Detection of replay attack
In order to detect a replay attack on a voice biometrics system, a speech signal is received at at least a first microphone and a second microphone. The speech signal has components at first and second frequencies. The method of detection comprises: obtaining information about a position of a source of the first frequency component of the speech signal, relative to the first and second microphones; obtaining information about a position of a source of the second frequency component of the speech signal, relative to the first and second microphones; comparing the position of the source of the first frequency component and the position of the source of the second frequency component; and determining that the speech signal may result from a replay attack if the position of the source of the first frequency component differs from the position of the source of the second frequency component by more than a threshold amount.
1. A method of detecting a replay attack on a voice biometrics system, the method comprising:
receiving a speech signal at at least a first microphone and a second microphone, wherein the speech signal has components at first and second frequencies;
obtaining information about a position of a source of the first frequency component of the speech signal, relative to the first and second microphones;
obtaining information about a position of a source of the second frequency component of the speech signal, relative to the first and second microphones;
comparing the position of the source of the first frequency component and the position of the source of the second frequency component; and
determining that the speech signal results from a replay attack if the position of the source of the first frequency component differs from the position of the source of the second frequency component by more than a threshold amount.
2. A method according to claim 1 , wherein obtaining information about the position of the source of the first frequency component of the speech signal, relative to the first and second microphones, comprises:
filtering the received speech signal to obtain the first frequency component; and
determining an angle of arrival of the first frequency component at the first and second microphones,
and wherein obtaining information about the position of the source of the second frequency component of the speech signal, relative to the first and second microphones, comprises:
filtering the received speech signal to obtain the second frequency component; and
determining an angle of arrival of the second frequency component at the first and second microphones.
3. A method according to claim 2 , wherein determining the angle of arrival of each frequency component at the first and second microphones comprises:
calculating a cross-correlation between the respective component of the speech signal received at the first microphone and said respective component of the speech signal received at the second microphone; and
obtaining information about the angle of arrival from a location of a peak in the calculated cross-correlation.
4. A method according to claim 1 , wherein obtaining information about the position of the source of the first frequency component of the speech signal, relative to the first and second microphones, comprises:
filtering the received speech signal to obtain the first frequency component; and
determining a time difference between arrival of the first frequency component at the first and second microphones,
and wherein obtaining information about the position of the source of the second frequency component of the speech signal, relative to the first and second microphones, comprises:
filtering the received speech signal to obtain the second frequency component; and
determining a time difference between arrival of the second frequency component at the first and second microphones.
5. A method according to claim 1 , wherein the first frequency component comprises frequencies in the range of below 1 kHz.
6. A method according to claim 5 , wherein the first frequency component comprises frequencies in the range of 100 Hz-1 kHz.
7. A method according to claim 1 , wherein the second frequency component comprises frequencies in the range of above 1 kHz.
8. A method according to claim 7 , wherein the second frequency component comprises frequencies in the range of 2 kHz-15 kHz.
9. A method according to claim 1 , comprising:
obtaining information about respective positions of sources of more than two frequency components of the speech signal, relative to the first and second microphones;
comparing the positions of the source of the frequency components; and
determining that the speech signal may result from a replay attack if the position of the source of one frequency component differs from the position of the source of at least one other frequency component by more than a threshold amount.
10. A method according to claim 1 , further comprising:
after comparing the position of the source of the first frequency component and the position of the source of the second frequency component, if the result of the comparing is indeterminate:
receiving the speech signal at a third microphone;
obtaining additional information about the position of the source of the first frequency component of the speech signal, relative to the first, second and third microphones;
obtaining additional information about the position of the source of the second frequency component of the speech signal, relative to the first, second and third microphones; and
comparing the position of the source of the first frequency component and the position of the source of the second frequency component based on said additional information.
11. A system for detecting a replay attack in a speaker recognition system, the system comprising an input for receiving a speech signal from at least a first microphone and a second microphone, and comprising a processor, and being configured for:
receiving a speech signal at at least a first microphone and a second microphone, wherein the speech signal has components at first and second frequencies;
obtaining information about a position of a source of the first frequency component of the speech signal, relative to the first and second microphones;
obtaining information about a position of a source of the second frequency component of the speech signal, relative to the first and second microphones;
comparing the position of the source of the first frequency component and the position of the source of the second frequency component; and
determining that the speech signal results from a replay attack if the position of the source of the first frequency component differs from the position of the source of the second frequency component by more than a threshold amount.
12. 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 .