TEMPEST and Side-Channel Attacks

Secrets can leak not through the data itself but through physical byproducts of computation: emissions, timing, power, and sound.

Leaking Without Sending

A side-channel attack extracts secrets not by breaking the algorithm but by observing the physical side effects of its execution. A device performing cryptography emits electromagnetic radiation, draws power in patterns, takes measurably different times for different inputs, and even makes faint sounds. Each of these can carry information about the secret being processed, letting a patient attacker reconstruct a key that the math itself protects perfectly.

Classes of Side Channel

Kronos motion — power balance

Timing: operations that take longer for some key bits than others
Power analysis: power draw correlated with the data being processed
Electromagnetic: emissions from circuits revealing internal activity
Acoustic: sounds from components that vary with computation
Cache and micro-architectural: shared CPU state leaking across processes

TEMPEST

TEMPEST refers to the study and control of compromising emanations, the electromagnetic and other signals that leak from equipment and could let an eavesdropper reconstruct displayed or processed data from a distance. Countermeasures include shielding enclosures, filtered power, physical separation, and equipment engineered to minimize emissions.

Defending Against Side Channels

Defenses aim to break the correlation between the secret and the observable. Constant-time algorithms remove timing differences. Masking and blinding randomize intermediate values so power and emissions carry no usable signal. Physical shielding and distance reduce what an attacker can measure at all.

Fusion Context

For a fusion program, the practical relevance is that the physical security of compute is not only about preventing access but also about limiting what can be observed. Where highly sensitive cryptographic operations occur, hardware security modules with side-channel resistance and controlled, shielded environments reduce leakage, complementing the logical controls that protect the Hyperion breeder and burner systems.