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Identity authentication based on Automatic Speaker Verification (ASV) has attracted extensive attention. Voice can be used as a substitute of password in many applications. However, the security of current ASV systems has been seriously challenged by many malicious spoofing attacks. Among all those attacks, replay attack is one of the biggest threats to the ASV System, where an adversary can use a pre-recorded speech sample of the legal user to access the ASV system. In this paper, we present a replay attack detection (RAD) scheme to distinguish normal speech and replayed speech. We focus on the distortion caused by loudspeaker: low-frequency attenuation and high-frequency harmonics, and present a suite of RAD features DL-RAD, including Harmonic Energy Ratio (HER), Low Spectral Ratio (LSR), Low Spectral Variance (LSV), and Low Spectral Difference Variance (LSDV), to describe the different characteristics between the normal speech signal and replay speech signal. SVM is adopted as a classifier to evaluate the performance of these features. Experiment results show that the True Positive Rate (TPR), True Negative Rate (TNR) of the proposed method are about 98.15% and 98.75% respectively, which are significantly better than the existing scheme. The proposed scheme can be applied to both text-dependent and text-independent ASV systems. [ABSTRACT FROM AUTHOR]

In this paper, a novel AMR adaptive steganographic scheme based on pitch delay of unvoiced speech (PDU-AAS) was proposed. The existing AMR steganographic schemes based on pitch delay destroy the short-time relative stability of pitch delay of voiced speech segments and they are easier to be detected by the existing steganographic schemes. Especially, the pitch delay distribution of AMR voiced and unvoiced speech segments are analyzed in detail, and based on this characteristic that the pitch delay sequence of AMR unvoiced speech do not have short-term relative stability, we proposed an AMR adaptive steganographic scheme which selects the embedded position adaptively in the unvoiced speech segment, which is determined by the distribution characteristic of the adjacent pitch delay, and embeds the secret message by modifying the pitch delay without destroying the short-time stability of the pitch delay. The experiment results shows that the scheme has good concealment and hiding capability. Most important of all, the comparing experiment results show that the scheme has good security to resist the detection of the existing steganalysis algorithms. The principle of the scheme can be applied to the other steganographic schemes based on the pitch delay of the speech codec, such as G723.1, G.729. [ABSTRACT FROM AUTHOR]