Power analysis

Power analysis is a form of side channel attack in which the attacker studies the power consumption of a cryptographic hardware device. These attacks rely on basic physical properties of the device: semiconductor devices are governed by the laws of physics, which dictate that changes in voltages within the device require very small movements of electric charges (currents). By measuring those currents, it is possible to learn a small amount of information about the data being manipulated.

Simple power analysis (SPA) involves visually interpreting power traces, or graphs of electrical activity over time. Differential power analysis (DPA) is a more advanced form of power analysis, which can allow an attacker to compute the intermediate values within cryptographic computations through statistical analysis of data collected from multiple cryptographic operations. SPA and DPA were introduced to the open cryptography community in 1998 by Paul Kocher, Joshua Jaffe and Benjamin Jun.^{[better source needed]}

In cryptography, a side channel attack is used to extract secret data from some secure device (such as a smart card, tamper-resistant "black box", or integrated circuit). Side-channel analysis is typically trying to non-invasively extract cryptographic keys and other secret information from the device. A simple example of this is the German tank problem: the serial numbers of tanks provide details of the production data for tanks. In physical security, a non-invasive attack would be similar to lock-picking, where a successful attack leaves no trace of the attacker being present.

Simple power analysis (SPA) is a side-channel attack which involves visual examination of graphs of the current used by a device over time. Variations in power consumption occur as the device performs different operations. For example, different instructions performed by a microprocessor will have differing power consumption profiles.

Codeflow that depends on a secret value will thus leak the code-flow via the power consumption monitoring (and thus also leak the secret value). As a simple example, consider a password check as follows:

This password check potentially contains a Timing attack, since the execution time is not constant. Observing the power consumption will make clear the number of loops executed. However, there is a mitigation possible. The function may not output to the user an exploitable result if, for example, there is a compensating delay before the response is returned. Or the code is structured to complete all the loops irrespective of the character position mismatching between the input and the secret-password. We can see one such sample code in the algorithm section of Timing attack.

Similarly, squaring and multiplication operations in RSA implementations can often be distinguished, enabling an adversary to compute the secret key. Even if the magnitude of the variations in power consumption are small, standard digital oscilloscopes can easily show the data-induced variations. Frequency filters and averaging functions (such as those built into oscilloscopes) are often used to filter out high-frequency components.

Differential power analysis (DPA) is a side-channel attack which involves statistically analyzing power consumption measurements from a cryptosystem. The attack exploits biases varying power consumption of microprocessors or other hardware while performing operations using secret keys. DPA attacks have signal processing and error correction properties which can extract secrets from measurements which contain too much noise to be analyzed using simple power analysis. Using DPA, an adversary can obtain secret keys by analyzing power consumption measurements from multiple cryptographic operations performed by a vulnerable smart card or other device.