it seems that the problem is wget, add --no-check-certificate
to your wget, and everything is ok.
# wget --no-check-certificate -O- https://download.newrelic.com/548C16BF.gpg | apt-key add -
--2014-01-12 09:29:30-- https://download.newrelic.com/548C16BF.gpg
Resolving download.newrelic.com (download.newrelic.com)... 50.31.164.159
Connecting to download.newrelic.com (download.newrelic.com)|50.31.164.159|:443... connected.
WARNING: cannot verify download.newrelic.com's certificate, issued by `/C=US/O=GeoTrust, Inc./CN=GeoTrust SSL CA':
Unable to locally verify the issuer's authority.
HTTP request sent, awaiting response... 200 OK
Length: 1682 (1.6K) [application/octet-stream]
Saving to: `STDOUT'
100%[=================================================================================================================================================>] 1,682 --.-K/s in 0s
2014-01-12 09:29:31 (15.1 MB/s) - written to stdout [1682/1682]
OK