The Galileo satellites metadata are information about the satellite properties which need to be known in order to properly implement advanced processing algorithms for precise orbit determination or Precise Point Positioning (PPP). These include physical characteristics such as mass, area or reflectivity, the attitude law and antenna parameters such as phase center offsets and variations. More information about PPP and GNSS data processing can be found in [3], [4] or [2]. For Galileo SIS details, please refer to [1].

[1] European GNSS (Galileo) Open Service Signal In Space Interface Control Document. European Union, 2016.
[2] B. Hofmann-Wellenhof. Global Positioning System Theory and Practice. Springer, 2001.
[3] J.M. Juan Zornoza J. Sanz Subirana, M. Hernández-Pajares. GNSS DATA PROCESSING. European Space Agency, 2013.
[4] A. Leick. GPS Satellite Surveying. Wiley-Interscience, 1994.

AONT = All Or Nothing Transforms = a secure way to transmit a document to a recipient in such a way that the recipient either gets the entire unmolested document in originally submitted form, or nothing at all. This idea goes back to Ronald Rivest of MIT. Very clever idea. It is crypto without being crypto in a legal sense.
See also https://github.com/dbmcclain/Math, https://github.com/dbmcclain/LispPlotter, https://github.com/dbmcclain/EBU-R128 and probably more.