In order to decrypt encrypted video stream you need encryption key. This key is not part of the stream. It should be obtained separately.
EXT-X-FAXS-CM header contains DRM meta-data and not the key.
This is excert from Adobe Media Server developer guide: The Adobe Access Server protected variant playlist also needs to include the #EXT-X-FAXS-CM tag. The value of #EXT-X-FAXS-CM tag in variant playlist is the relative URI referring to the DRM metadata of one of the individual streams.At the client, the #EXT-X-FAXS-CM tag in variant playlist will be used to create the DRM session. The same DRM session will be used for all encrypted M3U8 files inside the variant playlist.
Full guide can be found here: http://help.adobe.com/en_US/adobemediaserver/devguide/WS5262178513756206-4b6aabd1378392bb59-7fe8.html
There is also mention that faxs://faxs.adobe.com URI is for local key serving. So key obtained locally from a device.