Magento: Unknown cipher in list: TLSv1 to install new extensions

 

downloader/lib/Mage/HTTP/Client/Curl.php, try changing:

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

to

$this->curlOption(CURLOPT_SSLVERSION, CURL_SSLVERSION_TLSv1);