Three levels of Tempest standard NATO SDIP-27
Three different tempest standards can be defined. These are level A, B and C.
The tempest standard Level A is the strictest NATO-standard and is sometimes therefore referred to as ”Full”. Level A is applied to environments and devices where immediate eavesdropping can occur, from as close as the room next door (approximately 1 meters’ distance). This standard is thus for devices that are operated within the NATO Zone 0.
The tempest standard Level B is the next strictest NATO-standard, sometimes referred to as ”Immediate”. This standard is usually applied to devices where it is assumed that eavesdropping cannot occur from closer than a distance of 20 meters. This tempest standard is therefore for devices that are operated within the NATO Zone 1. This standard protects devices both from 20 meters’ free distance or through a comparable distance through building blocks and obstructions.
The tempest standard level C is sometimes referred to as ”Tactical”. This standard is applied to environments and devices within the NATO Zone 2 (where eavesdroppers are assumed to have a distance of at least 100 meters). This standard protects devices both from 100 meters’ free distance (or through a comparable distance through building blocks and obstructions).
Tempest levels complete standard list
Standard Full Intermediate Tactical
NATO Zones Zone 0 Zone 1 Zone 0
NATO SDIP-27 Level A Level B Level C
NATO AMSG AMSG 720B AMSG 788A AMSG 784
USA NSTISSAM Level I Level II Level III