This error is caused by a bug in certain configurations and version of your Magento setup.
At this point, you can either install the extension manually following our manual installation steps here
Or if you are technical or would have a developer that you use to maintain your store, take a at the following information on fixing the error:
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http://magento.stackexchange.com/questions/73748/magento-1-9-2-unknown-cipher-in-list-tlsv1
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http://magento.stackexchange.com/questions/73861/solution-to-magento-downloader-1-9-2-unknown-cipher-list
If you're unsure or need further help or explanation, just let us know