Method for detecting text information leakage in electromagnetic radiation from a computer display

Considering that the text information might be leaked through electromagnetic radiation from a computer display, a novel algorithm has been developed to detect the text information leakage. Motivated by the observation that the ‘text - space – text’ characteristic for electromagnetic radiation signal contains the text information, the authors proposed a method to describe this characteristic. In this method, sparse decomposition in wavelet was used and sub-band sparsity was defined. Variance mean ratio and correlation coefficients of sub-band sparsity were combined as the features of electromagnetic radiation signals. By using this method, the authors can accurately and efficiently detect the text information leakage in electromagnetic radiation from a computer display without reconstructing the displayed image.