Talking about the Voice Privacy Technology of Wireless Interphone
Most of the walkie-talkies now have private functions such as CTCSS and DTCSS. Generally speaking, when these private functions are set on the walkie-talkie, it is impossible to hear the contents of the call without knowing the private line code used, but this is not true voice privacy. Because its security function is very limited, it is only useful for unintentional eavesdroppers, but not for intentional eavesdroppers. For users who need confidentiality requirements, they cannot rely on the "private" line for confidentiality.
Voice privacy is the disguise of the call information, so that unauthorized people can not understand the contents of the call. The masqueraded speech is called clear speech, the masquerading process for speech information is called speech encryption, and the encrypted speech information is called secret speech. The set of rule programs used by the cipher is called encryption algorithm. Usually the algorithm is in a group. Under key control. The recipient uses the key to encrypt the opposite algorithm to restore the secret message to an understandable plain voice. This process is called decryption or decryption. The eavesdropper's process of launching a clear message from a secret message is called deciphering. ;
Voice encryption in the walkie-talkie is to process the call voice information to destroy its characteristics and reduce its intelligibility. After using the security function, the walkie-talkie will affect the voice quality to varying degrees, so pay attention to this problem when choosing the density. Most confidential device speech signals are encrypted and the decryption process is sensitive to channel distortion, interference and background noise. Cost factors should also be considered when selecting a secure device. The higher the security feature, the higher the cost of securing the device. Therefore, when selecting a security device, various factors such as voice quality, security level, and security equipment cost should be considered.
The voice privacy technology of the walkie-talkie is mainly divided into analog and digital voice security technologies. Frequency domain scrambling is the earliest analog voice privacy technology used in voice, and is still widely used today. There are three common techniques for frequency domain scrambling: scrambling, band-shifting and band-splitting, mainly using modulators and filters to achieve frequency shifting, frequency measurement and segmentation. Scrambling is a voice privacy technology that is mostly used in imported walkie-talkies. The scrambling is to exchange the high frequency and low frequency of the signal, that is, to move the high frequency part of the signal to the low frequency band and the low frequency part to the high frequency band. The scrambled signal has the same frequency band range as the original signal. Since the frequency component of the original speech signal is scrambled to reduce intelligibility, it plays a role in voice privacy. At the receiving end, the same scrambler is used to recover the signal. This type of scrambler is also the simplest voice scrambler. It is essentially an encoder. The common scrambler has no key, so its confidentiality is limited. In addition, there is a shifting frequency, and the frequency shifting is based on the frequency converter, and the two parties can use the agreed key for secure communication. This shifting the frequency converter becomes a true voice security machine. Another is band splitting, also known as band scrambling, which is one of the most commonly used techniques in analog voice secrecy. The method is to divide the original signal spectrum into several equal sub-bands, then rearrange the order of the sub-bands to achieve scrambling, and perform scrambling exchange on some sub-bands. In addition, there are voice privacy techniques such as time domain scrambling, two-dimensional scrambling, and analog-digital-modulo scrambling.
Digital voice security technology can achieve high security density and overcome the difficulty of both the density and voice quality in analog voice security technology. Therefore, digital voice privacy technology is mostly used in important occasions. Digital security systems include voice coding, decoders and digital modulation, demodulators, and channel coding and decoders. The working principle is that the analog voice signal is digitally encoded into a digital signal through a voice encoder (analog encoder), and then converted into a digital encrypted voice signal through an encryptor, corrected by a channel encoder, and then digitally modulated by a digital modulator. Turned into an analog signal suitable for transmission on the transmitting side channel. At the receiving end, the demodulator is restored to a digital signal, and then the voice signal is recovered by the channel decoder, the decryptor, and the digital-to-analog converter. The cipher uses serial cipher technology and packet cipher technology. Digital voice security technology is only a piece of noise for the eavesdropper because of the pseudo-random nature of the output encrypted signal, and the intelligibility is zero.
What kind of voice privacy technology is adopted depends on the needs of users. The general requirements for confidentiality use simple frequency domain scrambling technology, the use of two-dimensional encryption technology for higher security requirements, and the use of digital voice security technology for higher security requirements.
Why is the price of the digital walkie-talkie high?