Masking
Splitting every secret intermediate value into random shares, so that a power measurement of a single step reveals nothing useful.
In masking, each secret value is split into two or more shares, and each share looks random on its own. The cipher computes on the shares and recombines them only at the end, so a power measurement of any single step sees noise. The technique was popularised in the late 1990s as a countermeasure against differential power analysis and is now standard in smart cards and cryptographic hardware.
Masking is not free. Every masked operation costs performance and extra logic, and non-linear steps such as the S-box are the hard part. A masked implementation that recombines its shares in the wrong place leaks as much as an unmasked one, which is why masking is done with care and reviewed closely rather than simply switched on.