If you are getting the error “Unknown cipher in list: TLSv1” while installing Magento or updating it, chances are it’s because you are hosting on a Centos box and well, Centos is always a pain. To fix it:

Edit downloader/lib/Mage/HTTP/Client/Curl.php, and:

change

$this->curlOption(CURLOPT_SSL_CIPHER_LIST, 'TLSv1');

to

$this->curlOption(CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1);