2015-02-14 - GPG error

Header Data

From: jb <be***s@yahoo.com>
Message Hash: 7efe09653fcfd0648b610225206d621a78b8606b688d02fc9f67dcbf22bd4247
Message ID: <379676669.1153046.1423898968875.JavaMail.yahoo@mail.yahoo.com>
Reply To: N/A
UTC Datetime: 2015-02-14 00:29:28 UTC
Raw Date: Sat, 14 Feb 2015 07:29:28 +0000

Raw message 

hi tim..
this error message appears everytime i do sudo apt-get update.using ubuntu 12.04 LTS...grase 3.7.7.6
W: GPG error: http://packages.grasehotspot.org purewhite Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 43157839C830ED66

what will i do so that my grase will be updated?
tyjb

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