Complex sentence: As further explained below, this is the "GSM Active Key Extraction" method noted in the DEA's Harris Sole Source Notification, which is used to facilitate passive interception of GSM communications content.
Split into simpler sentences: As further explained below, this is the "GSM Active Key Extraction" method noted in the DEA's Harris Sole Source Notification. Once the encryption key is obtained, it is used to facilitate passive interception of GSM communications content.