环境：macOS Mojava version 10.14
在更新了Mac OS以后用ssh push 代码到服务器出现了下面这个错误。
ssh error: unable to negotiate with IP: no matching cipher found.Their offer: aes256-cbc,aes192-cbc,aes128-cbc...
Unable to negotiate with XX.X.X.XXX port XX: no matching cipher found. Their offer: aes256-cbc,aes192-cbc,aes128-cbc
fatal: Could not read from remote repository.
Please make sure you have the correct access rights
and the repository exists.
出现错误的原因是要连接的代码仓库服务端的ssh版本过低，客户端与服务端的 cipher 没有匹配上，我们需要在自己的客户端（升级OS后的Mac）重新启用老的 cipher ,这样就能重新建立起连接了。
具体步骤如下：
第一步：terminal 输入 sudo nano /etc/ssh/ssh_config
atcs-air:~ XXX$ sudo nano /etc/ssh/ssh_config
第二步：找到 Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc，删除这行前面的#号。
# Host *
# ForwardAgent no
# ForwardX11 no
# PasswordAuthentication yes
# HostbasedAuthentication no
# GSSAPIAuthentication no
# GSSAPIDelegateCredentials no
# BatchMode no
# CheckHostIP yes
# AddressFamily any
# ConnectTimeout 0
# StrictHostKeyChecking ask
# IdentityFile ~/.ssh/id_rsa
# IdentityFile ~/.ssh/id_dsa
# IdentityFile ~/.ssh/id_ecdsa
# IdentityFile ~/.ssh/id_ed25519
# Port 22
# Protocol 2
Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc
# MACs hmac-md5,hmac-sha1,umac-64@openssh.com
# EscapeChar ~
# Tunnel no
# TunnelDevice any:any
# PermitLocalCommand no
# VisualHostKey no
# ProxyCommand ssh -q -W %h:%p gateway.example.com
# RekeyLimit 1G 1h
Host *
SendEnv LANG LC_*
第三步：保存 ssh_config 这个文件，退出，然后就可以和以前一样通过ssh连接代码仓库服务器了。
https://discussions.apple.com/thread/8196671?answerId=32716986022#32716986022
