Linux免密登录的原理

本文主要记录linux免密登录的原理

前提

1. 有两台机器A和B
2. A需要免密登录机器B（反之则按照下面步骤从B操作到A）

实现原理

1. 在机器A上生成一对公私钥
2. A将公钥拷贝给B，在B中重命名为authorized_keys（放在当前用户目录下的.ssh目录下）
3. A向B发送一个登录链接请求
4. B得到A的登录请求信息后，在authorized_keys中查找，如果有相应的用户名和IP，则随机生成一个字符串string_text，并且使用A的公钥加密，随后发送给A
5. A接收到B发送过来的消息后，使用自己的私钥解密，然后将解密后的字符串发送给B
6. B接收到A解密后的字符串，检查是否与string_text一致，如果一致则允许免密登录

操作步骤

1. 在A机器上生成一对公私钥

dandeliondeMacBook-Pro:~ dandelion$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/dandelion/.ssh/id_rsa):
Created directory '/Users/dandelion/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /Users/dandelion/.ssh/id_rsa.
Your public key has been saved in /Users/dandelion/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:WOCu7RVGa82QBXWxg44lj6ERZZmjHM9yqcG1klCFCDU [email protected]
The key's randomart image is:
+---[RSA 2048]----+
|  .oEo++==o o.   |
|    ooo+=o o .   |
|     +oBB+o o    |
|     .O**&   .   |
|      +*S =      |
|     o.o .       |
|    . . .        |
|     . .         |
|      .          |
+----[SHA256]-----+
dandeliondeMacBook-Pro:~ dandelion$
dandeliondeMacBook-Pro:.ssh dandelion$ pwd
/Users/dandelion/.ssh
dandeliondeMacBook-Pro:.ssh dandelion$ ls
id_rsa      id_rsa.pub
dandeliondeMacBook-Pro:.ssh dandelion$

2. 将公钥拷贝到B机器
   方式一：

dandeliondeMacBook-Pro:.ssh dandelion$ ssh-copy-id -i id_rsa.pub [email protected]
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "id_rsa.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
[email protected]'s password:

Number of key(s) added:        1

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

dandeliondeMacBook-Pro:.ssh dandelion$

方式二：

1.拷贝A机器的公钥id_rsa.pub到B机器: scp id_rsa.pub [email protected]:/home
2.将A的公钥加到B的授权列表 .ssh/authorized_keys 若不存在，手动创建: cat /home/id_rsa.pub >> ../.ssh/authorized_keys
3..ssh目录的权限必须是700 ，chmod 700 .ssh
4.授权列表authorized_keys的权限必须是600，chmod 600 authorized_keys

3. 免密登录成功

dandeliondeMacBook-Pro:.ssh dandelion$ ssh [email protected]
Last login: Sat Mar 21 20:37:52 2020 from 192.168.3.26
[root@localhost ~]#

参考网站

Linux机器之间免密登录设置