Voice inversion
Encyclopedia
Voice Inversion scrambling
is an analog method of obscuring the content of a transmission. It sometimes used in public service radio, automobile racing, cordless telephones and the Family Radio Service
. Without a descrambler, the transmission makes the speaker sound like "Donald Duck
". It is called "voice inversion", but the technique operates on the passband of the information and so can be applied to any information being transmitted.
There are various forms of voice inversion which offer differing levels of security. Overall, voice inversion scrambling offers little true security as software and even hobbyist kits are available from kit makers for scrambling and descrambling. The cadence of the speech is not changed. It is often easy to guess what is happening in the conversation by listening for other audio cues like questions, short responses and other language cadences.
In the simplest form of voice inversion, the frequency
of each component is replaced with 
, where 
is the frequency of a carrier wave
. This can be done by modulating the speech signal with the carrier, then applying a low-pass filter
to select the lower sideband
. This will make the low tones of the voice sound like high ones and vice versa.
There are more advanced forms of voice inversion which are more complex and require more effort to descramble. One method is to use a random code to choose the carrier frequency and then change this code in real time. This is called Rolling Code voice inversion and one can often hear the "ticks" in the transmission which signal the changing of the inversion point.
Another method is Split Band Voice Inversion sometimes called VSB. This is where the band is split and then each band is inverted separately. A rolling code can also be added to this method for Split Band Variable Inversion.
Common carrier frequencies are: 2.868 kHz, 2.632 kHz, 2.718 kHz, 2.868 kHz, 3.023 kHz, 3.107 kHz, 3.196 kHz, 3.333 kHz, 3.339 kHz, 3.496 kHz, 3.729 kHz and 4.096 kHz.
Networks, 2001. Proceedings. Ninth IEEE International Conference on
Volume, Issue, 10-12 October 2001 Page(s): 140 - 145
Digital Object Identifier 10.1109/ICON.2001.962331
Summary: The scrambling scheme is a part of the conditional access system (CAS) that is used to prevent unauthorized access to Pay-TV systems. We propose a new scrambling scheme and key distribution scheme. The scrambling scheme is used in conjunction with ordinary encryption techniques, for protecting the digital video streams from unauthorized viewing. A hash function and a pseudo-random number generator are used to prepare the video stream before being encrypted. The proposed scheme helps reduce computational time and complexity while providing the same level of security as encrypting the entire video stream. In addition, the proposed secure key distribution scheme can be used with any, scrambling scheme e.g. with our scrambling scheme. By using the Chinese remainder theorem (CRT) for distributing parameters in the scrambling process, the security of the scheme can be increased. Moreover, our scheme can prevent two common problems, namely, smart card cloning and McCormac Hack.
Scrambler
In telecommunications, a scrambler is a device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device...
is an analog method of obscuring the content of a transmission. It sometimes used in public service radio, automobile racing, cordless telephones and the Family Radio Service
Family Radio Service
The Family Radio Service is an improved walkie talkie radio system authorized in the United States since 1996. This personal radio service uses channelized frequencies in the ultra high frequency band. It does not suffer the interference effects found on citizens' band at 27 MHz, or the...
. Without a descrambler, the transmission makes the speaker sound like "Donald Duck
Donald Duck
Donald Fauntleroy Duck is a cartoon character created in 1934 at Walt Disney Productions and licensed by The Walt Disney Company. Donald is an anthropomorphic white duck with a yellow-orange bill, legs, and feet. He typically wears a sailor suit with a cap and a black or red bow tie. Donald is most...
". It is called "voice inversion", but the technique operates on the passband of the information and so can be applied to any information being transmitted.
There are various forms of voice inversion which offer differing levels of security. Overall, voice inversion scrambling offers little true security as software and even hobbyist kits are available from kit makers for scrambling and descrambling. The cadence of the speech is not changed. It is often easy to guess what is happening in the conversation by listening for other audio cues like questions, short responses and other language cadences.
In the simplest form of voice inversion, the frequency
of each component is replaced with , where is the frequency of a carrier waveCarrier wave
In telecommunications, a carrier wave or carrier is a waveform that is modulated with an input signal for the purpose of conveying information. This carrier wave is usually a much higher frequency than the input signal...
. This can be done by modulating the speech signal with the carrier, then applying a low-pass filter
Low-pass filter
A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter...
to select the lower sideband
Sideband
In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, containing power as a result of the modulation process. The sidebands consist of all the Fourier components of the modulated signal except the carrier...
. This will make the low tones of the voice sound like high ones and vice versa.
There are more advanced forms of voice inversion which are more complex and require more effort to descramble. One method is to use a random code to choose the carrier frequency and then change this code in real time. This is called Rolling Code voice inversion and one can often hear the "ticks" in the transmission which signal the changing of the inversion point.
Another method is Split Band Voice Inversion sometimes called VSB. This is where the band is split and then each band is inverted separately. A rolling code can also be added to this method for Split Band Variable Inversion.
Common carrier frequencies are: 2.868 kHz, 2.632 kHz, 2.718 kHz, 2.868 kHz, 3.023 kHz, 3.107 kHz, 3.196 kHz, 3.333 kHz, 3.339 kHz, 3.496 kHz, 3.729 kHz and 4.096 kHz.
See also
- EncryptionEncryptionIn cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
- ScramblerScramblerIn telecommunications, a scrambler is a device that transposes or inverts signals or otherwise encodes a message at the transmitter to make the message unintelligible at a receiver not equipped with an appropriately set descrambling device...
- Secure CommunicationSecure communicationWhen two entities are communicating and do not want a third party to listen in, they need to communicate in a way not susceptible to eavesdropping or interception. This is known as communicating in a secure manner or secure communication...
- Scrambling and key distribution scheme for digital television - Secure voiceSecure voiceSecure voice is a term in cryptography for the encryption of voice communication over a range of communication types such as radio, telephone or IP.-History:...
General references
Kanjanarin, W.; Amornraksa, T.Networks, 2001. Proceedings. Ninth IEEE International Conference on
Volume, Issue, 10-12 October 2001 Page(s): 140 - 145
Digital Object Identifier 10.1109/ICON.2001.962331
Summary: The scrambling scheme is a part of the conditional access system (CAS) that is used to prevent unauthorized access to Pay-TV systems. We propose a new scrambling scheme and key distribution scheme. The scrambling scheme is used in conjunction with ordinary encryption techniques, for protecting the digital video streams from unauthorized viewing. A hash function and a pseudo-random number generator are used to prepare the video stream before being encrypted. The proposed scheme helps reduce computational time and complexity while providing the same level of security as encrypting the entire video stream. In addition, the proposed secure key distribution scheme can be used with any, scrambling scheme e.g. with our scrambling scheme. By using the Chinese remainder theorem (CRT) for distributing parameters in the scrambling process, the security of the scheme can be increased. Moreover, our scheme can prevent two common problems, namely, smart card cloning and McCormac Hack.