Attacks by auxiliary channel

The attacks by auxiliary channels belong to a vast family of cryptanalytic techniques which exploit unexpected properties of an algorithm of Cryptographie during its software or material implementation. Indeed, a “mathematical” safety inevitably does not guarantee a safety during the use in “practice”. In this field, the attacks are numerous and relate to various parameters, and one distinguishes two main categories from them:

  1. the invasive attacks which damage the material (even destroy it completely):

  2. * Attack by survey: it consists in placing a probe directly in the circuit to be studied, in order to observe its behavior (generally used in the case of drunk quantified);
  3. *…
  4. the not-invasive attacks which are satisfied to make an observation external of the system:
  5. * temporal Attack: study of time put to carry out certain operations;
  6. * acoustic Cryptanalyse: study of the noise generated by a computer or a machine which quantifies. Indeed, the processor emits noise which varies in intensity and in kind according to its consumption and the operations carried out;
  7. * Analysis of electromagnetic emanations: similar to the acoustic cryptanalyse but by using the electromagnetic radiation (emission of waves, analyzes of a thermal image, light emitted by a screen, etc);
  8. * analyzes consumption: an increased consumption indicates an important calculation and can give information on the key;
  9. * Attack by fault: voluntary introduction of errors into the system to cause certain revealing behaviors. Let us note that this type of attack can be regarded as invasive in certain cases (a laser can damage the material, etc);
  10. *…

These attacks can be combined to obtain secret information like the key of coding. Their implementation is closely related on the hardware or the attacked software.

Examples of attacks

An attack based over the response times was conducted by Serge Vaudenay on TLS/SSL, which forced the originators of the standard to make a critical update. Adi Shamir showed the effectiveness in practice acoustic cryptanalyse noise of a processor. A temporal attack on the mask of a processor was shown for an implementation of AES.

Solutions

The manufacturers of chips of coding aim at levelling the curve of electricity consumption to dissimulate the subjacent operations. Protections and shieldings make it possible to limit the radiation apart from the circuit. It is necessary also to take account of the impossible states which should not occur and must be treated correctly if they had suddenly been detected. To limit the error messages and the communication of various information with outside is also a solution but it penalizes the developers and the users of the system.

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