Effect of quantization noise in statistical key exchange
Josan, Madhur Swapan Singh
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In the Key Agreement Protocol using Feedback, legitimate users try to establish a secret key jointly by sharing information in public. They use locally generated band-limited, random signals to obscure information sent by them. The adversary does not have access to the local random signals of legitimate users and only relies on the public signals to decipher the information. The adversary can plan all sorts of attacks on the protocol in transient as well as steady state. In this study, the exploitation of quantization noise in steady state has been addressed. The adversary can use quantization noise to her advantage in order to decipher the information. Quantization noise gets incorporated when legitimate users digitize their baseband signals. The quantization noise being discussed here is same as the quantization error. The legitimate users cannot use a causal filter as it introduces an extra delay. Extra delay can be easily exploited by the adversary to decode the information. Therefore, legitimate users must perform real-time filtering in order to eliminate quantization noise. The Savitzky-Golay polynomial filtering technique is considered. It is used to reduce the quantization noise. The noise does get reduced but it does not get completely removed. Even small amount of quantization noise can be used by the adversary to decipher the information. She can employ the exhaustive search method to find out the filters being used by legitimate users. Once the adversary finds the right filter, security can be breached.