Two ways to resolve wireless call encryption

In professional wireless communication, voice is a simulated signal that changes continuously . It occupies a frequency band of 300HZ-3000Hz , and after voice encryption, it must be sent out within a certain transmission bandwidth. The encryption of professional wireless communication is mainly carried out in the professional frequency modulation machine (handset, mobile station) used by the user, that is, a security module is embedded in the professional frequency modulation machine used. There are two ways to encrypt voice signals: imitation encryption and digital encryption:

1. Voice digital encryption: Really complete the high security of confidentiality, which can be done after the digitization of speech. After digitizing the voice signal and then encrypting it, there are three main methods:

( 1 ) Substitute method : In the case of insisting that the plaintext symbol orientation is unchanged, the ciphertext symbol (character or bit) is used to replace the character in the plaintext with the character of the key. Give an example to clarify: a key for each letter rule expressly replaced by its first five letters of the audio, then with a f, b with g, c ..... with H, a plaintext after the "today" Encryption It became " ytifd " and it was confidential.

( 2 ) Transposition method: Although the friend in the plain text (characters or bits are unchanged, but the placement time is arranged according to the key, the symbol group with limited length is usually divided into audio symbols. Azimuth, the key is scrambled and rearranged, and the confidentiality is reached. For example, the length of the audio packet is 6 characters, and the key of the rule rearrangement is 362451 , if the plaintext is: M=a1a2a3a4a5a61b2b3b4b5b6\c1c2c3c4c5c6....., the encrypted audio E=a1a2a3a4a5a61b2b3b4b5b6\c1c2c3c4c5c6....., the audio encryption is completed.

( 3 ) Successive encryption algorithm: It converts each plaintext symbol into another ciphertext symbol by a mathematical operation. In practical use, the key of the communication system is not fixed, and is distributed randomly by the key distribution center. Such encrypted communication has higher security and security.

2 , voice signal imitation encryption: adhere to the imitation characteristics of voice and encrypt it, there are two main ways:

( 1 ) Frequency division method: for a voice occupying a bandwidth of 300 Hz-3000 Hz , divide it into several segments (divided into several segments according to the encryption level request), and then place the divided segments of the signals in the orientation to perform scrambling encryption. After processing, and then wirelessly transmitting, after arriving at the other party's acceptance, the signals of the various segments that are scrambled will be restored according to the given rules (keys) and restored to the original voice. This is the simplest scrambling method. Of course, its security is relatively poor. You can guess more than 50% after listening to it a few times . The scrambler is a commonly used encryption device before the voice digitization is processed.

( 2 ) Time division method: As we all know, speech is syllable. For example, the length of Chinese syllables is about 50-270ms . Time division method, the speech that is, the one or more syllables is divided into waveform segments, and placing them in position, and then transmits the given rules (key) disrupted rearrangement (encrypted), arrived After the other party accepts, the received signal will be restored according to the given rules (key).