我在我的mac上安装了composer来安装我需要的一些项目库。特别是tcpdf生成pdfs。每次我在终端跑：
作曲家需要tecnickcom / tcpdf，
我得到以下输出：
[Composer\Downloader\TransportException]
The "https://packagist.org/packages.json" file could not be downloaded: Failed to enable crypto
failed to open stream: operation failed
require [--dev] [--prefer-source] [--prefer-dist] [--no-progress] [--no-update] [--no-scripts] [--update-no-dev] [--update-with-dependencies] [--ignore-platform-reqs] [--prefer-stable] [--prefer-lowest] [--sort-packages] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--] [<packages>]...
有谁知道这个错误是什么意思？ 谢谢。