.. _mitigation_frequency_throttling_channel_attack:

Mitigation for Frequency Throttling Side-Channel Attack
=======================================================

More information about the attack can be found in 
`Intel Software Security Guidance <https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/best-practices/frequency-throttling-side-channel-guidance.html>`_ 
and in the published paper: Chen Liu, Abhishek Chakraborty, Nikhil Chawla, Neer Roggel. 2022. Frequency Throttling Side-Channel Attack. https://arxiv.org/pdf/2206.07012.pdf

Implemented in IPP Crypto mitigation was done for AES Encryption and Decryption in ECB (``ippsAESDecryptECB``, ``ippsAESEncryptECB``) and GCM (``ippsAES_GCMDecrypt``, ``ippsAES_GCMEncrypt``) modes and for AES CMAC (``ippsAES_CMACUpdate``) mode. 
Developed mitigation is based on random noise injections for every fixed amount of processing data. There are 3 new APIs that should be used to enable the mitigation for AES. 
The main difference between these APIs is that they work with different types of AES context - IppsAESSpec, IppsAES_GCMState, IppsAES_CMACState.

The general usage flow is ``GetSize -> Init -> SetupNoise -> Processing``. For example:

* **AES ECB mode**:

  * ippsAESGetSize()
  * ippsAESInit()
  * ippsAESSetupNoise()
  * ippsAESEncryptECB() / ippsAESDecryptECB()
  
* **AES GCM mode:**

  * ippsAES_GCMGetSize()
  * ippsAES_GCMInit()
  * ippsAES_GCMSetupNoise()
  
* **AES CMAC mode:**

  * ippsAES_CMACGetSize()
  * ippsAES_CMACInit()
  * ippsAES_CMACSetupNoise()

Mitigation can be enabled only explicitly by calling the corresponding ``SetupNoise`` function with a non-zero parameter ``noiseLevel`` (amount of noise injected). 
Accordingly, to disable mitigation in the flow, the ``SetupNoise`` function should be called with noiseLevel equal to 0. 

Calling ``ippsAESInit``, ``ippsAES_GCMInit``, ``ippsAES_CMACInit`` functions also reset mitigation parameters stored in the context, it also can be used to disable mitigation if it is enabled earlier.
Mitigation is available when AES-NI or VAES instructions present on the current CPU.


.. toctree::
   :maxdepth: 1

   ippsaessetupnoise
   ippsaes_gcmsetupnoise
   ippsaes_cmacsetupnoise