Detection of liveness
Detecting liveness of a speaker comprises: generating an ultrasound signal; receiving an audio signal comprising a reflection of the ultrasound signal; using the received audio signal comprising the reflection of the ultrasound signal to detect the liveness of a speaker; monitoring ambient ultrasound noise; and adjusting the operation of a system receiving the audio signal, based on a level of the reflected ultrasound and the monitored ambient ultrasound noise. The method can be used in a voice biometrics system, in which case detecting the liveness of a speaker comprises determining whether a received speech signal may be a product of a replay attack. The operation of the voice biometrics system may be adjusted based on a level of the reflected ultrasound and the monitored ambient ultrasound noise.
1. A method, for use in a voice biometrics system, for detecting the liveness of a speaker and determining whether a received speech signal may be a product of a replay attack, the method comprising:
generating an ultrasound signal;
receiving an audio signal comprising a reflection of the ultrasound signal;
using the received audio signal comprising the reflection of the ultrasound signal to detect the liveness of a speaker by:
detecting Doppler shifts in the reflection of the generated ultrasound signal;
determining a correlation between the detected Doppler shifts and the received speech signal;
determining whether the correlation exceeds a threshold correlation value; and
identifying whether the received speech signal may be the result of a replay attack on the voice biometrics system based on the threshold correlation value;
monitoring ambient ultrasound noise; and
adjusting the operation of the voice biometrics system, based on a level of the reflected ultrasound and the monitored ambient ultrasound noise;
wherein the threshold correlation value is adapted based on the monitored ambient ultrasound noise.
2. A method according to claim 1 , further comprising:
determining a reliance to be placed on the identification whether the received speech signal may be the result of a replay attack, based on the level of the monitored ambient ultrasound noise.
3. A method according to claim 2 , wherein determining the reliance to be placed on the identification comprises not performing the identification if the level of the monitored ambient ultrasound noise exceeds a first threshold level.
4. A system for liveness detection in a voice biometrics system, the system comprising:
at least one microphone input, for receiving an audio signal from a microphone; and
at least one transducer output, for transmitting a signal to an ultrasound transducer, and the system being configured for:
generating an ultrasound signal;
receiving an audio signal comprising a reflection of the ultrasound signal;
using the received audio signal comprising the reflection of the ultrasound signal to detect the liveness of a speaker by:
detecting Doppler shifts in the reflection of the generated ultrasound signal;
determining a correlation between the detected Doppler shifts and the received speech signal;
determining whether the correlation exceeds a threshold correlation value; and
identifying whether the received speech signal may be the result of a replay attack on the voice biometrics system based on the threshold correlation value;
monitoring ambient ultrasound noise; and
adjusting the operation of the voice biometrics system, based on a level of the reflected ultrasound and the monitored ambient ultrasound noise;
wherein the threshold correlation value is adapted based on the monitored ambient ultrasound noise.
5. A non-transitory computer readable storage medium having computer-executable instructions stored thereon that, when executed by processor circuitry, cause the processor circuitry to perform a method according to claim 1 .