一、SSH key简介

SSH key即SSH公钥，因为许多Git服务器都是支持使用SSH协议来访问，因此要通过SSH 协议来访问Git仓库需要向 Git 服务器提供 SSH 公钥

如果Git仓库未添加本地生成的SSH Key就会导致clone失败

$ git clone <git远程仓库地址>
Cloning into '项目名称'...
GitLab: The project you were looking for could not be found.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

二、生成SSH key的步骤

查看是否已经生成SSH Key
生成新的SSH Key
复制SSH Key添加到Git服务器

查看是否已经生成SSH Key

$ ls -al ~/.ssh
total 24
drwx------   5 <用户名>  staff   160 11  1  2018 .
drwxr-xr-x  54 <用户名>  staff  1728 12  6 13:36 ..
-rw-------   1 <用户名>  staff  1679 10 29  2018 id_rsa
-rw-r--r--@  1 <用户名>  staff   397 10 29  2018 id_rsa.pub
-rw-r--r--   1 <用户名>  staff   357  5 27  2019 known_hosts

查看SSH Key

$ cat /Users/<用户名>/.ssh/id_rsa.pub
ssh-rsa XXXXXXXXXXXX  <邮箱地址>

生成新的SSH Key

$ ssh-keygen -t rsa -C "<邮箱地址>"
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/<用户名>/.ssh/id_rsa):
/Users/<用户名>/.ssh/id_rsa already exists.
Overwrite (y/n)? y
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /Users/<用户名>/.ssh/id_rsa.
Your public key has been saved in /Users/<用户名>/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:XXXXXXXXXXXXXXX <邮箱地址>
The key's randomart image is:
+---[XXX XXX]----+
|      ..+*XxX .. |
|       .XX^ +..o|
|        ..% * oo+|
|       . + + +..=|
|        S * E. oo|
|         +    + .|
|          .  . . |
|                 |
|                 |
+----[XXXXXX]-----+

复制SSH Key添加到Git服务器

$ pbcopy < ~/.ssh/id_rsa.pub

到Git服务器添加SSH Key，重新clone项目成功

$ git clone  <git远程仓库地址>
Cloning into 'XXXXX'...
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Receiving objects: 100% (3/3), done.

注意：
如果提示： Are you sure you want to continue connecting (yes/no)?
直接输入yes回车

$ ssh -T git@e.coding.net
The authenticity of host 'e.coding.net (111.123.70.251)' can't be established.
RSA key fingerprint is SHA156:jok3FH7q5LJ6qxX7iPNehBgXXXXw001ErE77S0Dn+Vg/Ik.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'e.coding.net,111.123.70.251' (RSA) to the list of known hosts.
Coding 提示: Hello 黄小明, You've connected to Coding.net via SSH. This is a personal key.
黄小明，你好，你已经通过 SSH 协议认证 Coding.net 服务，这是一个个人公钥

参考文章：
git 如何解决The authenticity of host 'git.coding.net (123.59.86.7)' can't be established问题