|
|        . o o...=|
|         + .  . +|
|        S o  .o+*|
|            .=BBB|
|            o=*XE|
|             .*+B|
|             . oo|
+----[SHA256]-----+

//使用 ssh-copy-id 将公钥复制到远程系统上的正确位置
[root@localhost ~]# ls .ssh/
id_rsa  id_rsa.pub
[root@localhost ~]# ssh-copy-id -i ~/.ssh/id_rsa.pub root@172.16.12.138
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
The authenticity of host '172.16.12.138 (172.16.12.138)' can't be established.
ECDSA key fingerprint is SHA256:JK5WwrX8hynl3dyWO43e6+lcs6zn9oZn74z1H5X8F90.
ECDSA key fingerprint is MD5:01:4f:4f:4b:0e:45:a9:10:bb:d0:c0:dd:19:9a:9f:96.
Are you sure you want to continue connecting (yes/no)? yes
/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@172.16.12.138's password:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'root@172.16.12.138'"
and check to make sure that only the key(s) you wanted were added.

//使用 ssh 命令无命令登录远程主机
[root@localhost ~]# ssh root@172.16.12.138
Last login: Tue Jul 10 18:37:51 2018 from 172.16.12.1
[root@localhost ~]# ip a s ens33
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 00:0c:29:f4:5b:87 brd ff:ff:ff:ff:ff:ff
    inet 172.16.12.138/24 brd 172.16.12.255 scope global dynamic ens33
       valid_lft 1377sec preferred_lft 1377sec
    inet6 fe80::20c:29ff:fef4:5b87/64 scope link
       valid_lft forever preferred_lft forever
       
       
//使用 scp 命令传送文件到远程主机
[root@localhost ~]# scp test.sh root@172.16.12.138:/tmp
root@172.16.12.138's password:
test.sh                                                       100%   45    29.8KB/s   00:00

//使用 scp 命令从远程主机上下载文件到本地
[root@localhost ~]# ls
a  anaconda-ks.cfg  b  nginx-1.12.2  nginx-1.12.2.tar.gz  nohup.out  outfile  test.sh
[root@localhost ~]# rm -f test.sh
[root@localhost ~]# ls
a  anaconda-ks.cfg  b  nginx-1.12.2  nginx-1.12.2.tar.gz  nohup.out  outfile
[root@localhost ~]# scp root@172.16.12.138:/tmp/test.sh .
root@172.16.12.138's password:
test.sh                                                       100%   45    39.1KB/s   00:00
[root@localhost ~]# ls
a  anaconda-ks.cfg  b  nginx-1.12.2  nginx-1.12.2.tar.gz  nohup.out  outfile  test.sh

//scp命令常用选项
    -r      //递归复制
    -p      //保持权限
    -P      //端口
    -q      //静默模式
    -a      //全部复制