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Side-channel attack

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Side-channel attack

In computer security, a side-channel attack is a type of security exploit that leverages information inadvertently leaked by a system—such as timing, power consumption, or electromagnetic or acoustic emissions—to gain unauthorized access to sensitive information. These attacks differ from those targeting flaws in the design of cryptographic protocols or algorithms (notwithstanding the fact that cryptanalysis may identify vulnerabilities relevant to both types of attacks).

Some side-channel attacks require technical knowledge of the internal operation of the system, others such as differential power analysis are effective as black-box attacks. The rise of Web 2.0 applications and software-as-a-service has also significantly raised the possibility of side-channel attacks on the web, even when transmissions between a web browser and server are encrypted (e.g. through HTTPS or WiFi encryption), according to researchers from Microsoft Research and Indiana University.

Attempts to break a cryptosystem by deceiving or coercing people with legitimate access are not typically considered side-channel attacks: see social engineering and rubber-hose cryptanalysis.

General classes of side-channel attack include:

In all cases, the underlying principle is that physical effects caused by the operation of a cryptosystem (on the side) can provide useful extra information about secrets in the system, for example, the cryptographic key, partial state information, full or partial plaintexts and so forth. The term cryptophthora (secret degradation) is sometimes used to express the degradation of secret key material resulting from side-channel leakage.

A cache side-channel attack works by monitoring security critical operations such as AES T-table entry or modular exponentiation or multiplication or memory accesses. The attacker then is able to recover the secret key depending on the accesses made (or not made) by the victim, deducing the encryption key. Also, unlike some of the other side-channel attacks, this method does not create a fault in the ongoing cryptographic operation and is invisible to the victim.

In 2017, two CPU vulnerabilities (dubbed Meltdown and Spectre) were discovered, which can use a cache-based side channel to allow an attacker to leak memory contents of other processes and the operating system itself.

Timing attacks monitor data movement into and out of the CPU or memory on the hardware running the cryptosystem or algorithm. Simply by observing variations in how long it takes to perform cryptographic operations, it might be possible to determine the entire secret key. Such attacks involve statistical analysis of timing measurements and have even been demonstrated across networks.

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