Differential Power Analysis
Differential Power Analysis takes multiple traces of two sets of data, and then computes the difference of the average of these traces.
If the difference is close to zero, then the two sets are not correlated, and if the power-value (typically ≥ 0.05) is higher, correlation can be assumed to be possible. By leveraging faster hardware and common sense, the difficult-to-solve 128-bit AES key can be broken into 16 bytes, where each byte can be solved individually.
Testing each byte requires only 28, or 256 attempts, which means it would only take 16 x 256 or 4,096 attempts to be able to decipher the entire encryption key. This is another attack that was once the preserve of state-backed intelligence operations.
Like other side channel attacks, these range from the relatively simple (eavesdropping on a monitor via reflections) through to complex (communicating with an infected device via LED blinks). In a more hi-tech optical attack, lasers can be used to both read key strokes and inject faults that are later read to deduce the cryptographic key being sought.
Side Channel Attacks in General
Many of these attacks can be used to leverage other attacks, thus gaining more information about the target. If you are working in a high security environment, you will already know many of the ways to mitigate against these types of attacks. This is way many secure facility employ TEMPEST surveys. Regardless if you are working in a secure facility or not, there is chance someone is after your data and you need to look into ways to protect yourself.
The only way to fully protect against side channel attacks is to use your digital devices in a room buried deep underground, accessed by a long tunnel with shielded doors, lined with a Faraday cage, and running off of your own portable power supply. Luckily, very few people are in a position where the data they are working with is quite this sensitive. We are far more likely to fall victim to the “soft” end of side-channel access — BLE beacon powered advertising and the like, so rest easy.
Edited by Mario Vulcano