[!] Failed to connect to GitHub

昨天在执行pod update的时候提示如下错误

$ pod update BaiduMap-iOS-SDK
Updating local specs repositories
[!] Failed to connect to GitHub to update the CocoaPods/Specs specs repo - Please check if you are offline, or that GitHub is down

这是因为gitHub对验证权限做了调整引起的，移除了一些低加密标准协议，相关内容如下：

Weak cryptographic standards removed

February 23, 2018
Earlier today we permanently removed support for the following weak cryptographic standards on github.com and api.github.com:

• TLSv1/TLSv1.1: This applies to all HTTPS connections, including web, API, and Git connections to https://github.com and https://api.github.com.
• diffie-hellman-group1-sha1: This applies to all SSH connections to github.com
• diffie-hellman-group14-sha1: This applies to all SSH connections to github.com

This change was originally announced last year, with the final timeline for the removal posted three weeks ago. If you run into any issues or have any questions, please don’t hesitate to let us know.

解决这个问题需要更新opensll、ruby、cocoapod。

stackoverflow上提供了解决方案

$ which openssl
/usr/bin/openssl

$ openssl version
OpenSSL 0.9.8zh 14 Jan 2016

$ /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

$ brew update

$ brew install openssl

$ brew upgrade openssl

`` If you need to have this software first in your PATH run: echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.bash_profile

$ echo 'export PATH="/usr/local/opt/openssl/bin:$PATH"' >> ~/.bash_profile
$ source ~/.bash_profile

$ which openssl
/usr/local/opt/openssl/bin/openssl

$ openssl version
OpenSSL 1.0.2n  7 Dec 2017

$ brew install rbenv ruby-build

$ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile
$ echo 'if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi' >> ~/.bash_profile
$ source ~/.bash_profile

$ rbenv install --list

Available versions:
  1.8.5-p52
  1.8.5-p113
  1.8.5-p114
  1.8.5-p115
  1.8.5-p231
  1.8.6
:
  2.1.0
  2.1.1
  2.1.2
:

$ rbenv install 2.5.0

$ rbenv versions
* system (set by /Users/username/.rbenv/version)
  2.5.0

$ ruby --version
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]

$ rbenv global 2.5.0

$ rbenv versions
  system
* 2.5.0 (set by /Users/username/.rbenv/version)

$ ruby --version
ruby 2.0.0p648 (2015-12-16 revision 53162) [universal.x86_64-darwin16]

$ gem install cocoapods -n /usr/local/bin

$ which pod
/usr/local/bin/pod

$ pod --version
1.4.0

cocoapod升级到1.4.0，然后就可以自行pod update了